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000
FXUS63 KLOT 310604
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
104 AM CDT TUE MAR 31 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* WIND DIRECTIONS TODAY...WITH POTENTIAL FOR NORTH-NORTHEAST
  (350-020 DEG) WINDS EARLY SHIFTING TO NORTHWEST AND THEN
  POSSIBLE LAKE BREEZE IN THE AFTERNOON ESPECIALLY AT MDW.

* POTENTIAL FOR LOWER MVFR/HIGHER END IFR CIGS THIS MORNING.

RC

//DISCUSSION...UPDATED 06Z...

A CLIPPER LOW PRESSURE SYSTEM IS CENTERED OVER SOUTHERN WISCONSIN
EARLY THIS MORNING...WITH STRONG PRESSURE FALLS IMMEDIATELY AHEAD
OF IT RESULTING IN STRONG SOUTHWEST WINDS GUSTING UP TO 25 TO EVEN
30 KT OVER NORTHEAST ILLINOIS. WINDS WILL SHIFT TO NORTHWEST AND
THEN NORTH BEHIND THE LOW AND LAKE INFLUENCE COULD BRING A BRIEF
PERIOD OF NORTH-NORTHEAST WINDS TO ORD/MDW BETWEEN ABOUT 12Z AND
14Z. LOW CIGS OVER CENTRAL WISCONSIN MAY ALSO SPREAD
SOUTHWARD...AIDED BY THE LAKE INFLUENCE...BUT CONFIDENCE IS
LOW...SO HAVE ADDED SCT010 IN ORD/MDW/GYY TAFS FROM 13Z TO 15Z.

WIND DIRECTION FORECAST REMAINS TRICKY THROUGH THE DAY TODAY...BUT
CURRENT THINKING IS THAT WINDS WILL BACK TO WEST-NORTHWEST
EVERYWHERE EXCEPT GYY...WHICH WILL HOLD ONTO NORTHERLY WINDS GIVEN
PROXIMITY TO THE LAKE. PRESSURE GRADIENT WILL DIMINISH LATER IN
THE AFTERNOON...WITH LAKE BREEZE EXPECTED TO MAKE SOME HEADWAY
INLAND...THOUGH IT IS UNCERTAIN HOW FAR. HAVE INDICATED A WIND
SHIFT IN THE MDW TAF DURING THE LATE AFTERNOON BUT NOT BROUGHT THE
SHIFT TO ORD. LIGHT NORTHEAST WINDS COULD THEN REDEVELOP LATE
TONIGHT INTO EARLY WEDNESDAY.

RC


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND FORECAST THROUGH ABOUT 9Z-10Z TODAY...LOW
  THEREAFTER.

* LOW IN LOW CIG POTENTIAL THIS MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310604
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
104 AM CDT TUE MAR 31 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* WIND DIRECTIONS TODAY...WITH POTENTIAL FOR NORTH-NORTHEAST
  (350-020 DEG) WINDS EARLY SHIFTING TO NORTHWEST AND THEN
  POSSIBLE LAKE BREEZE IN THE AFTERNOON ESPECIALLY AT MDW.

* POTENTIAL FOR LOWER MVFR/HIGHER END IFR CIGS THIS MORNING.

RC

//DISCUSSION...UPDATED 06Z...

A CLIPPER LOW PRESSURE SYSTEM IS CENTERED OVER SOUTHERN WISCONSIN
EARLY THIS MORNING...WITH STRONG PRESSURE FALLS IMMEDIATELY AHEAD
OF IT RESULTING IN STRONG SOUTHWEST WINDS GUSTING UP TO 25 TO EVEN
30 KT OVER NORTHEAST ILLINOIS. WINDS WILL SHIFT TO NORTHWEST AND
THEN NORTH BEHIND THE LOW AND LAKE INFLUENCE COULD BRING A BRIEF
PERIOD OF NORTH-NORTHEAST WINDS TO ORD/MDW BETWEEN ABOUT 12Z AND
14Z. LOW CIGS OVER CENTRAL WISCONSIN MAY ALSO SPREAD
SOUTHWARD...AIDED BY THE LAKE INFLUENCE...BUT CONFIDENCE IS
LOW...SO HAVE ADDED SCT010 IN ORD/MDW/GYY TAFS FROM 13Z TO 15Z.

WIND DIRECTION FORECAST REMAINS TRICKY THROUGH THE DAY TODAY...BUT
CURRENT THINKING IS THAT WINDS WILL BACK TO WEST-NORTHWEST
EVERYWHERE EXCEPT GYY...WHICH WILL HOLD ONTO NORTHERLY WINDS GIVEN
PROXIMITY TO THE LAKE. PRESSURE GRADIENT WILL DIMINISH LATER IN
THE AFTERNOON...WITH LAKE BREEZE EXPECTED TO MAKE SOME HEADWAY
INLAND...THOUGH IT IS UNCERTAIN HOW FAR. HAVE INDICATED A WIND
SHIFT IN THE MDW TAF DURING THE LATE AFTERNOON BUT NOT BROUGHT THE
SHIFT TO ORD. LIGHT NORTHEAST WINDS COULD THEN REDEVELOP LATE
TONIGHT INTO EARLY WEDNESDAY.

RC


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND FORECAST THROUGH ABOUT 9Z-10Z TODAY...LOW
  THEREAFTER.

* LOW IN LOW CIG POTENTIAL THIS MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 310604
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
104 AM CDT TUE MAR 31 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* WIND DIRECTIONS TODAY...WITH POTENTIAL FOR NORTH-NORTHEAST
  (350-020 DEG) WINDS EARLY SHIFTING TO NORTHWEST AND THEN
  POSSIBLE LAKE BREEZE IN THE AFTERNOON ESPECIALLY AT MDW.

* POTENTIAL FOR LOWER MVFR/HIGHER END IFR CIGS THIS MORNING.

RC

//DISCUSSION...UPDATED 06Z...

A CLIPPER LOW PRESSURE SYSTEM IS CENTERED OVER SOUTHERN WISCONSIN
EARLY THIS MORNING...WITH STRONG PRESSURE FALLS IMMEDIATELY AHEAD
OF IT RESULTING IN STRONG SOUTHWEST WINDS GUSTING UP TO 25 TO EVEN
30 KT OVER NORTHEAST ILLINOIS. WINDS WILL SHIFT TO NORTHWEST AND
THEN NORTH BEHIND THE LOW AND LAKE INFLUENCE COULD BRING A BRIEF
PERIOD OF NORTH-NORTHEAST WINDS TO ORD/MDW BETWEEN ABOUT 12Z AND
14Z. LOW CIGS OVER CENTRAL WISCONSIN MAY ALSO SPREAD
SOUTHWARD...AIDED BY THE LAKE INFLUENCE...BUT CONFIDENCE IS
LOW...SO HAVE ADDED SCT010 IN ORD/MDW/GYY TAFS FROM 13Z TO 15Z.

WIND DIRECTION FORECAST REMAINS TRICKY THROUGH THE DAY TODAY...BUT
CURRENT THINKING IS THAT WINDS WILL BACK TO WEST-NORTHWEST
EVERYWHERE EXCEPT GYY...WHICH WILL HOLD ONTO NORTHERLY WINDS GIVEN
PROXIMITY TO THE LAKE. PRESSURE GRADIENT WILL DIMINISH LATER IN
THE AFTERNOON...WITH LAKE BREEZE EXPECTED TO MAKE SOME HEADWAY
INLAND...THOUGH IT IS UNCERTAIN HOW FAR. HAVE INDICATED A WIND
SHIFT IN THE MDW TAF DURING THE LATE AFTERNOON BUT NOT BROUGHT THE
SHIFT TO ORD. LIGHT NORTHEAST WINDS COULD THEN REDEVELOP LATE
TONIGHT INTO EARLY WEDNESDAY.

RC


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND FORECAST THROUGH ABOUT 9Z-10Z TODAY...LOW
  THEREAFTER.

* LOW IN LOW CIG POTENTIAL THIS MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310604
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
104 AM CDT TUE MAR 31 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* WIND DIRECTIONS TODAY...WITH POTENTIAL FOR NORTH-NORTHEAST
  (350-020 DEG) WINDS EARLY SHIFTING TO NORTHWEST AND THEN
  POSSIBLE LAKE BREEZE IN THE AFTERNOON ESPECIALLY AT MDW.

* POTENTIAL FOR LOWER MVFR/HIGHER END IFR CIGS THIS MORNING.

RC

//DISCUSSION...UPDATED 06Z...

A CLIPPER LOW PRESSURE SYSTEM IS CENTERED OVER SOUTHERN WISCONSIN
EARLY THIS MORNING...WITH STRONG PRESSURE FALLS IMMEDIATELY AHEAD
OF IT RESULTING IN STRONG SOUTHWEST WINDS GUSTING UP TO 25 TO EVEN
30 KT OVER NORTHEAST ILLINOIS. WINDS WILL SHIFT TO NORTHWEST AND
THEN NORTH BEHIND THE LOW AND LAKE INFLUENCE COULD BRING A BRIEF
PERIOD OF NORTH-NORTHEAST WINDS TO ORD/MDW BETWEEN ABOUT 12Z AND
14Z. LOW CIGS OVER CENTRAL WISCONSIN MAY ALSO SPREAD
SOUTHWARD...AIDED BY THE LAKE INFLUENCE...BUT CONFIDENCE IS
LOW...SO HAVE ADDED SCT010 IN ORD/MDW/GYY TAFS FROM 13Z TO 15Z.

WIND DIRECTION FORECAST REMAINS TRICKY THROUGH THE DAY TODAY...BUT
CURRENT THINKING IS THAT WINDS WILL BACK TO WEST-NORTHWEST
EVERYWHERE EXCEPT GYY...WHICH WILL HOLD ONTO NORTHERLY WINDS GIVEN
PROXIMITY TO THE LAKE. PRESSURE GRADIENT WILL DIMINISH LATER IN
THE AFTERNOON...WITH LAKE BREEZE EXPECTED TO MAKE SOME HEADWAY
INLAND...THOUGH IT IS UNCERTAIN HOW FAR. HAVE INDICATED A WIND
SHIFT IN THE MDW TAF DURING THE LATE AFTERNOON BUT NOT BROUGHT THE
SHIFT TO ORD. LIGHT NORTHEAST WINDS COULD THEN REDEVELOP LATE
TONIGHT INTO EARLY WEDNESDAY.

RC


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND FORECAST THROUGH ABOUT 9Z-10Z TODAY...LOW
  THEREAFTER.

* LOW IN LOW CIG POTENTIAL THIS MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 310316
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1016 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CHANCE OF A LAKE BREEZE/NORTHEAST WIND TUESDAY LATE AFTERNOON

IZZI

//DISCUSSION...UPDATED 03Z...

FRONT AND APPROACHING LOW CONTINUE TO PRESENT CHALLENGES IN
FORECASTING WIND DIRECTION. WINDS HAVE VEERED SOUTHEAST AND WITH
LOW NOW LOOKING TO PASS JUST NORTH OF THE TERMINALS WOULD EXPECT
WINDS TO VEER SOUTHWEST BEFORE VEERING WEST THEN SHIFTING NORTH
LATER TONIGHT. DOES APPEAR AS THOUGH THERE COULD BE A COUPLE HOURS
OF NORTH-NORTHEAST WINDS EARLY TUESDAY MORNING BEFORE LIKELY
BACKING MORE NORTH-NORTHWEST BY MID MORNING. CONFIDENCE IS LOW ON
WINDS LATE MORNING INTO AFTERNOON TOMORROW WITH DISTINCT
POSSIBILITY THAT LAKE BREEZE COULD MAKE IT THROUGH ORD/MDW RESULT
IN NE WINDS AROUND 10KT IN THE AFTERNOON. KEPT WINDS WESTERLY AT
THIS POINT BUT NEXT SHIFT MAY HAVE CONSIDER ADDING A LAKE BREEZE
WIND SHIFT TUES.

IZZI

UPDATED 00Z...

WINDS HAVE FLIPPED NORTHEAST THIS EVENING DUE TO DEVELOPING FRONT
WITH SOME ADDED INFLUENCE FROM LAKE MICHIGAN. NORTHEAST WINDS
AROUND 10KT LIKELY TO CONTINUE EARLY THIS EVENING UNTIL THE LOW
PRESSURE MOVES ACROSS NORTHERN ILLINOIS LATE THIS EVENING AT WHICH
TIME WINDS WILL LIKELY BECOME LIGHTER AND VARIABLE. ONCE THE LOW
PASSES OVERNIGHT LOOKS FOR NORTHERLY WINDS TO DEVELOP LATER
TONIGHT INTO EARLY TUESDAY MORNING. WINDS COULD BE CLOSE TO 10KT
AND AT THIS DISTANCE IT IS TOUGH TO SAY WHICH SIDE OF DUE NORTH
THEY WILL START THE DAY ON AT OHARE. CONFIDENCE IN WIND DIRECTION
IS FAIRLY LOW TUESDAY AS SYNOPTIC GRADIENT WOULD TEND TO FAVOR
WINDS BACKING TO NORTHWEST AND THEN WEST DURING THE
AFTERNOON...BUT WITH SPEEDS MOSTLY DROPPING BELOW 10KT A LAKE
BREEZE IS LIKELY TO DEVELOP. HOW FAR INLAND THE LAKE BREEZE MAKES
IT IS TOUGH TO PIN DOWN...BUT FOR NOW HAVE KEPT LAKE BREEZE/WIND
SHIFT TO THE EAST OUT OF THE TAFS WITH THINKING BEING ABOUT A 40
PERCENT CHANCE OF IT MAKING IT THROUGH ORD/MDW LATE TUESDAY
AFTERNOON.

GENERALLY EXPECT VFR CONDITIONS THROUGH THE PERIOD...THOUGH THERE
IS AN OUTSIDE CHANCE THAT THERE COULD BE SOME LAKE STRATUS EARLY
TUESDAY MORNING. FORECAST SOUNDINGS ARE HITTING THIS THREAT PRETTY
HARD...BUT LOW LEVELS ARE DRY AND THE PUSH OF MARINE AIR IS NOT
PARTICULARLY COLD SO HAVE KEPT ANY CIGS OUT OF THE TAFS FOR NOW
AND WILL JUST MONITOR SATELLITE TRENDS TONIGHT.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN WINDS TONIGHT...LOW CONFIDENCE IN WINDS
  TUESDAY
* MEDIUM-HIGH CONFIDENCE IN NO LAKE EFFECT CIGS LATE TONIGHT/EARLY
  TUESDAY MORNING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310009
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
709 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NORTHEAST WINDS AROUND 10KT EARLY TO MID EVENING
* CHANCE OF A LAKE BREEZE/NORTHEAST WIND TUESDAY LATE AFTERNOON

IZZI

//DISCUSSION...UPDATED 00Z...

WINDS HAVE FLIPPED NORTHEAST THIS EVENING DUE TO DEVELOPING FRONT
WITH SOME ADDED INFLUENCE FROM LAKE MICHIGAN. NORTHEAST WINDS
AROUND 10KT LIKELY TO CONTINUE EARLY THIS EVENING UNTIL THE LOW
PRESSURE MOVES ACROSS NORTHERN ILLINOIS LATE THIS EVENING AT WHICH
TIME WINDS WILL LIKELY BECOME LIGHTER AND VARIABLE. ONCE THE LOW
PASSES OVERNIGHT LOOKS FOR NORTHERLY WINDS TO DEVELOP LATER
TONIGHT INTO EARLY TUESDAY MORNING. WINDS COULD BE CLOSE TO 10KT
AND AT THIS DISTANCE IT IS TOUGH TO SAY WHICH SIDE OF DUE NORTH
THEY WILL START THE DAY ON AT OHARE. CONFIDENCE IN WIND DIRECTION
IS FAIRLY LOW TUESDAY AS SYNOPTIC GRADIENT WOULD TEND TO FAVOR
WINDS BACKING TO NORTHWEST AND THEN WEST DURING THE
AFTERNOON...BUT WITH SPEEDS MOSTLY DROPPING BELOW 10KT A LAKE
BREEZE IS LIKELY TO DEVELOP. HOW FAR INLAND THE LAKE BREEZE MAKES
IT IS TOUGH TO PIN DOWN...BUT FOR NOW HAVE KEPT LAKE BREEZE/WIND
SHIFT TO THE EAST OUT OF THE TAFS WITH THINKING BEING ABOUT A 40
PERCENT CHANCE OF IT MAKING IT THROUGH ORD/MDW LATE TUESDAY
AFTERNOON.

GENERALLY EXPECT VFR CONDITIONS THROUGH THE PERIOD...THOUGH THERE
IS AN OUTSIDE CHANCE THAT THERE COULD BE SOME LAKE STRATUS EARLY
TUESDAY MORNING. FORECAST SOUNDINGS ARE HITTING THIS THREAT PRETTY
HARD...BUT LOW LEVELS ARE DRY AND THE PUSH OF MARINE AIR IS NOT
PARTICULARLY COLD SO HAVE KEPT ANY CIGS OUT OF THE TAFS FOR NOW
AND WILL JUST MONITOR SATELLITE TRENDS TONIGHT.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN WINDS THROUGH MID EVENING
* LOW CONFIDENCE IN WINDS LATE THIS EVENING/EARLY OVERNIGHT
* MEDIUM CONFIDENCE IN WIND DIRECTION LATE TONIGHT THROUGH TUESDAY
* MEDIUM-HIGH CONFIDENCE IN NO LAKE EFFECT CIGS LATE TONIGHT/EARLY
  TUESDAY MORNING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310009
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
709 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NORTHEAST WINDS AROUND 10KT EARLY TO MID EVENING
* CHANCE OF A LAKE BREEZE/NORTHEAST WIND TUESDAY LATE AFTERNOON

IZZI

//DISCUSSION...UPDATED 00Z...

WINDS HAVE FLIPPED NORTHEAST THIS EVENING DUE TO DEVELOPING FRONT
WITH SOME ADDED INFLUENCE FROM LAKE MICHIGAN. NORTHEAST WINDS
AROUND 10KT LIKELY TO CONTINUE EARLY THIS EVENING UNTIL THE LOW
PRESSURE MOVES ACROSS NORTHERN ILLINOIS LATE THIS EVENING AT WHICH
TIME WINDS WILL LIKELY BECOME LIGHTER AND VARIABLE. ONCE THE LOW
PASSES OVERNIGHT LOOKS FOR NORTHERLY WINDS TO DEVELOP LATER
TONIGHT INTO EARLY TUESDAY MORNING. WINDS COULD BE CLOSE TO 10KT
AND AT THIS DISTANCE IT IS TOUGH TO SAY WHICH SIDE OF DUE NORTH
THEY WILL START THE DAY ON AT OHARE. CONFIDENCE IN WIND DIRECTION
IS FAIRLY LOW TUESDAY AS SYNOPTIC GRADIENT WOULD TEND TO FAVOR
WINDS BACKING TO NORTHWEST AND THEN WEST DURING THE
AFTERNOON...BUT WITH SPEEDS MOSTLY DROPPING BELOW 10KT A LAKE
BREEZE IS LIKELY TO DEVELOP. HOW FAR INLAND THE LAKE BREEZE MAKES
IT IS TOUGH TO PIN DOWN...BUT FOR NOW HAVE KEPT LAKE BREEZE/WIND
SHIFT TO THE EAST OUT OF THE TAFS WITH THINKING BEING ABOUT A 40
PERCENT CHANCE OF IT MAKING IT THROUGH ORD/MDW LATE TUESDAY
AFTERNOON.

GENERALLY EXPECT VFR CONDITIONS THROUGH THE PERIOD...THOUGH THERE
IS AN OUTSIDE CHANCE THAT THERE COULD BE SOME LAKE STRATUS EARLY
TUESDAY MORNING. FORECAST SOUNDINGS ARE HITTING THIS THREAT PRETTY
HARD...BUT LOW LEVELS ARE DRY AND THE PUSH OF MARINE AIR IS NOT
PARTICULARLY COLD SO HAVE KEPT ANY CIGS OUT OF THE TAFS FOR NOW
AND WILL JUST MONITOR SATELLITE TRENDS TONIGHT.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN WINDS THROUGH MID EVENING
* LOW CONFIDENCE IN WINDS LATE THIS EVENING/EARLY OVERNIGHT
* MEDIUM CONFIDENCE IN WIND DIRECTION LATE TONIGHT THROUGH TUESDAY
* MEDIUM-HIGH CONFIDENCE IN NO LAKE EFFECT CIGS LATE TONIGHT/EARLY
  TUESDAY MORNING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 310009
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
709 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NORTHEAST WINDS AROUND 10KT EARLY TO MID EVENING
* CHANCE OF A LAKE BREEZE/NORTHEAST WIND TUESDAY LATE AFTERNOON

IZZI

//DISCUSSION...UPDATED 00Z...

WINDS HAVE FLIPPED NORTHEAST THIS EVENING DUE TO DEVELOPING FRONT
WITH SOME ADDED INFLUENCE FROM LAKE MICHIGAN. NORTHEAST WINDS
AROUND 10KT LIKELY TO CONTINUE EARLY THIS EVENING UNTIL THE LOW
PRESSURE MOVES ACROSS NORTHERN ILLINOIS LATE THIS EVENING AT WHICH
TIME WINDS WILL LIKELY BECOME LIGHTER AND VARIABLE. ONCE THE LOW
PASSES OVERNIGHT LOOKS FOR NORTHERLY WINDS TO DEVELOP LATER
TONIGHT INTO EARLY TUESDAY MORNING. WINDS COULD BE CLOSE TO 10KT
AND AT THIS DISTANCE IT IS TOUGH TO SAY WHICH SIDE OF DUE NORTH
THEY WILL START THE DAY ON AT OHARE. CONFIDENCE IN WIND DIRECTION
IS FAIRLY LOW TUESDAY AS SYNOPTIC GRADIENT WOULD TEND TO FAVOR
WINDS BACKING TO NORTHWEST AND THEN WEST DURING THE
AFTERNOON...BUT WITH SPEEDS MOSTLY DROPPING BELOW 10KT A LAKE
BREEZE IS LIKELY TO DEVELOP. HOW FAR INLAND THE LAKE BREEZE MAKES
IT IS TOUGH TO PIN DOWN...BUT FOR NOW HAVE KEPT LAKE BREEZE/WIND
SHIFT TO THE EAST OUT OF THE TAFS WITH THINKING BEING ABOUT A 40
PERCENT CHANCE OF IT MAKING IT THROUGH ORD/MDW LATE TUESDAY
AFTERNOON.

GENERALLY EXPECT VFR CONDITIONS THROUGH THE PERIOD...THOUGH THERE
IS AN OUTSIDE CHANCE THAT THERE COULD BE SOME LAKE STRATUS EARLY
TUESDAY MORNING. FORECAST SOUNDINGS ARE HITTING THIS THREAT PRETTY
HARD...BUT LOW LEVELS ARE DRY AND THE PUSH OF MARINE AIR IS NOT
PARTICULARLY COLD SO HAVE KEPT ANY CIGS OUT OF THE TAFS FOR NOW
AND WILL JUST MONITOR SATELLITE TRENDS TONIGHT.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN WINDS THROUGH MID EVENING
* LOW CONFIDENCE IN WINDS LATE THIS EVENING/EARLY OVERNIGHT
* MEDIUM CONFIDENCE IN WIND DIRECTION LATE TONIGHT THROUGH TUESDAY
* MEDIUM-HIGH CONFIDENCE IN NO LAKE EFFECT CIGS LATE TONIGHT/EARLY
  TUESDAY MORNING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310009
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
709 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NORTHEAST WINDS AROUND 10KT EARLY TO MID EVENING
* CHANCE OF A LAKE BREEZE/NORTHEAST WIND TUESDAY LATE AFTERNOON

IZZI

//DISCUSSION...UPDATED 00Z...

WINDS HAVE FLIPPED NORTHEAST THIS EVENING DUE TO DEVELOPING FRONT
WITH SOME ADDED INFLUENCE FROM LAKE MICHIGAN. NORTHEAST WINDS
AROUND 10KT LIKELY TO CONTINUE EARLY THIS EVENING UNTIL THE LOW
PRESSURE MOVES ACROSS NORTHERN ILLINOIS LATE THIS EVENING AT WHICH
TIME WINDS WILL LIKELY BECOME LIGHTER AND VARIABLE. ONCE THE LOW
PASSES OVERNIGHT LOOKS FOR NORTHERLY WINDS TO DEVELOP LATER
TONIGHT INTO EARLY TUESDAY MORNING. WINDS COULD BE CLOSE TO 10KT
AND AT THIS DISTANCE IT IS TOUGH TO SAY WHICH SIDE OF DUE NORTH
THEY WILL START THE DAY ON AT OHARE. CONFIDENCE IN WIND DIRECTION
IS FAIRLY LOW TUESDAY AS SYNOPTIC GRADIENT WOULD TEND TO FAVOR
WINDS BACKING TO NORTHWEST AND THEN WEST DURING THE
AFTERNOON...BUT WITH SPEEDS MOSTLY DROPPING BELOW 10KT A LAKE
BREEZE IS LIKELY TO DEVELOP. HOW FAR INLAND THE LAKE BREEZE MAKES
IT IS TOUGH TO PIN DOWN...BUT FOR NOW HAVE KEPT LAKE BREEZE/WIND
SHIFT TO THE EAST OUT OF THE TAFS WITH THINKING BEING ABOUT A 40
PERCENT CHANCE OF IT MAKING IT THROUGH ORD/MDW LATE TUESDAY
AFTERNOON.

GENERALLY EXPECT VFR CONDITIONS THROUGH THE PERIOD...THOUGH THERE
IS AN OUTSIDE CHANCE THAT THERE COULD BE SOME LAKE STRATUS EARLY
TUESDAY MORNING. FORECAST SOUNDINGS ARE HITTING THIS THREAT PRETTY
HARD...BUT LOW LEVELS ARE DRY AND THE PUSH OF MARINE AIR IS NOT
PARTICULARLY COLD SO HAVE KEPT ANY CIGS OUT OF THE TAFS FOR NOW
AND WILL JUST MONITOR SATELLITE TRENDS TONIGHT.

IZZI


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN WINDS THROUGH MID EVENING
* LOW CONFIDENCE IN WINDS LATE THIS EVENING/EARLY OVERNIGHT
* MEDIUM CONFIDENCE IN WIND DIRECTION LATE TONIGHT THROUGH TUESDAY
* MEDIUM-HIGH CONFIDENCE IN NO LAKE EFFECT CIGS LATE TONIGHT/EARLY
  TUESDAY MORNING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...

WEDNESDAY...VFR.

THURSDAY...SHRA/SOME TSRA LIKELY. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...PRIMARILY VFR.

IZZI

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 302214
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
514 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NORTHEAST WINDS DEVELOP AND INCREASE TO AROUND 10KT THIS EVENING

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT EARLY AMD TO ORD/MDW TAF DUE TO EXPECTED INCREASING NORTHEAST
WINDS EARLY THIS EVENING AS LAKE ENHANCED NE WIND DEVELOPS AND
LIKELY PUSHES SPEEDS UP TO AT LEAST AROUND 10KT FOR A COUPLE HOURS
EARLY THIS EVENING. LOOKING LIKE WINDS COULD REMAIN NORTHEAST
THROUGH REST OF THE EVENING AND INTO THE OVERNIGHT THOUGH
CONFIDENCE IS LOW IN WHEN NE WINDS PICK UP TO 10KT EXACTLY AND ON
WIND DIRECTION IN GENERAL OVERNIGHT.

IZZI

UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN WINDS THIS EVENING...LOW CONFIDENCE IN
  WINDS OVERNIGHT...MEDIUM-HIGH CONFIDENCE IN WINDS TUESDAY

* LOW MEDIUM CONFIDENCE IN MVFR CIGS POTENTIAL TUES MORNING

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302214
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
514 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NORTHEAST WINDS DEVELOP AND INCREASE TO AROUND 10KT THIS EVENING

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT EARLY AMD TO ORD/MDW TAF DUE TO EXPECTED INCREASING NORTHEAST
WINDS EARLY THIS EVENING AS LAKE ENHANCED NE WIND DEVELOPS AND
LIKELY PUSHES SPEEDS UP TO AT LEAST AROUND 10KT FOR A COUPLE HOURS
EARLY THIS EVENING. LOOKING LIKE WINDS COULD REMAIN NORTHEAST
THROUGH REST OF THE EVENING AND INTO THE OVERNIGHT THOUGH
CONFIDENCE IS LOW IN WHEN NE WINDS PICK UP TO 10KT EXACTLY AND ON
WIND DIRECTION IN GENERAL OVERNIGHT.

IZZI

UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN WINDS THIS EVENING...LOW CONFIDENCE IN
  WINDS OVERNIGHT...MEDIUM-HIGH CONFIDENCE IN WINDS TUESDAY

* LOW MEDIUM CONFIDENCE IN MVFR CIGS POTENTIAL TUES MORNING

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 302214
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
514 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NORTHEAST WINDS DEVELOP AND INCREASE TO AROUND 10KT THIS EVENING

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT EARLY AMD TO ORD/MDW TAF DUE TO EXPECTED INCREASING NORTHEAST
WINDS EARLY THIS EVENING AS LAKE ENHANCED NE WIND DEVELOPS AND
LIKELY PUSHES SPEEDS UP TO AT LEAST AROUND 10KT FOR A COUPLE HOURS
EARLY THIS EVENING. LOOKING LIKE WINDS COULD REMAIN NORTHEAST
THROUGH REST OF THE EVENING AND INTO THE OVERNIGHT THOUGH
CONFIDENCE IS LOW IN WHEN NE WINDS PICK UP TO 10KT EXACTLY AND ON
WIND DIRECTION IN GENERAL OVERNIGHT.

IZZI

UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN WINDS THIS EVENING...LOW CONFIDENCE IN
  WINDS OVERNIGHT...MEDIUM-HIGH CONFIDENCE IN WINDS TUESDAY

* LOW MEDIUM CONFIDENCE IN MVFR CIGS POTENTIAL TUES MORNING

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302214
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
514 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NORTHEAST WINDS DEVELOP AND INCREASE TO AROUND 10KT THIS EVENING

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT EARLY AMD TO ORD/MDW TAF DUE TO EXPECTED INCREASING NORTHEAST
WINDS EARLY THIS EVENING AS LAKE ENHANCED NE WIND DEVELOPS AND
LIKELY PUSHES SPEEDS UP TO AT LEAST AROUND 10KT FOR A COUPLE HOURS
EARLY THIS EVENING. LOOKING LIKE WINDS COULD REMAIN NORTHEAST
THROUGH REST OF THE EVENING AND INTO THE OVERNIGHT THOUGH
CONFIDENCE IS LOW IN WHEN NE WINDS PICK UP TO 10KT EXACTLY AND ON
WIND DIRECTION IN GENERAL OVERNIGHT.

IZZI

UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN WINDS THIS EVENING...LOW CONFIDENCE IN
  WINDS OVERNIGHT...MEDIUM-HIGH CONFIDENCE IN WINDS TUESDAY

* LOW MEDIUM CONFIDENCE IN MVFR CIGS POTENTIAL TUES MORNING

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 302040
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 302040
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 302040
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302040
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 PM CDT MON MAR 30 2015

.SHORT TERM...
339 PM CDT

TONIGHT THROUGH WEDNESDAY NIGHT...

MAIN FOCUS IN THE NEAR TERM IS ON THE CLIPPERY-LIKE SYSTEM
CURRENTLY DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. SURFACE LOW
PRESSURE ANALYZED OVER SOUTHWEST MINNESOTA IS PROGGED TO CONTINUE
TO MOVE SOUTHEAST OVER NORTHEAST ILLINOIS LATE TONIGHT...THEN MOVE
QUICKLY OFF INTO OHIO BY TUESDAY MORNING. AHEAD OF THE
LOW...BREEZY WESTERLY WINDS HAVE WARMED TEMPS INTO THE 60S AND
EVEN AROUND 70 (STERLING IL) THIS AFTERNOON. AS THE LOW MOVES
SOUTHEAST TOWARD THE AREA HOWEVER...WINDS WILL LIKELY BACK TO THE
EAST/SOUTHEAST THIS EVENING AND WILL LIKELY CAUSE SOME TEMPERATURE
FLUCTUATONS AS FLOW SHIFT FROM OFFSHORE TO ONSHORE ALONG THE
ILLINOIS LAKE MICHIGAN SHORE. THUS OUR CURRENT MILD WEATHER WILL
LIKELY TURN CHILLIER AT LEAST ALONG THE LAKE LATER THIS EVENING.
IN ADDITION...AREA OF LIGHT TO MODERATE RAIN ACROSS WI WILL ALSO
SHIFT SOUTHEAST EARLY THIS EVENING... CLIPPING NORTHEAST IL AND
NORTHWEST INDIANA INTO TONIGHT. WHILE MUCH OF THE RAIN WILL BE
LIGHT...STEEP MID-LEVEL LAPSE RATES NOTED IN RAP SOUNDINGS AND A
PERIOD OF DECENT F-GEN FORCING AROUND 850 MB MAY PRODUCE SOME
HEAVIER BANDED SHOWERS THIS EVENING. SHOWERS WILL GRADUALLY PULL
OFF TO THE EAST AFTER MIDNIGHT AS THE BEST FORCING AND WARM/MOIST
ADVECTION SHIFTS AWAY FROM THE CWA WITH THE WAVE.

COOLER NORTH-NORTHEAST WINDS ARE IN STORE FOR THE AREA
TUESDAY...AS WEAK HIGH PRESSURE RIDGING SPREADS ACROSS THE REGION.
WHILE HIGHS IN THE 55-60 RANGE ARE EXPECTED WELL WEST/SOUTHWEST OF
THE LAKE... READINGS CLOSER TO THE SHORE WILL LIKELY NOT MAKE IT
OUT OF THE MID 40S. THE GOOD NEWS HOWEVER IS THAT THIS COOL DOWN
WILL BE BRIEF... AS UPPER RIDGE DEVELOPS ACROSS THE CENTRAL CONUS
TUESDAY NIGHT INTO WEDNESDAY...AS A DEEP TROUGH WORKS OUT OF THE
NORTHERN ROCKIES AND OUT ACROSS THE CANADIAN PRAIRIES. SURFACE
PRESSURE FALLS ACROSS THE NORTHERN PLAINS AND UPPER MIDWEST WILL
ALLOW WINDS TO SHIFT SOUTH WEDNESDAY...INCREASING THROUGH
WEDNESDAY NIGHT AS THE SURFACE LOW TRACKS NORTH OF THE BORDER.
WARMER TEMPS...IN THE UPPER 60S TO LOWER 70S...WILL MAKE FOR A
BREEZY MORE SPRING-LIKE DAY. A COLD FRONT TRAILING FROM THE
CANADIAN LOW WILL APPROACH THE AREA LATE WEDNESDAY NIGHT...WITH
MILD AND MORE HUMID CONDITIONS AHEAD OF THE BOUNDARY.
PRECIPITATION CHANCES WILL BE BEST IMMEDIATELY ALONG/AHEAD OF THE
FRONT AND MAINLY WEST OF OUR CWA THROUGH THE EVENING...BEFORE
INCREASING POTENTIAL FOR SHOWERS/THUNDERSTORMS SPREADS ACROSS
NORTHERN IL LATE WEDNESDAY NIGHT.

RATZER

&&

.LONG TERM...
339 PM CDT

THURSDAY THROUGH MONDAY...

SURFACE COLD FRONT CONTINUES TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA ON THURSDAY...WITH BEST CHANCE OF SHOWERS AND
THUNDERSTORMS FOR MOST OF THE CWA. POTENTIAL FOR SOME STRONG
THUNDERSTORMS MAY EVOLVE SOUTH OF THE FRONT (MAINLY OUR SOUTH
COUNTIES) DEPENDING UPON CLOUD COVER AND DESTABILIZATION BY
AFTERNOON...AS UPPER JET STREAK MOVES OVERHEAD AND SUPPORTS STRONG
DEEP LAYER SHEAR IN EXCESS OF 40 KTS. WITH THE FRONT MOVING
SLOWLY...TEMPS SHOULD REMAIN FAIRLY MILD...IN THE 60S EXCEPT FOR
AREAS NEAR THE LAKE WHERE WINDS MAY SHIFT ONSHORE BEHIND THE FRONT
LATER IN THE DAY.

THE COLD FRONT CONTINUES TO SAG SOUTH THURSDAY NIGHT INTO
FRIDAY...THOUGH GUIDANCE DOES SUPPORT A CONTINUED CHANCE OF PRECIP
INTO FRIDAY AS ANOTHER WAVE IS DEPICTED MOVING ALONG THE ELEVATED
BAROCLINIC ZONE NORTH OF THE SURFACE FRONT. COOLER AND DRIER
WEATHER DOES LOOK TO DEVELOP LATER FRIDAY AND FRIDAY NIGHT AS WEAK
HIGH PRESSURE MOVES IN. THE HIGH PRESSURE RIDGE THEN MOVES SOUTH
INTO OHIO VALLEY SATURDAY...WITH WINDS SHIFTING WEST AND ALLOWING
ANOTHER WARM UP. LONG RANGE SOLUTIONS INDICATE A SHORT WAVE MOVING
ACROSS THE NORTHERN LAKES AND TRAILING A COLD FRONT INTO AREA BY
SATURDAY EVENING HOWEVER...WITH ANOTHER WEAK HIGH MOVING ACROSS
THE AREA SATURDAY NIGHT AS COLD FRONT CONTINUES TO SAG SOUTH.

MODELS DIFFER A BIT IN DETAILS BY DAYS 6-7...BUT GENERALLY
INDICATE FRONT LIFTING BACK NORTH AS A WARM FRONT SUNDAY AS
SURFACE LOW PRESSURE DEVELOPS ACROSS THE PLAINS. PRECIP CHANCES
INCREASE DURING THE PERIOD IN THIS SCENARIO...WITH MILDER
TEMPERATURES POSSIBLY MUCH WARMER IF MORE AGGRESSIVE GFS PANS OUT
WITH WARM FRONT NORTH OF THE AREA.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301834
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
134 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301834
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
134 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
134 PM CDT

STRONGER WESTERLY WINDS OVER THE LAKE HAVE SINCE DIMINISHED THIS
AFTERNOON WITH A WEAK RIDGE OF HIGH PRESSURE OVERHEAD. ALONG WITH
THE DIMINISHING TREND THIS AFTERNOON...WINDS HAVE BECOME HIGHLY
VARIABLE ACROSS THE ENTIRE THE LAKE. EXPECT EITHER AN ONSHORE
COMPONENT OR A PERIOD OF VARIABLE WINDS OVER THE NEARSHORE THIS
AFTERNOON INTO THE EVENING...WITH A SOUTH TO EAST WIND OVER THE
OPEN WATERS. THIS WILL OCCUR UNTIL LATE IN THE EVENING...WHEN A
LOW PRESSURE SYSTEM QUICKLY MOVES SOUTHEAST TO THE SOUTHERN END OF
THE LAKE. INCREASING SPEEDS OVER THE ENTIRE LAKE BUT STILL
VARIABLE OVER THE SOUTH HALF...WILL THEN TRANSITION TO A NORTHERLY
WIND OVER ALL OF THE LAKE BY EARLY TUESDAY MORNING. SPEEDS MAY
STILL BE IN THE 15 TO 25 KT RANGE INITIALLY WITH THIS
TRANSITION...BUT WILL LIKELY OBSERVE A QUICK DIMINISHING TREND
THROUGH MIDDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301746
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1246 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301746
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1246 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301746
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1246 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301746
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1246 PM CDT MON MAR 30 2015

.UPDATE...

FOR MIDDAY UPDATE...
1246 9M CDT

HAVE RAISED TEMPS A COUPLE OF DEGREES THIS AFTERNOON BASED ON OBS
TRENDS...MODEL LOW LEVEL THERMAL PROGS...AND SLOWER ARRIVAL OF CLOUD
COVER THAN PREVIOUS FORECAST. SHOULD HAVE NO TROUBLE MAKING LOW (OR
EVEN MID) 60S ACROSS THE WESTERN CWA...AND AROUND 60 EAST. SOME
CONCERN THAT WEAKENING OF PRESSURE GRADIENT LATE THIS AFTERNOON AND
DEVELOPING WARM FRONTAL TROUGH SOUTHEAST OF EASTERN DAKOTAS LOW MAY
ALLOW LAKE BREEZE WINDS ALONG THE NORTH SHORE LATE...ALONG THE LINES
OF THE LAST SEVERAL RAP RUNS. ALSO TRIMMED BACK THICKER CLOUD COVER
UNTIL LATER THIS AFTERNOON.

OTHERWISE...NO CHANGES ATTM.

RATZER

&&

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT ARND 00Z...AND THEN VEER TO NORTH NORTHWEST AND GUST TO 18
  KT IN THE EARLY MORNING HOURS.

* GUSTY NORTHWEST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 18Z...

A WEAK LOW PRESSURE SYSTEM IS OVER THE EASTERN DAKOTAS AND IT WILL
TRACK OVER FAR NORTHEAST IL TONIGHT. WEST WINDS ARE GUSTING TO 25
KT AND THEY WILL DIMINISH AND BECOME EAST THIS EVENING AS THE LOW
APPROACHES. SOME GUIDANCE MEMBERS SUGGEST THE WINDS COULD BE
NORTHEAST AND ARND 10 KT...BUT DECIDED TO KEEP WINDS EAST AT 8 KT
FOR NOW AT MDW AND ORD. THE OTHER TERMINALS WILL SEE SOUTHWEST
WINDS THIS EVENING. ANY SHOWERS ACCOMPANYING THE LOW SHOULD FALL
WELL NORTH AND EAST OF THE TERMINALS OVER WI AND LAKE MI. WINDS
THEN VEER TO SW AT ALL OF THE TERMINALS AROUND MIDNIGHT AS THE
LOW MOVES OVER THE SOUTHERN END OF THE LAKE. WIND SPEEDS PICK UP
ALOFT AS WELL LEADING TO LLWS.

SOME GUIDANCE MEMBERS THEN FEATURE WINDS BECOMING NORTH AND
POSSIBLY NORTHEAST EARLY TUESDAY MORNING BEFORE BACKING TO NW.
DECIDED TO HOLD ON TO NORTH NORTHWEST WINDS GUSTING UP TO 20 KT.
GUIDANCE ALSO CONTINUES TO FEATURE MVFR OR LOWER CIGS MOVING
THROUGH BEHIND THE LOW AND ITS COLD FRONT TUESDAY MORNING.
MOISTURE DOES NOT LOOK OVERLY SIGNIFICANT SO KEPT SCATTERED MVFR
CIGS GOING. WINDS THEN BACK TO NW AND CONTINUE TO GUST UP TO 20 KT
IN THE LATE MORNING. IF CLOUD COVER IS THICKER THAN
FORECAST...THINKING GUSTS WILL NOT BE AS STRONG.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND DIRECTION THIS EVENING. MEDIUM
  CONFIDENCE IN WIND SPEED THIS EVENING...WINDS MAY BE STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301608
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1108 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* GUSTY WEST WINDS THIS AFTN DIMINISH AND BECOME EAST LESS THAN 10
  KT AFT 00Z...AND THEN BACK TO NORTHWEST AND GUST TO 18 KT IN
  THE EARLY MORNING HOURS.

* GUSTY NORTHEAST WINDS BY LATE MORNING TUESDAY.

* LLWS PSBL OVERNIGHT.

* MVFR CIGS PSBL IN THE MORNING.

JEE

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAY SHIFT ASSESS OBSERVATIONAL TRENDS
BEFORE MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST
FOR NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL
BECOME SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY
ENOUGH TO ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT
NOT AS FAR WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM CONFIDENCE IN WIND DIRECTION AND SPEED THIS
  EVENING...WINDS MAY BE MORE NE AND STRONGER.

* HIGH CONFIDENCE IN THE SHOWERS REMAINING EAST OF ORD AND MDW.

* MEDIUM CONFIDENCE IN LLWS TONIGHT.

* MEDIUM CONFIDENCE IN MVFR CIGS...LOW CONFIDENCE IN COVERAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301420
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
920 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* POTENTIAL IS INCREASING FOR A SHIFT TO NORTHEAST OR EAST WINDS
  THIS EVENING ARND 00Z.

* LLWS PSBL TONIGHT.

* MVFR CIGS PSBL TUESDAY MORNING...ALONG WITH GUSTY NNW WINDS.

JEE

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAYSHIFT ASSESS OBSERVATIONAL TRENDS BEFORE
MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST FOR
NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL BECOME
SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY ENOUGH TO
ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT NOT AS FAR
WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW CONFIDENCE IN WIND DIRECTION THIS EVENING...GUIDANCE IS
  STARTING TO HINT AT A SHIFT TO NE OR E WINDS ARND 00Z.

* MEDIUM CONFIDENCE IN LLWS TONIGHT.

* LOW CONFIDENCE IN MVFR CIGS AND COVERAGE TUESDAY MORNING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301420
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
920 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* POTENTIAL IS INCREASING FOR A SHIFT TO NORTHEAST OR EAST WINDS
  THIS EVENING ARND 00Z.

* LLWS PSBL TONIGHT.

* MVFR CIGS PSBL TUESDAY MORNING...ALONG WITH GUSTY NNW WINDS.

JEE

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAYSHIFT ASSESS OBSERVATIONAL TRENDS BEFORE
MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST FOR
NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL BECOME
SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY ENOUGH TO
ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT NOT AS FAR
WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW CONFIDENCE IN WIND DIRECTION THIS EVENING...GUIDANCE IS
  STARTING TO HINT AT A SHIFT TO NE OR E WINDS ARND 00Z.

* MEDIUM CONFIDENCE IN LLWS TONIGHT.

* LOW CONFIDENCE IN MVFR CIGS AND COVERAGE TUESDAY MORNING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301420
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
920 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* POTENTIAL IS INCREASING FOR A SHIFT TO NORTHEAST OR EAST WINDS
  THIS EVENING ARND 00Z.

* LLWS PSBL TONIGHT.

* MVFR CIGS PSBL TUESDAY MORNING...ALONG WITH GUSTY NNW WINDS.

JEE

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAYSHIFT ASSESS OBSERVATIONAL TRENDS BEFORE
MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST FOR
NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL BECOME
SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY ENOUGH TO
ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT NOT AS FAR
WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW CONFIDENCE IN WIND DIRECTION THIS EVENING...GUIDANCE IS
  STARTING TO HINT AT A SHIFT TO NE OR E WINDS ARND 00Z.

* MEDIUM CONFIDENCE IN LLWS TONIGHT.

* LOW CONFIDENCE IN MVFR CIGS AND COVERAGE TUESDAY MORNING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301420
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
920 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* POTENTIAL IS INCREASING FOR A SHIFT TO NORTHEAST OR EAST WINDS
  THIS EVENING ARND 00Z.

* LLWS PSBL TONIGHT.

* MVFR CIGS PSBL TUESDAY MORNING...ALONG WITH GUSTY NNW WINDS.

JEE

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAYSHIFT ASSESS OBSERVATIONAL TRENDS BEFORE
MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST FOR
NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL BECOME
SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY ENOUGH TO
ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT NOT AS FAR
WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW CONFIDENCE IN WIND DIRECTION THIS EVENING...GUIDANCE IS
  STARTING TO HINT AT A SHIFT TO NE OR E WINDS ARND 00Z.

* MEDIUM CONFIDENCE IN LLWS TONIGHT.

* LOW CONFIDENCE IN MVFR CIGS AND COVERAGE TUESDAY MORNING.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301159
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
659 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LOW POTENTIAL FOR WIND SHIFT TO NORTHEAST THIS EVENING.

* LOW LEVEL WIND SHEAR POSSIBLE TONIGHT.

* POTENTIAL FOR LOWER MVFR CIGS TUESDAY MORNING.

* GUSTY NORTH-NORTHWEST WINDS TUESDAY MORNING.

RC

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAYSHIFT ASSESS OBSERVATIONAL TRENDS BEFORE
MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST FOR
NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL BECOME
SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY ENOUGH TO
ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT NOT AS FAR
WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN WIND FORECAST THROUGH MID AFTERNOON...LOW-MEDIUM THIS
  EVENING/TONIGHT...MEDIUM-HIGH TUESDAY MORNING.

* MEDIUM IN LLWS TONIGHT.

* LOW IN LOWER MVFR CIG POTENTIAL TUESDAY MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301159
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
659 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LOW POTENTIAL FOR WIND SHIFT TO NORTHEAST THIS EVENING.

* LOW LEVEL WIND SHEAR POSSIBLE TONIGHT.

* POTENTIAL FOR LOWER MVFR CIGS TUESDAY MORNING.

* GUSTY NORTH-NORTHWEST WINDS TUESDAY MORNING.

RC

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAYSHIFT ASSESS OBSERVATIONAL TRENDS BEFORE
MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST FOR
NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL BECOME
SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY ENOUGH TO
ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT NOT AS FAR
WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN WIND FORECAST THROUGH MID AFTERNOON...LOW-MEDIUM THIS
  EVENING/TONIGHT...MEDIUM-HIGH TUESDAY MORNING.

* MEDIUM IN LLWS TONIGHT.

* LOW IN LOWER MVFR CIG POTENTIAL TUESDAY MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 301159
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
659 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* LOW POTENTIAL FOR WIND SHIFT TO NORTHEAST THIS EVENING.

* LOW LEVEL WIND SHEAR POSSIBLE TONIGHT.

* POTENTIAL FOR LOWER MVFR CIGS TUESDAY MORNING.

* GUSTY NORTH-NORTHWEST WINDS TUESDAY MORNING.

RC

//DISCUSSION...UPDATED 12Z...

AVIATION CONDITIONS WILL BE QUIET MOST OF THE DAY WITH WEST WINDS
BECOMING MODERATELY GUSTY AND INCREASING VFR CLOUDS BY MID DAY.
FOCUS WILL BE ON TRACK OF CLIPPER LOW PRESSURE SYSTEM CURRENTLY
OVER THE NORTHERN HIGH PLAINS THIS MORNING. IT IS EXPECTED TO
TRACK NORTH OF THE TERMINALS THIS EVENING...BUT SOME OF THE LATEST
HIGHER RESOLUTION GUIDANCE IS INDICATING A FARTHER SOUTH TRACK. IF
THIS OCCURS...A WIND SHIFT TO NORTHEAST WOULD BE POSSIBLE THIS
EVENING AT THE EASTERN TERMINALS...AS WELL AS A BETTER CHANCE FOR
RAIN SHOWERS. WILL LET DAYSHIFT ASSESS OBSERVATIONAL TRENDS BEFORE
MAKING ANY BIG CHANGES...AND HAVE STUCK WITH A DRY FORECAST FOR
NOW. IF TRACK OF LOW IS AS CURRENTLY EXPECTED...WINDS WILL BECOME
SOUTH-SOUTHWEST BY EARLY EVENING AND DIMINISH...LIKELY ENOUGH TO
ENABLE A WEAK LAKE BREEZE TO PUSH ONTO THE IL SHORE BUT NOT AS FAR
WEST AS ORD/MDW.

IN ADDITION...BASED ON CURRENT FORECAST TRACK OF THE LOW
PRESSURE JUST TO THE NORTHEAST OF THE TERMINALS...SOUTHWEST WINDS
WILL STRENGTHEN TONIGHT...WITH A BRIEF BUT SUBSTANTIAL INCREASE
IN WINDS ALOFT. THUS HAVE MAINTAINED A PERIOD OF LLWS IN THE TAFS.
BEHIND THE LOW...WINDS WILL SHIFT TO NORTH-NORTHWEST BY TUESDAY
MORNING AND EVENTUALLY NORTHEAST TUESDAY AFTERNOON FOR THE EASTERN
TERMINALS. WILL NEED TO WATCH FOR A PERIOD OF LOWER MVFR
CIGS TUESDAY MORNING...WHICH HAS BEEN HINTED AT IN THE ORD 30
HOUR TAF.

RC


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN WIND FORECAST THROUGH MID AFTERNOON...LOW-MEDIUM THIS
  EVENING/TONIGHT...MEDIUM-HIGH TUESDAY MORNING.

* MEDIUM IN LLWS TONIGHT.

* LOW IN LOWER MVFR CIG POTENTIAL TUESDAY MORNING.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT...VFR WITH NORTHEAST WINDS.

WEDNESDAY...VFR. MODERATELY GUSTY SOUTH WINDS DEVELOPING.

THURSDAY...SHRA LIKELY...CHANCE TSRA. PERIODIC IFR POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY AND SUNDAY...LIKELY VFR.

RC

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300929
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
429 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LOW LEVEL WIND SHEAR POSSIBLE TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300929
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
429 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNESDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION
AHEAD OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH
FORECAST LOWS PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE
LEANED TOWARD THE CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO
THE SYSTEM COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A
MAJORITY OF THE SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER
AND THUNDERSTORM CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND
QUITE POSSIBLY EVEN MORE SO INTO THURSDAY. WITH THE PARENT LOW
RACING EAST...THE COLD FRONT IS FORECAST TO SLOW WITH A PARALLEL
UPPER JET INCREASING OVERHEAD...BRINGING ANOTHER WAVE ALONG THE
BOUNDARY DURING FRIDAY OR SO. OVER THE PAST TWO DAYS...GUIDANCE
HAS NOT SURPRISINGLY VARIED WITH HOW THIS ALL WILL MESH TOGETHER
IN OUR REGION...AND LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS
AND THUNDERSTORMS ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR
LATE WEDNESDAY NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF
UNCERTAINTY ON FRIDAY. THERE ALSO IS HIGHER THAN NORMAL
UNCERTAINTY FOR TEMPERATURES THURSDAY AND FRIDAY...WITH THE LATTER
LIKELY BEING COOLER...IF NOT CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* LOW LEVEL WIND SHEAR POSSIBLE TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
429 AM CDT

MAIN MARINE CONCERN IN THE NEAR TERM IS WITH A POSSIBLE PERIOD OF
STRONGER SOUTHWEST WINDS IN THE NEARSHORE TONIGHT. A CLIPPER
SYSTEM WILL DIVE SOUTHEAST AND CROSS SOUTHERN LAKE MICHIGAN
LATE THIS EVENING INTO THE OVERNIGHT. THE PATH THE LOW TAKES WILL
DICTATE WIND SPEEDS...WITH CURRENT FORECAST FAVORING A SLIGHTLY
FARTHER NORTH PATH SUPPORTIVE OF SOUTHWEST TO WEST WINDS OF 20 TO
25 KT. HOWEVER...A FARTHER SOUTH PATH WOULD RESULT IN LIGHTER
WESTERLY WINDS. DUE TO THIS LINGERING UNCERTAINTY...HAVE HELD OFF
ON ISSUING A SMALL CRAFT ADVISORY. NORTH OF THE LOW...NORTHEAST
WINDS WILL INCREASE TO UP TO 25 KT AND SOME POTENTIAL FOR A BRIEF
PERIOD OF GUSTS UP TO 30 KT LATE TONIGHT. NORTHERLY WINDS WILL
PUSH DOWN THE LAKE IN THE WAKE OF THE CLIPPER LOW ON TUESDAY.
HOWEVER...SPEEDS WILL DIMINISH FAIRLY QUICKLY FROM EARLY 15 TO 20
KT/POSSIBLY 25 KT SPEEDS TO START THE DAY...SO WAVES WILL NOT HAVE
MUCH TIME TO BUILD ON SOUTHERN TIP OF THE LAKE.

LIGHT WINDS TUESDAY NIGHT DUE TO HIGH PRESSURE WILL SHIFT
SOUTHERLY AS THE HIGH SLIDES EAST ON WEDNESDAY. STRONGER WINDS
WILL RETURN TO THE LAKE WEDNESDAY NIGHT AS A LARGE LOW PRESSURE
SYSTEM ORGANIZES IN THE UPPER PLAINS NEAR THE INTERNATIONAL
BORDER. THIS WILL DRIVE STRONG SOUTHERLY WINDS WITH A STOUT
INVERSION FORECAST. SO THE CHALLENGE RETURNS AS TO HOW MUCH
MOMENTUM WILL BE TRANSFERED DOWN TO THE SURFACE. FOR RIGHT NOW IN
THE NORTH HAVE MENTIONED OCCASIONAL GALES WHILE IN THE SOUTH TO 30
KT. THE LOW WILL STEER A COLD FRONT ACROSS THE LAKE ON
THURSDAY...RIGHT NOW FAVORED EARLY IN THE DAY...WHICH WILL TURN
WINDS WESTERLY AND DIMINISH THEM IN SPEED.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 300840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNSEDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION AHEAD
OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH FORECAST LOWS
PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE LEANED TOWARD THE
CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO THE SYSTEM
COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A MAJORITY OF THE
SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER AND THUNDERSTORM
CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND QUITE POSSIBLY EVEN
MORE SO INTO THURSDAY. WITH THE PARENT LOW RACING EAST...THE COLD
FRONT IS FORECAST TO SLOW WITH A PARALLEL UPPER JET INCREASING
OVERHEAD...BRINGING ANOTHER WAVE ALONG THE BOUNDARY DURING FRIDAY
OR SO. OVER THE PAST TWO DAYS...GUIDANCE HAS NOT SURPRISINGLY
VARIED WITH HOW THIS ALL WILL MESH TOGETHER IN OUR REGION...AND
LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS AND THUNDERSTORMS
ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR LATE WEDNESDAY
NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF UNCERTAINTY ON FRIDAY.
THERE ALSO IS HIGHER THAN NORMAL UNCERTAINTY FOR TEMPERATURES
THURSDAY AND FRIDAY...WITH THE LATTER LIKELY BEING COOLER...IF NOT
CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 300840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNSEDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION AHEAD
OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH FORECAST LOWS
PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE LEANED TOWARD THE
CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO THE SYSTEM
COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A MAJORITY OF THE
SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER AND THUNDERSTORM
CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND QUITE POSSIBLY EVEN
MORE SO INTO THURSDAY. WITH THE PARENT LOW RACING EAST...THE COLD
FRONT IS FORECAST TO SLOW WITH A PARALLEL UPPER JET INCREASING
OVERHEAD...BRINGING ANOTHER WAVE ALONG THE BOUNDARY DURING FRIDAY
OR SO. OVER THE PAST TWO DAYS...GUIDANCE HAS NOT SURPRISINGLY
VARIED WITH HOW THIS ALL WILL MESH TOGETHER IN OUR REGION...AND
LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS AND THUNDERSTORMS
ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR LATE WEDNESDAY
NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF UNCERTAINTY ON FRIDAY.
THERE ALSO IS HIGHER THAN NORMAL UNCERTAINTY FOR TEMPERATURES
THURSDAY AND FRIDAY...WITH THE LATTER LIKELY BEING COOLER...IF NOT
CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNSEDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION AHEAD
OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH FORECAST LOWS
PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE LEANED TOWARD THE
CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO THE SYSTEM
COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A MAJORITY OF THE
SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER AND THUNDERSTORM
CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND QUITE POSSIBLY EVEN
MORE SO INTO THURSDAY. WITH THE PARENT LOW RACING EAST...THE COLD
FRONT IS FORECAST TO SLOW WITH A PARALLEL UPPER JET INCREASING
OVERHEAD...BRINGING ANOTHER WAVE ALONG THE BOUNDARY DURING FRIDAY
OR SO. OVER THE PAST TWO DAYS...GUIDANCE HAS NOT SURPRISINGLY
VARIED WITH HOW THIS ALL WILL MESH TOGETHER IN OUR REGION...AND
LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS AND THUNDERSTORMS
ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR LATE WEDNESDAY
NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF UNCERTAINTY ON FRIDAY.
THERE ALSO IS HIGHER THAN NORMAL UNCERTAINTY FOR TEMPERATURES
THURSDAY AND FRIDAY...WITH THE LATTER LIKELY BEING COOLER...IF NOT
CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT MON MAR 30 2015

.SHORT TERM...
340 AM CDT

TODAY THROUGH TUESDAY...

MAIN WEATHER FEATURE OF NOTE TODAY IS AN ALBERTA CLIPPER
CURRENTLY OVER THE NORTHERN CANADIAN PRAIRIES THAT WILL DIVE
SOUTHEAST TOWARD SOUTHERN LAKE MICHIGAN THIS EVENING IN NORTHWEST
FLOW ALOFT. MILD DOWNSLOPE FLOW FROM THE HIGH PLAINS WILL RESULT
IN TEMPERATURES WARMING TO THE UPPER 50S TO LOWER 60S TODAY...WITH
ASSOCIATED WARM ADVECTION RESULTING IN MIDLEVEL CLOUDS INCREASING
BY MID DAY. MODERATE WESTERLY WINDS WILL SHIFT SOUTHWEST AND
DIMINISH...ESPECIALLY CLOSER TO THE LAKE BY LATE DAY AS THE
CLIPPER APPROACHES. WEAKENING WIND FIELD IS EXPECTED TO ENABLE A
LAKE BREEZE TO SLIP JUST INLAND ALONG THE IL SHORE AND BRING LATE
DAY COOLING. HAVE CONCERN WITH THE TRACK OF THE CLIPPER...WITH THE
ECMWF DECIDEDLY FARTHER SOUTH...THOUGH NORTH OF PREVIOUS RUN.
OVERALL...EVEN FARTHER SOUTH TRACK WILL BRING ONLY A GLANCING BLOW
OF RAIN SHOWERS TO NORTHEAST THIRD OR QUARTER OF CWA....SO HAVENT
MADE BIG CHANGES TO SLIGHT/LOW CHC POPS DURING EVENING.

TEMPERATURES WILL REMAIN MILD IN LOWER-MID 40S TONIGHT THANKS TO
GUSTY WEST-SOUTHWEST WINDS AS CLIPPER PASSES TO NORTHEAST...BUT
THEN THERE WILL BE A FAIRLY STRONG COLD FRONT PASSAGE IN THE WAKE
OF IT. 850 MB TEMPS WILL COOL TO ABOUT -2 CELSIUS NEAR THE LAKE BY
MID DAY TUESDAY...ALONG WITH FAIRLY STRONG NORTHERLY FLOW.
THEREFORE...HAVE SHAVED SEVERAL DEGREES OFF OF PREVIOUS FORECAST
HIGHS...WITH ONLY MID TO UPPER 40S NEAR THE LAKE AND MID 50S TO
LOWER 60S WELL INLAND. WINDS WILL SHIFT NORTHEAST DUE TO LAKE
BREEZE INFLUENCE TUESDAY AFTERNOON AND LAKE COOLING WILL PUSH
INLAND DURING THE MID TO LATE AFTERNOON. EXPECTING A CHILLY MID TO
UPPER 30S ALONG THE SHORE BY SUNSET....SO A BIG CHANGE FROM THE
MILD TEMPERATURES TODAY.

RC

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNSEDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION AHEAD
OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH FORECAST LOWS
PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE LEANED TOWARD THE
CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO THE SYSTEM
COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A MAJORITY OF THE
SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER AND THUNDERSTORM
CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND QUITE POSSIBLY EVEN
MORE SO INTO THURSDAY. WITH THE PARENT LOW RACING EAST...THE COLD
FRONT IS FORECAST TO SLOW WITH A PARALLEL UPPER JET INCREASING
OVERHEAD...BRINGING ANOTHER WAVE ALONG THE BOUNDARY DURING FRIDAY
OR SO. OVER THE PAST TWO DAYS...GUIDANCE HAS NOT SURPRISINGLY
VARIED WITH HOW THIS ALL WILL MESH TOGETHER IN OUR REGION...AND
LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS AND THUNDERSTORMS
ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR LATE WEDNESDAY
NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF UNCERTAINTY ON FRIDAY.
THERE ALSO IS HIGHER THAN NORMAL UNCERTAINTY FOR TEMPERATURES
THURSDAY AND FRIDAY...WITH THE LATTER LIKELY BEING COOLER...IF NOT
CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 300837
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
337 AM CDT MON MAR 30 2015

.SHORT TERM...
334 AM CDT

THROUGH TUESDAY...

TO BE ISSUED SHORTLY.

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNSEDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION AHEAD
OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH FORECAST LOWS
PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE LEANED TOWARD THE
CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO THE SYSTEM
COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A MAJORITY OF THE
SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER AND THUNDERSTORM
CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND QUITE POSSIBLY EVEN
MORE SO INTO THURSDAY. WITH THE PARENT LOW RACING EAST...THE COLD
FRONT IS FORECAST TO SLOW WITH A PARALLEL UPPER JET INCREASING
OVERHEAD...BRINGING ANOTHER WAVE ALONG THE BOUNDARY DURING FRIDAY
OR SO. OVER THE PAST TWO DAYS...GUIDANCE HAS NOT SURPRISINGLY
VARIED WITH HOW THIS ALL WILL MESH TOGETHER IN OUR REGION...AND
LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS AND THUNDERSTORMS
ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR LATE WEDNESDAY
NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF UNCERTAINTY ON FRIDAY.
THERE ALSO IS HIGHER THAN NORMAL UNCERTAINTY FOR TEMPERATURES
THURSDAY AND FRIDAY...WITH THE LATTER LIKELY BEING COOLER...IF NOT
CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 300837
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
337 AM CDT MON MAR 30 2015

.SHORT TERM...
334 AM CDT

THROUGH TUESDAY...

TO BE ISSUED SHORTLY.

&&

.LONG TERM...
332 AM CDT

TUESDAY NIGHT THROUGH SUNDAY...

THE UPPER PATTERN WILL REMAIN PROGRESSIVE DURING THE MID TO LATTER
HALF OF THE WEEK INTO NEXT WEEKEND. HEIGHT RISES AND A LOWER TROP
THERMAL RIDGE WILL MOVE IN TOGETHER ON WEDNESDAY. THE STARTING POINT
OF THE DAY WILL BE NEAR TO JUST SLIGHTLY BELOW NORMAL...SO FEEL
COMFORTABLE GOING WITH WEDNESDAY HIGHS NEAR WHERE THEY
CLIMATOLOGICALLY SHOULD BE FOR 850MB TEMPERATURES OF 7-10C THIS
TIME OF YEAR. THIS SUPPORTS 60S IN MOST PLACES WITH THE IMMEDIATE
ILLINOIS LAKE SHORE POTENTIALLY HAVING SLIGHT COOLING GIVEN A
FORECAST WIND DIRECTION OF 170 DEGREES OR SO.

AN UPPER TROUGH MOVING ACROSS SOUTHERN CANADA WEDNSEDAY NIGHT
THROUGH THURSDAY IS FORECAST TO TAKE ADVANTAGE OF JET COUPLING TO
STRENGTHEN AS IT MOVES EAST...WITH A SURFACE REFLECTION FORECAST
AROUND 992 MB USING A MEAN GLOBAL SOLUTION. THE WARM ADVECTION AHEAD
OF THIS WILL LEAD TO A MILD NIGHT WEDNESDAY NIGHT WITH FORECAST LOWS
PRESENTLY IN THE LOWER TO MID 50S /YES LOWS/. HAVE LEANED TOWARD THE
CONSISTENTLY SLOWER EC SOLUTION WITH REGARD TO THE SYSTEM
COLD FRONT...WHICH IS SUPPORTED BY THE NAM AND A MAJORITY OF THE
SREF MEMBERS. THIS WOULD KEEP MOST OF THE SHOWER AND THUNDERSTORM
CHANCES CONFINED TO LATE WEDNESDAY NIGHT AND QUITE POSSIBLY EVEN
MORE SO INTO THURSDAY. WITH THE PARENT LOW RACING EAST...THE COLD
FRONT IS FORECAST TO SLOW WITH A PARALLEL UPPER JET INCREASING
OVERHEAD...BRINGING ANOTHER WAVE ALONG THE BOUNDARY DURING FRIDAY
OR SO. OVER THE PAST TWO DAYS...GUIDANCE HAS NOT SURPRISINGLY
VARIED WITH HOW THIS ALL WILL MESH TOGETHER IN OUR REGION...AND
LIKELY CHANGES WILL OCCUR. CHANCES FOR SHOWERS AND THUNDERSTORMS
ARE PRESENTLY MOST WARRANTED IN THE FORECAST FOR LATE WEDNESDAY
NIGHT AND THURSDAY...WITH A HIGH AMOUNT OF UNCERTAINTY ON FRIDAY.
THERE ALSO IS HIGHER THAN NORMAL UNCERTAINTY FOR TEMPERATURES
THURSDAY AND FRIDAY...WITH THE LATTER LIKELY BEING COOLER...IF NOT
CONSIDERABLY COOLER THAN THURSDAY.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300547
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1247 AM CDT MON MAR 30 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 300547
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1247 AM CDT MON MAR 30 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300547
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1247 AM CDT MON MAR 30 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* LOW LEVEL WIND SHEAR AROUND MIDNIGHT TONIGHT.

RC

//DISCUSSION...UPDATED 06Z...

CONDITIONS SHOULD GENERALLY REMAIN VFR THROUGH THE PERIOD. SCT TO
BKN VFR CLOUDS ARE STREAMING SOUTHEAST FROM SOUTHERN WI INTO
NORTHERN IL AND NW IN BUT SHOULD SHIFT EAST THIS
MORNING...FOLLOWED BY INCREASING VFR CLOUDS BY MID DAY. CURRENTLY
LIGHT WEST WINDS WILL INCREASE BY MID DAY AND GUST INTO THE MID-
HIGH TEENS INTO THE MID AFTERNOON. MAIN WEATHER FEATURE OF NOTE
IS A CLIPPER TYPE SYSTEM THAT WILL DIVE SOUTHEAST TODAY AND ACROSS
SOUTHERN LAKE MICHIGAN THIS EVENING. WINDS WILL SHIFT SOUTHWEST
LATE IN THE DAY IN ADVANCE OF THE CLIPPER AND MAY DIMINISH ENOUGH
TO ENABLE A LAKE BREEZE TO SLIP INLAND ALONG THE IMMEDIATE IL
SHORE...LIKELY WELL EAST OF ORD AND MDW. MOST GUIDANCE KEEPS
PRECIP WITH THE CLIPPER NORTH OF THE TERMINALS...SO HAVE STAYED
WITH A DRY FORECAST. SOUTHWEST WINDS WILL INCREASE TONIGHT AS THE
SYSTEM TRACKS JUST TO THE NORTHEAST...WITH A BRIEF BUT SUBSTANTIAL
INCREASE IN WINDS ALOFT. THUS HAVE INCLUDED A PERIOD OF LLWS IN
THE TAFS.

RC


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH IN LLWS TONIGHT.

* HIGH IN REMAINING ELEMENTS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300312
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1012 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* NONE

IZZI

//DISCUSSION...UPDATED 00Z...

COLD FRONT WILL CONTINUE TO MOVE ACROSS THE TERMINALS EARLY THIS
EVENING WITH A BRIEF PERIOD OF LIGHT RAIN/SPRINKLES ALONG THE
FRONT. SMALL AREA OF MVFR CIGS WILL PROBABLY AFFECT THE TERMINALS
ALONG AND IMMEDIATELY IN THE WAKE OF THE FRONT BEFORE SKIES GO SKC
LATER THIS EVENING. IN ADDITION...THE PUSH IMMEDIATELY BEHIND
FRONT COULD HAVE AN HOUR OR TWO OR STRONG NORTHWEST WINDS
POTENTIALLY GUSTING UP TO AROUND 30KT BEFORE WINDS BACK A BIT MORE
WESTERLY AND EASE MID-LATE EVENING. A VFR CEILING COULD MOVE BACK
IN WITH MID LEVEL CLOUDINESS AND POTENTAILLY SOME VIRGA OR EVEN
A SPRINKLE MONDAY AFTERNOON WITH CONTINUED LIGHT WESTERLY WINDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 300312
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1012 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* NONE

IZZI

//DISCUSSION...UPDATED 00Z...

COLD FRONT WILL CONTINUE TO MOVE ACROSS THE TERMINALS EARLY THIS
EVENING WITH A BRIEF PERIOD OF LIGHT RAIN/SPRINKLES ALONG THE
FRONT. SMALL AREA OF MVFR CIGS WILL PROBABLY AFFECT THE TERMINALS
ALONG AND IMMEDIATELY IN THE WAKE OF THE FRONT BEFORE SKIES GO SKC
LATER THIS EVENING. IN ADDITION...THE PUSH IMMEDIATELY BEHIND
FRONT COULD HAVE AN HOUR OR TWO OR STRONG NORTHWEST WINDS
POTENTIALLY GUSTING UP TO AROUND 30KT BEFORE WINDS BACK A BIT MORE
WESTERLY AND EASE MID-LATE EVENING. A VFR CEILING COULD MOVE BACK
IN WITH MID LEVEL CLOUDINESS AND POTENTAILLY SOME VIRGA OR EVEN
A SPRINKLE MONDAY AFTERNOON WITH CONTINUED LIGHT WESTERLY WINDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 300312
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1012 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* NONE

IZZI

//DISCUSSION...UPDATED 00Z...

COLD FRONT WILL CONTINUE TO MOVE ACROSS THE TERMINALS EARLY THIS
EVENING WITH A BRIEF PERIOD OF LIGHT RAIN/SPRINKLES ALONG THE
FRONT. SMALL AREA OF MVFR CIGS WILL PROBABLY AFFECT THE TERMINALS
ALONG AND IMMEDIATELY IN THE WAKE OF THE FRONT BEFORE SKIES GO SKC
LATER THIS EVENING. IN ADDITION...THE PUSH IMMEDIATELY BEHIND
FRONT COULD HAVE AN HOUR OR TWO OR STRONG NORTHWEST WINDS
POTENTIALLY GUSTING UP TO AROUND 30KT BEFORE WINDS BACK A BIT MORE
WESTERLY AND EASE MID-LATE EVENING. A VFR CEILING COULD MOVE BACK
IN WITH MID LEVEL CLOUDINESS AND POTENTAILLY SOME VIRGA OR EVEN
A SPRINKLE MONDAY AFTERNOON WITH CONTINUED LIGHT WESTERLY WINDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 292351
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
651 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* BRIEF PERIOD OF -RA/MVFR CIGS/30KT NW WINDS WITH FRONTAL PASSAGE
  THIS EVENING

IZZI

//DISCUSSION...UPDATED 00Z...

COLD FRONT WILL CONTINUE TO MOVE ACROSS THE TERMINALS EARLY THIS
EVENING WITH A BRIEF PERIOD OF LIGHT RAIN/SPRINKLES ALONG THE
FRONT. SMALL AREA OF MVFR CIGS WILL PROBABLY AFFECT THE TERMINALS
ALONG AND IMMEDIATELY IN THE WAKE OF THE FRONT BEFORE SKIES GO SKC
LATER THIS EVENING. IN ADDITION...THE PUSH IMMEDIATELY BEHIND
FRONT COULD HAVE AN HOUR OR TWO OR STRONG NORTHWEST WINDS
POTENTIALLY GUSTING UP TO AROUND 30KT BEFORE WINDS BACK A BIT MORE
WESTERLY AND EASE MID-LATE EVENING. A VFR CEILING COULD MOVE BACK
IN WITH MID LEVEL CLOUDINESS AND POTENTAILLY SOME VIRGA OR EVEN
A SPRINKLE MONDAY AFTERNOON WITH CONTINUED LIGHT WESTERLY WINDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN CIGS/PRECIP/WINDS THROUGH MID EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 292351
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
651 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* BRIEF PERIOD OF -RA/MVFR CIGS/30KT NW WINDS WITH FRONTAL PASSAGE
  THIS EVENING

IZZI

//DISCUSSION...UPDATED 00Z...

COLD FRONT WILL CONTINUE TO MOVE ACROSS THE TERMINALS EARLY THIS
EVENING WITH A BRIEF PERIOD OF LIGHT RAIN/SPRINKLES ALONG THE
FRONT. SMALL AREA OF MVFR CIGS WILL PROBABLY AFFECT THE TERMINALS
ALONG AND IMMEDIATELY IN THE WAKE OF THE FRONT BEFORE SKIES GO SKC
LATER THIS EVENING. IN ADDITION...THE PUSH IMMEDIATELY BEHIND
FRONT COULD HAVE AN HOUR OR TWO OR STRONG NORTHWEST WINDS
POTENTIALLY GUSTING UP TO AROUND 30KT BEFORE WINDS BACK A BIT MORE
WESTERLY AND EASE MID-LATE EVENING. A VFR CEILING COULD MOVE BACK
IN WITH MID LEVEL CLOUDINESS AND POTENTAILLY SOME VIRGA OR EVEN
A SPRINKLE MONDAY AFTERNOON WITH CONTINUED LIGHT WESTERLY WINDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN CIGS/PRECIP/WINDS THROUGH MID EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 292351
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
651 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* BRIEF PERIOD OF -RA/MVFR CIGS/30KT NW WINDS WITH FRONTAL PASSAGE
  THIS EVENING

IZZI

//DISCUSSION...UPDATED 00Z...

COLD FRONT WILL CONTINUE TO MOVE ACROSS THE TERMINALS EARLY THIS
EVENING WITH A BRIEF PERIOD OF LIGHT RAIN/SPRINKLES ALONG THE
FRONT. SMALL AREA OF MVFR CIGS WILL PROBABLY AFFECT THE TERMINALS
ALONG AND IMMEDIATELY IN THE WAKE OF THE FRONT BEFORE SKIES GO SKC
LATER THIS EVENING. IN ADDITION...THE PUSH IMMEDIATELY BEHIND
FRONT COULD HAVE AN HOUR OR TWO OR STRONG NORTHWEST WINDS
POTENTIALLY GUSTING UP TO AROUND 30KT BEFORE WINDS BACK A BIT MORE
WESTERLY AND EASE MID-LATE EVENING. A VFR CEILING COULD MOVE BACK
IN WITH MID LEVEL CLOUDINESS AND POTENTAILLY SOME VIRGA OR EVEN
A SPRINKLE MONDAY AFTERNOON WITH CONTINUED LIGHT WESTERLY WINDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN CIGS/PRECIP/WINDS THROUGH MID EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 292351
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
651 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* BRIEF PERIOD OF -RA/MVFR CIGS/30KT NW WINDS WITH FRONTAL PASSAGE
  THIS EVENING

IZZI

//DISCUSSION...UPDATED 00Z...

COLD FRONT WILL CONTINUE TO MOVE ACROSS THE TERMINALS EARLY THIS
EVENING WITH A BRIEF PERIOD OF LIGHT RAIN/SPRINKLES ALONG THE
FRONT. SMALL AREA OF MVFR CIGS WILL PROBABLY AFFECT THE TERMINALS
ALONG AND IMMEDIATELY IN THE WAKE OF THE FRONT BEFORE SKIES GO SKC
LATER THIS EVENING. IN ADDITION...THE PUSH IMMEDIATELY BEHIND
FRONT COULD HAVE AN HOUR OR TWO OR STRONG NORTHWEST WINDS
POTENTIALLY GUSTING UP TO AROUND 30KT BEFORE WINDS BACK A BIT MORE
WESTERLY AND EASE MID-LATE EVENING. A VFR CEILING COULD MOVE BACK
IN WITH MID LEVEL CLOUDINESS AND POTENTAILLY SOME VIRGA OR EVEN
A SPRINKLE MONDAY AFTERNOON WITH CONTINUED LIGHT WESTERLY WINDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM CONFIDENCE IN CIGS/PRECIP/WINDS THROUGH MID EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...VFR. WIND SHIFT TO NE WINDS PROBABLY 10KT OR GREATER.

WEDNESDAY...VFR. MODERATELY STRONG SOUTH WINDS DURING AFTERNOON.

WEDNESDAY NIGHT AND THURSDAY...PERIOD OF SHRA/TSRA. PERIODIC IFR
POSSIBLE.

FRIDAY...CHANCE OF MVFR CIGS. NE WINDS 10KT OR GREATER POSSIBLE.

SATURDAY...PROBABLY VFR.

IZZI

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 292144
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
444 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* STRONG SOUTHWEST WINDS THROUGH 23-00Z POSSIBLY GUSTING OVER 30KT
  AT TIMES
* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE AROUND
  00Z.
* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT AN EARLY 22Z AMENDMENT TO BACK OFF ON GUSTS THROUGH 23Z.
ACARS SOUNDINGS SHOW WINDS IN THE MIXED LAYER SLOWING EASING A
BIT. STRONGEST PRESSURE FALLS CONTINUE TO PUSH AWAY AND ANY
CLEARING LOOKS TO BE VERY SHORT LIVED AND CHANCES OF TOP OF THE
CHANNEL MIXING DOWN OF 35KT+ GUSTS ARE QUICKLY FADING. A BRIEF
GUST OR TWO UP TO 35KT CANNOT COMPLETELY BE RULED OUT BUT
PREVAILING GUSTS SHOULD REMAIN MOSTLY BELOW 30KT REST OF THE
AFTERNOON. BAND OF -RA/-SHRA IS DEVELOPING OVER SOUTHERN WI WITH
THE FRONT SO HAVE ADDED A SHORT PERIOD OF PREVAILING -RA/MVFR CIGS
AHEAD OF THE FRONT.

IZZI

UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THIS EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 292144
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
444 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* STRONG SOUTHWEST WINDS THROUGH 23-00Z POSSIBLY GUSTING OVER 30KT
  AT TIMES
* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE AROUND
  00Z.
* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT AN EARLY 22Z AMENDMENT TO BACK OFF ON GUSTS THROUGH 23Z.
ACARS SOUNDINGS SHOW WINDS IN THE MIXED LAYER SLOWING EASING A
BIT. STRONGEST PRESSURE FALLS CONTINUE TO PUSH AWAY AND ANY
CLEARING LOOKS TO BE VERY SHORT LIVED AND CHANCES OF TOP OF THE
CHANNEL MIXING DOWN OF 35KT+ GUSTS ARE QUICKLY FADING. A BRIEF
GUST OR TWO UP TO 35KT CANNOT COMPLETELY BE RULED OUT BUT
PREVAILING GUSTS SHOULD REMAIN MOSTLY BELOW 30KT REST OF THE
AFTERNOON. BAND OF -RA/-SHRA IS DEVELOPING OVER SOUTHERN WI WITH
THE FRONT SO HAVE ADDED A SHORT PERIOD OF PREVAILING -RA/MVFR CIGS
AHEAD OF THE FRONT.

IZZI

UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THIS EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 292144
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
444 PM CDT SUN MAR 29 2015

.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* STRONG SOUTHWEST WINDS THROUGH 23-00Z POSSIBLY GUSTING OVER 30KT
  AT TIMES
* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE AROUND
  00Z.
* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

IZZI

//DISCUSSION...UPDATED 22Z...

SENT AN EARLY 22Z AMENDMENT TO BACK OFF ON GUSTS THROUGH 23Z.
ACARS SOUNDINGS SHOW WINDS IN THE MIXED LAYER SLOWING EASING A
BIT. STRONGEST PRESSURE FALLS CONTINUE TO PUSH AWAY AND ANY
CLEARING LOOKS TO BE VERY SHORT LIVED AND CHANCES OF TOP OF THE
CHANNEL MIXING DOWN OF 35KT+ GUSTS ARE QUICKLY FADING. A BRIEF
GUST OR TWO UP TO 35KT CANNOT COMPLETELY BE RULED OUT BUT
PREVAILING GUSTS SHOULD REMAIN MOSTLY BELOW 30KT REST OF THE
AFTERNOON. BAND OF -RA/-SHRA IS DEVELOPING OVER SOUTHERN WI WITH
THE FRONT SO HAVE ADDED A SHORT PERIOD OF PREVAILING -RA/MVFR CIGS
AHEAD OF THE FRONT.

IZZI

UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THIS EVENING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 292036
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
336 PM CDT SUN MAR 29 2015


.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 292036
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
336 PM CDT SUN MAR 29 2015


.SHORT TERM...
334 PM CDT

THIS EVENING THROUGH THURSDAY...

LOW PRESSURE WAS MOVING NORTH OF THE GREAT LAKES OVER ONTARIO
THIS AFTERNOON...TRAILING AN OCCLUDED FRONT INTO THE UPPER
MISSISSIPPI VALLEY TO A TRIPLE POINT SOMEWHERE NEAR NORTHEAST
IOWA. FROM THERE A WARM FRONT EXTENDED SOUTH ALONG THE MISSISSIPPI
RIVER ITSELF...WHILE A COLD FRONT WAS A LITTLE FURTHER TO THE WEST
ACROSS CENTRAL AND EAST CENTRAL IOWA. THIS COMPLEX SYNOPSIS OF
SURFACE FEATURES WILL BRING SEVERAL HOURS OF CHANGABLE WEATHER
ACROSS THE FORECAST AREA... WITH SHOWERS EXITING TO THE
EAST/SOUTHEAST COUNTIES THIS AFTERNOON WHILE SOME CLEARING OF
CLOUD COVER WORKS IN FROM THE SOUTHWEST. TEMPERATURES BEHIND BOTH
THE WARM AND COLD FRONTS ARE WARMER THAN OUR CURRENT MID-UPPER
30S...THUS LATE DAY RISES IN TO THE 40S OR EVEN A FEW LOWER 50S
ARE EXPECTED THROUGH SUNSET. IN ADDITION... NEAR-TERM HIGH-RES
GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR SHOWERS TO
DEVELOP ALONG/AHEAD OF THE FRONT AS WE HEAD INTO EARLY
EVENING...THUS HAVE MAINTAINED A PERIOD OF CHANCE POPS WITH THE
FRONT FROM WEST TO EAST THROUGH MID-EVENING. GUSTY WINDS OF 30 TO
40 MPH...INITIALLY FROM THE SOUTH-SOUTHWEST AND THEN SHIFTING TO
THE WEST-NORTHWEST THIS EVENING...WILL CONTINUE AS WELL BEFORE
DIMINISHING TONIGHT. AIR MASS BEHIND THIS FRONT IS OF A PACIFIC
NATURE HOWEVER...AND MONDAY WILL BE MILDER THAN TODAY WITH MORE
SUNSHINE. A SHEARED MID-LEVEL WAVE APPROACHES IN NORTHWEST FLOW
ALOFT LATER MONDAY HOWEVER...WITH A SURFACE LOW PRESSURE
PROPAGATING SOUTHEAST FROM WI ACROSS SOUTHERN LAKE MICHIGAN AND
INTO INDIANA/OHIO BY TUESDAY MORNING. THIS WILL LIKELY BRING SOME
INCREASE IN CLOUD COVER TO EASTERN PARTS OF THE CWA LATER MONDAY
AFTERNOON AND NIGHT...WITH SOME GUIDANCE INDICATING LIGHT RAIN
DEVELOPING DURING THE EVENING.

THE LOW PULLS OFF TO THE SOUTHEAST ON TUESDAY...WITH TRAILING
COLD FRONT SAGGING ACROSS THE AREA AS SURFACE HIGH SPREADS ACROSS
THE NORTHERN LAKES. WHILE TEMPS SHOULD REACH THE UPPER 50S/NEAR 60
AWAY FROM THE LAKE...IT LOOKS LIKE THE FRONT/LAKE BREEZE COMBO
WILL LIKELY PRODUCE FALLING TEMPS ACROSS NORTHEAST IL/NORTHWEST
IND DURING THE AFTERNOON AS WINDS SHIFT NORTHEAST AND DROP TEMPS
NEAR THE LAKE. MORE AMPLIFIED UPPER TROUGH/LOW THEN COMES OUT OF
THE PACIFIC NORTHWEST AND ALONG THE INTERNATIONAL BORDER WEDNESDAY
HOWEVER...DEVELOPING DEEP SURFACE LOW WHICH MOVES INTO MANITOBA
AND WESTERN ONTARIO WEDNESDAY NIGHT. THIS RESULTS IN SOUTH WINDS
RETURNING AND BECOMING BREEZY...BUT PULLING TEMPS BACK UP ACROSS
THE CWA. LOW LEVEL THERMAL PROGS SUGGEST 70 MAY NOT BE OUT OF
REACH ESPECIALLY IN THE FAR WEST...WHILE 60S ARE LIKELY TO THE
EAST. COULD BE A LITTLE LAKE COOLING ALONG THE NORTH SHORE WITH
SLIGHT SOUTHEAST COMPONENT TO THE WIND ALONG THE LAKE.

RAIN AND THUNDERSTORM CHANCES THEN INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS COLD FRONT TRAILING FROM CANADIAN LOW APPROACHES AND
PASSES. THURSDAY COULD POTENTIALLY BE ANOTHER WARM DAY DEPENDING
ON TIMING OF THE COLD FRONT...AND CLOUD/PRECIP COVERAGE. MID 60S
APPEAR REASONABLE AT THIS DISTANCE.

RATZER

&&

.LONG TERM...
334 PM CDT

FRIDAY THROUGH SUNDAY...

THOUGH PATTERN REMAINS SOMEWHAT PROGRESSIVE THROUGH THE PERIOD...
GUIDANCE IN GOOD AGREEMENT IN DEVELOPING LARGE SCALE TROUGH OVER
THE EASTERN PORTION OF NORTH AMERICA FRIDAY INTO NEXT WEEKEND.
THIS SETS UP COOL HIGH PRESSURE ACROSS THE UPPER MIDWEST AND GREAT
LAKES... WITH RELATIVELY LOW PRECIP CHANCES. SOME MODERATION
EXPECTED AS THE HIGH MOVES EAST TOWARD THE END OF THE PERIOD.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 292000
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 03Z/10PM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 292000 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 292000 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
259 PM CDT

OBS ARE NOT SUPPORTING STORM FORCE GUSTS OVER THE NORTHERN HALF OF
THE LAKE SO WILL DROP THE STORM FORCE WARNING WITH THE AFTN UPDATE.
GUIDANCE ALSO HOLDS ON TO GALES OVER THE OPEN WATERS INTO THIS
EVENING SO EXTENDED THE OPEN WATER GALE WARNING INTO THIS EVENING.
WILL HOLD ON TO THE CURRENT NSH GALE WARNING UNTIL 7PM CDT/00Z. A
SMALL CRAFT ADVISORY WILL THEN BE NEEDED THROUGH 09Z/4AM CDT.

WITH HIGH PRESSURE TO OUR SE AND LOW PRESSURE TO OUR NORTH...WE ARE
UNDER A TIGHTENED PRESSURE GRADIENT RESULTING IN STRONG WINDS.  THE
GRADIENT WEAKENS AS BOTH FEATURES CONTINUE EAST AND THE LOWS COLD
FRONT SWINGS OVERHEAD THIS EVENING. WINDS WILL DIMINISH AND TURN
WEST BEHIND THE COLD FRONT.  LIGHT WINDS BECOME SOUTHEAST OR SOUTH
BY MONDAY EVENING AS A WEAK RIDGE SCOOTS BY.  A WEAK LOW PASSES OVER
THE SOUTHERN END OF THE LAKE LATE MONDAY NIGHT INTO TUESDAY MORNING
WITH EAST WINDS OVER THE NORTHERN HALF OF THE LAKE AND SOUTHWEST TO
WEST WINDS OVER THE SOUTHERN HALF BOTH 10-20 KT.  HIGH PRESSURE THEN
SLIDES OVER THE LAKE TUESDAY EVENING WITH WINDS BECOMING EAST
OVERNIGHT.  SOUTH WINDS INCREASE TO 30 KT WEDNESDAY AFTERNOON AHEAD
OF THE NEXT LOW THAT PASSES OVER ONTARIO THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 9 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* SOUTHWEST TO SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT AND
  EXPECTED TO INCREASE TO AROUND 35 KT FOR A FEW HOURS TOWARDS
  21Z. CANNOT RULE OUT GUSTS NEAR 40 KT FOR A SHORT TIME.

* WINDS TREND MORE SOUTHWEST THEN WEST TOWARD 00Z WITH SPEEDS
  EASING.

* CHANCE FOR SCATTERED SHOWERS WITH A COLD FRONTAL PASSAGE TOWARD
  00Z.

* SHORT PERIOD OF MVFR CIGS POSSIBLE EARLY THIS EVENING.

MDB

//DISCUSSION...UPDATED 20Z...

SATELLITE SHOWS A WEDGE OF SCATTERING SKIES NOSING INTO NORTHERN
ILLINOIS WHICH WILL SPREAD ACROSS ORD/MDW/DPA/GYY IN THE NEXT FEW
HOURS. THIS WILL LIKELY ALLOW MORE FREQUENT GUSTS AS WELL AS AN
INCREASE IN GUST MAGNITUDE. AREAS THAT HAVE SCATTERED TO THE WEST
ARE REACHING THEIR EXPECTED GUST POTENTIAL THOUGH WIND SPEEDS
ABOVE THE SURFACE ARE LOWER THERE THAN THEY ARE LOCALLY. THIS
RAISES THE CONCERN THAT GUSTS WILL EXCEED 35 KT FOR A SHORT TIME
AS MIXING DEEPENS WITH DECREASING CLOUD COVER AND COULD REACH 40
KT. WIND SPEEDS THEN EASE UP AS A COLD FRONT APPROACHES TOWARD
00Z. RETAINED TEMPO SHOWER MENTION FOR NOW AS THERE MAY BE SOME
DEVELOPMENT AHEAD OF THE FRONT BUT COVERAGE MAY BE MINIMAL.

FROM 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN WIND DIRECTION TRENDS/TIMING. HIGH CONFIDENCE
  IN 30 KT GUSTS WITH MEDIUM CONFIDENCE IN 35 KT GUSTS AND LOW
  CONFIDENCE THAT THEY WILL PUSH 40 KT. MEDIUM-HIGH CONFIDENCE IN
  HIGHEST GUSTS OCCURRING FOR A FEW HOURS STARTING AROUND 21Z.

* MEDIUM CONFIDENCE IN SOME SHOWER ACTIVITY WITH FRONTAL PASSAGE.

* MEDIUM CONFIDENCE THAT CHANCE FOR MVFR STRATUS IS LOW THIS
  EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291752
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1252 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LINGERING DRIZZLE/LIGHT RAIN EXITING WITHIN THE NEXT HOUR.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT WITH SOMEWHAT
  ERRATIC FREQUENCY. THINNING CLOUD COVER MAY ALLOW FOR INCREASED
  GUSTS AROUND 35 KT MID AFTERNOON.

* WINDS SHIFT WEST-NORTHWEST AROUND 00Z WITH SPEEDS EASING.

* MVFR CIGS POSSIBLE THIS EVENING.

MDB

//DISCUSSION...UPDATED 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN PRECIP FORECAST.

* MEDIUM-HIGH CONFIDENCE IN PERIODIC 30 KT GUSTS EARLY AFTERNOON.
  MEDIUM CONFIDENCE IN 35 KT GUSTS OCCURRING MID/LATE AFTERNOON.
  MEDIUM-HIGH CONFIDENCE IN TIMING OF WIND SHIFT.

* LOW CONFIDENCE IN MVFR POTENTIAL THIS EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291752
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1252 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LINGERING DRIZZLE/LIGHT RAIN EXITING WITHIN THE NEXT HOUR.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT WITH SOMEWHAT
  ERRATIC FREQUENCY. THINNING CLOUD COVER MAY ALLOW FOR INCREASED
  GUSTS AROUND 35 KT MID AFTERNOON.

* WINDS SHIFT WEST-NORTHWEST AROUND 00Z WITH SPEEDS EASING.

* MVFR CIGS POSSIBLE THIS EVENING.

MDB

//DISCUSSION...UPDATED 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN PRECIP FORECAST.

* MEDIUM-HIGH CONFIDENCE IN PERIODIC 30 KT GUSTS EARLY AFTERNOON.
  MEDIUM CONFIDENCE IN 35 KT GUSTS OCCURRING MID/LATE AFTERNOON.
  MEDIUM-HIGH CONFIDENCE IN TIMING OF WIND SHIFT.

* LOW CONFIDENCE IN MVFR POTENTIAL THIS EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291752
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1252 PM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LINGERING DRIZZLE/LIGHT RAIN EXITING WITHIN THE NEXT HOUR.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH-SOUTHWEST WINDS GUSTING TO AROUND 30 KT WITH SOMEWHAT
  ERRATIC FREQUENCY. THINNING CLOUD COVER MAY ALLOW FOR INCREASED
  GUSTS AROUND 35 KT MID AFTERNOON.

* WINDS SHIFT WEST-NORTHWEST AROUND 00Z WITH SPEEDS EASING.

* MVFR CIGS POSSIBLE THIS EVENING.

MDB

//DISCUSSION...UPDATED 18Z...

THE MAIN AREA OF PRECIP IS EXITING TO THE EAST WITH A SMALL AREA
OF DRIZZLE ON THE BACK EDGE...WHICH IS LEADING TO A LOWERING OF
CIGS TOWARDS 030...THOUGH THIS DOES NOT LOOK TO LAST BEYOND 19Z.
UPSTREAM OBS/SATELLITE TRENDS SUPPORT A THINNING OF CLOUDS INTO
MID AFTERNOON THOUGH SOME STRATO CU MAY FORM. COULD BE TOO
PESSIMISTIC WITH BROKEN LOWER LEVEL CLOUD COVER BY MID AFTERNOON.
WIND GUSTS HAVE BEEN ERRATIC BUT SHOWING SIGNS OF INCREASING TO
THE WEST WHERE CLOUDS ARE THINNING. WINDS QUICKLY INCREASE OFF THE
DECK SO IT WILL NOT TAKE MUCH TO REALIZE 30-35 KT GUSTS AT THE
SURFACE. FREQUENCY OF 30+ KT GUSTS LOOKS TO BE LOW BEFORE
20Z...BUT DECREASING LOWER CLOUD COVER WOULD BE SUPPORTIVE OF
INCREASED GUSTS BY MID AFTERNOON. SHOULD THERE BE A PERIOD OF
DECENT SUNSHINE THEN GUSTS MAY TOP 35 KT FOR A SHORT TIME.

A COLD FRONT WILL BE CROSSING THE AREA LATE THIS AFTERNOON AND
EARLY THIS EVENING TURNING WINDS WEST TO WEST-NORTHWEST. HAVE SPED
UP THE PASSAGE OF THE FRONT BY ABOUT AN HOUR AND BUMPED UP GUSTS A
BIT BEHIND IT. MVFR STRATUS MAY ALSO BECOME BROKEN FOR A FEW HOURS
BUT MUCH OF WHAT IS BEHIND THE FRONT NOW LOOKS TO BE DIURNALLY
DRIVEN SO OPTED TO KEEP SCATTERED MVFR LEVEL CLOUDS. WINDS WILL
EASE UP THROUGH THE EVENING WITH CLOUD COVER DIMINISHING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN PRECIP FORECAST.

* MEDIUM-HIGH CONFIDENCE IN PERIODIC 30 KT GUSTS EARLY AFTERNOON.
  MEDIUM CONFIDENCE IN 35 KT GUSTS OCCURRING MID/LATE AFTERNOON.
  MEDIUM-HIGH CONFIDENCE IN TIMING OF WIND SHIFT.

* LOW CONFIDENCE IN MVFR POTENTIAL THIS EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291659
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1159 AM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291659
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1159 AM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291659
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1159 AM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291659
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1159 AM CDT SUN MAR 29 2015

.UPDATE...

FOR LATE MORNING UPDATE...
1159 AM CDT

BAND OF RAIN...INITIALLY MIXED WITH SLEET AND SOME WET SNOW...WAS
MOVING ACROSS THE CENTRAL AND EASTERN PARTS OF THE FORECAST AREA AT
MIDDAY IN ASSOCIATION WITH WARM/MOIST ADVECTION COINCIDENT WITH
ELEVATED WARM FRONTAL FEATURE IN ADVANCE OF MID-LEVEL SHORT WAVE
TRACKING ACROSS THE UPPER MIDWEST. WHILE MANY METARS AND PING
PROJECT OBS HAVE REPORTED RAIN MIXED WITH SLEET/SNOW...SURFACE
TEMPERATURES HAVE WARMED INTO THE MID-UPPER 30S FOR THE MOST PART
AND WARMING LOW-LEVEL THERMAL PROFILES AND LOSS OF MOISTURE IN ICE
PRODUCTION LAYER SHOULD SUPPORT JUST RAIN FOR ANY LINGERING
PRECIPITATION BEHIND THE INITIAL BAND INTO THIS AFTERNOON. AS FOR
TIMING...INITIAL HEAVIER BAND SHOULD CONTINUE TO MOVE EAST OF THE
CWA EARLY THIS AFTERNOON...THOUGH ADDITIONAL SHOWERS ARE EXPECTED TO
DEVELOP LATER AS COLD FRONT CURRENTLY ACROSS CENTRAL IOWA APPROACHES
ALONG WITH SUPPORT FROM SECOND VORT DIGGING INTO THE REGION FROM THE
NORTHWEST. THESE SHOWERS SHOULD EXIT THE AREA EARLY THIS EVENING AS
COLD FRONT SWEEPS THROUGH.

OTHERWISE...VERY GUSTY SOUTH WINDS WILL CONTINUE TO SLOWLY WARM
TEMPERATURES ACROSS THE AREA THROUGH LATE AFTERNOON...WITH UPSTREAM
TEMPS FROM THE MID 40S TO AROUND 50 EXPECTED TO SPREAD INTO THE CWA
LATE. SOUTH WINDS WILL CONTINUE TO GUST NEAR 40 MPH BEFORE
EVENTUALLY SHIFTING WEST AND DIMINISHING A BIT EARLY THIS EVENING
BEHIND THE COLD FRONT.

RATZER

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291624
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1124 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291624
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1124 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291624
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1124 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291624
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1124 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* RAIN EXITING TOWARD 1730Z. BRIEF MVFR VSBY POSSIBLE UNTIL THEN.
  ADDITIONAL SHOWERS POSSIBLE LATE AFTERNOON.

* SOUTH TO SOUTH-SOUTHWEST WINDS GUSTING 30-35 KT THROUGH THE
  AFTERNOON BECOMING WEST THEN NORTHWEST WITH COLD FRONTAL
  PASSAGE 00 OR 01Z.

* CIGS MAY LOWER TO NEAR 030 THIS AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

PRECIP IS MOVING ACROSS THE CHICAGO/NW IN TERMINALS AND EXITING
THE RFD AREA. UPSTREAM OBS BEHIND THE RAINFALL SHOW LOWER GUSTS
BUT WOULD EXPECT THIS TO BE SHORT LIVED WITH MIXING RECOVERING.
WILL NEED TO KEEP AN EYE ON THIS THOUGH. CLOUD COVER MAY MAY
ULTIMATELY TEMPER THE FREQUENCY OF GUSTS...ESPECIALLY PRIOR TO
18Z. OBS SHOW A SMALL AREA OF MVFR CIGS ACROSS NORTHEAST IOWA AND
MAY SKIRT RFD INTO MIDDAY BUT WILL KEEP THIS NORTH OF THE OTHER
TERMINALS FOR NOW. SOME SPOTTY SHOWERS OR SPRINKLES MAY LINGER
THROUGH THE AFTERNOON BUT WILL DRY THE TAFS OUT UNTIL LATE
AFTERNOON WHEN THE COLD FRONT MAY BRING SOME SHOWERS AHEAD OF IT.
MAY ALSO NEED TO SPEED UP THE COLD FRONTAL PASSAGE TIMING BY ABOUT
AN HOUR OR SO WITH UPCOMING TAFS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE IN PRECIP TIMING. AND THAT MVFR VSBY IN RAIN
  WOULD BE BRIEF.

* HIGH CONFIDENCE IN 30-35 KT GUSTS AND DIRECTION THROUGH THE
  AFTERNOON. THERE COULD BE A BRIEF LULL IN GUSTS IMMEDIATELY
  FOLLOWING PRECIP.

* MEDIUM CONFIDENCE IN CIG TRENDS.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291412
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
912 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* RAIN ARRIVES 1530-16Z OR SO WITH BRIEF PERIOD OF SLEET OR SNOW
  POSSIBLE AT ONSET. ADDITIONAL SHOWERS POSSIBLE THROUGH EARLY
  AFTERNOON.
* MVFR CIGS POSSIBLE...MAINLY THIS AFTERNOON.
* CHANCE OF ANOTHER ROUND OF BRIEF RAIN SHOWERS
  TOWARD SUNSET.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF PRECIP IS NOW APPROACHING RFD AND WILL BE REACHING THE
CHICAGO AREA 1530-16Z OR SO. THE BAND HAS NARROWED QUITE A BIT
OVER THE LAST HOUR OR TWO SO DURATION OF THE MORE SOLID PRECIP
LOOKS TO BE 60-90 MIN...WITH SOME ADDITIONAL SCATTERED SHOWER
ACTIVITY TRAILING IT. BASED ON LATEST SURFACE TEMPS FZRA WILL
OCCUR FOR A TIME AT RFD ALONG WITH A MIX OF RAIN AND SLEET OR
SNOW...BUT TEMPS WILL WARM SO FZRA MAY BE SHORT LIVED.
ELSEWHERE...MAINLY RAIN LOOKS TO OCCUR BUT CANNOT RULE OUT SOME
SLEET OR POSSIBLY SOME SNOW AT ONSET.

WIND GUSTS ARE COMING UP SPORADICALLY AND GUSTS MAY BE TEMPERED
DURING PRECIP BUT 30-35 KT GUSTS STILL LOOK ON TRACK AND SHOULD
DEVELOP AHEAD OF THE PRECIP AS WELL. NOT MUCH IN THE WAY OF MVFR
CIGS UPSTREAM BUT EXPECT DEVELOPMENT THIS AFTERNOON AROUND 030.
AM A LITTLE CONCERNED THAT GUSTS COULD BE A LITTLE UNDERDONE THIS
AFTERNOON IF CLOUD COVER IS NOT AS WIDESPREAD OR WE MIX A LITTLE
DEEPER. WILL NEED TO MONITOR AS WARMING OCCURS OVER THE NEXT FEW
HOURS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING.
* MEDIUM-HIGH IN BEST CHANCE FOR MVFR BEING THIS AFTERNOON BUT LOW
  THAT IT WILL OCCUR.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291412
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
912 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* RAIN ARRIVES 1530-16Z OR SO WITH BRIEF PERIOD OF SLEET OR SNOW
  POSSIBLE AT ONSET. ADDITIONAL SHOWERS POSSIBLE THROUGH EARLY
  AFTERNOON.
* MVFR CIGS POSSIBLE...MAINLY THIS AFTERNOON.
* CHANCE OF ANOTHER ROUND OF BRIEF RAIN SHOWERS
  TOWARD SUNSET.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF PRECIP IS NOW APPROACHING RFD AND WILL BE REACHING THE
CHICAGO AREA 1530-16Z OR SO. THE BAND HAS NARROWED QUITE A BIT
OVER THE LAST HOUR OR TWO SO DURATION OF THE MORE SOLID PRECIP
LOOKS TO BE 60-90 MIN...WITH SOME ADDITIONAL SCATTERED SHOWER
ACTIVITY TRAILING IT. BASED ON LATEST SURFACE TEMPS FZRA WILL
OCCUR FOR A TIME AT RFD ALONG WITH A MIX OF RAIN AND SLEET OR
SNOW...BUT TEMPS WILL WARM SO FZRA MAY BE SHORT LIVED.
ELSEWHERE...MAINLY RAIN LOOKS TO OCCUR BUT CANNOT RULE OUT SOME
SLEET OR POSSIBLY SOME SNOW AT ONSET.

WIND GUSTS ARE COMING UP SPORADICALLY AND GUSTS MAY BE TEMPERED
DURING PRECIP BUT 30-35 KT GUSTS STILL LOOK ON TRACK AND SHOULD
DEVELOP AHEAD OF THE PRECIP AS WELL. NOT MUCH IN THE WAY OF MVFR
CIGS UPSTREAM BUT EXPECT DEVELOPMENT THIS AFTERNOON AROUND 030.
AM A LITTLE CONCERNED THAT GUSTS COULD BE A LITTLE UNDERDONE THIS
AFTERNOON IF CLOUD COVER IS NOT AS WIDESPREAD OR WE MIX A LITTLE
DEEPER. WILL NEED TO MONITOR AS WARMING OCCURS OVER THE NEXT FEW
HOURS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING.
* MEDIUM-HIGH IN BEST CHANCE FOR MVFR BEING THIS AFTERNOON BUT LOW
  THAT IT WILL OCCUR.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291412
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
912 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* RAIN ARRIVES 1530-16Z OR SO WITH BRIEF PERIOD OF SLEET OR SNOW
  POSSIBLE AT ONSET. ADDITIONAL SHOWERS POSSIBLE THROUGH EARLY
  AFTERNOON.
* MVFR CIGS POSSIBLE...MAINLY THIS AFTERNOON.
* CHANCE OF ANOTHER ROUND OF BRIEF RAIN SHOWERS
  TOWARD SUNSET.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF PRECIP IS NOW APPROACHING RFD AND WILL BE REACHING THE
CHICAGO AREA 1530-16Z OR SO. THE BAND HAS NARROWED QUITE A BIT
OVER THE LAST HOUR OR TWO SO DURATION OF THE MORE SOLID PRECIP
LOOKS TO BE 60-90 MIN...WITH SOME ADDITIONAL SCATTERED SHOWER
ACTIVITY TRAILING IT. BASED ON LATEST SURFACE TEMPS FZRA WILL
OCCUR FOR A TIME AT RFD ALONG WITH A MIX OF RAIN AND SLEET OR
SNOW...BUT TEMPS WILL WARM SO FZRA MAY BE SHORT LIVED.
ELSEWHERE...MAINLY RAIN LOOKS TO OCCUR BUT CANNOT RULE OUT SOME
SLEET OR POSSIBLY SOME SNOW AT ONSET.

WIND GUSTS ARE COMING UP SPORADICALLY AND GUSTS MAY BE TEMPERED
DURING PRECIP BUT 30-35 KT GUSTS STILL LOOK ON TRACK AND SHOULD
DEVELOP AHEAD OF THE PRECIP AS WELL. NOT MUCH IN THE WAY OF MVFR
CIGS UPSTREAM BUT EXPECT DEVELOPMENT THIS AFTERNOON AROUND 030.
AM A LITTLE CONCERNED THAT GUSTS COULD BE A LITTLE UNDERDONE THIS
AFTERNOON IF CLOUD COVER IS NOT AS WIDESPREAD OR WE MIX A LITTLE
DEEPER. WILL NEED TO MONITOR AS WARMING OCCURS OVER THE NEXT FEW
HOURS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING.
* MEDIUM-HIGH IN BEST CHANCE FOR MVFR BEING THIS AFTERNOON BUT LOW
  THAT IT WILL OCCUR.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291412
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
912 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* RAIN ARRIVES 1530-16Z OR SO WITH BRIEF PERIOD OF SLEET OR SNOW
  POSSIBLE AT ONSET. ADDITIONAL SHOWERS POSSIBLE THROUGH EARLY
  AFTERNOON.
* MVFR CIGS POSSIBLE...MAINLY THIS AFTERNOON.
* CHANCE OF ANOTHER ROUND OF BRIEF RAIN SHOWERS
  TOWARD SUNSET.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF PRECIP IS NOW APPROACHING RFD AND WILL BE REACHING THE
CHICAGO AREA 1530-16Z OR SO. THE BAND HAS NARROWED QUITE A BIT
OVER THE LAST HOUR OR TWO SO DURATION OF THE MORE SOLID PRECIP
LOOKS TO BE 60-90 MIN...WITH SOME ADDITIONAL SCATTERED SHOWER
ACTIVITY TRAILING IT. BASED ON LATEST SURFACE TEMPS FZRA WILL
OCCUR FOR A TIME AT RFD ALONG WITH A MIX OF RAIN AND SLEET OR
SNOW...BUT TEMPS WILL WARM SO FZRA MAY BE SHORT LIVED.
ELSEWHERE...MAINLY RAIN LOOKS TO OCCUR BUT CANNOT RULE OUT SOME
SLEET OR POSSIBLY SOME SNOW AT ONSET.

WIND GUSTS ARE COMING UP SPORADICALLY AND GUSTS MAY BE TEMPERED
DURING PRECIP BUT 30-35 KT GUSTS STILL LOOK ON TRACK AND SHOULD
DEVELOP AHEAD OF THE PRECIP AS WELL. NOT MUCH IN THE WAY OF MVFR
CIGS UPSTREAM BUT EXPECT DEVELOPMENT THIS AFTERNOON AROUND 030.
AM A LITTLE CONCERNED THAT GUSTS COULD BE A LITTLE UNDERDONE THIS
AFTERNOON IF CLOUD COVER IS NOT AS WIDESPREAD OR WE MIX A LITTLE
DEEPER. WILL NEED TO MONITOR AS WARMING OCCURS OVER THE NEXT FEW
HOURS.

MDB

FROM 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING.
* MEDIUM-HIGH IN BEST CHANCE FOR MVFR BEING THIS AFTERNOON BUT LOW
  THAT IT WILL OCCUR.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WEATHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 7
     PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291155 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
655 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* ONE HOUR PERIOD OR SO OF SLEET OR SNOW POSSIBLE AT ONSET OF
  PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON WITH AT LEAST
  TEMPORARY MVFR CONDITIONS. CHANCE OF ANOTHER ROUND OF BRIEF
  RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.


//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291155 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
655 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* ONE HOUR PERIOD OR SO OF SLEET OR SNOW POSSIBLE AT ONSET OF
  PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON WITH AT LEAST
  TEMPORARY MVFR CONDITIONS. CHANCE OF ANOTHER ROUND OF BRIEF
  RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.


//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 291155 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
655 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* ONE HOUR PERIOD OR SO OF SLEET OR SNOW POSSIBLE AT ONSET OF
  PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON WITH AT LEAST
  TEMPORARY MVFR CONDITIONS. CHANCE OF ANOTHER ROUND OF BRIEF
  RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.


//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 291155 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
655 AM CDT SUN MAR 29 2015

.UPDATE...
652 AM CDT

KEEPING A CLOSE EYE ON SURFACE TEMPERATURES AS AN AREA OF
PRECIPITATION ADVANCES EASTWARD ACROSS IA TOWARDS NORTHWEST
ILLINOIS. THERE HAVE BEEN MULTIPLE REPORTS OF FREEZING RAIN AND
ICING IN IOWA INTO SOUTHWEST WISCONSIN EARLY THIS MORNING. THESE
AREAS WERE MORE VULNERABLE FOR THIS PRECIP TYPE GIVEN IT BEGAN
BEFORE DAYBREAK ALLOWING TEMPERATURES NOT TO MODERATE. FOR OUR
FORECAST AREA...SURFACE TEMPERATURES ARE LIKELY TO WARM TO ABOVE
FREEZING BEFORE PRECIPITATION BEGINS NEAR ROCKFORD AND THE I-39
CORRIDOR FROM 9-10 AM...HOWEVER WET BULB COOLING WILL LIKELY
BRING THE TEMPERATURE DOWN A FEW DEGREES AT ONSET IF THE PRECIP IS
MODERATE ENOUGH. THIS COULD RESULT IN BRIEF FREEZING RAIN ACROSS
NORTH CENTRAL ILLINOIS...WHICH ALREADY DID HAVE A BRIEF CHANCE IN
THE FORECAST FOR...BUT DAY SHIFT MAY NEED TO ADDRESS WITH SEPARATE
STATEMENT.

MTF

&&

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILITY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* SOUTHERLY WINDS QUICKLY INCREASING WITH OCCASIONAL GUSTS AROUND
  35 KT FROM MID-MORNING THROUGH MID-AFTERNOON.
* ONE HOUR PERIOD OR SO OF SLEET OR SNOW POSSIBLE AT ONSET OF
  PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON WITH AT LEAST
  TEMPORARY MVFR CONDITIONS. CHANCE OF ANOTHER ROUND OF BRIEF
  RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 12Z...

SOUTHERLY WINDS ARE ALREADY INCREASING EARLY THIS MORNING WITH
GUSTS OVER 20 KT BEING NOTED ACROSS NORTHERN ILLINOIS...AND MUCH
STRONGER WINDS WITHIN A COUPLE THOUSAND FEET AGL ABLE TO BE MIXED
DOWN BY MID-MORNING. EXPECTING THE WIND DIRECTION TO VEER EVER SO
SLIGHTLY THIS MORNING...BUT STILL BE 190-210 WHEN GUSTS REACH
AROUND 35 KT AT TAF SITES BY MID-LATE MORNING.

A 3-4 HOUR PERIOD OF RAIN SHOWERS WILL MOVE FROM WEST-TO-EAST
ACROSS THE AREA FROM MID MORNING THROUGH EARLY AFTERNOON. A
TEMPORARY PERIOD OF MIXED PRECIPITATION IS LIKELY AT
ONSET...ESPECIALLY AT RFD...BUT EVEN BRIEFLY AT THE CHICAGOLAND
TAF SITES. THIS IS MOST FAVORED TO BE SLEET OR SNOW IF IT
OCCURS...THOUGH FOR RFD IT COULD ALSO BE FREEZING RAIN BASED ON
UPSTREAM OBSERVATIONS. WILL MONITOR TRENDS CLOSELY TO SEE IF THAT
NEEDS TO BE ADDED INTO THE RFD TAF. A WARMING ATMOSPHERE WILL
LIKELY ALLOW SHOWER ACTIVITY TO BE RAIN BY EARLY AFTERNOON.

AS A COLD FRONT APPROACHES...WINDS WILL TURN SOUTHWEST THIS
AFTERNOON AND THEN WESTERLY BEHIND THE FRONTAL PASSAGE WHICH WILL
BE NEAR OR SLIGHTLY AFTER SUNDOWN. WIND SPEEDS WILL ALSO DECREASE
SOME THOUGH STILL WITH SOME GUSTS DURING THE EVENING. IN
ADDITION...IT APPEARS THERE WILL BE SOME LIGHT RAIN SHOWERS ALONG
THIS FRONT AS WELL.


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN GUSTS REACHING 35
  KT AND TIMING.
* MEDIUM IN BRIEF SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.


//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...SLIGHT CHANCE OF RAIN AND MVFR. SOUTHWEST WINDS.
TUESDAY...VFR. NORTHEAST WINDS.
WEDNESDAY...CHANCE OF TSRA DURING THE NIGHT. SOUTH WINDS.
THURSDAY...CHANCE OF RAIN. WEST WINDS.
FRIDAY...CHANCE OF RAIN. NORTHEAST WINDS.
SATURDAY...VFR. WEST WINDS.

MTF

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS PRIOR TO 13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF SLEET OR SNOW POSSIBLE AT
  ONSET OF PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON SUNDAY WITH AT
  LEAST TEMPORARY MVFR CONDITIONS. CHANCE OF MORE BRIEF RAIN
  SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* MEDIUM IN SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR TO HOUR AND A HALF.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 290915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS PRIOR TO 13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF SLEET OR SNOW POSSIBLE AT
  ONSET OF PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON SUNDAY WITH AT
  LEAST TEMPORARY MVFR CONDITIONS. CHANCE OF MORE BRIEF RAIN
  SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* MEDIUM IN SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR TO HOUR AND A HALF.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS PRIOR TO 13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF SLEET OR SNOW POSSIBLE AT
  ONSET OF PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON SUNDAY WITH AT
  LEAST TEMPORARY MVFR CONDITIONS. CHANCE OF MORE BRIEF RAIN
  SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* MEDIUM IN SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR TO HOUR AND A HALF.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 290915
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
415 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS PRIOR TO 13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF SLEET OR SNOW POSSIBLE AT
  ONSET OF PRECIP LATE THIS MORNING...WHICH COULD BRING BRIEF IFR
  CONDITIONS.
* PERIOD OF RAIN SHOWERS THROUGH EARLY AFTERNOON SUNDAY WITH AT
  LEAST TEMPORARY MVFR CONDITIONS. CHANCE OF MORE BRIEF RAIN
  SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* MEDIUM IN SNOW/SLEET POTENTIAL AT BEGINNING OF
  PRECIPITATION...WHILE HIGH THAT IT WOULD LAST NO MORE THAN AN
  HOUR TO HOUR AND A HALF.
* HIGH IN PRECIP TIMING AND LOW-MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
358 AM CDT

AN ACTIVE MARINE WETAHER PERIOD WILL BE SEEN OVER LAKE MICHIGAN
THE NEXT 24 HOURS AS A QUICK-MOVING AND DEEPENING LOW PRESSURE
SYSTEM CRUISES EASTWARD ACROSS ONTARIO. THE RAPID MOVEMENT OF THIS
SYSTEM WILL DRIVE STRONG SOUTHERLY GALES TODAY...WITH EVEN STORM
FORCE WINDS EXPECTED ACROSS THE NORTH LATE THIS MORNING THROUGH
MID AFTERNOON. THE SOUTH HALF IS MOST FAVORED TO HAVE 40
KT...POSSIBLY AT TIMES 45 KT GALES. IN THE ILLINOIS AND INDIANA
NEARSHORE THE SOUTH GALES ARE EXPECTED BY MID MORNING AND WILL
LAST THROUGH THE DAY.

THE SYSTEM COLD FRONT WILL MOVE ACROSS THE LAKE FROM WEST TO EAST
VERY LATE TODAY INTO EARLY THIS EVENING. THIS WILL BRING A
DIMINISHING AND TURNING TO THE WEST-NORTHWEST OF THE WINDS.

A CLIPPER SYSTEM WILL DROP OVER THE LAKE ON MONDAY NIGHT. THERE
REMAINS UNCERTAINTY ON SPECIFIC TIMING OF THIS...BUT DO THINK A
PERIOD OF SMALL CRAFT ADVISORY CRITERIA WINDS ARE POSSIBLE ON BOTH
THE ILLINOIS AND INDIANA NEARSHORES.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
350 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
350 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

MONDAY THROUGH SATURDAY...

IN GENERAL A MILDER WEATHER PATTERN WILL BE IN PLACE ON MONDAY
THROUGH THURSDAY...THOUGH WITH SOME EXCEPTIONS IN THE DAY TO DAY
DETAILS. WHILE AREA WILL BE UNDER NORTHWEST FLOW AT THE MID AND
UPPER LEVELS BEHIND SUNDAY`S DEPARTING WAVE ON MONDAY...IT WILL BE
A DOWNSLOPING/WARM ADVECTIVE REGIME. THIS WILL ESPECIALLY BE THE
CASE DURING THE AFTERNOON AS WAA RAMPS UP IN ADVANCE OF A CLIPPER
SYSTEM DROPPING SOUTHEAST ACROSS THE UPPER MIDWEST. 850 MB TEMPS
WILL WARM TO THE MID SINGLE DIGITS CELSIUS AND 925 MB TEMPS TO
AROUND 10 CELSIUS BY EARLY EVENING...WHICH WILL YIELD HIGHS A BIT
ABOVE NORMAL IN THE MID 50S TO LOWER 60S. WILL NEED TO WATCH FOR A
LAKE BREEZE DURING THE LATE AFTERNOON AS GRADIENT WILL WEAKEN WITH
APPROACH OF CLIPPER.

SIMILAR TO PREVIOUS SHIFT...THERE IS DECENT AGREEMENT BETWEEN THE
GFS AND ECMWF ON TRACK OF THE SYSTEM TO THE NORTH OF THE CWA
MONDAY EVENING AND NIGHT. THIS KEEP THE BRUNT OF THE PRECIP TO OUR
NORTH...WITH JUST A GLANCING BLOW OF LOW POPS IN THE NORTHEAST
THIRD OF THE CWA. IN THE WAKE OF THIS SYSTEM...THE AIR MASS WILL
NOT UNDERGO MUCH COOLING...BUT GUIDANCE HAS COME INTO GOOD
AGREEMENT ON A FAVORABLE SETUP FOR A STRONG LAKE BREEZE TO PUSH
INLAND ON TUESDAY. HIGHS WILL REACH THE UPPER 50S TO MID 60S
INLAND AND LOWER TO MID 50S ALONG THE SHORE...FOLLOWED BY RAPID
COOLING INTO THE UPPER 30S TO LOWER 40S CLOSER TO THE LAKE DURING
THE MID TO LATE AFTERNOON.

IN THE MID TO LATE WEEK PERIOD...OPERATIONAL AND ENSEMBLE
GUIDANCE IS IN FAIR AGREEMENT IN THE SYNOPTIC PATTERN...HOWEVER
THERE ARE SIGNIFICANT TIMING DIFFERENCES. MIDLEVEL RIDGING WILL
FOCUS INTO THE MIDWEST ON WEDNESDAY...WITH GOOD SOUTHERLY LOW
LEVEL WARM AND MOIST ADVECTION (850 MB AND 925 MB TEMPS WARMING TO
10-15 CELSIUS BY LATE WEDS) RESULTING IN HIGHS AT LEAST IN THE
60S...AND THEN DEWPOINTS SURGING INTO THE 50S WEDNESDAY NIGHT. A
FAIRLY STRONG SURFACE LOW LOOKS TO RIDE ALONG THE CANADIAN
BORDER...WITH SHOWERS AND POSSIBLY THUNDERSTORMS DEVELOPING
ALONG/AHEAD OF TRAILING COLD FRONT GIVEN PRESENCE OF FAIRLY MOIST
AIRMASS. TIMING DISCREPANCY BETWEEN THE GFS/GEFS AND ECMWF IN THIS
FRONTAL SYSTEM IS FAIRLY SUBSTANTIAL...WITH GFS FAVORING MUCH
QUICKER WEDNESDAY NIGHT INTO THURSDAY TIMING AND ECMWF FAVORING
THURSDAY AFTERNOON INTO THURSDAY NIGHT. THIS WILL ULTIMATELY
PLACEMENT OF POPS AND HOW FAST COOLING TO NEAR OR BELOW NORMAL
LEVELS WILL ARRIVE LATER IN THE WEEK. OF NOTE...00Z ECMWF DID
ABANDON IDEA FROM PAST FEW RUNS OF SIGNIFICANT SYNOPTIC SYSTEM
OVER THE REGION ON FRIDAY...BUT PERIOD WILL NEED TO BE WATCHED AS
IT DID HAVE GOOD ENSEMBLE SUPPORT PRIOR TO 00 UTC CYCLE.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 290840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

TO BE ISSUED SHORTLY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

TO BE ISSUED SHORTLY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 290840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

TO BE ISSUED SHORTLY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT SUN MAR 29 2015

.SHORT TERM...
338 AM CDT

THROUGH TONIGHT...

A WELL-DEFINED UPPER CIRCULATION IS SEEN ON EARLY MORNING WATER
VAPOR IMAGERY MOVING SOUTHEASTWARD INTO SOUTHERN MN EARLY THIS
MORNING. THIS IS A QUICK-MOVING PACIFIC SYSTEM AND DESPITE MUCH OF
THE GULF BEING CUT OFF...DOES HAVE AN AXIS OF MOISTURE/SATURATION
WITHIN ITS WARM ADVECTION WING WITH SHOWERS FROM SOUTHERN MN ACROSS
IA. AS THIS ELEVATED WARM AND MOIST ADVECTION TRANSLATES OVER OUR
AREA THIS MORNING...IT WILL BE THE PRIMARY FOCUS FOR
PRECIPITATION...BRINGING A 3-4 HOUR PERIOD FROM WEST-TO-EAST.

RECENT LIGHTNING STRIKES AROUND 330 AM NEAR THE TWIN CITIES INDICATE
THE PRESENCE OF ELEVATED INSTABILITY AND RAP SOUNDINGS DO TRANSLATE
STEEP LAPSE RATES ABOVE 750MB INTO THE AREA WITHIN THIS ZONE OF
PRECIPITATION. WITH THIS INSTABILITY AND THE COMPACT AREA OF STRONG
QG FORCING OF THE UPPER WAVE...THERE MAY BE ENOUGH
INTENSITY/DYNAMICS OF PRECIPITATION AT FIRST FOR A BRIEF BUT
MODERATE INTENSITY MIX WITH SLEET OR SNOW. THIS CHANCE...WHICH HAS
INCREASED...LOOKS TO BE NORTH OF I-80 AND PRIOR TO NOON. HIGH-
RESOLUTION CONVECTIVE ALLOWING MODELS DO SHOW HIGHER SIMULATED
REFLECTIVITY AND HYDROMETEORS/PRECIP TYPE FAVORING THIS BRIEF
MIX...THOUGH THE SPECIFICS VARY FROM MODEL TO MODEL. AM NOT
EXPECTING THIS TO BE A BIG DEAL IN THE AREAS IT BRIEFLY OCCURS DUE
TO WARMING LOW-LEVEL TEMPS...THOUGH VISIBILTY COULD SHARPLY COME
DOWN FOR A NARROW WINDOW OF TIME.

RAIN SHOWERS SHOULD END FROM WEST TO EAST FOR MOST AREA BY EARLY-MID
AFTERNOON. THE COVERAGE OF SHOWERS BEHIND THE LEADING EDGE MAY NOT
BE AS WIDESPREAD AS THOUGHT EARLIER...BUT STILL FEEL A FEW HOUR
WINDOW OF CATEGORICAL POPS COVERS THIS SITUATION WELL. THE UPPER LOW
IN TANDEM WITH THE LOW-LEVEL COLD FRONT MAY HELP PROVIDE SOME
REGENERATING SHOWERS ACROSS FAR NORTHERN AND NORTHEAST ILLINOIS LATE
THIS AFTERNOON. MOST AREAS SHOULD FINISH UNDER 0.15 OF AN INCH.

THE OTHER CONCERN FOR TODAY IS THE STRONG WINDS. WHILE THE SURFACE
LOW WITH THIS SYSTEM IS WELL NORTH IN ONTARIO TODAY...THE RAPID
PROGRESSION OF THE SYSTEM WILL BRING PRESSURE FALLS OF 4-6MB PER
3HR MOVING DIRECTLY OVER THE AREA THIS MORNING. THIS ISALLOBARIC
COMPONENT AS WELL AS SOME SHALLOW BUT LIKELY REALIZED MIXING OF
STOUT GUSTS WILL BRING REGULAR 20-27 MPH WINDS WITH 35-40 MPH
GUSTS FROM MID-MORNING THROUGH EARLY AFTERNOON...BASICALLY IN
TANDEM WITH THE PRECIPITATION WINDOW. THIS IS A LITTLE BELOW WIND
ADVISORY CRITERIA BUT SOMETHING STILL TO NOTE SO WILL CONTINUE
SPS.

TEMPERATURES SHOULD CLIMB FROM SUNRISE THROUGH PRECIP START
TIME...AND THEN HOLD STEADY OR SLIGHTLY DIP IN THE FIRST 1-2 HOURS
DUE TO WET BULB COOLING. TEMPERATURES WILL WARM THIS AFTERNOON AS
DOWNSLOPE WARM ADVECTION IS DRAGGED THIS FAR EAST WITHIN THE PACIFIC
SYSTEM WARM SECTOR. HIGHS IN THE LOWER-MID 40S NORTH TO AROUND 50
TOWARD PONTIAC SHOULD BE REACHED LATE IN THE AFTERNOON/EARLY EVENING
JUST AHEAD OF THE COLD FRONT

MTF

&&

.LONG TERM...
338 AM CDT

TO BE ISSUED SHORTLY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

MTF/IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779 UNTIL 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 290541
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1241 AM CDT SUN MAR 29 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 290541
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1241 AM CDT SUN MAR 29 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 290541
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1241 AM CDT SUN MAR 29 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290541
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1241 AM CDT SUN MAR 29 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* STRONG SOUTHERLY WINDS DEVELOPING SOON AFTER SUNRISE.
* CHANCE OF LLWS BETWEEN 09Z-13Z.
* ONE TO POSSIBLY TWO HOUR PERIOD OF GRAUPEL/SLEET OR SNOW
  POSSIBLE AT ONSET OF PRECIP LATE THIS MORNING.
* PERIOD OF RAIN THROUGH EARLY AFTERNOON SUNDAY WITH MVFR
  CONDITIONS. CHANCE OF MORE BRIEF RAIN SHOWERS TOWARD SUNSET.


//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE WILL CONTINUE TO SCOOT AWAY FROM THE REGION WITH
SOUTHERLY WINDS INCREASING THROUGH DAYBREAK. AS ROBUST PRESSURE
FALLS ENVELOP THE REGION BY MID-MORNING...WIND SPEEDS AND GUSTS
WILL ESCALATE WITH GUSTS TO AROUND 35 KT FAVORED GIVEN STRONG
WINDS JUST OFF THE DECK. THE DIRECTION IS VERY LIKELY TO BE
SLIGHTLY WEST OF DUE SOUTH...BUT NOT BY MUCH.

PRECIPITATION IS EXPECTED TO FILL IN ACROSS IOWA DURING THE PRE-
SUNRISE HOURS AND MOVE INTO AND ACROSS NORTHERN ILLINOIS DURING
THE MID-LATE MORNING. THIS PRECIPITATION LOOKS TO LAST ABOUT 3-4
HOURS IN ANY ONE PLACE AND BE SOMEWHAT SHOWERY...SO FLUCTUATIONS
IN VISIBILITY AND EVEN CIGS ARE LIKELY. AT ONSET...OBSERVATIONAL
TRENDS AND MODEL GUIDANCE DO SUPPORT A MIX OF RAIN WITH ICE
PELLETS OR POSSIBLY EVEN SNOW. THIS COULD COME DOWN AT A FAIRLY
HIGH RATE...ALTHOUGH IS FAVORED TO LAST AS A MIX/FROZEN PRECIP
FOR ONLY A SHORT PERIOD OF TIME IF IT WERE TO COME TO FRUITION.
RAIN SHOWERS SHOULD CONTINUE INTO EARLY-MID AFTERNOON BEFORE AN
END...WITH POSSIBLY SOME BRIEF LIGHT SHOWERS AS THE COLD FRONT
MOVES INTO THE AREA NEAR/JUST PRIOR TO SUNSET. THIS FRONT WILL
SHIFT WINDS WEST WHICH WILL REMAIN GUSTY THROUGH THIS EVENING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN WIND DIRECTION TODAY. MEDIUM-HIGH IN SPEEDS.
* LOW-MEDIUM IN SNOW/SLEET/GRAUPEL POTENTIAL AT BEGINNING WITH
  HIGH THAT IT WOULD LAST NO MORE THAN TWO HOURS AT THE MOST.
* HIGH IN PRECIP TIMING AND MEDIUM IN VISIBILITY DURING.
* LOW IN TRUE LLWS EARLY THIS MORNING BUT HIGH IN 40-45 KT WINDS
  ABOVE 1000 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290305
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1005 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* STRONG SOUTHERLY WINDS DEVELOP EARLY-MID MORNING SUNDAY
* CHANCE OF LLWS EARLY SUNDAY MORNING
* PERIOD OF SNOW/GRAUPEL/SLEET POSSIBLE AT ONSET OF PRECIP LATE
  SUNDAY MORNING
* PERIOD OF RAIN THROUGH EARLY-MID AFTERNOON SUNDAY W/MVFR CIGS
  AND VSBY

IZZI

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL MOVE OFF TO THE EAST TONIGHT ALLOWING LAKE
INFLUENCED EAST WINDS TO TURN SOUTHEAST THIS EVENING. FAST MOVING
STORM SYSTEM WILL RESULT IN WINDS BECOMING SOUTHERLY AND
INCREASING PRIOR TO SUNRISE. WINDS AROUND 2000FT AGL WILL INCREASE
TO 50-60KT BY EARLY-MID MORNING SUNDAY AT BASE OF SHARP INVERSION
POSSIBLY RESULTING IN SOME LLWS REPORTS SUNDAY MORNING THOUGH
SUSPECT TURBULENCE MAY BE MORE OF AN ISSUE THAN LLWS SO HELD OFF
ON INCLUDING LLWS IN TAFS FOR NOW. WINDS WILL QUICKLY INCREASE TO
20-25KT WITH GUSTS OF 33-38KT PRIMARILY FROM 190-200 BETWEEN
12-15Z WITH GUSTS IN THE NEIGHBORHOOD OF 35KT LIKELY TO CONTINUE
THROUGH THE LATE MORNING BEFORE PERHAPS EASING SLIGHTLY EARLY IN
THE AFTERNOON THOUGH LIKELY REMAINING NEAR/SLIGHTLY ABOVE 30KT.
BAND OF PRECIPITATION WILL MOVE ACROSS THE TERMINALS LATE SUNDAY
MORNING THROUGH MID AFTERNOON WITH PRECIP POTENTIALLY STARTING AS
A PERIOD OF SNOW...SLEET...OR POSSIBLY SOME GRAUPEL GIVEN THE
STEEP MID-LEVEL LAPSE RATES AND STRONG LOW LEVEL JET WITH SOME
CONVECTIVE ELEMENTS WITHIN THE PRECIP BAND. WARMING TEMPS SHOULD
RESULT IN FAIRLY QUICK CHANGE OVER TO RAIN AFTER ONSET OF PRECIP.
SOME SHOWERS COULD ACCOMPANY COLD FRONT MOVING THROUGH THE REGION
EARLY SUNDAY EVENING WITH WINDS SHIFTING TO NORTHWEST BEHIND THE
FRONT AND GRADUALLY EASING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* LOW-MEDIUM CONFIDENCE IN SNOW/SLEET/GRAUPEL POTENTIAL
* HIGH CONFIDENCE IN PRECIP TIMING
* LOW CONFIDENCE IN POTENTIAL FOR LLWS EARLY SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS/GUSTS SUNDAY

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 290305
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1005 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* STRONG SOUTHERLY WINDS DEVELOP EARLY-MID MORNING SUNDAY
* CHANCE OF LLWS EARLY SUNDAY MORNING
* PERIOD OF SNOW/GRAUPEL/SLEET POSSIBLE AT ONSET OF PRECIP LATE
  SUNDAY MORNING
* PERIOD OF RAIN THROUGH EARLY-MID AFTERNOON SUNDAY W/MVFR CIGS
  AND VSBY

IZZI

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL MOVE OFF TO THE EAST TONIGHT ALLOWING LAKE
INFLUENCED EAST WINDS TO TURN SOUTHEAST THIS EVENING. FAST MOVING
STORM SYSTEM WILL RESULT IN WINDS BECOMING SOUTHERLY AND
INCREASING PRIOR TO SUNRISE. WINDS AROUND 2000FT AGL WILL INCREASE
TO 50-60KT BY EARLY-MID MORNING SUNDAY AT BASE OF SHARP INVERSION
POSSIBLY RESULTING IN SOME LLWS REPORTS SUNDAY MORNING THOUGH
SUSPECT TURBULENCE MAY BE MORE OF AN ISSUE THAN LLWS SO HELD OFF
ON INCLUDING LLWS IN TAFS FOR NOW. WINDS WILL QUICKLY INCREASE TO
20-25KT WITH GUSTS OF 33-38KT PRIMARILY FROM 190-200 BETWEEN
12-15Z WITH GUSTS IN THE NEIGHBORHOOD OF 35KT LIKELY TO CONTINUE
THROUGH THE LATE MORNING BEFORE PERHAPS EASING SLIGHTLY EARLY IN
THE AFTERNOON THOUGH LIKELY REMAINING NEAR/SLIGHTLY ABOVE 30KT.
BAND OF PRECIPITATION WILL MOVE ACROSS THE TERMINALS LATE SUNDAY
MORNING THROUGH MID AFTERNOON WITH PRECIP POTENTIALLY STARTING AS
A PERIOD OF SNOW...SLEET...OR POSSIBLY SOME GRAUPEL GIVEN THE
STEEP MID-LEVEL LAPSE RATES AND STRONG LOW LEVEL JET WITH SOME
CONVECTIVE ELEMENTS WITHIN THE PRECIP BAND. WARMING TEMPS SHOULD
RESULT IN FAIRLY QUICK CHANGE OVER TO RAIN AFTER ONSET OF PRECIP.
SOME SHOWERS COULD ACCOMPANY COLD FRONT MOVING THROUGH THE REGION
EARLY SUNDAY EVENING WITH WINDS SHIFTING TO NORTHWEST BEHIND THE
FRONT AND GRADUALLY EASING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* LOW-MEDIUM CONFIDENCE IN SNOW/SLEET/GRAUPEL POTENTIAL
* HIGH CONFIDENCE IN PRECIP TIMING
* LOW CONFIDENCE IN POTENTIAL FOR LLWS EARLY SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS/GUSTS SUNDAY

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 282349
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* STRONG SOUTHERLY WINDS DEVELOP EARLY-MID MORNING SUNDAY
* CHANCE OF LLWS EARLY SUNDAY MORNING
* PERIOD OF SNOW/GRAUPEL/SLEET POSSIBLE AT ONSET OF PRECIP LATE
  SUNDAY MORNING
* PERIOD OF RAIN THROUGH EARLY-MID AFTERNOON SUNDAY W/MVFR CIGS
  AND VSBY

IZZI

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL MOVE OFF TO THE EAST TONIGHT ALLOWING LAKE
INFLUENCED EAST WINDS TO TURN SOUTHEAST THIS EVENING. FAST MOVING
STORM SYSTEM WILL RESULT IN WINDS BECOMING SOUTHERLY AND
INCREASING PRIOR TO SUNRISE. WINDS AROUND 2000FT AGL WILL INCREASE
TO 50-60KT BY EARLY-MID MORNING SUNDAY AT BASE OF SHARP INVERSION
POSSIBLY RESULTING IN SOME LLWS REPORTS SUNDAY MORNING THOUGH
SUSPECT TURBULENCE MAY BE MORE OF AN ISSUE THAN LLWS SO HELD OFF
ON INCLUDING LLWS IN TAFS FOR NOW. WINDS WILL QUICKLY INCREASE TO
20-25KT WITH GUSTS OF 33-38KT PRIMARILY FROM 190-200 BETWEEN
12-15Z WITH GUSTS IN THE NEIGHBORHOOD OF 35KT LIKELY TO CONTINUE
THROUGH THE LATE MORNING BEFORE PERHAPS EASING SLIGHTLY EARLY IN
THE AFTERNOON THOUGH LIKELY REMAINING NEAR/SLIGHTLY ABOVE 30KT.
BAND OF PRECIPITATION WILL MOVE ACROSS THE TERMINALS LATE SUNDAY
MORNING THROUGH MID AFTERNOON WITH PRECIP POTENTIALLY STARTING AS
A PERIOD OF SNOW...SLEET...OR POSSIBLY SOME GRAUPEL GIVEN THE
STEEP MID-LEVEL LAPSE RATES AND STRONG LOW LEVEL JET WITH SOME
CONVECTIVE ELEMENTS WITHIN THE PRECIP BAND. WARMING TEMPS SHOULD
RESULT IN FAIRLY QUICK CHANGE OVER TO RAIN AFTER ONSET OF PRECIP.
SOME SHOWERS COULD ACCOMPANY COLD FRONT MOVING THROUGH THE REGION
EARLY SUNDAY EVENING WITH WINDS SHIFTING TO NORTHWEST BEHIND THE
FRONT AND GRADUALLY EASING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN SNOW/SLEET/GRAUPEL POTENTIAL
* HIGH CONFIDENCE IN PRECIP TIMING
* LOW CONFIDENCE IN POTENTIAL FOR LLWS EARLY SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS/GUSTS SUNDAY

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 282349
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* STRONG SOUTHERLY WINDS DEVELOP EARLY-MID MORNING SUNDAY
* CHANCE OF LLWS EARLY SUNDAY MORNING
* PERIOD OF SNOW/GRAUPEL/SLEET POSSIBLE AT ONSET OF PRECIP LATE
  SUNDAY MORNING
* PERIOD OF RAIN THROUGH EARLY-MID AFTERNOON SUNDAY W/MVFR CIGS
  AND VSBY

IZZI

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL MOVE OFF TO THE EAST TONIGHT ALLOWING LAKE
INFLUENCED EAST WINDS TO TURN SOUTHEAST THIS EVENING. FAST MOVING
STORM SYSTEM WILL RESULT IN WINDS BECOMING SOUTHERLY AND
INCREASING PRIOR TO SUNRISE. WINDS AROUND 2000FT AGL WILL INCREASE
TO 50-60KT BY EARLY-MID MORNING SUNDAY AT BASE OF SHARP INVERSION
POSSIBLY RESULTING IN SOME LLWS REPORTS SUNDAY MORNING THOUGH
SUSPECT TURBULENCE MAY BE MORE OF AN ISSUE THAN LLWS SO HELD OFF
ON INCLUDING LLWS IN TAFS FOR NOW. WINDS WILL QUICKLY INCREASE TO
20-25KT WITH GUSTS OF 33-38KT PRIMARILY FROM 190-200 BETWEEN
12-15Z WITH GUSTS IN THE NEIGHBORHOOD OF 35KT LIKELY TO CONTINUE
THROUGH THE LATE MORNING BEFORE PERHAPS EASING SLIGHTLY EARLY IN
THE AFTERNOON THOUGH LIKELY REMAINING NEAR/SLIGHTLY ABOVE 30KT.
BAND OF PRECIPITATION WILL MOVE ACROSS THE TERMINALS LATE SUNDAY
MORNING THROUGH MID AFTERNOON WITH PRECIP POTENTIALLY STARTING AS
A PERIOD OF SNOW...SLEET...OR POSSIBLY SOME GRAUPEL GIVEN THE
STEEP MID-LEVEL LAPSE RATES AND STRONG LOW LEVEL JET WITH SOME
CONVECTIVE ELEMENTS WITHIN THE PRECIP BAND. WARMING TEMPS SHOULD
RESULT IN FAIRLY QUICK CHANGE OVER TO RAIN AFTER ONSET OF PRECIP.
SOME SHOWERS COULD ACCOMPANY COLD FRONT MOVING THROUGH THE REGION
EARLY SUNDAY EVENING WITH WINDS SHIFTING TO NORTHWEST BEHIND THE
FRONT AND GRADUALLY EASING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN SNOW/SLEET/GRAUPEL POTENTIAL
* HIGH CONFIDENCE IN PRECIP TIMING
* LOW CONFIDENCE IN POTENTIAL FOR LLWS EARLY SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS/GUSTS SUNDAY

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 282349
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* STRONG SOUTHERLY WINDS DEVELOP EARLY-MID MORNING SUNDAY
* CHANCE OF LLWS EARLY SUNDAY MORNING
* PERIOD OF SNOW/GRAUPEL/SLEET POSSIBLE AT ONSET OF PRECIP LATE
  SUNDAY MORNING
* PERIOD OF RAIN THROUGH EARLY-MID AFTERNOON SUNDAY W/MVFR CIGS
  AND VSBY

IZZI

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL MOVE OFF TO THE EAST TONIGHT ALLOWING LAKE
INFLUENCED EAST WINDS TO TURN SOUTHEAST THIS EVENING. FAST MOVING
STORM SYSTEM WILL RESULT IN WINDS BECOMING SOUTHERLY AND
INCREASING PRIOR TO SUNRISE. WINDS AROUND 2000FT AGL WILL INCREASE
TO 50-60KT BY EARLY-MID MORNING SUNDAY AT BASE OF SHARP INVERSION
POSSIBLY RESULTING IN SOME LLWS REPORTS SUNDAY MORNING THOUGH
SUSPECT TURBULENCE MAY BE MORE OF AN ISSUE THAN LLWS SO HELD OFF
ON INCLUDING LLWS IN TAFS FOR NOW. WINDS WILL QUICKLY INCREASE TO
20-25KT WITH GUSTS OF 33-38KT PRIMARILY FROM 190-200 BETWEEN
12-15Z WITH GUSTS IN THE NEIGHBORHOOD OF 35KT LIKELY TO CONTINUE
THROUGH THE LATE MORNING BEFORE PERHAPS EASING SLIGHTLY EARLY IN
THE AFTERNOON THOUGH LIKELY REMAINING NEAR/SLIGHTLY ABOVE 30KT.
BAND OF PRECIPITATION WILL MOVE ACROSS THE TERMINALS LATE SUNDAY
MORNING THROUGH MID AFTERNOON WITH PRECIP POTENTIALLY STARTING AS
A PERIOD OF SNOW...SLEET...OR POSSIBLY SOME GRAUPEL GIVEN THE
STEEP MID-LEVEL LAPSE RATES AND STRONG LOW LEVEL JET WITH SOME
CONVECTIVE ELEMENTS WITHIN THE PRECIP BAND. WARMING TEMPS SHOULD
RESULT IN FAIRLY QUICK CHANGE OVER TO RAIN AFTER ONSET OF PRECIP.
SOME SHOWERS COULD ACCOMPANY COLD FRONT MOVING THROUGH THE REGION
EARLY SUNDAY EVENING WITH WINDS SHIFTING TO NORTHWEST BEHIND THE
FRONT AND GRADUALLY EASING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN SNOW/SLEET/GRAUPEL POTENTIAL
* HIGH CONFIDENCE IN PRECIP TIMING
* LOW CONFIDENCE IN POTENTIAL FOR LLWS EARLY SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS/GUSTS SUNDAY

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 282349
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* STRONG SOUTHERLY WINDS DEVELOP EARLY-MID MORNING SUNDAY
* CHANCE OF LLWS EARLY SUNDAY MORNING
* PERIOD OF SNOW/GRAUPEL/SLEET POSSIBLE AT ONSET OF PRECIP LATE
  SUNDAY MORNING
* PERIOD OF RAIN THROUGH EARLY-MID AFTERNOON SUNDAY W/MVFR CIGS
  AND VSBY

IZZI

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL MOVE OFF TO THE EAST TONIGHT ALLOWING LAKE
INFLUENCED EAST WINDS TO TURN SOUTHEAST THIS EVENING. FAST MOVING
STORM SYSTEM WILL RESULT IN WINDS BECOMING SOUTHERLY AND
INCREASING PRIOR TO SUNRISE. WINDS AROUND 2000FT AGL WILL INCREASE
TO 50-60KT BY EARLY-MID MORNING SUNDAY AT BASE OF SHARP INVERSION
POSSIBLY RESULTING IN SOME LLWS REPORTS SUNDAY MORNING THOUGH
SUSPECT TURBULENCE MAY BE MORE OF AN ISSUE THAN LLWS SO HELD OFF
ON INCLUDING LLWS IN TAFS FOR NOW. WINDS WILL QUICKLY INCREASE TO
20-25KT WITH GUSTS OF 33-38KT PRIMARILY FROM 190-200 BETWEEN
12-15Z WITH GUSTS IN THE NEIGHBORHOOD OF 35KT LIKELY TO CONTINUE
THROUGH THE LATE MORNING BEFORE PERHAPS EASING SLIGHTLY EARLY IN
THE AFTERNOON THOUGH LIKELY REMAINING NEAR/SLIGHTLY ABOVE 30KT.
BAND OF PRECIPITATION WILL MOVE ACROSS THE TERMINALS LATE SUNDAY
MORNING THROUGH MID AFTERNOON WITH PRECIP POTENTIALLY STARTING AS
A PERIOD OF SNOW...SLEET...OR POSSIBLY SOME GRAUPEL GIVEN THE
STEEP MID-LEVEL LAPSE RATES AND STRONG LOW LEVEL JET WITH SOME
CONVECTIVE ELEMENTS WITHIN THE PRECIP BAND. WARMING TEMPS SHOULD
RESULT IN FAIRLY QUICK CHANGE OVER TO RAIN AFTER ONSET OF PRECIP.
SOME SHOWERS COULD ACCOMPANY COLD FRONT MOVING THROUGH THE REGION
EARLY SUNDAY EVENING WITH WINDS SHIFTING TO NORTHWEST BEHIND THE
FRONT AND GRADUALLY EASING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN SNOW/SLEET/GRAUPEL POTENTIAL
* HIGH CONFIDENCE IN PRECIP TIMING
* LOW CONFIDENCE IN POTENTIAL FOR LLWS EARLY SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS/GUSTS SUNDAY

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 282157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
457 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* LAKE BREEZE INFLUENCED EASTERLY WINDS INTO EARLY EVENING
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT

RATZER/IZZI

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 282157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
457 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* LAKE BREEZE INFLUENCED EASTERLY WINDS INTO EARLY EVENING
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT

RATZER/IZZI

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 282157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
457 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* LAKE BREEZE INFLUENCED EASTERLY WINDS INTO EARLY EVENING
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT

RATZER/IZZI

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 282157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
457 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* LAKE BREEZE INFLUENCED EASTERLY WINDS INTO EARLY EVENING
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT

RATZER/IZZI

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER/IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 281947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
247 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 281947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
247 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 281850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
150 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 281850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
150 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 281850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
150 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 281850
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
150 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 281732
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1232 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
425 AM CDT

MAIN MARINE CONCERN CONTINUES TO BE WITH SOUTH-SOUTHWEST GALES ON
SUNDAY. HAVE ISSUED A GALE WARNING FOR THE ENTIRE LAKE...INCLUDING
THE NEARSHORE WATERS. STRONG LOW PRESSURE WILL TRACK NEAR OR NORTH
OF LAKE SUPERIOR AND EXPANSIVE HIGH PRESSURE WILL DEPART TO THE
SOUTHEAST US...WITH TIGHT PRESSURE GRADIENT AND STRONG PRESSURE
FALLS AHEAD OF COLD FRONT TRAILING FROM THE LOW. SOUTH-SOUTHWEST
WINDS WILL QUICKLY RAMP UP AND BECOME STRONGEST ON THE NORTHERN
PORTION OF THE LAKE...WHERE THERE REMAINS SOME POTENTIAL FOR GUSTS
APPROACHING STORM FORCE FOR A FEW HOUR WINDOW MID TO LATE SUNDAY
MORNING. HAVE STAYED WITH 45 KT SPEED MENTION IN GLF...BUT MAY
NEED TO ADD OCCASIONAL STORM GUSTS IN SUBSEQUENT ISSUANCES. IN THE
NEARSHORE AND SOUTH HALF...EXPECTING SPEEDS OF 35 TO 40 KT. WINDS
WILL SHIFT WEST BEHIND THE COLD FRONT SUNDAY EVENING...WITH SPEEDS
REMAINING ELEVATED AROUND 30 KT ACROSS THE OPEN WATERS. WILL NEED
TO WATCH FOR A RENEWED PERIOD OF GALES ON THE NORTH HALF CLOSEST
TO THE DEPARTING LOW PRESSURE AREA.

A CLIPPER TYPE SYSTEM WILL THEN MOVE ACROSS THE LAKE MONDAY
NIGHT...WITH UNCERTAINTY IN THE PATH OF THIS SYSTEM...FOLLOWED BY
HIGH PRESSURE MID WEEK AND THEN A COLD FRONTAL PASSAGE WEDNESDAY
NIGHT. THERE IS SOME POTENTIAL FOR A STRONGER SYSTEM APPROACHING
THE LAKE LATER IN THE WEEK...BUT PLENTY OF UNCERTAINTY DUE TO
SIGNIFICANT DIFFERENCES IN FORECAST GUIDANCE.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 281732
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1232 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
425 AM CDT

MAIN MARINE CONCERN CONTINUES TO BE WITH SOUTH-SOUTHWEST GALES ON
SUNDAY. HAVE ISSUED A GALE WARNING FOR THE ENTIRE LAKE...INCLUDING
THE NEARSHORE WATERS. STRONG LOW PRESSURE WILL TRACK NEAR OR NORTH
OF LAKE SUPERIOR AND EXPANSIVE HIGH PRESSURE WILL DEPART TO THE
SOUTHEAST US...WITH TIGHT PRESSURE GRADIENT AND STRONG PRESSURE
FALLS AHEAD OF COLD FRONT TRAILING FROM THE LOW. SOUTH-SOUTHWEST
WINDS WILL QUICKLY RAMP UP AND BECOME STRONGEST ON THE NORTHERN
PORTION OF THE LAKE...WHERE THERE REMAINS SOME POTENTIAL FOR GUSTS
APPROACHING STORM FORCE FOR A FEW HOUR WINDOW MID TO LATE SUNDAY
MORNING. HAVE STAYED WITH 45 KT SPEED MENTION IN GLF...BUT MAY
NEED TO ADD OCCASIONAL STORM GUSTS IN SUBSEQUENT ISSUANCES. IN THE
NEARSHORE AND SOUTH HALF...EXPECTING SPEEDS OF 35 TO 40 KT. WINDS
WILL SHIFT WEST BEHIND THE COLD FRONT SUNDAY EVENING...WITH SPEEDS
REMAINING ELEVATED AROUND 30 KT ACROSS THE OPEN WATERS. WILL NEED
TO WATCH FOR A RENEWED PERIOD OF GALES ON THE NORTH HALF CLOSEST
TO THE DEPARTING LOW PRESSURE AREA.

A CLIPPER TYPE SYSTEM WILL THEN MOVE ACROSS THE LAKE MONDAY
NIGHT...WITH UNCERTAINTY IN THE PATH OF THIS SYSTEM...FOLLOWED BY
HIGH PRESSURE MID WEEK AND THEN A COLD FRONTAL PASSAGE WEDNESDAY
NIGHT. THERE IS SOME POTENTIAL FOR A STRONGER SYSTEM APPROACHING
THE LAKE LATER IN THE WEEK...BUT PLENTY OF UNCERTAINTY DUE TO
SIGNIFICANT DIFFERENCES IN FORECAST GUIDANCE.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 281732
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1232 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
425 AM CDT

MAIN MARINE CONCERN CONTINUES TO BE WITH SOUTH-SOUTHWEST GALES ON
SUNDAY. HAVE ISSUED A GALE WARNING FOR THE ENTIRE LAKE...INCLUDING
THE NEARSHORE WATERS. STRONG LOW PRESSURE WILL TRACK NEAR OR NORTH
OF LAKE SUPERIOR AND EXPANSIVE HIGH PRESSURE WILL DEPART TO THE
SOUTHEAST US...WITH TIGHT PRESSURE GRADIENT AND STRONG PRESSURE
FALLS AHEAD OF COLD FRONT TRAILING FROM THE LOW. SOUTH-SOUTHWEST
WINDS WILL QUICKLY RAMP UP AND BECOME STRONGEST ON THE NORTHERN
PORTION OF THE LAKE...WHERE THERE REMAINS SOME POTENTIAL FOR GUSTS
APPROACHING STORM FORCE FOR A FEW HOUR WINDOW MID TO LATE SUNDAY
MORNING. HAVE STAYED WITH 45 KT SPEED MENTION IN GLF...BUT MAY
NEED TO ADD OCCASIONAL STORM GUSTS IN SUBSEQUENT ISSUANCES. IN THE
NEARSHORE AND SOUTH HALF...EXPECTING SPEEDS OF 35 TO 40 KT. WINDS
WILL SHIFT WEST BEHIND THE COLD FRONT SUNDAY EVENING...WITH SPEEDS
REMAINING ELEVATED AROUND 30 KT ACROSS THE OPEN WATERS. WILL NEED
TO WATCH FOR A RENEWED PERIOD OF GALES ON THE NORTH HALF CLOSEST
TO THE DEPARTING LOW PRESSURE AREA.

A CLIPPER TYPE SYSTEM WILL THEN MOVE ACROSS THE LAKE MONDAY
NIGHT...WITH UNCERTAINTY IN THE PATH OF THIS SYSTEM...FOLLOWED BY
HIGH PRESSURE MID WEEK AND THEN A COLD FRONTAL PASSAGE WEDNESDAY
NIGHT. THERE IS SOME POTENTIAL FOR A STRONGER SYSTEM APPROACHING
THE LAKE LATER IN THE WEEK...BUT PLENTY OF UNCERTAINTY DUE TO
SIGNIFICANT DIFFERENCES IN FORECAST GUIDANCE.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 281732
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1232 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE INFLUENCED EAST-NORTHEAST WINDS THIS AFTERNOON
  GENERALLY 8-10 KT RANGE.
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING.
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT.

RATZER

//DISCUSSION...UPDATED 18Z...

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
425 AM CDT

MAIN MARINE CONCERN CONTINUES TO BE WITH SOUTH-SOUTHWEST GALES ON
SUNDAY. HAVE ISSUED A GALE WARNING FOR THE ENTIRE LAKE...INCLUDING
THE NEARSHORE WATERS. STRONG LOW PRESSURE WILL TRACK NEAR OR NORTH
OF LAKE SUPERIOR AND EXPANSIVE HIGH PRESSURE WILL DEPART TO THE
SOUTHEAST US...WITH TIGHT PRESSURE GRADIENT AND STRONG PRESSURE
FALLS AHEAD OF COLD FRONT TRAILING FROM THE LOW. SOUTH-SOUTHWEST
WINDS WILL QUICKLY RAMP UP AND BECOME STRONGEST ON THE NORTHERN
PORTION OF THE LAKE...WHERE THERE REMAINS SOME POTENTIAL FOR GUSTS
APPROACHING STORM FORCE FOR A FEW HOUR WINDOW MID TO LATE SUNDAY
MORNING. HAVE STAYED WITH 45 KT SPEED MENTION IN GLF...BUT MAY
NEED TO ADD OCCASIONAL STORM GUSTS IN SUBSEQUENT ISSUANCES. IN THE
NEARSHORE AND SOUTH HALF...EXPECTING SPEEDS OF 35 TO 40 KT. WINDS
WILL SHIFT WEST BEHIND THE COLD FRONT SUNDAY EVENING...WITH SPEEDS
REMAINING ELEVATED AROUND 30 KT ACROSS THE OPEN WATERS. WILL NEED
TO WATCH FOR A RENEWED PERIOD OF GALES ON THE NORTH HALF CLOSEST
TO THE DEPARTING LOW PRESSURE AREA.

A CLIPPER TYPE SYSTEM WILL THEN MOVE ACROSS THE LAKE MONDAY
NIGHT...WITH UNCERTAINTY IN THE PATH OF THIS SYSTEM...FOLLOWED BY
HIGH PRESSURE MID WEEK AND THEN A COLD FRONTAL PASSAGE WEDNESDAY
NIGHT. THERE IS SOME POTENTIAL FOR A STRONGER SYSTEM APPROACHING
THE LAKE LATER IN THE WEEK...BUT PLENTY OF UNCERTAINTY DUE TO
SIGNIFICANT DIFFERENCES IN FORECAST GUIDANCE.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 281711
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1211 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* LAKE BREEZE BRINGING EAST WINDS OF 8-10 KT THIS AFTERNOON.
* 40-45 KT SW WINDS BETWEEN 1000-2000 FT NEAR DAYBREAK SUNDAY
  POSSIBLY CREATING LLWS.
* PRECIPITATION BEGINNING SUNDAY MORNING MOST FAVORED TO BE RAIN
  BUT COULD BE MIXED WITH SNOW OR SLEET.
* SOUTH-SOUTHWEST WINDS GUSTING TO 30 KT OR HIGHER BY LATE SUNDAY
  MORNING.

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE WILL REMAIN OVER THE AREA TODAY. THIS WILL ALLOW
ONSHORE FLOW FROM THE LAKE TO INCREASE SLIGHTLY LATE THIS MORNING
INTO AFTERNOON WITH A LAKE BREEZE. THERE MAY BE SOME SPEEDS OF 10
KT OR SLIGHTLY HIGHER DURING THE EARLY AFTERNOON...BUT THESE
SPEEDS ARE EXPECTED TO BE SHORT-LIVED AS THE HIGH IS LITERALLY
RIGHT OVERHEAD AND THE ATMOSPHERIC WIND SPEEDS SHOULD BE LOW.

AS LOW PRESSURE MOVES ACROSS FAR SOUTHERN CANADA LATER
TONIGHT...SOUTHERLY SURFACE WINDS WILL INCREASE TO OVER 10
KT...AND QUICKLY BECOME GUSTY AFTER DAYBREAK SUNDAY. THERE IS A
PERIOD JUST PRIOR TO DAYBREAK WHERE THERE COULD BE LOW-LEVEL WIND
SHEAR WITH 40-45 KT SOUTH-SOUTHWEST FLOW BY 1000-1500 FT OFF THE
DECK. AT THIS TIME THAT DOES NOT LOOK LIKE IT WOULD REACH TRUE
CRITERIA.

SUNDAY MORNING WILL BRING PRECIPITATION TO THE REGION AS THE
AFOREMENTIONED LOW PRESSURE SYSTEM MOVES EAST. A PLUME OF DEEPER
MOISTURE AND CONVERGENCE OVER THE REGION SHOULD BRING A 6 HOUR
WINDOW OR SO OF PRECIPITATION. THIS IS MOST FAVORED TO BE
RAIN...ESPECIALLY DURING THE LAST FEW HOURS /EARLY SUNDAY
AFTERNOON/. HOWEVER DURING THE MORNING HOURS THERE IS THE
POTENTIAL TO MIX WITH SNOW OR SLEET. MORE DETAILS WILL BE WORKED
OUT WITH THIS IN TAFS LATER TODAY...BUT FOR NOW HAVE INCLUDED A
PROB30 IN THE ORD TAF.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM-HIGH IN TIMING AND MAGNITUDE OF LAKE BREEZE. MEDIUM THAT
  SPEEDS WILL STAY MAINLY 9+ KT OR LESS.
* MEDIUM-HIGH IN 40-45KT SW LOW-LEVEL JET WINDS NEAR DAYBREAK
  SUNDAY. LOW IN TRUE LLWS.
* HIGH IN PRECIPITATION BY MID SUNDAY MORNING. LOW IN
  PRECIPITATION TYPE AT ONSET.

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
425 AM CDT

MAIN MARINE CONCERN CONTINUES TO BE WITH SOUTH-SOUTHWEST GALES ON
SUNDAY. HAVE ISSUED A GALE WARNING FOR THE ENTIRE LAKE...INCLUDING
THE NEARSHORE WATERS. STRONG LOW PRESSURE WILL TRACK NEAR OR NORTH
OF LAKE SUPERIOR AND EXPANSIVE HIGH PRESSURE WILL DEPART TO THE
SOUTHEAST US...WITH TIGHT PRESSURE GRADIENT AND STRONG PRESSURE
FALLS AHEAD OF COLD FRONT TRAILING FROM THE LOW. SOUTH-SOUTHWEST
WINDS WILL QUICKLY RAMP UP AND BECOME STRONGEST ON THE NORTHERN
PORTION OF THE LAKE...WHERE THERE REMAINS SOME POTENTIAL FOR GUSTS
APPROACHING STORM FORCE FOR A FEW HOUR WINDOW MID TO LATE SUNDAY
MORNING. HAVE STAYED WITH 45 KT SPEED MENTION IN GLF...BUT MAY
NEED TO ADD OCCASIONAL STORM GUSTS IN SUBSEQUENT ISSUANCES. IN THE
NEARSHORE AND SOUTH HALF...EXPECTING SPEEDS OF 35 TO 40 KT. WINDS
WILL SHIFT WEST BEHIND THE COLD FRONT SUNDAY EVENING...WITH SPEEDS
REMAINING ELEVATED AROUND 30 KT ACROSS THE OPEN WATERS. WILL NEED
TO WATCH FOR A RENEWED PERIOD OF GALES ON THE NORTH HALF CLOSEST
TO THE DEPARTING LOW PRESSURE AREA.

A CLIPPER TYPE SYSTEM WILL THEN MOVE ACROSS THE LAKE MONDAY
NIGHT...WITH UNCERTAINTY IN THE PATH OF THIS SYSTEM...FOLLOWED BY
HIGH PRESSURE MID WEEK AND THEN A COLD FRONTAL PASSAGE WEDNESDAY
NIGHT. THERE IS SOME POTENTIAL FOR A STRONGER SYSTEM APPROACHING
THE LAKE LATER IN THE WEEK...BUT PLENTY OF UNCERTAINTY DUE TO
SIGNIFICANT DIFFERENCES IN FORECAST GUIDANCE.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 281711
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1211 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* LAKE BREEZE BRINGING EAST WINDS OF 8-10 KT THIS AFTERNOON.
* 40-45 KT SW WINDS BETWEEN 1000-2000 FT NEAR DAYBREAK SUNDAY
  POSSIBLY CREATING LLWS.
* PRECIPITATION BEGINNING SUNDAY MORNING MOST FAVORED TO BE RAIN
  BUT COULD BE MIXED WITH SNOW OR SLEET.
* SOUTH-SOUTHWEST WINDS GUSTING TO 30 KT OR HIGHER BY LATE SUNDAY
  MORNING.

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE WILL REMAIN OVER THE AREA TODAY. THIS WILL ALLOW
ONSHORE FLOW FROM THE LAKE TO INCREASE SLIGHTLY LATE THIS MORNING
INTO AFTERNOON WITH A LAKE BREEZE. THERE MAY BE SOME SPEEDS OF 10
KT OR SLIGHTLY HIGHER DURING THE EARLY AFTERNOON...BUT THESE
SPEEDS ARE EXPECTED TO BE SHORT-LIVED AS THE HIGH IS LITERALLY
RIGHT OVERHEAD AND THE ATMOSPHERIC WIND SPEEDS SHOULD BE LOW.

AS LOW PRESSURE MOVES ACROSS FAR SOUTHERN CANADA LATER
TONIGHT...SOUTHERLY SURFACE WINDS WILL INCREASE TO OVER 10
KT...AND QUICKLY BECOME GUSTY AFTER DAYBREAK SUNDAY. THERE IS A
PERIOD JUST PRIOR TO DAYBREAK WHERE THERE COULD BE LOW-LEVEL WIND
SHEAR WITH 40-45 KT SOUTH-SOUTHWEST FLOW BY 1000-1500 FT OFF THE
DECK. AT THIS TIME THAT DOES NOT LOOK LIKE IT WOULD REACH TRUE
CRITERIA.

SUNDAY MORNING WILL BRING PRECIPITATION TO THE REGION AS THE
AFOREMENTIONED LOW PRESSURE SYSTEM MOVES EAST. A PLUME OF DEEPER
MOISTURE AND CONVERGENCE OVER THE REGION SHOULD BRING A 6 HOUR
WINDOW OR SO OF PRECIPITATION. THIS IS MOST FAVORED TO BE
RAIN...ESPECIALLY DURING THE LAST FEW HOURS /EARLY SUNDAY
AFTERNOON/. HOWEVER DURING THE MORNING HOURS THERE IS THE
POTENTIAL TO MIX WITH SNOW OR SLEET. MORE DETAILS WILL BE WORKED
OUT WITH THIS IN TAFS LATER TODAY...BUT FOR NOW HAVE INCLUDED A
PROB30 IN THE ORD TAF.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM-HIGH IN TIMING AND MAGNITUDE OF LAKE BREEZE. MEDIUM THAT
  SPEEDS WILL STAY MAINLY 9+ KT OR LESS.
* MEDIUM-HIGH IN 40-45KT SW LOW-LEVEL JET WINDS NEAR DAYBREAK
  SUNDAY. LOW IN TRUE LLWS.
* HIGH IN PRECIPITATION BY MID SUNDAY MORNING. LOW IN
  PRECIPITATION TYPE AT ONSET.

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
425 AM CDT

MAIN MARINE CONCERN CONTINUES TO BE WITH SOUTH-SOUTHWEST GALES ON
SUNDAY. HAVE ISSUED A GALE WARNING FOR THE ENTIRE LAKE...INCLUDING
THE NEARSHORE WATERS. STRONG LOW PRESSURE WILL TRACK NEAR OR NORTH
OF LAKE SUPERIOR AND EXPANSIVE HIGH PRESSURE WILL DEPART TO THE
SOUTHEAST US...WITH TIGHT PRESSURE GRADIENT AND STRONG PRESSURE
FALLS AHEAD OF COLD FRONT TRAILING FROM THE LOW. SOUTH-SOUTHWEST
WINDS WILL QUICKLY RAMP UP AND BECOME STRONGEST ON THE NORTHERN
PORTION OF THE LAKE...WHERE THERE REMAINS SOME POTENTIAL FOR GUSTS
APPROACHING STORM FORCE FOR A FEW HOUR WINDOW MID TO LATE SUNDAY
MORNING. HAVE STAYED WITH 45 KT SPEED MENTION IN GLF...BUT MAY
NEED TO ADD OCCASIONAL STORM GUSTS IN SUBSEQUENT ISSUANCES. IN THE
NEARSHORE AND SOUTH HALF...EXPECTING SPEEDS OF 35 TO 40 KT. WINDS
WILL SHIFT WEST BEHIND THE COLD FRONT SUNDAY EVENING...WITH SPEEDS
REMAINING ELEVATED AROUND 30 KT ACROSS THE OPEN WATERS. WILL NEED
TO WATCH FOR A RENEWED PERIOD OF GALES ON THE NORTH HALF CLOSEST
TO THE DEPARTING LOW PRESSURE AREA.

A CLIPPER TYPE SYSTEM WILL THEN MOVE ACROSS THE LAKE MONDAY
NIGHT...WITH UNCERTAINTY IN THE PATH OF THIS SYSTEM...FOLLOWED BY
HIGH PRESSURE MID WEEK AND THEN A COLD FRONTAL PASSAGE WEDNESDAY
NIGHT. THERE IS SOME POTENTIAL FOR A STRONGER SYSTEM APPROACHING
THE LAKE LATER IN THE WEEK...BUT PLENTY OF UNCERTAINTY DUE TO
SIGNIFICANT DIFFERENCES IN FORECAST GUIDANCE.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO




000
FXUS63 KLOT 281711
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1211 PM CDT SAT MAR 28 2015

.UPDATE...
1207 PM CDT

HIGH PRESSURE SPANNING THE REGION PROVIDING QUIET WEATHER
TODAY...BUT WITH CHILLY CONDITIONS IN PLACE. TEMPS STILL IN THE
LOW 30S FOR MOST LOCATIONS AT THIS TIME WITH ONSHORE FLOW LIMITING
TEMPS IN THE 20S STILL FOR LOCATIONS NEAR THE LAKE. SUNNY SKIES
WILL PREVAIL TODAY WITH TEMPS GENERALLY IN THE MID TO UPPER
30S...ALTHOUGH SOME LOCATIONS COULD TOP AT AROUND 40 DEGREES THIS
AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* LAKE BREEZE BRINGING EAST WINDS OF 8-10 KT THIS AFTERNOON.
* 40-45 KT SW WINDS BETWEEN 1000-2000 FT NEAR DAYBREAK SUNDAY
  POSSIBLY CREATING LLWS.
* PRECIPITATION BEGINNING SUNDAY MORNING MOST FAVORED TO BE RAIN
  BUT COULD BE MIXED WITH SNOW OR SLEET.
* SOUTH-SOUTHWEST WINDS GUSTING TO 30 KT OR HIGHER BY LATE SUNDAY
  MORNING.

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE WILL REMAIN OVER THE AREA TODAY. THIS WILL ALLOW
ONSHORE FLOW FROM THE LAKE TO INCREASE SLIGHTLY LATE THIS MORNING
INTO AFTERNOON WITH A LAKE BREEZE. THERE MAY BE SOME SPEEDS OF 10
KT OR SLIGHTLY HIGHER DURING THE EARLY AFTERNOON...BUT THESE
SPEEDS ARE EXPECTED TO BE SHORT-LIVED AS THE HIGH IS LITERALLY
RIGHT OVERHEAD AND THE ATMOSPHERIC WIND SPEEDS SHOULD BE LOW.

AS LOW PRESSURE MOVES ACROSS FAR SOUTHERN CANADA LATER
TONIGHT...SOUTHERLY SURFACE WINDS WILL INCREASE TO OVER 10
KT...AND QUICKLY BECOME GUSTY AFTER DAYBREAK SUNDAY. THERE IS A
PERIOD JUST PRIOR TO DAYBREAK WHERE THERE COULD BE LOW-LEVEL WIND
SHEAR WITH 40-45 KT SOUTH-SOUTHWEST FLOW BY 1000-1500 FT OFF THE
DECK. AT THIS TIME THAT DOES NOT LOOK LIKE IT WOULD REACH TRUE
CRITERIA.

SUNDAY MORNING WILL BRING PRECIPITATION TO THE REGION AS THE
AFOREMENTIONED LOW PRESSURE SYSTEM MOVES EAST. A PLUME OF DEEPER
MOISTURE AND CONVERGENCE OVER THE REGION SHOULD BRING A 6 HOUR
WINDOW OR SO OF PRECIPITATION. THIS IS MOST FAVORED TO BE
RAIN...ESPECIALLY DURING THE LAST FEW HOURS /EARLY SUNDAY
AFTERNOON/. HOWEVER DURING THE MORNING HOURS THERE IS THE
POTENTIAL TO MIX WITH SNOW OR SLEET. MORE DETAILS WILL BE WORKED
OUT WITH THIS IN TAFS LATER TODAY...BUT FOR NOW HAVE INCLUDED A
PROB30 IN THE ORD TAF.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM-HIGH IN TIMING AND MAGNITUDE OF LAKE BREEZE. MEDIUM THAT
  SPEEDS WILL STAY MAINLY 9+ KT OR LESS.
* MEDIUM-HIGH IN 40-45KT SW LOW-LEVEL JET WINDS NEAR DAYBREAK
  SUNDAY. LOW IN TRUE LLWS.
* HIGH IN PRECIPITATION BY MID SUNDAY MORNING. LOW IN
  PRECIPITATION TYPE AT ONSET.

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.MARINE...
425 AM CDT

MAIN MARINE CONCERN CONTINUES TO BE WITH SOUTH-SOUTHWEST GALES ON
SUNDAY. HAVE ISSUED A GALE WARNING FOR THE ENTIRE LAKE...INCLUDING
THE NEARSHORE WATERS. STRONG LOW PRESSURE WILL TRACK NEAR OR NORTH
OF LAKE SUPERIOR AND EXPANSIVE HIGH PRESSURE WILL DEPART TO THE
SOUTHEAST US...WITH TIGHT PRESSURE GRADIENT AND STRONG PRESSURE
FALLS AHEAD OF COLD FRONT TRAILING FROM THE LOW. SOUTH-SOUTHWEST
WINDS WILL QUICKLY RAMP UP AND BECOME STRONGEST ON THE NORTHERN
PORTION OF THE LAKE...WHERE THERE REMAINS SOME POTENTIAL FOR GUSTS
APPROACHING STORM FORCE FOR A FEW HOUR WINDOW MID TO LATE SUNDAY
MORNING. HAVE STAYED WITH 45 KT SPEED MENTION IN GLF...BUT MAY
NEED TO ADD OCCASIONAL STORM GUSTS IN SUBSEQUENT ISSUANCES. IN THE
NEARSHORE AND SOUTH HALF...EXPECTING SPEEDS OF 35 TO 40 KT. WINDS
WILL SHIFT WEST BEHIND THE COLD FRONT SUNDAY EVENING...WITH SPEEDS
REMAINING ELEVATED AROUND 30 KT ACROSS THE OPEN WATERS. WILL NEED
TO WATCH FOR A RENEWED PERIOD OF GALES ON THE NORTH HALF CLOSEST
TO THE DEPARTING LOW PRESSURE AREA.

A CLIPPER TYPE SYSTEM WILL THEN MOVE ACROSS THE LAKE MONDAY
NIGHT...WITH UNCERTAINTY IN THE PATH OF THIS SYSTEM...FOLLOWED BY
HIGH PRESSURE MID WEEK AND THEN A COLD FRONTAL PASSAGE WEDNESDAY
NIGHT. THERE IS SOME POTENTIAL FOR A STRONGER SYSTEM APPROACHING
THE LAKE LATER IN THE WEEK...BUT PLENTY OF UNCERTAINTY DUE TO
SIGNIFICANT DIFFERENCES IN FORECAST GUIDANCE.

RC/MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

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