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000
FXUS63 KLOT 180314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* BREEZY EAST-NORTHEAST WINDS SATURDAY. GUSTS NEAR 20 KT.

RATZER

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

LAKE BREEZE...MAKING ITS SECOND ATTEMPT...IS JUST PASSING ACROSS
MDW AND WILL CROSS ORD WITHIN THE HOUR. WINDS SHIFT EAST BEHIND
BOUNDARY...BUT SHOULD TREND EAST-SOUTHEAST WITH SPEEDS GENERALLY
LESS THAN 10 KT EARLY THIS EVENING. WINDS THEN BECOME LIGHT AND
SOMEWHAT VARIABLE OVERNIGHT...THEN SHIFT NORTHEAST BY SATURDAY
MORNING AS A COLD FRONT SETTLES ACROSS THE REGION AND LOW PRESSURE
DEVELOPS ACROSS THE PLAINS. NORTHEAST WINDS WILL LIKELY GUST 15-20
KTS FROM MID-MORNING ONWARD...EVENTUALLY BECOMING MORE EASTERLY BY
SATURDAY EVENING WITH GUSTS DIMINISHING.

RELATIVELY DRY FLOW OFF THE LAKE SHOULD LIMIT CEILINGS TO VFR
THROUGH THE PERIOD.

RATZER

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

* HIGH ALL ELEMENTS.

RATZER

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

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST WINDS
BECOMING NORTHEAST.

MONDAY...CHANCE OF SHRA/MVFR EARLY...IMPROVING TO VFR. GUSTY WEST
WINDS.

TUESDAY...SLGT CHANCE SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

RATZER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...9 AM SATURDAY TO 4
     PM SATURDAY.

&&

$$

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 180314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* BREEZY EAST-NORTHEAST WINDS SATURDAY. GUSTS NEAR 20 KT.

RATZER

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

LAKE BREEZE...MAKING ITS SECOND ATTEMPT...IS JUST PASSING ACROSS
MDW AND WILL CROSS ORD WITHIN THE HOUR. WINDS SHIFT EAST BEHIND
BOUNDARY...BUT SHOULD TREND EAST-SOUTHEAST WITH SPEEDS GENERALLY
LESS THAN 10 KT EARLY THIS EVENING. WINDS THEN BECOME LIGHT AND
SOMEWHAT VARIABLE OVERNIGHT...THEN SHIFT NORTHEAST BY SATURDAY
MORNING AS A COLD FRONT SETTLES ACROSS THE REGION AND LOW PRESSURE
DEVELOPS ACROSS THE PLAINS. NORTHEAST WINDS WILL LIKELY GUST 15-20
KTS FROM MID-MORNING ONWARD...EVENTUALLY BECOMING MORE EASTERLY BY
SATURDAY EVENING WITH GUSTS DIMINISHING.

RELATIVELY DRY FLOW OFF THE LAKE SHOULD LIMIT CEILINGS TO VFR
THROUGH THE PERIOD.

RATZER

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

* HIGH ALL ELEMENTS.

RATZER

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

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST WINDS
BECOMING NORTHEAST.

MONDAY...CHANCE OF SHRA/MVFR EARLY...IMPROVING TO VFR. GUSTY WEST
WINDS.

TUESDAY...SLGT CHANCE SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

RATZER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...9 AM SATURDAY TO 4
     PM SATURDAY.

&&

$$

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 180314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1014 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* BREEZY EAST-NORTHEAST WINDS SATURDAY. GUSTS NEAR 20 KT.

RATZER

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

LAKE BREEZE...MAKING ITS SECOND ATTEMPT...IS JUST PASSING ACROSS
MDW AND WILL CROSS ORD WITHIN THE HOUR. WINDS SHIFT EAST BEHIND
BOUNDARY...BUT SHOULD TREND EAST-SOUTHEAST WITH SPEEDS GENERALLY
LESS THAN 10 KT EARLY THIS EVENING. WINDS THEN BECOME LIGHT AND
SOMEWHAT VARIABLE OVERNIGHT...THEN SHIFT NORTHEAST BY SATURDAY
MORNING AS A COLD FRONT SETTLES ACROSS THE REGION AND LOW PRESSURE
DEVELOPS ACROSS THE PLAINS. NORTHEAST WINDS WILL LIKELY GUST 15-20
KTS FROM MID-MORNING ONWARD...EVENTUALLY BECOMING MORE EASTERLY BY
SATURDAY EVENING WITH GUSTS DIMINISHING.

RELATIVELY DRY FLOW OFF THE LAKE SHOULD LIMIT CEILINGS TO VFR
THROUGH THE PERIOD.

RATZER

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

* HIGH ALL ELEMENTS.

RATZER

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

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST WINDS
BECOMING NORTHEAST.

MONDAY...CHANCE OF SHRA/MVFR EARLY...IMPROVING TO VFR. GUSTY WEST
WINDS.

TUESDAY...SLGT CHANCE SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

RATZER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...9 AM SATURDAY TO 4
     PM SATURDAY.

&&

$$

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 180002
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
702 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTING WEST ACROSS ORD/MDW NOW. WINDS TO BECOME
  EAST-SOUTHEAST BEHIND LAKE BREEZE...GENERALLY LESS THAN 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY. GUSTS NEAR 20 KT.

RATZER

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

LAKE BREEZE...MAKING ITS SECOND ATTEMPT...IS JUST PASSING ACROSS
MDW AND WILL CROSS ORD WITHIN THE HOUR. WINDS SHIFT EAST BEHIND
BOUNDARY...BUT SHOULD TREND EAST-SOUTHEAST WITH SPEEDS GENERALLY
LESS THAN 10 KT EARLY THIS EVENING. WINDS THEN BECOME LIGHT AND
SOMEWHAT VARIABLE OVERNIGHT...THEN SHIFT NORTHEAST BY SATURDAY
MORNING AS A COLD FRONT SETTLES ACROSS THE REGION AND LOW PRESSURE
DEVELOPS ACROSS THE PLAINS. NORTHEAST WINDS WILL LIKELY GUST 15-20
KTS FROM MID-MORNING ONWARD...EVENTUALLY BECOMING MORE EASTERLY BY
SATURDAY EVENING WITH GUSTS DIMINISHING.

RELATIVELY DRY FLOW OFF THE LAKE SHOULD LIMIT CEILINGS TO VFR
THROUGH THE PERIOD.

RATZER


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

* HIGH ALL ELEMENTS.

RATZER

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

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST WINDS
BECOMING NORTHEAST.

MONDAY...CHANCE OF SHRA/MVFR EARLY...IMPROVING TO VFR. GUSTY WEST
WINDS.

TUESDAY...SLGT CHANCE SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

RATZER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 180002
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
702 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTING WEST ACROSS ORD/MDW NOW. WINDS TO BECOME
  EAST-SOUTHEAST BEHIND LAKE BREEZE...GENERALLY LESS THAN 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY. GUSTS NEAR 20 KT.

RATZER

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

LAKE BREEZE...MAKING ITS SECOND ATTEMPT...IS JUST PASSING ACROSS
MDW AND WILL CROSS ORD WITHIN THE HOUR. WINDS SHIFT EAST BEHIND
BOUNDARY...BUT SHOULD TREND EAST-SOUTHEAST WITH SPEEDS GENERALLY
LESS THAN 10 KT EARLY THIS EVENING. WINDS THEN BECOME LIGHT AND
SOMEWHAT VARIABLE OVERNIGHT...THEN SHIFT NORTHEAST BY SATURDAY
MORNING AS A COLD FRONT SETTLES ACROSS THE REGION AND LOW PRESSURE
DEVELOPS ACROSS THE PLAINS. NORTHEAST WINDS WILL LIKELY GUST 15-20
KTS FROM MID-MORNING ONWARD...EVENTUALLY BECOMING MORE EASTERLY BY
SATURDAY EVENING WITH GUSTS DIMINISHING.

RELATIVELY DRY FLOW OFF THE LAKE SHOULD LIMIT CEILINGS TO VFR
THROUGH THE PERIOD.

RATZER


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

* HIGH ALL ELEMENTS.

RATZER

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

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST WINDS
BECOMING NORTHEAST.

MONDAY...CHANCE OF SHRA/MVFR EARLY...IMPROVING TO VFR. GUSTY WEST
WINDS.

TUESDAY...SLGT CHANCE SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

RATZER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 180002
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
702 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTING WEST ACROSS ORD/MDW NOW. WINDS TO BECOME
  EAST-SOUTHEAST BEHIND LAKE BREEZE...GENERALLY LESS THAN 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY. GUSTS NEAR 20 KT.

RATZER

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

LAKE BREEZE...MAKING ITS SECOND ATTEMPT...IS JUST PASSING ACROSS
MDW AND WILL CROSS ORD WITHIN THE HOUR. WINDS SHIFT EAST BEHIND
BOUNDARY...BUT SHOULD TREND EAST-SOUTHEAST WITH SPEEDS GENERALLY
LESS THAN 10 KT EARLY THIS EVENING. WINDS THEN BECOME LIGHT AND
SOMEWHAT VARIABLE OVERNIGHT...THEN SHIFT NORTHEAST BY SATURDAY
MORNING AS A COLD FRONT SETTLES ACROSS THE REGION AND LOW PRESSURE
DEVELOPS ACROSS THE PLAINS. NORTHEAST WINDS WILL LIKELY GUST 15-20
KTS FROM MID-MORNING ONWARD...EVENTUALLY BECOMING MORE EASTERLY BY
SATURDAY EVENING WITH GUSTS DIMINISHING.

RELATIVELY DRY FLOW OFF THE LAKE SHOULD LIMIT CEILINGS TO VFR
THROUGH THE PERIOD.

RATZER


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

* HIGH ALL ELEMENTS.

RATZER

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

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST WINDS
BECOMING NORTHEAST.

MONDAY...CHANCE OF SHRA/MVFR EARLY...IMPROVING TO VFR. GUSTY WEST
WINDS.

TUESDAY...SLGT CHANCE SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

RATZER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 180002
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
702 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTING WEST ACROSS ORD/MDW NOW. WINDS TO BECOME
  EAST-SOUTHEAST BEHIND LAKE BREEZE...GENERALLY LESS THAN 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY. GUSTS NEAR 20 KT.

RATZER

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

LAKE BREEZE...MAKING ITS SECOND ATTEMPT...IS JUST PASSING ACROSS
MDW AND WILL CROSS ORD WITHIN THE HOUR. WINDS SHIFT EAST BEHIND
BOUNDARY...BUT SHOULD TREND EAST-SOUTHEAST WITH SPEEDS GENERALLY
LESS THAN 10 KT EARLY THIS EVENING. WINDS THEN BECOME LIGHT AND
SOMEWHAT VARIABLE OVERNIGHT...THEN SHIFT NORTHEAST BY SATURDAY
MORNING AS A COLD FRONT SETTLES ACROSS THE REGION AND LOW PRESSURE
DEVELOPS ACROSS THE PLAINS. NORTHEAST WINDS WILL LIKELY GUST 15-20
KTS FROM MID-MORNING ONWARD...EVENTUALLY BECOMING MORE EASTERLY BY
SATURDAY EVENING WITH GUSTS DIMINISHING.

RELATIVELY DRY FLOW OFF THE LAKE SHOULD LIMIT CEILINGS TO VFR
THROUGH THE PERIOD.

RATZER


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

* HIGH ALL ELEMENTS.

RATZER

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

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST WINDS
BECOMING NORTHEAST.

MONDAY...CHANCE OF SHRA/MVFR EARLY...IMPROVING TO VFR. GUSTY WEST
WINDS.

TUESDAY...SLGT CHANCE SHRA...BUT MAINLY VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA. MAINLY VFR. WEST-NORTHWEST WINDS.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

RATZER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
508 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTED BACK EAST...NOW DRIFTING BACK WEST AND LOOKS
  LIKE WIND SHIFT AROUND 00Z TO THE EAST-SOUTHEAST. SHOULD BE
  GENERALLY LESS THAN 10 KTS.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

RATZER

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

RATZER

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

* MEDIUM-HIGH WITH SLOW-MOVING LAKE BREEZE TIMING NEXT FEW HOURS.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
508 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTED BACK EAST...NOW DRIFTING BACK WEST AND LOOKS
  LIKE WIND SHIFT AROUND 00Z TO THE EAST-SOUTHEAST. SHOULD BE
  GENERALLY LESS THAN 10 KTS.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

RATZER

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

RATZER

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

* MEDIUM-HIGH WITH SLOW-MOVING LAKE BREEZE TIMING NEXT FEW HOURS.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
508 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTED BACK EAST...NOW DRIFTING BACK WEST AND LOOKS
  LIKE WIND SHIFT AROUND 00Z TO THE EAST-SOUTHEAST. SHOULD BE
  GENERALLY LESS THAN 10 KTS.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

RATZER

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

RATZER

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

* MEDIUM-HIGH WITH SLOW-MOVING LAKE BREEZE TIMING NEXT FEW HOURS.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
508 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LAKE BREEZE DRIFTED BACK EAST...NOW DRIFTING BACK WEST AND LOOKS
  LIKE WIND SHIFT AROUND 00Z TO THE EAST-SOUTHEAST. SHOULD BE
  GENERALLY LESS THAN 10 KTS.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

RATZER

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

RATZER

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

* MEDIUM-HIGH WITH SLOW-MOVING LAKE BREEZE TIMING NEXT FEW HOURS.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172039
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
339 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172039
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
339 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172039
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
339 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172039
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
339 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

MAIN UNCERTAINTY IS WITH PROGRESSION OF ENERGY EMANATING FROM
UPPER LOW AS IT OPENS UP AND TRACKS EAST. TYPICAL TREND IS SLOWER
WITH THESE SYSTEMS AND OTHER THAN GEM BEING FAST OUTLIER...THIS IS
HOW MOST GUIDANCE TRENDED TODAY. WEAKENING MIDLEVEL SHORT
WAVE/VORT MAX SHOULD PASS OVER WESTERN CWA SATURDAY NIGHT...BUT
DRIER EAST-SOUTHEAST FLOW SHOULD KEEP MUCH OF THE AREA DRY. ONLY
HAVE LOW CHANCE POPS DURING EVENING IN FAR WESTERN CWA. INCREASING
CLOUDS WILL KEEP MOST LOWS IN 50S....EXCEPT 40S ALONG IL SHORE.

CONFIDENCE IS HIGH IN THERE BEING RAIN SHOWERS ON SUNDAY AS
SURFACE LOW ASSOCIATED WITH UPPER LEVEL ENERGY DEVELOPS AND TRACKS
TOWARD AREA. HAVE KEPT CATEGORICAL POPS CONFINED TO SOUTH OF I-80
THROUGH MID-DAY THEN SPREAD THEM NORTH FOR THE AFTERNOON. MODELS
IN GOOD AGREEMENT ON SYNOPTIC SETUP...BUT EXPECT CHANGES IN TRACK
OF SURFACE LOW...WHICH WILL AFFECT PLACEMENT OF BANDS OF HEAVIER
RAINFALL IN SEASONABLY MOIST AIRMASS ADVECTED NORTHWARD. FAIRLY
COOL TEMPERATURES ALOFT COULD SUPPORT AN ISOLATED TSRA
THREAT...BUT PROGGED MUCAPE AND MIDLAPSE RATES DO NOT SUPPORT MORE
THAN SLIGHT CHANCE TSRA MENTION. CLOUDS WILL KEEP INLAND TEMPS IN
60S...WITH CURRENT FAVORED TRACK OF SFC LOW RESULTING IN STEADY
ONSHORE WINDS ESPECIALLY INTO IL AND HIGHS ONLY AROUND 50.

UPPER LEVEL TROUGHINESS WILL LINGER OVER THE REGION THROUGH MUCH
OF NEXT WEEK THANKS TO REDEVELOPMENT OF HIGHLY AMPLIFIED WESTERN
RIDGING. THEREFORE...THE NICE PATTERN WE HAVE BEEN IN WILL BE
REPLACED BY UNSEASONABLY COOL TEMPS...WITH HIGHS IN 50S AND LOWS
ONLY IN 30S AND 40S. BEST CHANCE FOR RAIN SHOWERS WILL BE ON
MONDAY WITH STRONGER UPPER DISTURBANCE WRAPPING AROUND LARGE UPPER
TROUGH/LOW...WITH CHANCES THE REST OF THE WEEK TIED TO FAST MOVING
TOUGH TO PIN DOWN DISTURBANCES IN WEST-NORTHWEST FLOW. ANY NIGHTS
THAT CLEAR OUT COULD PRESENT A CHANCE FOR AT LEAST PATCHY FROST.

RC

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172015
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

TO BE ISSUED SHORTLY.

RC

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 172015
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
315 PM CDT FRI APR 17 2015

.SHORT TERM...
315 PM CDT

THROUGH SATURDAY...

MAIN WEATHER FEATURE OF NOTE THIS AFTERNOON ON W/V IMAGERY IS
PROMINENT CLOSED UPPER LOW OVER THE FOUR CORNERS REGION...RESULTING
IN BROAD RIDGING OVER THE TOP OF OUR AREA. PRESENCE OF MIDLEVEL
MOISTURE AND DEEP MIXING OF WARM AIRMASS TODAY ENABLED FAIRLY
EXTENSIVE HIGH BASED CU FIELD TO DEVELOP. MODEL RH FIELDS INDICATE
FAIRLY HIGH MOISTURE IN H9-H8 LAYER THROUGH THE NIGHT...SO STILL
EXPECTING GENERALLY PARTLY CLOUDY SKIES TONIGHT. IF CLEARING DOES
OCCUR...MAY NEED TO ADD PATCHY FOG/HZ IN OUTLYING AREAS AS SHOWN
ON MET MOS GUIDANCE. WEAK LAKE BREEZE BOUNDARY WILL WASH OUT THIS
EVENING...FOLLOWED BY LIGHT/VRB WINDS OVERNIGHT. AIRMASS WILL
REMAIN MILD AT AROUND +10C AT 850 MB AND 925 MB TEMPS IN MID TEENS
CELSIUS...SO EXPECTING OVERNIGHT LOWS TO ONLY DROP TO THE LOWER TO
MID 50S.

COLD FRONT BOUNDARY TRAILING FROM WEAK LOW PRESSURE MOVING INTO
QUEBEC SATURDAY MORNING WILL SERVE AS A BACKDOOR FRONT AND TURN
WINDS TO A GUSTY NORTHEAST TO EAST-NORTHEAST DIRECTION ON SATURDAY
NORTH OF I-80. THIS WILL RESULT IN TEMPERATURES ONLY TOPPING OUT
IN THE 50S ALONG THE LAKEFRONT...AS WELL AS COOLER CONDITIONS FOR
INLAND AREAS CLOSER TO THE LAKE. AIRMASS WILL STILL REMAIN
SIMILARLY MILD UNDER BROAD RIDGING ALOFT...SO AREAS WELL AWAY FROM
THE LAKE EXPECTED TO STILL REACH THE 70S...WITH UPPER 70S SOUTH OF
THE IL AND KANKAKEE RIVERS. MOISTURE MAY POOL AS FRONT SETTLES
INTO SOUTHERN/SOUTHWESTERN CWA...SO FAIRLY EXTENSIVE HIGHER BASED
CU FIELD COULD AGAIN DEVELOP. SOME GUIDANCE...NAMELY THE
GFS...BREAKS OUT SHOWER ACTIVITY DURING THE AFTERNOON CLOSER TO
THE FRONTAL BOUNDARY. HOWEVER...THIS APPEARS TO BE OVERDONE GIVEN
PRESENCE OF MID/UPPER RIDGING AND MEAGER INSTABILITY. CANNOT
COMPLETELY RULE OUT VERY ISOLATED SHRA/SPRINKLES IN SOUTH/SW
CWA...BUT HAVE MAINTAINED DRY FORECAST IN GRIDS.

RC

RC

&&

.LONG TERM...
315 PM CDT

SATURDAY NIGHT THROUGH FRIDAY...

TO BE ISSUED SHORTLY.

RC

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171933
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171933
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171933
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171933
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
233 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS UNDER 10 KT IN THE WAKE OF A LAKE BREEZE.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

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

* HIGH WITH ALL ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171920
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
220 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE TURNING THE WINDS EASTERLY AFTER 20 UTC. WINDS LOOK
  TO REMAIN UNDER 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 19Z...

* MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171920
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
220 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE TURNING THE WINDS EASTERLY AFTER 20 UTC. WINDS LOOK
  TO REMAIN UNDER 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 19Z...

* MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171920
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
220 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE TURNING THE WINDS EASTERLY AFTER 20 UTC. WINDS LOOK
  TO REMAIN UNDER 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 19Z...

* MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
220 PM CDT

HIGH PRESSURE STRETCHED ACROSS THE REGION IS HELPING FOR
CONTINUED LIGHTER WINDS OVER THE LAKE TODAY...LIGHT AND VARIABLE
FOR MOST OF THE LAKE. LOW PRESSURE MOVING THROUGH THE REGION JUST
NORTH OF THE LAKE WILL ALLOW A FRONTAL BOUNDARY TO MOVE SOUTH DOWN
THE LAKE LATE TONIGHT INTO EARLY SATURDAY MORNING. AS THIS
OCCURS...STRONGER HIGH PRESSURE WILL BUILD EAST SOUTHEAST ACROSS
THE REGION. SOUTHERLY FLOW WILL THEN TURN TO THE NORTHWEST AND
NORTH LATE TONIGHT INTO SATURDAY WITH SPEEDS INCREASING TO THE 15
TO 25 KT RANGE...WITH RELATIVELY STABLE CONDITIONS OVER THE LAKE
HELPING TO LIMIT SPEEDS. WINDS WILL CONTINUE TO TURN MORE
NORTHEAST AND EAST SATURDAY INTO SATURDAY NIGHT LIKELY REMAINING
IN THE 15 TO 25 KT RANGE...ESPECIALLY FOR THE SOUTHERN HALF OF THE
LAKE WHERE A TIGHTER PRESSURE GRADIENT OWING TO AN APPROACHING LOW
PRESSURE SYSTEM WILL REMAIN. SOME UNCERTAINTY REMAINS WITH THE
EXACT TRACK OF THIS LOW SUNDAY AND SUNDAY NIGHT AS IT MOVES
NORTHEAST NEAR THE LAKE...WITH THIS UNCERTAINTY SPILLING INTO
EXACT WIND DIRECTION/SPEEDS.

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 171902
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
202 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE TURNING THE WINDS EASTERLY AFTER 20 UTC. WINDS LOOK
  TO REMAIN UNDER 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 19Z...

* MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171902
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
202 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE TURNING THE WINDS EASTERLY AFTER 20 UTC. WINDS LOOK
  TO REMAIN UNDER 10 KT.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

//DISCUSSION...UPDATED 19Z...

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 19Z...

* MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171717
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1217 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* CHANCE OF A LAKE BREEZE TURNING THE WINDS EASTERLY LATE THIS
  AFTERNOON.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

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

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB


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

* LOW-MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171717
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1217 PM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* CHANCE OF A LAKE BREEZE TURNING THE WINDS EASTERLY LATE THIS
  AFTERNOON.

* BREEZY EAST-NORTHEAST WINDS SATURDAY.

KJB

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

SURFACE HIGH PRESSURE OVER THE REGION WILL CREATE LIGHT WINDS OVER
THE AREA TODAY...AND THIS WILL ALLOW A LAKE BREEZE TO SLOWLY EASE
INLAND ACROSS NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA. I
PUSHED OFF THE TIMING OF THIS FEATURE GETTING TO KORD AND KMDW UNTIL
VERY LATE THIS AFTERNOON. THERE IS EVEN A CHANCE THAT THE LAKE
BREEZE NEVER MAKES IT FAR ENOUGH INLAND TO IMPACT THESE TERMINALS
PRIOR TO IT DISSIPATING EARLY THIS EVENING. HOWEVER...IF IT IS ABLE
TO MOVE ACROSS THE TERMINALS...THERE WILL BE A WIND SHIFT OUT OF THE
EAST...THOUGH WIND SPEEDS WOULD LIKELY REMAIN BELOW 10 KT.

A COLD FRONT WILL SHIFT DOWN THE LAKE VERY LATE TONIGHT INTO EARLY
SATURDAY MORNING. THIS WILL SET THE STAGE FOR BREEZY EAST-
NORTHEASTERLY WINDS ACROSS THE TERMINALS ON SATURDAY. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH THE PERIOD.

KJB


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

* LOW-MEDIUM WITH LAKE BREEZE TIMING LATE THIS AFTERNOON.

* HIGH WITH ALL OTHER ELEMENTS.

KJB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171616
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1116 AM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE POSSIBLE LATER THIS AFTERNOON TURNING WINDS FROM
  WEST/SOUTHWEST TO EAST.

BEACHLER/KB

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...LOW-MEDIUM
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER/KB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171616
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1116 AM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE POSSIBLE LATER THIS AFTERNOON TURNING WINDS FROM
  WEST/SOUTHWEST TO EAST.

BEACHLER/KB

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...LOW-MEDIUM
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER/KB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171509
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1009 AM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE POSSIBLE LATER THIS AFTERNOON TURNING WINDS FROM
  WEST/SOUTHWEST TO EAST.

BEACHLER/KB

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM CONFIDENCE
  IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER/KB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171509
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1009 AM CDT FRI APR 17 2015

.UPDATE...
1002 AM CDT

DENSE FOG WHICH WAS IN PLACE ACROSS EAST CENTRAL ILLINOIS AND
NORTHWEST INDIANA EARLIER THIS MORNING HAS SINCE DISSIPATED...WITH
THE ADVISORY ALLOWED TO EXPIRE. ANY REMAINING LOW STRATUS WILL
SCATTER OUT OVER THE NEXT COUPLE OF HOURS WHILE ISOLATED AREAS OF
MID CLOUDS THIS MORNING LIKEWISE SCATTER...WITH PARTLY CLOUDY TO
MOSTLY SUNNY SKIES EXPECTED FOR THE REMAINDER OF THE DAY. A WARM
AIRMASS IN PLACE WILL FURTHER WARM WITH WELL ABOVE TEMPS IN THE
UPPER 70S EXPECTED...WITH MAX TEMPS AROUND 70 EXPECTED NEAR THE
LAKE. A QUICK RISE IN TEMPS IS ALREADY OCCURRING AND DID ADJUST
TEMPS UP 2-3 DEGREES FOR TODAY...WITH TEMPS AROUND 80 DEFINITELY
NOT OUT OF THE QUESTION. OFFSHORE FLOW THIS MORNING WILL DIMINISH
AND THEN TURN ONSHORE BY EARLY TO MID AFTERNOON...WITH TEMPS NEAR
THE LAKE COOLING INTO LATE AFTERNOON.

RODRIGUEZ

&&

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE POSSIBLE LATER THIS AFTERNOON TURNING WINDS FROM
  WEST/SOUTHWEST TO EAST.

BEACHLER/KB

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM CONFIDENCE
  IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER/KB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.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 171330
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
830 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* LAKE BREEZE POSSIBLE LATER THIS AFTERNOON TURNING WINDS FROM
  WEST/SOUTHWEST TO EAST.

BEACHLER/KB

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM CONFIDENCE
  IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER/KB

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 9 AM
     FRIDAY.

IN...DENSE FOG ADVISORY...INZ010-INZ011-INZ019 UNTIL 9 AM FRIDAY.

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 171149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

* LAKE BREEZE POSSIBLE AFT 18Z TURNING WINDS FROM WEST/SOUTHWEST
  TO EAST.

BEACHLER

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER


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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 9 AM
     FRIDAY.

IN...DENSE FOG ADVISORY...INZ010-INZ011-INZ019 UNTIL 9 AM FRIDAY.

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 171149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

* LAKE BREEZE POSSIBLE AFT 18Z TURNING WINDS FROM WEST/SOUTHWEST
  TO EAST.

BEACHLER

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER


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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 9 AM
     FRIDAY.

IN...DENSE FOG ADVISORY...INZ010-INZ011-INZ019 UNTIL 9 AM FRIDAY.

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 171149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

* LAKE BREEZE POSSIBLE AFT 18Z TURNING WINDS FROM WEST/SOUTHWEST
  TO EAST.

BEACHLER

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER


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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 9 AM
     FRIDAY.

IN...DENSE FOG ADVISORY...INZ010-INZ011-INZ019 UNTIL 9 AM FRIDAY.

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 171149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

* LAKE BREEZE POSSIBLE AFT 18Z TURNING WINDS FROM WEST/SOUTHWEST
  TO EAST.

BEACHLER

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

HIGH PRESSURE CONTINUES TO LINGER OVERHEAD AND PROVIDE LIGHT AND
VARIABLE WINDS THIS MORNING. SOME PATCHY FOG HAS
DEVELOPED...HOWEVER VSBYS SHUD REMAIN NO LOWER THAN 4SM AT THE TAF
SITES. FURTHER SOUTH ACROSS CENTRAL IL/IN...FOG IS MORE DENSE AND
LIMITING VSBYS TO ARND 1/4SM OR LESS. THIS WILL ALL IMPROVE BY
13-14Z. AS THE DAY PROGRESSES...A LAKE BREEZE MAY BEGIN TO DEVELOP
AND PUSH INLAND. GUIDANCE CONTINUES TO LEAN TOWARDS AN 18Z PASSAGE
AT MDW/GYY...AND ARND 19Z FOR ORD. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER


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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

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

SATURDAY NIGHT...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

THURSDAY...MAINLY VFR. CHC OF SHRA EARLY.

BEACHLER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 9 AM
     FRIDAY.

IN...DENSE FOG ADVISORY...INZ010-INZ011-INZ019 UNTIL 9 AM FRIDAY.

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 170909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
409 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
409 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUOIS/BENTON COUNTIES.
WHILE OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEWHERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

KMD

&&

.LONG TERM...
408 AM CDT

SATURDAY NIGHT THROUGH THURSDAY...

WHILE SOME ENERGY IN THE SW FLOW WILL BE NEARING THE REGION...IT
SHOULD BE MOSTLY DRY SATURDAY EVENING AND POSSIBLY OVERNIGHT. THEN
IT THE TEETER-TOTTER WILL BE SHIFTING BACK DOWNWARD IN OUR NECK OF
THE WOODS AFTER A TASTE OF SUMMER IN MANY PLACES FRIDAY. BUT THE BIG
COOL DOWN WILL NOT COME RIGHT AWAY. THE FOUR CORNERS LOW BY SUNDAY
DAYBREAK WILL STILL ONLY BE IN THE CENTRAL PLAINS. AT THE
SURFACE...HIGH PRESSURE DEPARTS EAST WITH A LOW LEVEL BAROCLINIC
ZONE IN PLACE DUE TO THE EAST FLOW OFF THE LAKE AND THE WARM SW FLOW
AHEAD OF THE UPPER LOW. WHILE SOME MODEL PLACEMENT OF LOWS IN THE
EXTENDED ARE INCONSISTENT..THE THEME IS FOR INCREASED MOISTURE
TRANSPORT IN THE MODERATE PWAT AIR OVER THE BAROCLINIC ZONE TO
TRIGGER A ROUND OF SHOWERS AND POSSIBLY A FEW THUNDERSTORMS ON
SUNDAY. WITH A FREEZING LEVEL ABOVE 10,000 FEET AND A VERY MOIST
ATMOSPHERIC COLUMN...THIS LOOKS MORE LIKE A SHOWERS AND ISOLATED T-
STORMS WITH LOCALLY HEAVY DOWNPOUR SETUP THAN A SEVERE WEATHER SETUP
AT THIS POINT. MODELS ARE IN FAIR AGREEMENT ON MUCH OF THIS HEAVIER
RAIN OCCURRING SUNDAY.

FOLLOWING THIS FIRST WAVE THAT NEVER REALLY CONGEALS WITH A PACIFIC
LOW WORKING SOUTHEAST THROUGH THE NORTHERN PLAINS...THERE COULD
STILL BE SOME SHOWERS SUNDAY NIGHT AHEAD OF A COLD FRONT.

MONDAY LOOKS TO BE A COOL DAY WITH SOME SHOWERS ABOUT...THEN THE
UPPER LOW SLOWLY MOVES EAST ON TUESDAY. TUESDAY MOST PLACES DON`T
GET OUT OF THE 50S AS THE SOUTHERN EDGE OF THE COLDER AIR GLIDES
ON THROUGH. WILL HAVE TO SEE HOW FAR SOUTH AND HOW LONG THE UPPER
LOW LINGERS ACROSS THE REGION...WHICH WILL DETERMINE THE EXTENT OF
SHOWER ACTIVITY. BUT EITHER WAY IT WILL REMAIN ON THE COOL SIDE.

KMD

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170858
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
358 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170858
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
358 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170858
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
358 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170858
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
358 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
354 AM CDT

WEAK RIDGE OF HIGH PRESSURE REMAINS OVER THE CENTRAL GREAT LAKES
TODAY...AND WILL SLOWLY SLIDE SOUTHEAST. A WEAK FRONTAL BOUNDARY
WILL BEGIN TO SLIDE SOUTH ACROSS THE LAKE THIS
AFTERNOON...ALTHOUGH NOT MAKE MUCH OF A PUSH UNTIL LATE TONIGHT
INTO EARLY SATURDAY. MEANWHILE ANOTHER STRONGER RIDGE OF HIGH
PRESSURE OVER CENTRAL CANADA WILL SLIDE SOUTH INTO THE CENTRAL
PLAINS. THIS WILL HELP TO STRENGTHEN THE FRONTAL BOUNDARY LATE
TONIGHT...AND ALLOW WINDS TO QUICKLY INCREASE ACROSS THE NORTHERN
PORTIONS OF LAKE MICHIGAN LATE TONIGHT. AS THE BOUNDARY SLIDES
SOUTH ACROSS THE LAKE...WINDS WILL QUICKLY TURN FROM SOUTHWEST TO
NORTH/NORTHEAST AND GUST UP TO 25KT. IT CURRENTLY APPEARS WINDS
WILL NOT REMAIN GUSTY VERY LONG...SO WAVES SHOULD NOT BUILD MUCH
HIGHER THAN 3 TO 5 FT ALONG THE SOUTHERN PORTIONS OF THE LAKE.
HIGH PRESSURE THEN SHIFTS EAST SUNDAY...WITH A LOW PRESSURE
DEVELOPING IN THE CENTRAL PLAINS AND APPROACHING THE WESTERN GREAT
LAKES EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170844
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
344 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170844
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
344 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170844
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
344 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170844
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
344 AM CDT FRI APR 17 2015

.SHORT TERM...
342 AM CDT

THROUGH SATURDAY...

SHORT TERM CONCERNS FOCUS AROUND SOME MORNING FOG...LOCALLY DENSE IN
THE FAR SOUTHERN/EASTERN PORTIONS OF THE CWA. WILL THEN HAVE SOME
WARMER CONDITIONS FOR MOST PLACES TODAY...SOME COOLING
SATURDAY...ESPECIALLY CLOSER TO THE LAKE.

THE UPPER AIR PATTERN EARLY THIS MORNING IS CHARACTERIZED BY A DEEP
UPPER LOW OVER THE FOUR CORNERS REGION...PROGRESSIVE WEST/NORTHWEST
FLOW IN SOUTHERN CANADA AND EXTENDING INTO THE ATLANTIC. OUR REGION
IS IN BETWEEN WITH WEAK UPPER LEVEL RIDGING IN PLACE. AT THE
SURFACE...WEAK HIGH PRESSURE IS DRAPED ACROSS THE AREA AND TO THE
EAST. SOME LIGHT SW FLOW EXISTS...BUT WITH SOME RAIN LAST NIGHT
DEWPOINTS REMAIN ELEVATED IN THE WEAK FLOW REGIME...RESULTING IN
AREAS OF FOG...LOCALLY DENSE IN CENTRAL ILLINOIS AND INDIANA...BUT
SOME OF THESE FOG EXTENDS INT FORD/IROQUIS/BENTON COUNTIES. WHILE
OBSERVATIONS ARE LIMITED...DENSE FOG IS BEING OBSERVED FROM
KTIP...KDNV...TO KLAF...AND A SIMILIAR AIR MASS IS IN PLACE IN OUR
SOUTHERN TIER OF COUNTIES. A DENSE FOG ADVISORY WILL CONTINUE FOR
THESE AREAS UNTIL A LITTLE AFTER DAYBREAK. EXPECT SOME PATCHY FOG
ELSEHWERE...THOUGH LARGELY SOUTH OF I-88 AND AWAY FROM CHICAGO.

THE PATTERN CHANGES LITTLE TODAY OTHER THAN SOME SUBTLE INCREASES IN
UPPER LEVEL HEIGHTS. THE LOWER LEVEL AIR MASS WARMS A BIT
THOUGH...AND LOCAL CLIMO SUGGESTS A WARM DAY FOR MOST AREAS WITH MID
70S WITH VERY DEEP MIXING REALIZING 850 TEMPS OF +10/11. WITH THE
LIGHT PRESSURE GRADIENT...EXPECT ANOTHER LAKE BREEZE TODAY WHICH
SHOULD LEAD TO AFTERNOON COOLING.

THE UPPER FLOW AMPLIFIES ACROSS THE CONTINENTAL USA ON FRI NIGHT
INTO SATURDAY AS THE UPPER LOW SLOWLY MEANDERS EAST. MEANWHILE...THE
NORTHERN STREAM ENERGY WILL SKOOT SOUTHEAST ACROSS QUEBEC AND DRIVE
A BIT OF A COLD FRONT DOWN THE LAKE FOR SATURDAY. WHILE THIS IS NOT
A STRONG FRONT...IT WILL MARKEDLY INCREASE THE ONSHORE FLOW KEEPING
AREAS IN THE INNER TIER OF COUNTIES QUITE A BIT COOLER THAN
FRIDAY...AND MOST NOTICEABLY AT THE LAKE/DOWNTOWN WHERE IT WILL BE
MUCH COOLER. MEANWHILE AREAS IN THE FAR WEST SHOULD STILL BE ABLE TO
TAG 70-ISH. EXPECT SOME CONTINUED MID AND HIGH CLOUDINESS.

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

NOTE: A MORE CURRENT DISCUSSION WILL BE FORTHCOMING...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER

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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY...ILZ033-ILZ039 UNTIL 9 AM FRIDAY.

IN...DENSE FOG ADVISORY...INZ019 UNTIL 9 AM FRIDAY.

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 170544
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1244 AM CDT FRI APR 17 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER


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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 170544
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1244 AM CDT FRI APR 17 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* VFR CONDS THRU ENTIRE TAF.

BEACHLER

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

WEAK RIDGE OF HIGH PRESSURE CONTINUES TO PROVIDE MINIMAL CLOUD
COVER ALONG WITH VERY LIGHT WINDS. VRB WINDS AT MANY AIRFIELDS
THRU DAYBREAK OF 3-5KT...THEN WINDS BECOME MORE UNIFORM FROM THE
SOUTHWEST. AS THE DAY PROGRESSES...SOME CLOUDS WILL DEVELOP ARND
5KFT AGL. IN ADDITION GUIDANCE CONTINUES TO SUGGEST A LAKE BREEZE
DEVELOPING AND QUICKLY PUSHING INLAND DURING THE AFTN HOURS. STILL
LOOKS ON TRACK FOR 20-21Z TO ARRIVE AT ORD/MDW AND WILL ALLOW
WINDS TO QUICKLY FLIP TO THE EAST. SPEEDS WILL BRIEFLY INCREASE
WITH THE WIND SHIFT TO ARND 8-10KT...THEN SETTLE BACK TO 4-6KT FOR
LATE FRI EVE.

BEACHLER


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

* HIGH CONFIDENCE IN CIGS/VSBY.

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MIDDAY...MEDIUM/HIGH
  CONFIDENCE IN LAKE BREEZE TIMING AND WIND SPEEDS.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 170306
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1006 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT WINDS VARIABLE/WEST 5 KT OR LESS OVERNIGHT.

* LIGHT WEST WINDS BECOMING EAST-SOUTHEAST AGAIN FRIDAY AFTERNOON
  WITH LAKE BREEZE.

* PATCHY FOG POSSIBLE LATE TONIGHT MAINLY SOUTH/SOUTHEAST OF
  ORD/MDW.

RATZER

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

WEAK HIGH PRESSURE ACROSS THE REGION EARLY THIS EVENING. LIGHT AND
VARIABLE WINDS HAVE ALLOWED LAKE BREEZE TO PUSH INLAND ACROSS CHI
TERMINALS...WITH WINDS BECOMING EAST-SOUTHEAST LESS THAN 10 KT
THIS EVENING AND GENERALLY LIGHT/VARIABLE OVERNIGHT AS SURFACE
HIGH PRESSURE RIDGE ONLY SLOWLY DRIFTS EAST. WITH WEAK RIDGE JUST
OFF TO THE EAST FRIDAY MORNING...VARIABLE/MAINLY WEST WINDS LESS
THAN 10 KT ARE EXPECTED DURING THE MORNING. DEVELOPMENT OF ANOTHER
LAKE BREEZE IS LIKELY WITH WEAK BOUNDARY LAYER FLOW...THOUGH
GUIDANCE VARIES WITH TIMING/POSITION.

OTHERWISE...VFR CONDITIONS WILL PREDOMINATE THROUGH THE TAF
PERIOD. THERE IS SOME POTENTIAL FOR PATCHY MVFR FOG DEVELOPMENT
MAINLY SOUTH/SOUTHEAST OF CHICAGO LATE TONIGHT...ESPECIALLY WHERE
MORE RAIN OCCURRED EARLIER THIS MORNING AND CLOUDS CLEARED LATER
THIS AFTERNOON. GYY WOULD PERHAPS MOST LIKELY TO EXPERIENCE FOG...
THOUGH CONFIDENCE LOW WITH DRIER AIR CURRENTLY IN PLACE BEHIND
LAKE BREEZE.

RATZER

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

* HIGH IN TRENDS ALL ELEMENTS THROUGH TONIGHT.

* MEDIUM IN LAKE BREEZE TIMING FRIDAY.

* LOW IN ANY PATCHY FOG AFFECTING ORD/MDW OVERNIGHT.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 170306
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1006 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT WINDS VARIABLE/WEST 5 KT OR LESS OVERNIGHT.

* LIGHT WEST WINDS BECOMING EAST-SOUTHEAST AGAIN FRIDAY AFTERNOON
  WITH LAKE BREEZE.

* PATCHY FOG POSSIBLE LATE TONIGHT MAINLY SOUTH/SOUTHEAST OF
  ORD/MDW.

RATZER

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

WEAK HIGH PRESSURE ACROSS THE REGION EARLY THIS EVENING. LIGHT AND
VARIABLE WINDS HAVE ALLOWED LAKE BREEZE TO PUSH INLAND ACROSS CHI
TERMINALS...WITH WINDS BECOMING EAST-SOUTHEAST LESS THAN 10 KT
THIS EVENING AND GENERALLY LIGHT/VARIABLE OVERNIGHT AS SURFACE
HIGH PRESSURE RIDGE ONLY SLOWLY DRIFTS EAST. WITH WEAK RIDGE JUST
OFF TO THE EAST FRIDAY MORNING...VARIABLE/MAINLY WEST WINDS LESS
THAN 10 KT ARE EXPECTED DURING THE MORNING. DEVELOPMENT OF ANOTHER
LAKE BREEZE IS LIKELY WITH WEAK BOUNDARY LAYER FLOW...THOUGH
GUIDANCE VARIES WITH TIMING/POSITION.

OTHERWISE...VFR CONDITIONS WILL PREDOMINATE THROUGH THE TAF
PERIOD. THERE IS SOME POTENTIAL FOR PATCHY MVFR FOG DEVELOPMENT
MAINLY SOUTH/SOUTHEAST OF CHICAGO LATE TONIGHT...ESPECIALLY WHERE
MORE RAIN OCCURRED EARLIER THIS MORNING AND CLOUDS CLEARED LATER
THIS AFTERNOON. GYY WOULD PERHAPS MOST LIKELY TO EXPERIENCE FOG...
THOUGH CONFIDENCE LOW WITH DRIER AIR CURRENTLY IN PLACE BEHIND
LAKE BREEZE.

RATZER

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

* HIGH IN TRENDS ALL ELEMENTS THROUGH TONIGHT.

* MEDIUM IN LAKE BREEZE TIMING FRIDAY.

* LOW IN ANY PATCHY FOG AFFECTING ORD/MDW OVERNIGHT.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162358
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
658 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT LAKE BREEZE EAST-SOUTHEAST WINDS LESS THAN 10 KT THIS
  EVENING BECOMING VARIABLE/WEST 5 KT OR LESS OVERNIGHT.

* LIGHT WEST WINDS BECOMING EAST-SOUTHEAST AGAIN FRIDAY AFTERNOON
  WITH LAKE BREEZE.

* PATCHY FOG POSSIBLE LATE TONIGHT MAINLY SOUTH/SOUTHEAST OF
  ORD/MDW.

RATZER

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

WEAK HIGH PRESSURE ACROSS THE REGION EARLY THIS EVENING. LIGHT AND
VARIABLE WINDS HAVE ALLOWED LAKE BREEZE TO PUSH INLAND ACROSS CHI
TERMINALS...WITH WINDS BECOMING EAST-SOUTHEAST LESS THAN 10 KT
THIS EVENING AND GENERALLY LIGHT/VARIABLE OVERNIGHT AS SURFACE
HIGH PRESSURE RIDGE ONLY SLOWLY DRIFTS EAST. WITH WEAK RIDGE JUST
OFF TO THE EAST FRIDAY MORNING...VARIABLE/MAINLY WEST WINDS LESS
THAN 10 KT ARE EXPECTED DURING THE MORNING. DEVELOPMENT OF ANOTHER
LAKE BREEZE IS LIKELY WITH WEAK BOUNDARY LAYER FLOW...THOUGH
GUIDANCE VARIES WITH TIMING/POSITION.

OTHERWISE...VFR CONDITIONS WILL PREDOMINATE THROUGH THE TAF
PERIOD. THERE IS SOME POTENTIAL FOR PATCHY MVFR FOG DEVELOPMENT
MAINLY SOUTH/SOUTHEAST OF CHICAGO LATE TONIGHT...ESPECIALLY WHERE
MORE RAIN OCCURRED EARLIER THIS MORNING AND CLOUDS CLEARED LATER
THIS AFTERNOON. GYY WOULD PERHAPS MOST LIKELY TO EXPERIENCE FOG...
THOUGH CONFIDENCE LOW WITH DRIER AIR CURRENTLY IN PLACE BEHIND
LAKE BREEZE.

RATZER


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

* HIGH IN TRENDS ALL ELEMENTS THROUGH TONIGHT.

* MEDIUM IN LAKE BREEZE TIMING FRIDAY.

* LOW IN ANY PATCHY FOG AFFECTING ORD/MDW OVERNIGHT.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162358
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
658 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT LAKE BREEZE EAST-SOUTHEAST WINDS LESS THAN 10 KT THIS
  EVENING BECOMING VARIABLE/WEST 5 KT OR LESS OVERNIGHT.

* LIGHT WEST WINDS BECOMING EAST-SOUTHEAST AGAIN FRIDAY AFTERNOON
  WITH LAKE BREEZE.

* PATCHY FOG POSSIBLE LATE TONIGHT MAINLY SOUTH/SOUTHEAST OF
  ORD/MDW.

RATZER

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

WEAK HIGH PRESSURE ACROSS THE REGION EARLY THIS EVENING. LIGHT AND
VARIABLE WINDS HAVE ALLOWED LAKE BREEZE TO PUSH INLAND ACROSS CHI
TERMINALS...WITH WINDS BECOMING EAST-SOUTHEAST LESS THAN 10 KT
THIS EVENING AND GENERALLY LIGHT/VARIABLE OVERNIGHT AS SURFACE
HIGH PRESSURE RIDGE ONLY SLOWLY DRIFTS EAST. WITH WEAK RIDGE JUST
OFF TO THE EAST FRIDAY MORNING...VARIABLE/MAINLY WEST WINDS LESS
THAN 10 KT ARE EXPECTED DURING THE MORNING. DEVELOPMENT OF ANOTHER
LAKE BREEZE IS LIKELY WITH WEAK BOUNDARY LAYER FLOW...THOUGH
GUIDANCE VARIES WITH TIMING/POSITION.

OTHERWISE...VFR CONDITIONS WILL PREDOMINATE THROUGH THE TAF
PERIOD. THERE IS SOME POTENTIAL FOR PATCHY MVFR FOG DEVELOPMENT
MAINLY SOUTH/SOUTHEAST OF CHICAGO LATE TONIGHT...ESPECIALLY WHERE
MORE RAIN OCCURRED EARLIER THIS MORNING AND CLOUDS CLEARED LATER
THIS AFTERNOON. GYY WOULD PERHAPS MOST LIKELY TO EXPERIENCE FOG...
THOUGH CONFIDENCE LOW WITH DRIER AIR CURRENTLY IN PLACE BEHIND
LAKE BREEZE.

RATZER


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

* HIGH IN TRENDS ALL ELEMENTS THROUGH TONIGHT.

* MEDIUM IN LAKE BREEZE TIMING FRIDAY.

* LOW IN ANY PATCHY FOG AFFECTING ORD/MDW OVERNIGHT.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162358
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
658 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT LAKE BREEZE EAST-SOUTHEAST WINDS LESS THAN 10 KT THIS
  EVENING BECOMING VARIABLE/WEST 5 KT OR LESS OVERNIGHT.

* LIGHT WEST WINDS BECOMING EAST-SOUTHEAST AGAIN FRIDAY AFTERNOON
  WITH LAKE BREEZE.

* PATCHY FOG POSSIBLE LATE TONIGHT MAINLY SOUTH/SOUTHEAST OF
  ORD/MDW.

RATZER

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

WEAK HIGH PRESSURE ACROSS THE REGION EARLY THIS EVENING. LIGHT AND
VARIABLE WINDS HAVE ALLOWED LAKE BREEZE TO PUSH INLAND ACROSS CHI
TERMINALS...WITH WINDS BECOMING EAST-SOUTHEAST LESS THAN 10 KT
THIS EVENING AND GENERALLY LIGHT/VARIABLE OVERNIGHT AS SURFACE
HIGH PRESSURE RIDGE ONLY SLOWLY DRIFTS EAST. WITH WEAK RIDGE JUST
OFF TO THE EAST FRIDAY MORNING...VARIABLE/MAINLY WEST WINDS LESS
THAN 10 KT ARE EXPECTED DURING THE MORNING. DEVELOPMENT OF ANOTHER
LAKE BREEZE IS LIKELY WITH WEAK BOUNDARY LAYER FLOW...THOUGH
GUIDANCE VARIES WITH TIMING/POSITION.

OTHERWISE...VFR CONDITIONS WILL PREDOMINATE THROUGH THE TAF
PERIOD. THERE IS SOME POTENTIAL FOR PATCHY MVFR FOG DEVELOPMENT
MAINLY SOUTH/SOUTHEAST OF CHICAGO LATE TONIGHT...ESPECIALLY WHERE
MORE RAIN OCCURRED EARLIER THIS MORNING AND CLOUDS CLEARED LATER
THIS AFTERNOON. GYY WOULD PERHAPS MOST LIKELY TO EXPERIENCE FOG...
THOUGH CONFIDENCE LOW WITH DRIER AIR CURRENTLY IN PLACE BEHIND
LAKE BREEZE.

RATZER


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

* HIGH IN TRENDS ALL ELEMENTS THROUGH TONIGHT.

* MEDIUM IN LAKE BREEZE TIMING FRIDAY.

* LOW IN ANY PATCHY FOG AFFECTING ORD/MDW OVERNIGHT.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162358
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
658 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT LAKE BREEZE EAST-SOUTHEAST WINDS LESS THAN 10 KT THIS
  EVENING BECOMING VARIABLE/WEST 5 KT OR LESS OVERNIGHT.

* LIGHT WEST WINDS BECOMING EAST-SOUTHEAST AGAIN FRIDAY AFTERNOON
  WITH LAKE BREEZE.

* PATCHY FOG POSSIBLE LATE TONIGHT MAINLY SOUTH/SOUTHEAST OF
  ORD/MDW.

RATZER

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

WEAK HIGH PRESSURE ACROSS THE REGION EARLY THIS EVENING. LIGHT AND
VARIABLE WINDS HAVE ALLOWED LAKE BREEZE TO PUSH INLAND ACROSS CHI
TERMINALS...WITH WINDS BECOMING EAST-SOUTHEAST LESS THAN 10 KT
THIS EVENING AND GENERALLY LIGHT/VARIABLE OVERNIGHT AS SURFACE
HIGH PRESSURE RIDGE ONLY SLOWLY DRIFTS EAST. WITH WEAK RIDGE JUST
OFF TO THE EAST FRIDAY MORNING...VARIABLE/MAINLY WEST WINDS LESS
THAN 10 KT ARE EXPECTED DURING THE MORNING. DEVELOPMENT OF ANOTHER
LAKE BREEZE IS LIKELY WITH WEAK BOUNDARY LAYER FLOW...THOUGH
GUIDANCE VARIES WITH TIMING/POSITION.

OTHERWISE...VFR CONDITIONS WILL PREDOMINATE THROUGH THE TAF
PERIOD. THERE IS SOME POTENTIAL FOR PATCHY MVFR FOG DEVELOPMENT
MAINLY SOUTH/SOUTHEAST OF CHICAGO LATE TONIGHT...ESPECIALLY WHERE
MORE RAIN OCCURRED EARLIER THIS MORNING AND CLOUDS CLEARED LATER
THIS AFTERNOON. GYY WOULD PERHAPS MOST LIKELY TO EXPERIENCE FOG...
THOUGH CONFIDENCE LOW WITH DRIER AIR CURRENTLY IN PLACE BEHIND
LAKE BREEZE.

RATZER


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

* HIGH IN TRENDS ALL ELEMENTS THROUGH TONIGHT.

* MEDIUM IN LAKE BREEZE TIMING FRIDAY.

* LOW IN ANY PATCHY FOG AFFECTING ORD/MDW OVERNIGHT.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...VFR. EAST WINDS.

SUNDAY...SHRA/ISOLATED TSRA. MVFR LIKELY/IFR POSSIBLE. EAST-
SOUTHEAST WINDS.

MONDAY...CHANCE SHRA. MVFR/IFR EARLY...IMPROVING TO VFR BY AFTN. GUSTY
WEST WINDS.

TUESDAY...VFR. GUSTY WEST WINDS.

WEDNESDAY...SLGT CHANCE SHRA/MVFR...OTHERWISE VFR. WEST WINDS.

RATZER

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162200
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
500 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* WEAK LAKE BREEZE WITH GENERALLY EAST WINDS LESS THAN 10 KT
  THROUGH REMAINDER OF AFTERNOON.

RATZER

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162200
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
500 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* WEAK LAKE BREEZE WITH GENERALLY EAST WINDS LESS THAN 10 KT
  THROUGH REMAINDER OF AFTERNOON.

RATZER

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162034
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
334 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162034
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
334 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162034
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
334 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162034
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
334 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
334 PM CDT

A RIDGE OF HIGH PRESSURE STRETCHED ACROSS THE REGION IS ALLOWING
FOR LIGHTER WINDS TO BE IN PLACE TODAY. ALTHOUGH LOW PRESSURE OVER
WESTERN QUEBEC WILL SLOWLY MOVE EAST TONIGHT WITH A TRAILING COLD
FRONT MOVING ACROSS THE NORTHERN GREAT LAKES TONIGHT INTO FRIDAY
MORNING...EXPECT LIGHTER WINDS TO REMAIN IN PLACE. THESE LIGHTER
WINDS WILL CONTINUE INTO THE START OF THE WEEKEND...AS HIGH
PRESSURE CONTINUES TO DOMINATE.

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 162029
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
329 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE LOW
AHEAD OF THE UPPER TROUGH.  THIS SURFACE FEATURE IS ACTUALLY MORE OF
A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH AND ONE
CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE. THE FIRST
SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO EARLY
SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA MONDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 162029
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
329 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE LOW
AHEAD OF THE UPPER TROUGH.  THIS SURFACE FEATURE IS ACTUALLY MORE OF
A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH AND ONE
CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE. THE FIRST
SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO EARLY
SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA MONDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 162029 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
329 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 162029 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
329 PM CDT THU APR 16 2015

.SHORT TERM...
319 PM CDT

THROUGH SATURDAY...

A LOOP OF 500MB HEIGHT FORECASTS OVER THE NEXT WEEK SUGGESTS THE
ATMOSPHERE WILL BE IN SLOW MOTION...OR AS OUR STUDENT VOLUNTEER MORE
CORRECTLY CALLS IT...IN A BIT OF A BLOCKING PATTERN.  ENSEMBLES AND
DETERMINISTIC MODELS BOTH AGREE IN LIFTING A SOUTHERN STREAM CUTOFF
LOW OUT OF THE FOUR CORNERS REGION...MERGING IT WITH A DEVELOPING
NORTHERN STREAM LOW OVER THE PLAINS LATE THIS WEEKEND...AND VERY
SLOWLY TAKING IT ACROSS THE WESTERN GREAT LAKES EARLY NEXT WEEK.
THE MOVEMENT OF THIS SYSTEM IS ACTUALLY SO SLOW THAT IT DOES NOT
EVEN EXIT ONTARIO BY THE END OF THIS FORECAST PERIOD LATE NEXT WEEK.
THIS WOULD TEND TO SUPPORT A FEW DAYS OF COOL AND POSSIBLY WET
WEATHER FOR MUCH OF THE GREAT LAKES REGION.  BEFORE WE REVERT TO
HIGHS MORE TYPICAL OF LATE MARCH THAN LATE APRIL...WE WILL BE ABLE
TO EXPERIENCE A TASTE OF LATE JUNE TOMORROW AND SATURDAY AS RIDGING
ALOFT AND HIGH PRESSURE AT THE SURFACE BRING DRY WEATHER AND HIGHS
IN THE MIDDLE TO UPPER 70S...EXCEPT OF COURSE NEAR THE LAKE.

IN THE NEAR TERM...LIGHT AND VARIABLE WINDS OVER THE AREA WILL
PERSIST THROUGH THE NIGHT BEFORE GRADUALLY TURNING WEST TO
SOUTHWEST TOMORROW AND BRINGING IN WARMER AIR...EXCEPT WHERE THE
COOL LAKE BREEZE WILL DOMINATE. SATURDAY WILL AGAIN SEE WARM
SOUTHERLY FLOW GRADUALLY BACKING SOUTHEAST AND IN SOME AREAS
ACROSS NORTHERN ILLINOIS...ALL THE WAY AROUND TO THE EAST. THESE
EASTERLY WINDS WILL PRODUCE A CONSIDERABLY COOLER AFTERNOON FOR
LOCATIONS IN ILLINOIS ADJACENT TO THE LAKE THAN FOR LOCATIONS
FARTHER WEST AND SOUTH.

LENNING

&&

.LONG TERM...
319 PM CDT

SATURDAY NIGHT THROUGH THURSDAY...

BY SATURDAY NIGHT INTO SUNDAY THE TRANSITION TO A COOLER AND MORE
UNSETTLED PATTERN BEGINS WITH THE APPROACH OF A COMPLEX SURFACE
LOW AHEAD OF THE UPPER TROUGH. THIS SURFACE FEATURE IS ACTUALLY
MORE OF A THREE-LOBED COLLECTION OF LOWS WITH TWO CENTERS SOUTH
AND ONE CENTER NORTH THAN A SINGLE LARGE EXTRATROPICAL CYCLONE.
THE FIRST SOUTHERN LOBE CROSSES THE LOCAL AREA SATURDAY NIGHT INTO
EARLY SUNDAY BUT KEEPS THE BETTER MOISTURE AND INSTABILITY TRAPPED
FARTHER SOUTH AND PROBABLY WILL ONLY SUPPORT SHOWERS RATHER THAN
CONVECTION. AS THIS FIRST LOW MOVES EAST OF THE AREA...CONVECTION
CHANCES INCREASE AS WE BRIEFLY GET INTO ITS TRAILING WARM SECTOR
ON SUNDAY AFTERNOON AND EVENING. THE SECOND SOUTHERN LOBE THEN
CROSSES THE AREA SUNDAY NIGHT BRINGING A CONTINUED PERIOD OF TSRA
TRANSITIONING BACK TO SHOWERS.

AS THE COMPLEX SURFACE LOW EXITS THE AREA DURING THE DAY
MONDAY ALONG WITH A CORRESPONDING SHORTWAVE ALOFT...LOW LEVEL
FORCING WILL BE MOSTLY ABSENT FOR THE REMAINDER OF THE WEEK BUT
CYCLONIC FLOW ALOFT WITH POCKETS OF ENHANCED VORTICITY WILL
CONTINUE TO SUPPORT COOL TEMPERATURES IN THE 50S AND VERY LIKELY
SOME PERIODS OF SHOWERS ESPECIALLY AS STRONGER SHORTWAVES MOVE
OVERHEAD. WILL NOT ATTEMPT TO PIN DOWN THE TIMING OF THESE
FEATURES AT THIS RANGE...OTHER THAN TO CARRY PREVAILING LOW CHANCE
POPS TOWARD THE MIDDLE OF NEXT WEEK.

LENNING

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161959
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
259 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161710
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1210 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161710
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1210 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161710
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1210 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161710
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1210 PM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT AND VARIABLE WINDS FAVORING EAST AND NORTHEAST THROUGH THE
  AFTERNOON.

MDB

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

MVFR LEVEL CLOUDS ARE QUICKLY ERODING LEAVING A VFR DECK OF AROUND
6000 FT. THIS DECK WILL MOVE DRIFT EAST AND PROBABLY ERODE A BIT
THROUGH THE AFTERNOON WITH SOME STRATO CU DEVELOPING ON THE
FRINGES...WHICH WOULD ALSO BE VFR. OTHERWISE LIGHT AND VARIABLE
WINDS WILL BE THE RULE THROUGH THE AFTERNOON AND EVEN THE REST OF
THE NIGHT. EXPECT THAT ORD/MDW WILL FAVOR AN EAST TO NORTHEAST
DIRECTION THANKS TO LAKE INFLUENCES BUT STILL SEE QUITE A BIT OF
VARIABILITY. GYY WOULD LIKELY BE NORTH TO NORTHEAST WITH
VARIABILITY. MANY AREAS WILL PROBABLY EVEN GO CALM AT TIMES. THERE
MAY BE SOME FOG THAT DEVELOPS TONIGHT BUT GIVEN THE DRY CONDITIONS
OF THE PAST FEW DAYS AND ONLY SOME SPOTTY SHOWERS/DRIZZLE THIS
MORNING THE POTENTIAL IS PRETTY LOW.

MDB

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

* HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161626
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1126 AM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT NORTHEAST WINDS WHICH WILL BE VARIABLE AT TIMES.

* MVFR CIGS IMPROVING TO VFR MID/LATE AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

IFR HAS IMPROVED TO MVFR EXCEPT FOR AREAS SOUTH OF THE TERMINALS.
AM STILL THINKING THAT ORD/MDW MAY SEE LOWERING OF CIGS TOWARDS
015 IN THE NEXT 1-2 HRS BEFORE LIFTING AND EVENTUALLY SCATTERING
OCCURS. WINDS HAVE DROPPED OFF AND THE DIRECTION HAS BECOME QUITE
VARIABLE ACROSS THE TERMINALS BUT EXPECT THE LAKE INFLUENCE TO
PROVIDE A SOMEWHAT STEADIER EAST TO NORTHEAST DIRECTION AT ORD/MDW
AND NORTH TO NORTHEAST DIRECTION AT GYY LATER THIS AFTERNOON. MAY
ALSO SEE A SLIGHT BUMP IN SPEEDS AS THIS OCCURS.

MDB

FROM 12Z...

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN

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

* HIGH CONFIDENCE IN IN MVFR CIGS PERSISTING THROUGH EARLY
  AFTERNOON WITH MEDIUM CONFIDENCE IN TIMING OF SCATTERING.

* HIGH CONFIDENCE IN LIGHT WIND SPEEDS AND VARIABLE WIND
  DIRECTION. MEDIUM-HIGH CONFIDENCE IT WILL FAVOR A NORTHEAST TO
  EAST DIRECTION.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161626
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1126 AM CDT THU APR 16 2015

.UPDATE...
1113 AM CDT

TEMPERATURE AND PRECIPITATION TRENDS APPEAR TO BE ON TRACK LATE
THIS MORNING UNDER SIGNIFICANT CLOUD COVER WITH A FEW AREAS OF
PATCHY DRIZZLE MAINLY SOUTH OF THE LAKE. LIGHT WINDS UNDER THE
CLOUD DECK ARE NOT ASSISTING THE MIXING OUT OF LOW LEVEL
MOISTURE...BUT RAP RH TRENDS AND RECENT SATELLITE LOOPS SUGGEST
THE CLOUDS WILL BE SCATTERING OUT LATER THIS AFTERNOON WHICH
WOULD ALLOW TEMPERATURES TO CLIMB RAPIDLY AS SEEN ACROSS NORTHWEST
ILLINOIS AND EASTERN IOWA. FOR AREAS THAT DO NOT MANAGE TO CLEAR
AS EARLY...HIGHS MAY NEED TO BE TWEAKED DOWNWARD A FEW DEGREES.

LENNING

&&

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT NORTHEAST WINDS WHICH WILL BE VARIABLE AT TIMES.

* MVFR CIGS IMPROVING TO VFR MID/LATE AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

IFR HAS IMPROVED TO MVFR EXCEPT FOR AREAS SOUTH OF THE TERMINALS.
AM STILL THINKING THAT ORD/MDW MAY SEE LOWERING OF CIGS TOWARDS
015 IN THE NEXT 1-2 HRS BEFORE LIFTING AND EVENTUALLY SCATTERING
OCCURS. WINDS HAVE DROPPED OFF AND THE DIRECTION HAS BECOME QUITE
VARIABLE ACROSS THE TERMINALS BUT EXPECT THE LAKE INFLUENCE TO
PROVIDE A SOMEWHAT STEADIER EAST TO NORTHEAST DIRECTION AT ORD/MDW
AND NORTH TO NORTHEAST DIRECTION AT GYY LATER THIS AFTERNOON. MAY
ALSO SEE A SLIGHT BUMP IN SPEEDS AS THIS OCCURS.

MDB

FROM 12Z...

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN

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

* HIGH CONFIDENCE IN IN MVFR CIGS PERSISTING THROUGH EARLY
  AFTERNOON WITH MEDIUM CONFIDENCE IN TIMING OF SCATTERING.

* HIGH CONFIDENCE IN LIGHT WIND SPEEDS AND VARIABLE WIND
  DIRECTION. MEDIUM-HIGH CONFIDENCE IT WILL FAVOR A NORTHEAST TO
  EAST DIRECTION.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161609
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1109 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* LIGHT NORTHEAST WINDS WHICH WILL BE VARIABLE AT TIMES.

* MVFR CIGS IMPROVING TO VFR MID/LATE AFTERNOON.

MDB

//DISCUSSION...UPDATED 16Z...

IFR HAS IMPROVED TO MVFR EXCEPT FOR AREAS SOUTH OF THE TERMINALS.
AM STILL THINKING THAT ORD/MDW MAY SEE LOWERING OF CIGS TOWARDS
015 IN THE NEXT 1-2 HRS BEFORE LIFTING AND EVENTUALLY SCATTERING
OCCURS. WINDS HAVE DROPPED OFF AND THE DIRECTION HAS BECOME QUITE
VARIABLE ACROSS THE TERMINALS BUT EXPECT THE LAKE INFLUENCE TO
PROVIDE A SOMEWHAT STEADIER EAST TO NORTHEAST DIRECTION AT ORD/MDW
AND NORTH TO NORTHEAST DIRECTION AT GYY LATER THIS AFTERNOON. MAY
ALSO SEE A SLIGHT BUMP IN SPEEDS AS THIS OCCURS.

MDB

FROM 12Z...

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN

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

* HIGH CONFIDENCE IN IN MVFR CIGS PERSISTING THROUGH EARLY
  AFTERNOON WITH MEDIUM CONFIDENCE IN TIMING OF SCATTERING.

* HIGH CONFIDENCE IN LIGHT WIND SPEEDS AND VARIABLE WIND
  DIRECTION. MEDIUM-HIGH CONFIDENCE IT WILL FAVOR A NORTHEAST TO
  EAST DIRECTION.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
904 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* EAST TO NORTHEAST WINDS THROUGH THE AFTERNOON WITH SPEEDS
  DIMINISHING INTO MIDDAY. MAY END UP LIGHT AND VARIABLE BY
  MID/LATE AFTERNOON.

* MVFR CIGS AROUND 020 LIKELY LOWERING TOWARD 010 OR 015 LATE
  MORNING BEFORE LIFTING THIS AFTERNOON. ANOTHER PERIOD OF IFR
  POSSIBLE LATE THIS MORNING.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF IFR CIGS THAT DEVELOPED FROM MDW TO ORD EARLIER HAS NOW
SHIFTED FURTHER INLAND AND IS AFFECTING AREAS FROM IKK-PNT-DPA AND
INTO SOUTHERN WISCONSIN. ORD/MDW HAVE LOST THE IFR AND SUSPECT
THAT DRIER EASTERLY FLOW OFF THE LAKE HAS HELPED THIS OCCUR. WINDS
JUST ABOVE THE SURFACE WEAKEN AND TURN SOUTHWESTERLY LATE THIS
MORNING WHICH MAY BE ENOUGH TO ALLOW THE LOWER CLOUDS TO MOVE
BACK TO THE NORTHEAST. BASES SHOULD LIFT WITH TIME BUT IT APPEARS
THAT LOWER MVFR CLOUDS IN THE 010-015 RANGE WILL MOVE BACK INTO
ORD/MDW LATER THIS MORNING. THERE IS A CHANCE THAT THIS CLOUD DECK
MAY REMAIN IFR A BIT LONGER SO CANNOT RULE OUT A SHORT PERIOD OF
IFR AT ORD/MDW. AM ALSO EXPECTING WINDS TO REMAIN EAST TO
NORTHEAST AT ORD/MDW THIS AFTERNOON WITH LAKE INFLUENCE AIDING
THIS. THE GRADIENT WILL BE WEAKENING SO LIGHT AND VARIABLE MAY
ULTIMATELY OCCUR BY LATE AFTERNOON. OTHERWISE...WITH THE IFR/MVFR
MOVING WESTWARD RFD MAY BE IMPACTED IN THE NEXT FEW HOURS SO HAVE
ADDED A SCATTERED MVFR LAYER FOR A SHORT TIME. IT IS POSSIBLE
THESE LOWER CLOUDS DO NOT MAKE IT THAT FAR WEST THOUGH.

MDB

FROM 12Z...

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN

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

* MEDIUM-HIGH CONFIDENCE IN MVFR CIGS PERSISTING THROUGH MID
  AFTERNOON. MEDIUM CONFIDENCE IN TIMING OF SCATTERING. MEDIUM
  CONFIDENCE IN CIGS LOWERING TOWARD 010-015 LATE MORNING. MEDIUM
  CONFIDENCE THAT CHANCE OF IFR RETURNING IS LOW.

* MEDIUM-HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
904 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* EAST TO NORTHEAST WINDS THROUGH THE AFTERNOON WITH SPEEDS
  DIMINISHING INTO MIDDAY. MAY END UP LIGHT AND VARIABLE BY
  MID/LATE AFTERNOON.

* MVFR CIGS AROUND 020 LIKELY LOWERING TOWARD 010 OR 015 LATE
  MORNING BEFORE LIFTING THIS AFTERNOON. ANOTHER PERIOD OF IFR
  POSSIBLE LATE THIS MORNING.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF IFR CIGS THAT DEVELOPED FROM MDW TO ORD EARLIER HAS NOW
SHIFTED FURTHER INLAND AND IS AFFECTING AREAS FROM IKK-PNT-DPA AND
INTO SOUTHERN WISCONSIN. ORD/MDW HAVE LOST THE IFR AND SUSPECT
THAT DRIER EASTERLY FLOW OFF THE LAKE HAS HELPED THIS OCCUR. WINDS
JUST ABOVE THE SURFACE WEAKEN AND TURN SOUTHWESTERLY LATE THIS
MORNING WHICH MAY BE ENOUGH TO ALLOW THE LOWER CLOUDS TO MOVE
BACK TO THE NORTHEAST. BASES SHOULD LIFT WITH TIME BUT IT APPEARS
THAT LOWER MVFR CLOUDS IN THE 010-015 RANGE WILL MOVE BACK INTO
ORD/MDW LATER THIS MORNING. THERE IS A CHANCE THAT THIS CLOUD DECK
MAY REMAIN IFR A BIT LONGER SO CANNOT RULE OUT A SHORT PERIOD OF
IFR AT ORD/MDW. AM ALSO EXPECTING WINDS TO REMAIN EAST TO
NORTHEAST AT ORD/MDW THIS AFTERNOON WITH LAKE INFLUENCE AIDING
THIS. THE GRADIENT WILL BE WEAKENING SO LIGHT AND VARIABLE MAY
ULTIMATELY OCCUR BY LATE AFTERNOON. OTHERWISE...WITH THE IFR/MVFR
MOVING WESTWARD RFD MAY BE IMPACTED IN THE NEXT FEW HOURS SO HAVE
ADDED A SCATTERED MVFR LAYER FOR A SHORT TIME. IT IS POSSIBLE
THESE LOWER CLOUDS DO NOT MAKE IT THAT FAR WEST THOUGH.

MDB

FROM 12Z...

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN

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

* MEDIUM-HIGH CONFIDENCE IN MVFR CIGS PERSISTING THROUGH MID
  AFTERNOON. MEDIUM CONFIDENCE IN TIMING OF SCATTERING. MEDIUM
  CONFIDENCE IN CIGS LOWERING TOWARD 010-015 LATE MORNING. MEDIUM
  CONFIDENCE THAT CHANCE OF IFR RETURNING IS LOW.

* MEDIUM-HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
904 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* EAST TO NORTHEAST WINDS THROUGH THE AFTERNOON WITH SPEEDS
  DIMINISHING INTO MIDDAY. MAY END UP LIGHT AND VARIABLE BY
  MID/LATE AFTERNOON.

* MVFR CIGS AROUND 020 LIKELY LOWERING TOWARD 010 OR 015 LATE
  MORNING BEFORE LIFTING THIS AFTERNOON. ANOTHER PERIOD OF IFR
  POSSIBLE LATE THIS MORNING.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF IFR CIGS THAT DEVELOPED FROM MDW TO ORD EARLIER HAS NOW
SHIFTED FURTHER INLAND AND IS AFFECTING AREAS FROM IKK-PNT-DPA AND
INTO SOUTHERN WISCONSIN. ORD/MDW HAVE LOST THE IFR AND SUSPECT
THAT DRIER EASTERLY FLOW OFF THE LAKE HAS HELPED THIS OCCUR. WINDS
JUST ABOVE THE SURFACE WEAKEN AND TURN SOUTHWESTERLY LATE THIS
MORNING WHICH MAY BE ENOUGH TO ALLOW THE LOWER CLOUDS TO MOVE
BACK TO THE NORTHEAST. BASES SHOULD LIFT WITH TIME BUT IT APPEARS
THAT LOWER MVFR CLOUDS IN THE 010-015 RANGE WILL MOVE BACK INTO
ORD/MDW LATER THIS MORNING. THERE IS A CHANCE THAT THIS CLOUD DECK
MAY REMAIN IFR A BIT LONGER SO CANNOT RULE OUT A SHORT PERIOD OF
IFR AT ORD/MDW. AM ALSO EXPECTING WINDS TO REMAIN EAST TO
NORTHEAST AT ORD/MDW THIS AFTERNOON WITH LAKE INFLUENCE AIDING
THIS. THE GRADIENT WILL BE WEAKENING SO LIGHT AND VARIABLE MAY
ULTIMATELY OCCUR BY LATE AFTERNOON. OTHERWISE...WITH THE IFR/MVFR
MOVING WESTWARD RFD MAY BE IMPACTED IN THE NEXT FEW HOURS SO HAVE
ADDED A SCATTERED MVFR LAYER FOR A SHORT TIME. IT IS POSSIBLE
THESE LOWER CLOUDS DO NOT MAKE IT THAT FAR WEST THOUGH.

MDB

FROM 12Z...

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN

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

* MEDIUM-HIGH CONFIDENCE IN MVFR CIGS PERSISTING THROUGH MID
  AFTERNOON. MEDIUM CONFIDENCE IN TIMING OF SCATTERING. MEDIUM
  CONFIDENCE IN CIGS LOWERING TOWARD 010-015 LATE MORNING. MEDIUM
  CONFIDENCE THAT CHANCE OF IFR RETURNING IS LOW.

* MEDIUM-HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
904 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* EAST TO NORTHEAST WINDS THROUGH THE AFTERNOON WITH SPEEDS
  DIMINISHING INTO MIDDAY. MAY END UP LIGHT AND VARIABLE BY
  MID/LATE AFTERNOON.

* MVFR CIGS AROUND 020 LIKELY LOWERING TOWARD 010 OR 015 LATE
  MORNING BEFORE LIFTING THIS AFTERNOON. ANOTHER PERIOD OF IFR
  POSSIBLE LATE THIS MORNING.

MDB

//DISCUSSION...UPDATED 14Z...

BAND OF IFR CIGS THAT DEVELOPED FROM MDW TO ORD EARLIER HAS NOW
SHIFTED FURTHER INLAND AND IS AFFECTING AREAS FROM IKK-PNT-DPA AND
INTO SOUTHERN WISCONSIN. ORD/MDW HAVE LOST THE IFR AND SUSPECT
THAT DRIER EASTERLY FLOW OFF THE LAKE HAS HELPED THIS OCCUR. WINDS
JUST ABOVE THE SURFACE WEAKEN AND TURN SOUTHWESTERLY LATE THIS
MORNING WHICH MAY BE ENOUGH TO ALLOW THE LOWER CLOUDS TO MOVE
BACK TO THE NORTHEAST. BASES SHOULD LIFT WITH TIME BUT IT APPEARS
THAT LOWER MVFR CLOUDS IN THE 010-015 RANGE WILL MOVE BACK INTO
ORD/MDW LATER THIS MORNING. THERE IS A CHANCE THAT THIS CLOUD DECK
MAY REMAIN IFR A BIT LONGER SO CANNOT RULE OUT A SHORT PERIOD OF
IFR AT ORD/MDW. AM ALSO EXPECTING WINDS TO REMAIN EAST TO
NORTHEAST AT ORD/MDW THIS AFTERNOON WITH LAKE INFLUENCE AIDING
THIS. THE GRADIENT WILL BE WEAKENING SO LIGHT AND VARIABLE MAY
ULTIMATELY OCCUR BY LATE AFTERNOON. OTHERWISE...WITH THE IFR/MVFR
MOVING WESTWARD RFD MAY BE IMPACTED IN THE NEXT FEW HOURS SO HAVE
ADDED A SCATTERED MVFR LAYER FOR A SHORT TIME. IT IS POSSIBLE
THESE LOWER CLOUDS DO NOT MAKE IT THAT FAR WEST THOUGH.

MDB

FROM 12Z...

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN

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

* MEDIUM-HIGH CONFIDENCE IN MVFR CIGS PERSISTING THROUGH MID
  AFTERNOON. MEDIUM CONFIDENCE IN TIMING OF SCATTERING. MEDIUM
  CONFIDENCE IN CIGS LOWERING TOWARD 010-015 LATE MORNING. MEDIUM
  CONFIDENCE THAT CHANCE OF IFR RETURNING IS LOW.

* MEDIUM-HIGH CONFIDENCE IN WIND FORECAST.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161140
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
640 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* SHOWERS THROUGH LATE THIS MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THIS MORNING.

* NORTHEAST LESS THAN 10 KT THURSDAY.

KREIN

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

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN


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

* MEDIUM CONFIDENCE IN TIMING OF END OF SHRA.

* MEDIUM CONFIDENCE IN TIMING OF IMPROVEMENT OF CIGS TO VFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161140
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
640 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* SHOWERS THROUGH LATE THIS MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THIS MORNING.

* NORTHEAST LESS THAN 10 KT THURSDAY.

KREIN

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

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN


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

* MEDIUM CONFIDENCE IN TIMING OF END OF SHRA.

* MEDIUM CONFIDENCE IN TIMING OF IMPROVEMENT OF CIGS TO VFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161140
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
640 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* SHOWERS THROUGH LATE THIS MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THIS MORNING.

* NORTHEAST LESS THAN 10 KT THURSDAY.

KREIN

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

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN


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

* MEDIUM CONFIDENCE IN TIMING OF END OF SHRA.

* MEDIUM CONFIDENCE IN TIMING OF IMPROVEMENT OF CIGS TO VFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 161140
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
640 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* SHOWERS THROUGH LATE THIS MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THIS MORNING.

* NORTHEAST LESS THAN 10 KT THURSDAY.

KREIN

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

A WEAK MID LEVEL CIRCULATION MOVING NWD ALONG THE IL/IN BORDER.
SCT SHOWERS ASSOCIATED WITH THE MID LEVEL CIRCULATION HAVE MOVED
INTO FAR NERN IL AND NWRN IN...MAINLY IMPACTING GYY/ORD/MDW. THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND AT DPA IS DIMINISHING
AS THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATER THIS MORNING. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS THROUGH LATE THIS MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
POSSIBLE MAY NOT IMPROVE TO VFR UNTIL THIS AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...AND SHOULD REMAIN TO THE SOUTHEAST.

WITH A WEAK GRADIENT IN PLACE...WINDS ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE THE MORE INLAND SITES DPA
AND RFD ARE LIKELY SEE LIGHT NORTH-NORTHWEST WINDS THIS AFTERNOON.

KREIN


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

* MEDIUM CONFIDENCE IN TIMING OF END OF SHRA.

* MEDIUM CONFIDENCE IN TIMING OF IMPROVEMENT OF CIGS TO VFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...

FRIDAY NIGHT...VFR. WX NIL. SOUTHEAST WINDS LESS THAN 10 KT.

SATURDAY...VFR...THEN SLIGHT CHANCE SHRA/MVFR AFTER MIDNIGHT. EAST
WINDS 10-15 KT.

SUNDAY...LIKELY SHRA/CHANCE TSRA. MVFR POSSIBLE. EAST WINDS 10-15
KT...BECMG NORTHWEST LESS THAN 10 KT OVERNIGHT.

MONDAY...CHANCE SHRA MONDAY...SLIGHT CHANCE SHRA OVERNIGHT. MVFR
POSSIBLE. WEST TO NORTHWEST WINDS 10-15 KT.

TUESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS 15-20KT
TUESDAY...DIMINISHING TO 5-10 KT OVERNIGHT.

WEDNESDAY...SLIGHT CHANCE SHRA...OTRW VFR. WEST WINDS LESS THAN 10
KT.

KREIN

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARLY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 160927
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
427 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* POTENTIAL FOR SHOWERS THROUGH EARLY THURSDAY MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THURSDAY MORNING.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

//DISCUSSION...UPDATED 09Z...

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...SHOULD REMAINING TO THE SOUTHEAST.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 160927
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
427 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* POTENTIAL FOR SHOWERS THROUGH EARLY THURSDAY MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THURSDAY MORNING.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

//DISCUSSION...UPDATED 09Z...

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...SHOULD REMAINING TO THE SOUTHEAST.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 160927
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
427 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* POTENTIAL FOR SHOWERS THROUGH EARLY THURSDAY MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THURSDAY MORNING.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

//DISCUSSION...UPDATED 09Z...

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...SHOULD REMAINING TO THE SOUTHEAST.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 160927
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
427 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* POTENTIAL FOR SHOWERS THROUGH EARLY THURSDAY MORNING.

* A PERIOD OF MVFR OR POSSIBLY IFR THROUGH LATE THURSDAY MORNING.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

//DISCUSSION...UPDATED 09Z...

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR...AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

THERE IS ALSO A CHANCE FOR SOME THUNDERSTORMS INVOF THE
CIRCULATION CENTER...BUT IT IS UNLIKELY THAT ANY THUNDER WILL
IMPACT THE TERMINALS...SHOULD REMAINING TO THE SOUTHEAST.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* MEDIUM-HIGH CONFIDENCE IN WIND TRENDS.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 160804
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
304 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* EAST WINDS ARND 10 KT OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* A PERIOD OF MVFR/IFR LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

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

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR... AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* LOW-MEDIUM CONFIDENCE IN TRENDS THURSDAY.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 160804
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
304 AM CDT THU APR 16 2015

.SHORT TERM...
304 AM CDT

THROUGH FRIDAY...

COMPACT BUT STRONG VORT IS MOVING NORTHWARD ACROSS ILLINOIS THIS
MORNING AND DRIVING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
NORTHWARD ACROSS FAR EASTERN ILLINOIS AND WESTERN INDIANA EARLY THIS
MORNING. THIS ACTIVITY WILL AFFECT CHICAGO AREA AND NW INDY INTO THE
EARLY MORNING HOURS BEFORE MOVING OUT OF THE REGION. FAIRLY
EXTENSIVE CLOUD COVER UPSTREAM AND WITH RAIN LIKELY TO FURTHER
SATURATED THE COLUMN AM CONCERNED THAT CLOUD COVER COULD BE FAIRLY
PREVALENT ACROSS ESPECIALLY EASTERN PORTIONS OF THE CWA INTO AT
LEAST THE FIRST PART OF THE AFTERNOON WHICH SHOULD SLOW TEMPERATURE
RISE AND LIKELY KEEP TEMPS FROM GETTING ABOVE GUIDANCE TODAY UNLIKE
THE PAST COUPLE DAYS.

IN THE WAKE OF THIS MORNING`S SHORTWAVE LOOK FOR HEIGHT RISES AS
UPPER RIDGING BUILDS INTO THE REGION IN ADVANCE OF THE BIG WESTERN
CUT-OFF LOW. RISING HEIGHTS AND WARMING LOW/MID LEVEL LOOK TO SET
THE STAGE FOR A COUPLE OF RATHER TOASTY DAYS AWAY FROM THE
LAKEFRONT. PROGGED 925MB TEMPS INTO THE MID TEENS CELSIUS SUPPORT
HIGHS AROUND 80F AND HAVE BUMPED TEMPS IN THE GRIDS UPWARD TOWARD
THE DIRECTION...AND GIVEN THE RECENT COOL BIAS IN GUIDANCE ITS
POSSIBLE THAT THESE FORECAST GRIDS COULD END UP TOO COOL STILL WITH
80F+ ACROSS MOST OF THE CWA FRIDAY AND SATURDAY.

IZZI

&&

.LONG TERM...
304 AM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

GUIDANCE IS REMAINS IN RELATIVELY GOOD AGREEMENT ON THE EJECTION OF
THE BIG WESTERN CLOSED LOW WITH SHOWERS AND THUNDERSTORMS IN ADVANCE
OF THIS SYSTEM EXPECTED TO ARRIVE PROBABLY SUNDAY AND COULD STICK
AROUND AT TIMES INTO SUNDAY NIGHT. GFS REMAINS IS ON THE FASTER END
OF THE GUIDANCE ENVELOPE...BUT GIVEN THE TENDENCY FOR THESE SYSTEMS
TO BE SLOWER THAN PROGGED HAVE KEPT POPS BELOW GUIDANCE SAT NIGHT
MORE IN LINE WITH THE SLOWER GEM SOLUTION.

THE WESTERN CUT OFF LOW IS PROGGED TO PHASE WITH AMPLIFYING NORTHERN
STREAM LONG TROUGH THAT LOOKS TO STALL OUT OVER THE GREAT LAKES
REGION NEXT WEEK. THIS WILL RESULT IN AN END TO THE ABOVE AVERAGE
TEMPERATURES THAT HAVE DOMINATED MUCH OF THIS MONTH...BUT LOOKS TO
BE A FAIRLY DRY PATTERN THROUGH THURSDAY.

IZZI

&&

.AVIATION...

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

* EAST WINDS ARND 10 KT OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* A PERIOD OF MVFR/IFR LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

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

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR... AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* LOW-MEDIUM CONFIDENCE IN TRENDS THURSDAY.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
304 AM CDT

A RELATIVELY QUIET PERIOD OF WEATHER IS EXPECTED FOR LAKE MICHIGAN
FOR THE NEXT SEVERAL DAYS. HIGH PRESSURE CENTERED OVER SOUTHERN
QUEBEC WILL MOVE OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE
OVER NORTHERN ONTARIO MOVES ACROSS JAMES BAY. MEANWHILE...LOW
PRESSURE OVER THE CENTRAL PLAINS WILL SLOWLY DRIFT SOUTHEAST. WITH
A WEAK PRESSURE GRADIENT OVER THE LAKE...LIGHT WINDS WILL COVER
THE OPEN WATERS WHILE ONSHORE FLOW AND A LAKE BREEZE DEVELOP OVER
THE NEARSHORE WATERS TODAY. A SIMILARY SETUP IS EXPECTED FOR
FRIDAY...BUT THEN A DEEPENING LOW WILL PASS TO THE NORTH OF LAKE
SUPERIOR FRIDAY EVENING WITH AN ASSOCIATED COLD FRONT PUSHING
SOUTH DOWN LAKE MICHIGAN FRIDAY NIGHT...ALLOWING FOR STRENGTHENING
NORTH TO NORTHEAST WINDS TO DEVELOP OVER THE LAKE FOLLOWING THE
FROPA...BUT DO NOT EXPECT WINDS TO EXCEED 20-25 KT. HIGH PRESSURE
WILL THEN BUILD SOUTHEAST ACROSS THE GREAT LAKES AND ONTARIO
FRIDAY NIGHT INTO SATURDAY.

&&

.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 160557
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 AM CDT THU APR 16 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST WINDS ARND 10 KT OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* A PERIOD OF MVFR/IFR LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

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

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR... AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* LOW-MEDIUM CONFIDENCE IN TRENDS THURSDAY.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160557
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 AM CDT THU APR 16 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST WINDS ARND 10 KT OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* A PERIOD OF MVFR/IFR LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

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

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR... AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* LOW-MEDIUM CONFIDENCE IN TRENDS THURSDAY.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160557
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 AM CDT THU APR 16 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST WINDS ARND 10 KT OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* A PERIOD OF MVFR/IFR LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

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

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR... AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* LOW-MEDIUM CONFIDENCE IN TRENDS THURSDAY.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160557
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 AM CDT THU APR 16 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST WINDS ARND 10 KT OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* A PERIOD OF MVFR/IFR LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

KREIN

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

THE EAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY LOW
LEVEL AIR ACROSS MUCH OF NORTHERN ILLINOIS...WHILE SOUTH-
SOUTHEAST WINDS ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT OVER
NORTHWESTERN INDIANA AS A WEAK MID LEVEL CIRCULATION MOVES NWD
ALONG THE IL/IN BORDER. SCT SHOWERS ASSOCIATED WITH THE MID LEVEL
CIRCULATION ARE SLOWLY MOVING NWD INTO NWRN IN...BUT ARE HAVING
SOME TROUBLE OVERCOMING THE DRY LOW LEVEL AIR...SO IT WILL STILL
TAKE SOME TIME FOR RAIN TO REACH THE SURFACE. STILL FEEL THAT
THERE IS SOME POTENTIAL FOR SHRA AT THE CHICAGO AREA
TERMINALS...ESPECIALLY GYY AND MDW...BUT ORD/DPA STILL HAVE SOME
POTENTIAL AS WELL. WILL MAINTAIN THE VCSH AT RFD...THOUGH THE
POTENTIAL FOR ANY PCPN REACHING THE GROUND THERE IS DIMINISHING AS
THE MID LEVEL CIRCULATION SHOULD TAKE A TURN TO THE NORTHEAST
LATE TONIGHT. WITH THE ARRIVAL OF SHOWERS OVER THE EASTERN
TERMINALS...FORECAST SOUNDINGS INDICATE A PERIOD OF MVFR... AND
POSSIBLY IFR CIGS EARLY THURSDAY MORNING. LIGHT WINDS BY THAT
TIME SUGGEST MVFR CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER...AND
MAY NOT IMPROVE TO VFR UNTIL THURSDAY AFTERNOON.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

KREIN

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

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY.

* MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR CIGS...MEDIUM IN IFR.

* LOW-MEDIUM CONFIDENCE IN TRENDS THURSDAY.

KREIN

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160301
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1001 PM CDT WED APR 15 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160301
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1001 PM CDT WED APR 15 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160100 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
800 PM CDT WED APR 15 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160100 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
800 PM CDT WED APR 15 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. RAOBS FROM DVN AND ILX AT 00Z DO INDICATE WARM
ADVECTION PROFILES FROM JUST OFF THE DECK ALL THE DAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160100 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
800 PM CDT WED APR 15 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. RAOBS FROM DVN AND ILX AT 00Z DO INDICATE WARM
ADVECTION PROFILES FROM JUST OFF THE DECK ALL THE DAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 160100 CCA
AFDLOT

AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
800 PM CDT WED APR 15 2015

.UPDATE...
758 PM CDT

HAVE ONLY MADE SLIGHT ADJUSTMENTS TO THE REST OF TONIGHT FORECAST.
A PICTURESQUE SKY OF VIRGA FROM CIRRUS/HIGH BASED ALTOCU OUT OUR
WINDOW AT SUNDOWN AND SHARED WITH US BY SEVERAL OF OUR SOCIAL
MEDIA FOLLOWERS. THE RAOB FROM DVN AT 00Z INDICATES A WARM
ADVECTION PROFILE FROM JUST OFF THE DECK ALL THE WAY UP...WITH
MOISTENING OCCURRING 15000 FT AND ABOVE ALONG WITH SOME MODEST
LAPSE RATES...THOUGH VERY DRY STILL BELOW THAT. AT ILX THIS
SATURATED LAYER IS DOWN TO 6000 FT WITH PRONOUNCED DRYING BELOW.

WATER VAPOR IMAGERY INDICATES A COMPACT BUT MOISTURE-STARVED
CIRCULATION IN SOUTHWEST ILLINOIS ADVANCING NORTHEAST...WITH SOME
SHOWER ACTIVITY REACHING THE GROUND AHEAD OF IT IN THE CENTRALIA
AND EFFINGHAM AREAS. TIMING THIS CORRIDOR OF FORCING WOULD MOVE
IT INTO THE SOUTHERN FORECAST AREA AROUND 11 PM. RAP AND NAM
FORECASTS INDICATE MOVE VEERED/SOUTHERLY PROFILES DOWN TO
900MB...WITH FORECAST MOISTURE TRANSPORT AND ADIABATIC LIFT
LIKELY TO AID IN SATURATION FOR AT LEAST SCATTERED LIGHT SHOWERS
ACROSS THE EASTERN FORECAST AREA. THAT IS IN LINE WITH GOING
FORECAST AND FOR THE MOST PART CURRENT HIGH-RES GUIDANCE. JUST
HAVE SLOWED THE START TIME OF POPS DOWN SLIGHTLY...BUT ALL IN ALL
A NEGLIGIBLE CHANGE TO WORDING FOR MOST AREAS. RAINFALL AMOUNTS
UNDER 0.15 OF AN INCH LOOK GOOD...WITH MOST OF NORTH CENTRAL
ILLINOIS NOT SEEING MORE THAN A TRACE.

GOING TEMPERATURES AND IMPROVING RELATIVE HUMIDITY VALUES LOOK ON
TRACK.

MTF

&&

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

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 152348
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
648 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152348
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
648 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152348
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
648 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152348
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
648 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS 10-15 KT THIS EVENING GRADUALLY DIMINISHING
  OVERNIGHT.

* POTENTIAL FOR SHOWERS TONIGHT/EARLY THURSDAY MORNING.

* LOWERING VFR CEILINGS BY LATE EVENING...A PERIOD OF MVFR/IFR
  LIKELY EARLY THURSDAY.

* NORTHEAST WINDS 10 KT OR LESS THURSDAY.

RATZER

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

EAST-NORTHEAST WINDS PERSIST ACROSS THE TERMINALS EARLY THIS
EVENING AS FORECAST AREA REMAINS BETWEEN HIGH PRESSURE TO THE
NORTHEAST OF THE LAKES AND A WEAK AREA OF LOW PRESSURE OVER THE
LOWER MISSISSIPPI VALLEY. WINDS HAVE LOST SOME OF THEIR HIGHER
GUSTS WITH THE LOWERING SUN ANGLE AND INCREASING CLOUD COVER
ALLOWING BOUNDARY LAYER TO COOL A BIT...THOUGH SPEEDS 10-15 KT
SHOULD PERSIST INTO THIS EVENING BEFORE THE GRADIENT WEAKENS
SLOWLY OVERNIGHT.

THE EAST-NORTHEAST LOW LEVEL FLOW WAS MAINTAINING ADVECTION OF DRY
LOW LEVEL AIR ACROSS THE REGION...WHILE SOUTH-SOUTHEAST WINDS
ALOFT WERE PULLING MOISTURE NORTHWARD ALOFT AS THE SURFACE LOW
OVER THE LOWER MISSISSIPPI VALLEY MOVES SLOWLY NORTHEAST. VFR
CEILINGS WILL THICKEN AND LOWER THROUGH LATE EVENING WITH A FEW
SPOTTY SHOWERS LIKELY STRUGGLING TO PRODUCE PRECIP THROUGH THE DRY
LAYER CLOSER TO THE SURFACE...BUT EVENTUALLY SHOWERS SHOULD MOVE
INTO THE AREA WITH THE BEST MOISTURE TRANSPORT FOCUSED ACROSS
NORTHEAST IL/NORTHWEST INDIANA 09-13Z THURSDAY MORNING BEFORE
SHIFTING EAST. SOME WEAK ELEVATED INSTABILITY IS NOTED IN FORECAST
SOUNDINGS...WITH THE POTENTIAL FOR ISOLATED TSRA...THOUGH COVERAGE
IS EXPECTED TO BE TOO LOW TO INCLUDE IN TAFS. BETTER COVERAGE
PERHAPS FARTHER SOUTH ALONG THE IL/IN STATE LINE. THE BEST FORCING
AND MOISTURE FEED REMAINS GENERALLY EAST OF KRFD...WITH LOWEST
CHANCES OF RAIN AND LOWER CEILINGS THERE. WITH THE ARRIVAL OF
SHOWERS OVER THE EASTERN TERMINALS...FORECAST SOUNDINGS AND
STATISTICAL GUIDANCE DOES INDICATE A PERIOD OF MVFR...POSSIBLY
IFR EARLY THURSDAY MORNING. LIGHT WINDS BY THAT TIME SUGGEST MVFR
CIGS MAY BE A LITTLE SLOW TO LIFT/SCATTER DURING THE
MORNING/MIDDAY.

WEAK GRADIENT AND LIGHT WINDS THURSDAY ARE EXPECTED TO BECOME
NORTHEAST NEAR LAKE MICHIGAN...WHILE INLAND SITES DPA AND RFD ARE
LIKELY SEE LIGHT NORTH-NORTHWEST WINDS.

RATZER

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

* HIGH CONFIDENCE IN WIND/CLOUD TRENDS THROUGH THIS EVENING.

* MEDIUM CONFIDENCE IN SHRA COVERAGE/TIMING OVERNIGHT AND EARLY
  THURSDAY. MEDIUM-HIGH CONFIDENCE IN PERIOD OF MVFR
  CIGS...MEDIUM IN IFR.

* MEDIUM CONFIDENCE IN LIGHT WIND DIRECTION DETAILS THURSDAY.

* HIGH CONFIDENCE ANY TSRA WILL BE ISOLATED/LOW COVERAGE.

RATZER

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

FRIDAY...VFR. LIGHT VARIABLE WINDS BECOMING SOUTHEAST.

SATURDAY...VFR. CHANCE OF SHRA WITH MVFR POSSIBLE SATURDAY NIGHT.
NORTHEAST WINDS.

SUNDAY...CHANCE SHRA. MVFR POSSIBLE. EAST-NORTHEAST WINDS.

MONDAY...CHANCE SHRA EARLY. MVFR IMPROVING TO VFR. WEST-NORTHWEST
WINDS.

TUESDAY...VFR. CHANCE SHRA TUES NGT. WEST WINDS.

RATZER

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152203
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
503 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR A PERIOD OF IFR CIGS EARLY THURSDAY

ED F/RATZER

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F/RATZER

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152203
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
503 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR A PERIOD OF IFR CIGS EARLY THURSDAY

ED F/RATZER

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F/RATZER

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152203
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
503 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR A PERIOD OF IFR CIGS EARLY THURSDAY

ED F/RATZER

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F/RATZER

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152203
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
503 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST-NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR A PERIOD OF IFR CIGS EARLY THURSDAY

ED F/RATZER

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F/RATZER

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152051
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
351 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152051
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
351 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152051
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
351 PM CDT WED APR 15 2015

.SHORT TERM...
339 PM CDT

THROUGH FRIDAY...

BETTER AGREEMENT BETWEEN DETERMINISTIC MODELS AND THEIR ENSEMBLE
COUNTERPARTS IS PROVIDING INCREASED FORECAST CONFIDENCE FOR THE
REMAINDER OF THE WEEK AND INTO EARLY NEXT WEEK.  THE PRIMARY UPPER
LEVEL FEATURES BEING TRACKED INCLUDE A LARGE SOUTHERN STREAM LOW
DIGGING INTO THE FOUR CORNERS...A DOWNSTREAM RIDGE WITH EMBEDDED
SHORTWAVES...AND A CLOSED LOW PROJECTED TO DEVELOP IN A DEEPENING
NORTHERN STREAM TROUGH AND MERGE LATE IN THE WEEKEND WITH THE SYSTEM
THAT FINALLY WILL BE LIFTING OUT OF THE DESERT SOUTHWEST.  AT LOWER
LEVELS...MODELS AGREE IN LIFTING A WEAK SURFACE TROUGH ACROSS THE
AREA TONIGHT AND IN TAKING A MORE DEVELOPED LOW PRESSURE SYSTEM
ACROSS THE AREA SATURDAY NIGHT INTO SUNDAY IN CONJUNCTION WITH THE
MERGING UPPER TROUGHS.

FOR THIS EVENING AND OVERNIGHT...THE AREA OF SHOWERS AND ISOLATED
TSRA STRETCHING FROM NORTHWEST IA ACROSS MO AND INTO KY IS
CORRELATED WITH A GRADIENT OF ENHANCED MOISTURE FLUX DEPICTED IN THE
RAP. AS THIS GRADIENT LIFTS NORTH...PRECIP CHANCES INCREASE TOWARD
MIDNIGHT AND ESPECIALLY IN THE PREDAWN HOURS.  FORECAST SOUNDINGS
TREND TOWARD MOIST ADIABATIC AND DEEPLY SATURATED...SO PWATS
INCREASE CONSIDERABLY OVERNIGHT BUT INSTABILITY IS TALL AND SKINNY.
BETTER CHANCE OF TSRA WILL LIKELY REMAIN SOUTH AND EAST OF THE METRO
AREA.

DURING THE DAYTIME THURSDAY AND ESPECIALLY INTO THURSDAY
NIGHT...HEIGHTS INCREASE ALOFT AS THE UPPER SHORTWAVES MOVE EAST OF
THE AREA AND LOWER LEVELS DRY OUT.  WILL CARRY LOW CHANCE POPS INTO
THE THURSDAY MORNING HOURS AND EARLY AFTERNOON BUT KEEP THURSDAY
NIGHT AND FRIDAY DRY.

LENNING

&&

.LONG TERM...
339 PM CDT

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER ANOTHER QUIET DAY ON SATURDAY...THE MERGING NORTHERN AND
SOUTHERN STREAM TROUGHS AND DEVELOPMENT OF A CLOSED SURFACE LOW IN
THE LEE OF THE ROCKIES WILL BRING INCREASED PRECIP CHANCES TO THE
AREA FOR SATURDAY NIGHT AND SUNDAY. WITH THE CENTER OF THE SURFACE
LOW PASSING SOUTH OF THE AREA ACROSS CENTRAL ILLINOIS...AM SEEING
GOOD SUPPORT FOR SHOWERS SATURDAY NIGHT AND EARLY SUNDAY BUT NOT
MUCH IN THE WAY OF CONVECTION UNTIL THE LOW PUSHES A WARM FRONT
THROUGH THE AREA AROUND MIDDAY AND BRIEFLY MOVES THE AREA INTO
THE WARM SECTOR AHEAD OF THE TRAILING COLD FRONT. THE PEAK PERIOD
FOR TSRA WOULD APPEAR TO BE SUNDAY AFTERNOON AND EVENING.

AFTER THE SURFACE LOW LIFTS WELL NORTH OF THE AREA SUNDAY NIGHT
INTO MONDAY...CYCLONIC FLOW ALOFT AND RESIDUAL BOUNDARY LAYER
MOISTURE MAY CONTINUE TO SUPPORT THE CHANCE OF SHOWERS INTO
MONDAY...BUT A RIDGE OF HIGH PRESSURE WILL BEGIN TO BUILD FROM THE
PLAINS INTO THE SOUTHERN GREAT LAKES BY TUESDAY...AGAIN DRYING
THINGS OUT FOR AT LEAST THE FIRST HALF OF THE WEEK.

LENNING

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 152001
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
301 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST NORTHEAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151854
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
154 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151854
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
154 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151854
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
154 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151854
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
154 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
153 PM CDT

A RIDGE OF HIGH PRESSURE CENTERED JUST TO THE NORTHEAST OF THE
GREAT LAKES IS ALLOWING FOR LIGHTER WINDS ACROSS THE LAKE
TODAY...BUT WITH THE HIGHEST WINDS OF 10 TO 20 KT BEING OBSERVED
OVER THE SOUTHERN HALF. EASTERLY WINDS OF 10 TO 20 KT WILL
CONTINUE TONIGHT FOR THE SOUTH HALF AND THE NEARSHORE AS A TIGHTER
PRESSURE GRADIENT REMAINS...AND WITH MORE STABLE CONDITIONS
HELPING TO KEEP WIND SPEEDS DOWN. SURFACE PATTERN BEGINS TO RELAX
LATER TONIGHT INTO THURSDAY MORNING WHILE SPEEDS DIMINISH AND WITH
WINDS LIKELY BECOMING VARIABLE DURING THE DAY THURSDAY. THIS
RELAXED PATTERN LOOKS TO PERSIST THROUGH THE END OF THE WORK
WEEK...WITH GENERALLY LIGHTER SPEEDS IN PLACE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 PM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EAST WINDS OCCASIONALLY GUSTY THIS AFTERNOON

* RAIN SHOWERS TONIGHT/EARLY THURSDAY

* POTENTIAL FOR PERIOD OF IFR CIGS EARLY THURSDAY

ED F

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

EAST WINDS WILL BE OCCASIONALLY GUSTY THIS AFTERNOON AS HIGH
PRESSURE NORTH OF LAKE HURON MOVES AWAY. GUSTS WILL SUBSIDE AROUND
7 PM BUT A BRISK EAST FLOW WILL CONTINUE INTO THE OVERNIGHT.
MEANWHILE LOW PRESSURE OVER THE MID MISSISSIPPI VALLEY WILL DRAW
MOIST AIR NORTHWARD INTO THE AREA TONIGHT. CLOUDS WILL LOWER AND
THICKEN AS THIS OCCURS. THERE MAY BE 2 SEPARATE PERIODS OF RAIN.
THE FIRST, EXPECTED TO BE LITTLE MORE THAN SPRINKLES OR A LIGHT
SHOWER... IF THAT... IS CURRENTLY EXPECTED DURING 03Z-05Z.

THE SECOND AND MORE SUBSTANTIAL PERIOD OF RAIN SHOWERS IS
CURRENTLY ANTICIPATED BETWEEN 09Z-13Z. IT IS DURING THIS TIME
CIGS ARE ALSO EXPECTED TO LOWER TO MVFR WITH A PERIOD OF IFR CIGS
POSSIBLY LASTING FOR A FEW HOURS DURING THIS WINDOW. ATMOSPHERE
VERTICAL PROFILES SHOWING SOME ELEVATED INSTABILITY THUS CAN NOT RULE
OUT AN EMBEDDED THUNDERSHOWER FROM 09Z-13Z BUT BELIEVE ANY
COVERAGE OF THUNDER WILL BE VERY LIMITED.

RAIN MOVES EAST THURSDAY AFTER DAYBREAK BUT MVFR CIGS EXPECTED TO
PERSIST INTO MUCH OF THE DAY WITH DRY AIR VERY SLOW TO MOVE IN.

ED F

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

* HIGH CONFIDENCE IN ALL FORECAST DETAILS THIS AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN CIG AND WIND TRENDS TONIGHT AND
  THURSDAY.

* MEDIUM CONFIDENCE IN TIMING OF SHOWERS AND TRENDS IN VSBY
  FORECASTS TONIGHT AND THURSDAY.

* LOW CONFIDENCE IN TIMING AND DURATION OF IFR CIGS.

* LOW CONFIDENCE ON OCCURRENCE OF THUNDER.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1107 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EASTERLY WINDS BECOMING GUSTY THIS AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY THURSDAY MORNING
  WITH SCATTERED SHOWERS.

ED F

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MORE MOIST AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151601
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1101 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EASTERLY WINDS BECOMING GUSTY THIS AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY THURSDAY MORNING
  WITH SCATTERED SHOWERS.

ED F

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MORE MOIST AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151601
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1101 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.FIRE WEATHER...
1054 AM CDT

A RED FLAG WARNING HAS BEEN ISSUED FOR TODAY...MAINLY FOR AREAS
ALONG AND SOUTH OF INTERSTATE 80.

INCREASING EASTERLY WINDS AND GUSTS THIS MORNING INTO THE
AFTERNOON WILL PERSIST...WITH 20 FT WINDS LIKELY AT OR ABOVE 20
MPH. DAY TIME MIXING WILL ALLOW DEWPOINTS TO DROP OVER THE NEXT
ONE TO TWO HOURS WITH ANOTHER DAY OF VERY LOW RELATIVE HUMIDITY
VALUES EXPECTED. THE COMBINATION OF STRONG WINDS...LOW RELATIVE
HUMIDITY...AND LOW FUEL MOISTURES OF AROUND 8 PERCENT WILL RESULT
IN CRITICAL FIRE WEATHER CONDITIONS.

RODRIGUEZ

&&

.AVIATION...

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

* EASTERLY WINDS BECOMING GUSTY THIS AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY THURSDAY MORNING
  WITH SCATTERED SHOWERS.

ED F

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MORE MOIST AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...RED FLAG WARNING...ILZ019-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
     ILZ039 UNTIL 7 PM WEDNESDAY.

IN...RED FLAG WARNING...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 PM
     WEDNESDAY.

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 151427
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
927 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS BECOMING GUSTY THIS AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY THURSDAY MORNING
  WITH SCATTERED SHOWERS.

ED F

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MORE MOIST AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 151427
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
927 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS BECOMING GUSTY THIS AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY THURSDAY MORNING
  WITH SCATTERED SHOWERS.

ED F

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MORE MOIST AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 151427
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
927 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS BECOMING GUSTY THIS AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY THURSDAY MORNING
  WITH SCATTERED SHOWERS.

ED F

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MORE MOIST AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 151427
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
927 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS BECOMING GUSTY THIS AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY THURSDAY MORNING
  WITH SCATTERED SHOWERS.

ED F

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MORE MOIST AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN

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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

ED F

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 151135
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
635 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY TOMORROW
  MORNING.

KREIN

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MOISTER AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN


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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 151135
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
635 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY TOMORROW
  MORNING.

KREIN

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MOISTER AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN


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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 151135
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
635 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY TOMORROW
  MORNING.

KREIN

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MOISTER AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN


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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 151135
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
635 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

* CIGS LOWERING TO MVFR LEVELS LATE TONIGHT OR EARLY TOMORROW
  MORNING.

KREIN

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

HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO WILL SPREAD
NORTHEAST TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY
TODAY. WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS
WILL ALLOW FOR STRONGER EASTERLY WINDS TO DEVELOP WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY SOME LIGHT SHOWER ACTIVITY MAY SPREAD INTO FAR NERN IL AND
NWRN IN AS A MID LEVEL IMPULSE MOVES INTO THE OHIO VALLEY LATE
TONIGHT. ALSO...WINDS SHOULD BACK MORE NELY LAKE TONIGHT AND EARLY
TOMORROW...DRAWING COOLER...MOISTER AIR INLAND OFF OF LAKE
MICHIGAN POSSIBLY LEADING TO CIGS LOWERING TO MVFR LEVELS.

KREIN


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

* MEDIUM CONFIDENCE IN CIG/PCPN TRENDS LATE TONIGHT.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

THURSDAY NIGHT...VFR. WX NIL. NELY WINDS BECMG LGT/VRBL.

FRIDAY...VFR. WX NIL. SELY WINDS BECMG NWLY OVERNIGHT.

SATURDAY...VFR. SLIGHT CHANCE SHRA SATURDAY NIGHT. NLY WINDS BECMG
NELY OVERNIGHT.

SUNDAY...CHANCE SHRA. CHANCE MVFR CIGS. ELY WINDS.

MONDAY...CHANCE SHRA AND MVFR CIGS EARLY...OTRW VFR. NWLY WINDS
BECMG WLY.

TUESDAY...CHANCE SHRA TUESDAY NIGHT. WLY WINDS.

KREIN

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
403 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
403 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150825
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150825
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150825
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150825
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CDT WED APR 15 2015

.SHORT TERM...
325 AM CDT

THROUGH THURSDAY...

TODAY SHOULD BE LARGELY A CARBON COPY OF TUESDAY...THOUGH WITH A BIT
STIFFER OF A WIND OFF THE LAKE WITH LAKE COOLING PLAYING A BIT MORE
PROMINENT ROLE THAN ON TUESDAY. BIGGEST ITEM IN THE SHORT TERM
PERIOD IS WITH PRECIP CHANCES TONIGHT INTO THURSDAY MORNING. WELL
DEFINED SHORTWAVE TROUGH OVER NEW MEXICO IS PROGGED TO EJECT
NORTHEAST INTO THE MIDWEST TONIGHT AND LIKELY DAMPEN OUT AS IT
ENCOUNTERS THE SLOWLY RETREATING UPPER RIDGE...HOWEVER UNLIKELY LAST
NIGHT MOST GUIDANCE NOW SUGGESTS SUFFICIENT FORCING AND MOISTURE
WILL BE LEFT OVER TO ALLOW FOR SHOWERS TO SPREAD NORTH INTO THE
EASTERN PORTIONS OF OUR CWA AND HAVE BEEFED UP POPS THERE TONIGHT
INTO THURSDAY MORNING...PERHAPS NOT HIGH ENOUGH.

IZZI

&&

.LONG TERM...
325 AM CDT

THURSDAY NIGHT THROUGH TUESDAY...

NO BIG CHANGES TO THE FORECAST IN THE LONGER TERM. THE WRF-NAM
SUGGESTS A BIT OF A SOUTHWESTERLY GRADIENT COULD SET UP FRIDAY
ALLOWING TEMPS TO WARM UP FURTHER...ESPECIALLY NEAR THE LAKE.
HOWEVER GFS/ECMWF ARE LIGHTER WITH THE WINDS AND WOULD STILL ALLOW
FOR LAKE COOLING...ALBEIT WEAKER THAN TODAY.

AS FOR THE BIG CUT OFF LOW OUT WEST...GFS/ECMWF ARE ACTUALLY IN
DECENT AGREEMENT ON HAVING IT SIT AND TWIRL AROUND WEST OF US
THROUGH SATURDAY BEFORE AMPLIFYING NORTHERN STREAM TROUGH DIGS SOUTH
INTO THE NORTHERN ROCKIES KICKING THE WESTERN SYSTEM OUT INTO OUR
NECK OF THE WOODS BY SUNDAY. GIVEN THE TENDENCY FOR MODELS TO
STRUGGLE WITH HANDLING OF THESE CUT OFF CONFIDENCE IS LOWER THAN
AVERAGE...BUT GIVEN THE CONSISTENCY WITH THE BETTER DEFINED NORTHERN
STREAM KICKER IT IS POSSIBLE THAT THIS LATEST SOLUTION MAY BE MORE
LIKELY TO PAN OUT THAN EARLIER RUNS. IN THE WAKE OF THE SHOWERS AND
THUNDERSTORMS WITH THAT SYSTEM AN UPPER TROUGH LOOKS TO PROVIDE THE
REGION WITH COOLER THAN AVERAGE TEMPERATURES NEXT WEEK...THOUGH
WESTERLY SURFACE WINDS WILL KEEP LAKE COOLING AT BAY MAKING TEMPS A
BIT OF A WASH COMPARED TO TEMPS THIS WEEK NEAR THE LAKE...WHILE
POINTS INLAND SEE MORE SUBSTANTIAL COOLING.

IZZI

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150748
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
248 AM CDT WED APR 15 2015

.UPDATE...
851 PM CDT

ONLY MINOR ADJUSTMENTS MADE TO GOING FORECAST FOR TONIGHT. GIVEN
HOW DRY THE LOW TO MID-LEVEL ATMOSPHERE IS BASED ON DVN AND ILX
SOUNDING...AND ESPECIALLY AT THE SURFACE GIVEN THE RECORD DRY
AFTERNOON HUMIDITY /13 PERCENT FOR CHICAGO/...TEMPERATURES LIKELY
WILL DROP QUICKLY WHERE THERE ARE PRONOUNCED BREAKS IN THE CIRRUS.
THAT IS A BIT CHALLENGING TO SAY WHERE AND HOW LONG AS THE HOLES
HAVE UNDULATED AND LIKELY WILL THROUGH OVERNIGHT. DVN AND ILX
RAOBS INDICATED QUITE A BIT OF MOISTURE 450MB AND ABOVE...SO WILL
BANK ON SOME CLOUDS MORE OFTEN THAN NOT...BUT CONCEIVABLY SOME
OUTLYING PLACES COULD DROP TO OR A LITTLE BELOW FREEZING IF MORE
PERSISTENT CLEARING WERE TO DEVELOP.

MTF

&&

.SHORT TERM...
336 PM CDT

THROUGH THURSDAY...

AN AMPLIFIED PATTERN ALOFT IS NOT BEING HANDLED IN A VERY SIMILAR
MANNER BY THE VARIOUS DETERMINISTIC MODELS BUT ALL HAVE A BASIC
AGREEMENT IN DIGGING A BROAD UPPER LOW INTO THE FOUR CORNERS REGION
OVER THE NEXT TWO DAYS.  DOWNSTREAM RIDGING WILL SUPPORT CONTINUED
MILD TEMPERATURES AND RELATIVELY LIGHT WINDS LOCALLY...OPENING THE
DOOR FOR MESOSCALE FACTORS LIKE THE COLD LAKE TO BE THE PRIMARY
DRIVER OF TRENDS IN THE NEAR TERM.

THE DOMINANCE OF THE RIDGE TONIGHT AND TOMORROW WILL KEEP THE AREA
DRY...BUT STARTING WEDNESDAY NIGHT AND CONTINUING DURING THE DAYTIME
PERIOD THURSDAY...A WEAK UPPER LEVEL TROUGH DOWNSTREAM OF THE MAIN
FEATURE AND INCREASING SURFACE MOISTURE WRAPPING INTO A WEAK LOW
PRESSURE SYSTEM MOVING SOUTH OF THE AREA WILL SUPPORT SLIGHTLY
INCREASED CHANCES OF RAINFALL...BUT MAINLY SOUTH AND EAST.  MODEL
SOUNDINGS AND MUCAPE FORECASTS BOTH INDICATE THAT CONVECTION WILL BE
ISOLATED AT BEST OVER THE LOCAL FORECAST AREA...SO WILL JUST CARRY
MAINLY A MENTION OF RAIN WITH SLIGHT CHANCES OF TSRA ADDED FOR
THURSDAY AFTERNOON.

LENNING

&&

.LONG TERM...
336 PM CDT

THURSDAY NIGHT THROUGH TUESDAY...

THE DETERMINISTIC GFS/ECMWF/NAM BEGIN TO DIVERGE QUITE A BIT MORE BY
LATE IN THE WEEK...SO FORECAST UNCERTAINTY INCREASES FOR FRIDAY AND
THE WEEKEND.  THE PRIMARY QUESTION IS THE MOVEMENT OF THE BROAD
UPPER TROUGH OUT OF THE FOUR CORNERS AREA AND INTO THE MIDWEST.  THE
GFS IS BY FAR THE FASTEST IN LIFTING THE TROUGH AND ITS ASSOCIATED
SURFACE FEATURES INTO THE AREA...WHILE THE NAM AND ECMWF KEEP THE
UPPER LOW SPINNING OVER NEW MEXICO INTO FRIDAY NIGHT.

WITH SO MUCH DISAGREEMENT AND NO STRONG SIGNALS EVEN THROUGH THE
WEEKEND...WILL INCLUDE PERIODS OF SLIGHT CHANCE TO CHANCE POPS TO
ACCOUNT FOR THE INFLUENCE OF SHORTWAVE ENERGY BEING EJECTED FROM
THE TROUGH AND OVER THE LOCAL AREA...AND FOR THE POSSIBILITY THAT
THE MAIN LOW ITSELF MOVES OUT EARLIER AS PER THE GFS.

THERE IS ACTUALLY MORE AGREEMENT IN THE MODELS IN BUILDING THE
NEXT DOME OF HIGH PRESSURE OVER THE MIDWEST AND OHIO VALLEY STARTING
EARLY NEXT WEEK...SO AFTER THE POTENTIALLY UNSETTLED WEEKEND AND
EARLY PART OF NEXT WEEK...A DRYING TREND WILL BE REINTRODUCED FOR
TUESDAY.

LENNING

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150748
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
248 AM CDT WED APR 15 2015

.UPDATE...
851 PM CDT

ONLY MINOR ADJUSTMENTS MADE TO GOING FORECAST FOR TONIGHT. GIVEN
HOW DRY THE LOW TO MID-LEVEL ATMOSPHERE IS BASED ON DVN AND ILX
SOUNDING...AND ESPECIALLY AT THE SURFACE GIVEN THE RECORD DRY
AFTERNOON HUMIDITY /13 PERCENT FOR CHICAGO/...TEMPERATURES LIKELY
WILL DROP QUICKLY WHERE THERE ARE PRONOUNCED BREAKS IN THE CIRRUS.
THAT IS A BIT CHALLENGING TO SAY WHERE AND HOW LONG AS THE HOLES
HAVE UNDULATED AND LIKELY WILL THROUGH OVERNIGHT. DVN AND ILX
RAOBS INDICATED QUITE A BIT OF MOISTURE 450MB AND ABOVE...SO WILL
BANK ON SOME CLOUDS MORE OFTEN THAN NOT...BUT CONCEIVABLY SOME
OUTLYING PLACES COULD DROP TO OR A LITTLE BELOW FREEZING IF MORE
PERSISTENT CLEARING WERE TO DEVELOP.

MTF

&&

.SHORT TERM...
336 PM CDT

THROUGH THURSDAY...

AN AMPLIFIED PATTERN ALOFT IS NOT BEING HANDLED IN A VERY SIMILAR
MANNER BY THE VARIOUS DETERMINISTIC MODELS BUT ALL HAVE A BASIC
AGREEMENT IN DIGGING A BROAD UPPER LOW INTO THE FOUR CORNERS REGION
OVER THE NEXT TWO DAYS.  DOWNSTREAM RIDGING WILL SUPPORT CONTINUED
MILD TEMPERATURES AND RELATIVELY LIGHT WINDS LOCALLY...OPENING THE
DOOR FOR MESOSCALE FACTORS LIKE THE COLD LAKE TO BE THE PRIMARY
DRIVER OF TRENDS IN THE NEAR TERM.

THE DOMINANCE OF THE RIDGE TONIGHT AND TOMORROW WILL KEEP THE AREA
DRY...BUT STARTING WEDNESDAY NIGHT AND CONTINUING DURING THE DAYTIME
PERIOD THURSDAY...A WEAK UPPER LEVEL TROUGH DOWNSTREAM OF THE MAIN
FEATURE AND INCREASING SURFACE MOISTURE WRAPPING INTO A WEAK LOW
PRESSURE SYSTEM MOVING SOUTH OF THE AREA WILL SUPPORT SLIGHTLY
INCREASED CHANCES OF RAINFALL...BUT MAINLY SOUTH AND EAST.  MODEL
SOUNDINGS AND MUCAPE FORECASTS BOTH INDICATE THAT CONVECTION WILL BE
ISOLATED AT BEST OVER THE LOCAL FORECAST AREA...SO WILL JUST CARRY
MAINLY A MENTION OF RAIN WITH SLIGHT CHANCES OF TSRA ADDED FOR
THURSDAY AFTERNOON.

LENNING

&&

.LONG TERM...
336 PM CDT

THURSDAY NIGHT THROUGH TUESDAY...

THE DETERMINISTIC GFS/ECMWF/NAM BEGIN TO DIVERGE QUITE A BIT MORE BY
LATE IN THE WEEK...SO FORECAST UNCERTAINTY INCREASES FOR FRIDAY AND
THE WEEKEND.  THE PRIMARY QUESTION IS THE MOVEMENT OF THE BROAD
UPPER TROUGH OUT OF THE FOUR CORNERS AREA AND INTO THE MIDWEST.  THE
GFS IS BY FAR THE FASTEST IN LIFTING THE TROUGH AND ITS ASSOCIATED
SURFACE FEATURES INTO THE AREA...WHILE THE NAM AND ECMWF KEEP THE
UPPER LOW SPINNING OVER NEW MEXICO INTO FRIDAY NIGHT.

WITH SO MUCH DISAGREEMENT AND NO STRONG SIGNALS EVEN THROUGH THE
WEEKEND...WILL INCLUDE PERIODS OF SLIGHT CHANCE TO CHANCE POPS TO
ACCOUNT FOR THE INFLUENCE OF SHORTWAVE ENERGY BEING EJECTED FROM
THE TROUGH AND OVER THE LOCAL AREA...AND FOR THE POSSIBILITY THAT
THE MAIN LOW ITSELF MOVES OUT EARLIER AS PER THE GFS.

THERE IS ACTUALLY MORE AGREEMENT IN THE MODELS IN BUILDING THE
NEXT DOME OF HIGH PRESSURE OVER THE MIDWEST AND OHIO VALLEY STARTING
EARLY NEXT WEEK...SO AFTER THE POTENTIALLY UNSETTLED WEEKEND AND
EARLY PART OF NEXT WEEK...A DRYING TREND WILL BE REINTRODUCED FOR
TUESDAY.

LENNING

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
245 AM CDT

.MARINE...HIGH PRESSURE CENTERED OVER THE SOUTHERN TIP OF JAMES
BAY...EXTENDS ACROSS THE GREAT LAKES TO THE OHIO VALLEY. THIS HIGH
WILL CONTINUE TO MOVE EAST AS ONE LOW PRESSURE SYSTEM DEVELOPS
OVER THE NORTHERN PLAINS AND A SECOND LOW DEVELOPS OVER EASTERN
COLORADO WEDNESDAY MORNING. THE NORTHERN LOW WILL TRACK NORTHEAST
TO HUDSON BAY BY THURSDAY MORNING WHILE THE SOUTHERN LOW MOVES
INTO THE SOUTHERN PLAINS. EASTERLY WINDS TODAY TURN SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL PUSH SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY.

KREIN

&&

.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 150543
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1243 AM CDT WED APR 15 2015

.UPDATE...
851 PM CDT

ONLY MINOR ADJUSTMENTS MADE TO GOING FORECAST FOR TONIGHT. GIVEN
HOW DRY THE LOW TO MID-LEVEL ATMOSPHERE IS BASED ON DVN AND ILX
SOUNDING...AND ESPECIALLY AT THE SURFACE GIVEN THE RECORD DRY
AFTERNOON HUMIDITY /13 PERCENT FOR CHICAGO/...TEMPERATURES LIKELY
WILL DROP QUICKLY WHERE THERE ARE PRONOUNCED BREAKS IN THE CIRRUS.
THAT IS A BIT CHALLENGING TO SAY WHERE AND HOW LONG AS THE HOLES
HAVE UNDULATED AND LIKELY WILL THROUGH OVERNIGHT. DVN AND ILX
RAOBS INDICATED QUITE A BIT OF MOISTURE 450MB AND ABOVE...SO WILL
BANK ON SOME CLOUDS MORE OFTEN THAN NOT...BUT CONCEIVABLY SOME
OUTLYING PLACES COULD DROP TO OR A LITTLE BELOW FREEZING IF MORE
PERSISTENT CLEARING WERE TO DEVELOP.

MTF

&&

.SHORT TERM...
336 PM CDT

THROUGH THURSDAY...

AN AMPLIFIED PATTERN ALOFT IS NOT BEING HANDLED IN A VERY SIMILAR
MANNER BY THE VARIOUS DETERMINISTIC MODELS BUT ALL HAVE A BASIC
AGREEMENT IN DIGGING A BROAD UPPER LOW INTO THE FOUR CORNERS REGION
OVER THE NEXT TWO DAYS.  DOWNSTREAM RIDGING WILL SUPPORT CONTINUED
MILD TEMPERATURES AND RELATIVELY LIGHT WINDS LOCALLY...OPENING THE
DOOR FOR MESOSCALE FACTORS LIKE THE COLD LAKE TO BE THE PRIMARY
DRIVER OF TRENDS IN THE NEAR TERM.

THE DOMINANCE OF THE RIDGE TONIGHT AND TOMORROW WILL KEEP THE AREA
DRY...BUT STARTING WEDNESDAY NIGHT AND CONTINUING DURING THE DAYTIME
PERIOD THURSDAY...A WEAK UPPER LEVEL TROUGH DOWNSTREAM OF THE MAIN
FEATURE AND INCREASING SURFACE MOISTURE WRAPPING INTO A WEAK LOW
PRESSURE SYSTEM MOVING SOUTH OF THE AREA WILL SUPPORT SLIGHTLY
INCREASED CHANCES OF RAINFALL...BUT MAINLY SOUTH AND EAST.  MODEL
SOUNDINGS AND MUCAPE FORECASTS BOTH INDICATE THAT CONVECTION WILL BE
ISOLATED AT BEST OVER THE LOCAL FORECAST AREA...SO WILL JUST CARRY
MAINLY A MENTION OF RAIN WITH SLIGHT CHANCES OF TSRA ADDED FOR
THURSDAY AFTERNOON.

LENNING

&&

.LONG TERM...
336 PM CDT

THURSDAY NIGHT THROUGH TUESDAY...

THE DETERMINISTIC GFS/ECMWF/NAM BEGIN TO DIVERGE QUITE A BIT MORE BY
LATE IN THE WEEK...SO FORECAST UNCERTAINTY INCREASES FOR FRIDAY AND
THE WEEKEND.  THE PRIMARY QUESTION IS THE MOVEMENT OF THE BROAD
UPPER TROUGH OUT OF THE FOUR CORNERS AREA AND INTO THE MIDWEST.  THE
GFS IS BY FAR THE FASTEST IN LIFTING THE TROUGH AND ITS ASSOCIATED
SURFACE FEATURES INTO THE AREA...WHILE THE NAM AND ECMWF KEEP THE
UPPER LOW SPINNING OVER NEW MEXICO INTO FRIDAY NIGHT.

WITH SO MUCH DISAGREEMENT AND NO STRONG SIGNALS EVEN THROUGH THE
WEEKEND...WILL INCLUDE PERIODS OF SLIGHT CHANCE TO CHANCE POPS TO
ACCOUNT FOR THE INFLUENCE OF SHORTWAVE ENERGY BEING EJECTED FROM
THE TROUGH AND OVER THE LOCAL AREA...AND FOR THE POSSIBILITY THAT
THE MAIN LOW ITSELF MOVES OUT EARLIER AS PER THE GFS.

THERE IS ACTUALLY MORE AGREEMENT IN THE MODELS IN BUILDING THE
NEXT DOME OF HIGH PRESSURE OVER THE MIDWEST AND OHIO VALLEY STARTING
EARLY NEXT WEEK...SO AFTER THE POTENTIALLY UNSETTLED WEEKEND AND
EARLY PART OF NEXT WEEK...A DRYING TREND WILL BE REINTRODUCED FOR
TUESDAY.

LENNING

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
130 PM CDT

.MARINE... HIGH PRESSURE OVER THE LAKE TODAY WILL MERGE WITH
CANADIAN HIGH PRESSURE TONIGHT AND SHIFT TO THE EASTERN LAKES ON
WEDNESDAY. THE HIGH WILL THEN GLIDE EAST TO THE ATLANTIC SEABOARD
THURSDAY. MEANWHILE...LOW PRESSURE JUST EAST OF THE NORTHERN ROCKIES
WILL CONTINUE EAST THROUGH THE CANADIAN PRAIRIES WEDNESDAY AND
REACH NORTHERN QUEBEC JUST EAST OF JAMES BAY ON THURSDAY EVENING.
EASTERLY WINDS TONIGHT AND WEDNESDAY TURN SOUTH/SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL SPREAD SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY AFTER A PERIOD OF ONSHORE FLOW
/SOUTH-SOUTHEASTERLY FLOW BEFORE THIS TIME.

KMD

&&

.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 150543
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1243 AM CDT WED APR 15 2015

.UPDATE...
851 PM CDT

ONLY MINOR ADJUSTMENTS MADE TO GOING FORECAST FOR TONIGHT. GIVEN
HOW DRY THE LOW TO MID-LEVEL ATMOSPHERE IS BASED ON DVN AND ILX
SOUNDING...AND ESPECIALLY AT THE SURFACE GIVEN THE RECORD DRY
AFTERNOON HUMIDITY /13 PERCENT FOR CHICAGO/...TEMPERATURES LIKELY
WILL DROP QUICKLY WHERE THERE ARE PRONOUNCED BREAKS IN THE CIRRUS.
THAT IS A BIT CHALLENGING TO SAY WHERE AND HOW LONG AS THE HOLES
HAVE UNDULATED AND LIKELY WILL THROUGH OVERNIGHT. DVN AND ILX
RAOBS INDICATED QUITE A BIT OF MOISTURE 450MB AND ABOVE...SO WILL
BANK ON SOME CLOUDS MORE OFTEN THAN NOT...BUT CONCEIVABLY SOME
OUTLYING PLACES COULD DROP TO OR A LITTLE BELOW FREEZING IF MORE
PERSISTENT CLEARING WERE TO DEVELOP.

MTF

&&

.SHORT TERM...
336 PM CDT

THROUGH THURSDAY...

AN AMPLIFIED PATTERN ALOFT IS NOT BEING HANDLED IN A VERY SIMILAR
MANNER BY THE VARIOUS DETERMINISTIC MODELS BUT ALL HAVE A BASIC
AGREEMENT IN DIGGING A BROAD UPPER LOW INTO THE FOUR CORNERS REGION
OVER THE NEXT TWO DAYS.  DOWNSTREAM RIDGING WILL SUPPORT CONTINUED
MILD TEMPERATURES AND RELATIVELY LIGHT WINDS LOCALLY...OPENING THE
DOOR FOR MESOSCALE FACTORS LIKE THE COLD LAKE TO BE THE PRIMARY
DRIVER OF TRENDS IN THE NEAR TERM.

THE DOMINANCE OF THE RIDGE TONIGHT AND TOMORROW WILL KEEP THE AREA
DRY...BUT STARTING WEDNESDAY NIGHT AND CONTINUING DURING THE DAYTIME
PERIOD THURSDAY...A WEAK UPPER LEVEL TROUGH DOWNSTREAM OF THE MAIN
FEATURE AND INCREASING SURFACE MOISTURE WRAPPING INTO A WEAK LOW
PRESSURE SYSTEM MOVING SOUTH OF THE AREA WILL SUPPORT SLIGHTLY
INCREASED CHANCES OF RAINFALL...BUT MAINLY SOUTH AND EAST.  MODEL
SOUNDINGS AND MUCAPE FORECASTS BOTH INDICATE THAT CONVECTION WILL BE
ISOLATED AT BEST OVER THE LOCAL FORECAST AREA...SO WILL JUST CARRY
MAINLY A MENTION OF RAIN WITH SLIGHT CHANCES OF TSRA ADDED FOR
THURSDAY AFTERNOON.

LENNING

&&

.LONG TERM...
336 PM CDT

THURSDAY NIGHT THROUGH TUESDAY...

THE DETERMINISTIC GFS/ECMWF/NAM BEGIN TO DIVERGE QUITE A BIT MORE BY
LATE IN THE WEEK...SO FORECAST UNCERTAINTY INCREASES FOR FRIDAY AND
THE WEEKEND.  THE PRIMARY QUESTION IS THE MOVEMENT OF THE BROAD
UPPER TROUGH OUT OF THE FOUR CORNERS AREA AND INTO THE MIDWEST.  THE
GFS IS BY FAR THE FASTEST IN LIFTING THE TROUGH AND ITS ASSOCIATED
SURFACE FEATURES INTO THE AREA...WHILE THE NAM AND ECMWF KEEP THE
UPPER LOW SPINNING OVER NEW MEXICO INTO FRIDAY NIGHT.

WITH SO MUCH DISAGREEMENT AND NO STRONG SIGNALS EVEN THROUGH THE
WEEKEND...WILL INCLUDE PERIODS OF SLIGHT CHANCE TO CHANCE POPS TO
ACCOUNT FOR THE INFLUENCE OF SHORTWAVE ENERGY BEING EJECTED FROM
THE TROUGH AND OVER THE LOCAL AREA...AND FOR THE POSSIBILITY THAT
THE MAIN LOW ITSELF MOVES OUT EARLIER AS PER THE GFS.

THERE IS ACTUALLY MORE AGREEMENT IN THE MODELS IN BUILDING THE
NEXT DOME OF HIGH PRESSURE OVER THE MIDWEST AND OHIO VALLEY STARTING
EARLY NEXT WEEK...SO AFTER THE POTENTIALLY UNSETTLED WEEKEND AND
EARLY PART OF NEXT WEEK...A DRYING TREND WILL BE REINTRODUCED FOR
TUESDAY.

LENNING

&&

.AVIATION...

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

* EASTERLY WINDS INCREASING OVER 10 KT BY MID-MORNING WEDNESDAY
  AND BECOMING GUSTY IN THE AFTERNOON.

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

HIGH PRESSURE CENTERED OVER LOWER MICHIGAN WILL SPREAD NORTHEAST
TO QUEBEC AND THE EASTERN GREAT LAKES THROUGH THE DAY WEDNESDAY.
WITH TROUGHING DEVELOPING OVER THE CENTRAL PLAINS...THIS WILL
ALLOW FOR STRONGER EASTERLY WINDS ON WEDNESDAY...WITH SUSTAINED
SPEEDS IN EXCESS OF 10 KT. GUSTS TO 18KT ARE LIKELY IN THE
AFTERNOON AS WELL. HIGH CLOUDS WILL THICKEN AND LOWER THROUGH THE
DAY WEDNESDAY BUT ANY LIGHT SHOWER ACTIVITY IS EXPECTED TO REMAIN
TO THE SOUTH AND SOUTHEAST OF THE TERMINALS THROUGH THE TAF
PERIOD.

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

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

THURSDAY...VFR. EAST WINDS LIKELY AROUND 10 KT.
FRIDAY...SLIGHT CHANCE OF SHOWERS. SOUTHEAST WINDS.
SATURDAY...NORTHEAST WINDS.
SUNDAY...CHANCE OF SHOWERS. EAST WINDS.
MONDAY...CHANCE OF SHOWERS. NORTHWEST WINDS.

MTF

&&

.MARINE...
130 PM CDT

.MARINE... HIGH PRESSURE OVER THE LAKE TODAY WILL MERGE WITH
CANADIAN HIGH PRESSURE TONIGHT AND SHIFT TO THE EASTERN LAKES ON
WEDNESDAY. THE HIGH WILL THEN GLIDE EAST TO THE ATLANTIC SEABOARD
THURSDAY. MEANWHILE...LOW PRESSURE JUST EAST OF THE NORTHERN ROCKIES
WILL CONTINUE EAST THROUGH THE CANADIAN PRAIRIES WEDNESDAY AND
REACH NORTHERN QUEBEC JUST EAST OF JAMES BAY ON THURSDAY EVENING.
EASTERLY WINDS TONIGHT AND WEDNESDAY TURN SOUTH/SOUTHEAST
THURSDAY. ANOTHER WEAK LOW WILL PUSH NORTHEAST ACROSS THE LAKE
FRIDAY EVENING AHEAD OF A COLD FRONT THAT WILL SPREAD SOUTH DOWN
THE LAKE FRIDAY NIGHT INTO SATURDAY MORNING. THIS FRONT WILL TURN
WINDS AROUND TO THE NORTH SATURDAY AFTER A PERIOD OF ONSHORE FLOW
/SOUTH-SOUTHEASTERLY FLOW BEFORE THIS TIME.

KMD

&&

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

$$

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