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000
FXUS63 KLOT 160255
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
955 PM CDT TUE APR 15 2014

.DISCUSSION...
856 PM CDT

VERY MINOR ADJUSTMENTS TONIGHT. SFC RIDGE HAS BECOME RATHER
DIFFUSE...ALTHOUGH OBS WOULD SUGGEST THE CENTER IS PLACED ACROSS
NORTHERN INDIANA. THE SFC RIDGE INFLUENCE STRETCHES
NORTH/NORTHWEST TO NORTHWEST ONTARIO THEN SOUTH THROUGH THE TENN
VALLEY. HOWEVER JUST WEST OF THIS FEATURE A SFC LOW CONTINUES TO
DEVELOP AND SLIDE EAST TOWARDS THE WESTERN GREAT LAKES. THE
GRADIENT IS MUCH TIGHTER JUST WEST OF THE CWFA...SO IT APPEARS THE
LIGHT AND VARIABLE WINDS WILL QUICKLY TURN SOUTHEASTERLY AND
INCREASE BY DAYBREAK.

EXPECT TEMPS TO STILL RADIATE EFFICIENTLY OVER THE NEXT SEVERAL
HOURS...HOWEVER THE RATE OF FALL MAY DECREASE ARND MIDNIGHT OR
SHORTLY AFTER AS SOUTHEAST WINDS BEGIN TO INCREASE AND ENOUGH
FRICTION ALOFT MAY INHIBIT THE ABILITY FOR THE SFC TO CONTINUE TO
COOL. A FEW LOCATIONS MAY EVEN EXPERIENCE TEMPS RISING A DEGREE OR
TWO...MAINLY IN OUR WESTERN CWFA AFTER MIDNIGHT. OTHERWISE EXPECT
TEMPS TO STILL FALL INTO THE MID/UPR 20S TO LOWER 30S CLOSER TO
THE LAKE.

BEACHLER

//PREV DISCUSSION...
340 PM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH CLOUD COVER AND TEMPS
THIS EVENING...SOME UP AND DOWN WITH TEMPS OVER THE NEXT COUPLE OF
DAYS...AND THEN INCREASING CHANCES FOR PRECIP LATE IN THE WORK
WEEK.

IN THE NEAR TERM...CLOUD COVER REMAINS OVER THE CWA AND HAS
REMAINED ON THE THICKER SIDE FOR MOST OF THE DAY. THIS HAS LIMITED
DAYTIME WARMING TODAY...WITH TEMPS STRUGGLING TO GET INTO THE
UPPER 30S. ALTHOUGH CLOUD COVER IS ON A DIMINISHING TREND...DID
KEEP AT LEAST SOME PARTLY CLOUDY MENTION INTO EARLY THIS EVENING
WITH THIS STRATOCU DECK CONTINUING A SLOW DIMINISHING TREND. ANY
REMAINING ISOL FLURRIES ACROSS THE AREA WILL LIKEWISE
DIMINISH...BUT MORE LIKELY AT A QUICKER RATE THAN THE CLOUD COVER.
THEN WITH MID/HIGH LEVEL CLOUD COVER TO THE WEST/NORTHWEST
REMAINING OFF TO THE WEST...A PERIOD OF MOSTLY CLEAR SKIES WILL BE
OBSERVED TONIGHT. DESPITE WARMING ALOFT TONIGHT...SURFACE RIDGE
WITH RELAXED GRADIENT AND CLEAR SKIES SHOULD ALLOW FOR ANOTHER
COLD NIGHT TONIGHT WITH LOW TEMPS IN THE 20S EXPECTED FOR MOST OF
THE CWA. CONFIDENCE IS SOMEWHAT LOWER FOR LOW TEMPS ACROSS THE
WESTERN CWA TONIGHT...AS SOUTHERLY PICKS BACK UP WITH THE SURFACE
RIDGE QUICKLY SHIFTING TO THE EAST OF THE CWA.
NONETHELESS...ANOTHER NIGHT WITH TEMPS WELL BELOW NORMAL WILL
LIKELY BE OBSERVED.

EXPECT WEDNESDAY TO BE DRY...AS WAA PERSISTS AND HELPS START A
TREND TOWARDS MORE NORMAL TEMPS WITH HIGH TEMPS EXPECTED TO BE IN
THE 50S. THIS WARMER AIR WILL BE RIDING ALONG SOME STRONG
SOUTHERLY WINDS...AS PRESSURE GRADIENT REALLY TIGHTENS UP AND
SPEEDS INCREASE INTO THE AFTERNOON. WITH MID/UPPER LEVEL TROUGH
PUSHING EAST THROUGH THE CENTRAL PLAINS DURING THE DAY...HIGH
LEVEL CLOUD COVER WILL BE ON THE INCREASE. FORECAST GUIDANCE IN
AGREEMENT WITH THIS MID LEVEL TROUGH TO SWING EAST JUST NORTH OF
THE CWA WEDNESDAY NIGHT...WITH BEST FORCING AND PRECIP TO STAY
NORTH OF THE CWA. HAVE KEPT THE CWA DRY BUT WILL NEED TO MONITOR
THE POTENTIAL FOR SOME WAA PRECIP TO POSSIBLE DEVELOP ACROSS
SOUTHERN WISCONSIN...WHICH COULD CLIP AREAS RIGHT ALONG THE BORDER
IN NORTHERN ILLINOIS. ATTENDANT SURFACE LOW WILL LIFT THROUGH
SOUTHERN WISCONSIN THURSDAY MORNING WHILE WEAKENING...BUT WITH
MOST OF THE CWA EXPECTED TO BE IN THE WARM SECTOR. IN THIS WARMER
AIR MASS...TEMPS WILL BE IN THE 50S AND LOW 60S ACROSS THE
SOUTHERN HALF OF THE CWA ON THURSDAY. IT DOES LOOK LIKE SOME
SLIGHT COOLING WILL OCCUR LATE IN THE DAY/EVENING AS A WEAK
FRONT/TROUGH MOVES THROUGH THE CWA. AS THIS IS
OCCURRING...APPROACHING LONGWAVE TROUGH WILL HELP USHER SOME WEAK
IMPULSES WHICH SHOULD AID IN THE DEVELOPMENT OF RAIN THURSDAY
EVENING/NIGHT. DID INCREASE POPS AND COVERAGE OF POPS THURSDAY
NIGHT AS PRECIP IS APPEARING TO BE MORE LIKELY...BUT WITH SOME
UNCERTAINTY AS TO THE EXACT PLACEMENT OF PRECIP AXIS. COLDER AIR
WILL BE TRYING TO WORK SOUTH ACROSS THE AREA THURSDAY NIGHT INTO
FRIDAY MORNING...WITH THE RAIN/SNOW LINE TRYING TO INCH ITS WAY
CLOSE TO THE CWA. ALTHOUGH...IT DOES APPEAR THAT THIS LINE WILL
REMAIN NORTH OF THE CWA...AS DEEPER MOISTURE MOISTURE/CRYSTALS
WILL BE LOST BY THE TIME THERMAL PROFILES WOULD BE SUPPORTIVE OF
SNOW. DRYING TREND WILL OCCUR DURING THE DAY FRIDAY WITH SLIGHTLY
COOLER TEMPS IN THE 40S AND 50S. EXPECT THIS RETURN TO COOLER
WEATHER TO BRIEF AS WARMING TREND IS EXPECTED INTO THE WEEKEND.

RODRIGUEZ

&&

.AVIATION...

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

* LIGHT SOUTH-SOUTHEAST WINDS OVERNIGHT BECOMING STRONG SOUTH
  WEDNESDAY...WITH GUSTS 30-35 KT POSSIBLE IN THE AFTERNOON.

* POTENTIAL FOR LLWS LATE WEDNESDAY EVENING AS GUSTS
  DIMINISH...WITH WINDS 20045-50KT AROUND 2000 FT AGL.

RATZER

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

SURFACE HIGH PRESSURE RIDGE ALONG IL/IN BORDER AND OVER SOUTHERN
LAKE MICHIGAN WILL CONTINUE TO DRIFT EAST THIS EVENING WILL ALLOW
DECREASING WESTERLY WINDS TO SHIFT TO THE SOUTHEAST OVER THE NEXT
1-3 HRS. LAKE BREEZE HAD DEVELOPED AND MOVED AS FAR INLAND AS MDW
BEFORE RETREATING A BIT...BUT DEPARTURE OF RIDGE AXIS TO EAST
SHOULD ALLOW FOR A LARGE SCALE SHIFT TO SOUTHEAST WINDS ACROSS THE
AREA.

FOCUS THEN SHIFTS TO STRONG SOUTH WINDS EXPECTED WEDNESDAY IN
RESPONSE TO AN AREA OF LOW PRESSURE DEVELOPING INTO THE UPPER
MIDWEST. TIGHTENING PRESSURE GRADIENT APPEARS TO SUPPORT SUSTAINED
WINDS AROUND 20 KT BY AFTERNOON...WITH GUSTS INTO THE 30-35 KT
RANGE POSSIBLE PER FORECAST SOUNDINGS DEPICTING MIXING TO
4000-5000 FT AGL. SURFACE LOW LIFTS INTO WESTERN WISCONSIN
WEDNESDAY EVENING ALLOWING THE GRADIENT TO EASE SLIGHTLY. DEGREE
OF BOUNDARY LAYER DECOUPLING SOMEWHAT UNCERTAIN AFTER SUNSET WITH
STRONG WINDS CONTINUING...THOUGH BY LATE EVENING EXPECT DECREASED
GUSTS. THIS SETS UP THE POTENTIAL FOR NON-CONVECTIVE LOW LEVEL
WIND SHEAR HOWEVER...WITH MODELS DEPICTING LOW LEVEL JET FROM
ABOUT 200 DEGREES AT 45-50KT AT 2000 FT AGL.

OTHERWISE...CURRENT VFR STRATOCU DECK EXPECTED TO ERODE QUICKLY
EARLY THIS EVENING WITH STRONG SUBSIDENCE DEVELOPING AND DRY AIR
IN PLACE. MID/HIGH VFR CLOUDS ALREADY RACING SOUTHEAST ACROSS THE
NORTHERN PLAINS SHOULD RESULT IN INCREASING MID-CLOUDS LATER
TONIGHT. MODEL TIME/HEIGHT DEPICTIONS INDICATE VFR MID DECK WILL
REMAIN ACROSS AREA IN 10-15 KFT RANGE THROUGH WEDNESDAY. LOW
CLOUDS WILL BE ABSENT...WITH SOUTHERN PORTION OF SURFACE HIGH
PRESSURE RIDGE EFFECTIVELY BLOCKING MOISTURE RETURN FROM THE GULF
OF MEXICO.

RATZER

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

* MEDIUM CONFIDENCE IN GUSTS ABATING AND TRUE LLWS CONDITIONS
  DEVELOPING WEDNESDAY EVENING.

* HIGH CONFIDENCE ALL OTHER ELEMENTS.

RATZER

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

THURSDAY...CHC RA LATE AFTN/NGT. MAINLY VFR.

FRIDAY...CHC RA/MVFR EARLY...THEN VFR.

SATURDAY...VFR.

SUNDAY...CHC RA.

MONDAY...SLGT CHC RA.

RATZER

&&

.MARINE...
303 PM CDT

HIGH PRESSURE STRETCHED FROM MANITOBA TO THE WESTERN GULF COAST WILL
WORK EASTWARD TONIGHT AND CONSOLIDATE INTO A BETTER ORGANIZED AREA
OF HIGH PRESSURE OVER THE OHIO VALLEY INTO WEDNESDAY MORNING. SOME
RESIDUAL GUSTY WINDS ACROSS THE FAR EASTERN SECTION OF LAKE MICHIGAN
THIS AFTERNOON WILL DIMINISH INTO THE EVENING AS THE PRESSURE
GRADIENT WEAKENS. SHOULD SEE QUITE A BIT OF VARIABILITY IN WIND
DIRECTION THIS EVENING BEFORE A STEADIER SOUTH WIND DEVELOPS OVER
THE SOUTHERN TWO THIRDS OF THE LAKE OVERNIGHT...WITH AN EASTERLY
DIRECTION FAR NORTH THANKS TO A DEVELOPING WARM FRONTAL BOUNDARY.
SOUTH TO SOUTHEAST WINDS WILL INCREASE MARKEDLY WEDNESDAY MORNING
AND SHOULD EASILY GUSTS TO 30 KT ACROSS CENTRAL AND SOUTHERN
PORTIONS OF THE LAKE...ESPECIALLY OVER THE WESTERN HALF. DO SEE SOME
POTENTIAL FOR GALES THOUGH THEY MAY BE SHORT LIVED OR
INFREQUENT...OR CONFINED TO THE NEARSHORE WATERS GIVEN THE SHORE
PARALLEL FLOW SLIGHT ONSHORE COMPONENT SUGGESTING ANY LAKEWARD
EXTENT OF MIXING FROM LAND WOULD BE MINIMAL. IL/IN NEARSHORE WATERS
WILL SOLIDLY FALL INTO SMALL CRAFT CRITERIA. CANNOT RULE OUT GALES
THERE AS WELL BUT THE STRONGER WINDS JUST ABOVE THE SURFACE ARE
FOCUSED FURTHER WEST OF THE LAKE BUT WILL NEED TO MONITOR.

LOW PRESSURE WILL TRACK FROM NEBRASKA/SOUTH DAKOTA TO NORTHERN LAKE
MICHIGAN INTO THURSDAY BRINGING A COOL FRONT DOWN THE LAKE LATER
THURSDAY. THIS WILL SHIFT WINDS TO THE NORTH. THE LOW WILL BE
WEAKENING AS IT PASSES AND THE PRESSURE GRADIENT BETWEEN IT AND HIGH
PRESSURE TO THE NORTH WILL BE FAIRLY BAGGY. THIS COMBINED WITH A
FAIRLY WEAK PUSH OF COLDER AIR WILL RESULT IN RATHER MODEST WINDS
FOR A FRONTAL PASSAGE AND SPEEDS WILL LIKELY BE QUITE A BIT WEAKER
WITH THE FRONTAL PASSAGE LATER THURSDAY INTO FRIDAY. HIGH PRESSURE
RIDGING THEN WORKS EASTWARD ACROSS THE LAKE FRIDAY AND SATURDAY
KEEPING WINDS ON THE LIGHT SIDE. ANOTHER WEAK LOW MAY MOVE INTO THE
REGION LATER IN THE WEEKEND.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM WEDNESDAY TO 4 AM THURSDAY.

&&

$$

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

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









000
FXUS63 KLOT 160202
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
902 PM CDT TUE APR 15 2014

.DISCUSSION...
856 PM CDT

VERY MINOR ADJUSTMENTS TONIGHT. SFC RIDGE HAS BECOME RATHER
DIFFUSE...ALTHOUGH OBS WOULD SUGGEST THE CENTER IS PLACED ACROSS
NORTHERN INDIANA. THE SFC RIDGE INFLUENCE STRETCHES
NORTH/NORTHWEST TO NORTHWEST ONTARIO THEN SOUTH THROUGH THE TENN
VALLEY. HOWEVER JUST WEST OF THIS FEATURE A SFC LOW CONTINUES TO
DEVELOP AND SLIDE EAST TOWARDS THE WESTERN GREAT LAKES. THE
GRADIENT IS MUCH TIGHTER JUST WEST OF THE CWFA...SO IT APPEARS THE
LIGHT AND VARIABLE WINDS WILL QUICKLY TURN SOUTHEASTERLY AND
INCREASE BY DAYBREAK.

EXPECT TEMPS TO STILL RADIATE EFFICIENTLY OVER THE NEXT SEVERAL
HOURS...HOWEVER THE RATE OF FALL MAY DECREASE ARND MIDNIGHT OR
SHORTLY AFTER AS SOUTHEAST WINDS BEGIN TO INCREASE AND ENOUGH
FRICTION ALOFT MAY INHIBIT THE ABILITY FOR THE SFC TO CONTINUE TO
COOL. A FEW LOCATIONS MAY EVEN EXPERIENCE TEMPS RISING A DEGREE OR
TWO...MAINLY IN OUR WESTERN CWFA AFTER MIDNIGHT. OTHERWISE EXPECT
TEMPS TO STILL FALL INTO THE MID/UPR 20S TO LOWER 30S CLOSER TO
THE LAKE.

BEACHLER

&&

.PREV DISCUSSION...
340 PM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH CLOUD COVER AND TEMPS
THIS EVENING...SOME UP AND DOWN WITH TEMPS OVER THE NEXT COUPLE OF
DAYS...AND THEN INCREASING CHANCES FOR PRECIP LATE IN THE WORK
WEEK.

IN THE NEAR TERM...CLOUD COVER REMAINS OVER THE CWA AND HAS
REMAINED ON THE THICKER SIDE FOR MOST OF THE DAY. THIS HAS LIMITED
DAYTIME WARMING TODAY...WITH TEMPS STRUGGLING TO GET INTO THE
UPPER 30S. ALTHOUGH CLOUD COVER IS ON A DIMINISHING TREND...DID
KEEP AT LEAST SOME PARTLY CLOUDY MENTION INTO EARLY THIS EVENING
WITH THIS STRATOCU DECK CONTINUING A SLOW DIMINISHING TREND. ANY
REMAINING ISOL FLURRIES ACROSS THE AREA WILL LIKEWISE
DIMINISH...BUT MORE LIKELY AT A QUICKER RATE THAN THE CLOUD COVER.
THEN WITH MID/HIGH LEVEL CLOUD COVER TO THE WEST/NORTHWEST
REMAINING OFF TO THE WEST...A PERIOD OF MOSTLY CLEAR SKIES WILL BE
OBSERVED TONIGHT. DESPITE WARMING ALOFT TONIGHT...SURFACE RIDGE
WITH RELAXED GRADIENT AND CLEAR SKIES SHOULD ALLOW FOR ANOTHER
COLD NIGHT TONIGHT WITH LOW TEMPS IN THE 20S EXPECTED FOR MOST OF
THE CWA. CONFIDENCE IS SOMEWHAT LOWER FOR LOW TEMPS ACROSS THE
WESTERN CWA TONIGHT...AS SOUTHERLY PICKS BACK UP WITH THE SURFACE
RIDGE QUICKLY SHIFTING TO THE EAST OF THE CWA.
NONETHELESS...ANOTHER NIGHT WITH TEMPS WELL BELOW NORMAL WILL
LIKELY BE OBSERVED.

EXPECT WEDNESDAY TO BE DRY...AS WAA PERSISTS AND HELPS START A
TREND TOWARDS MORE NORMAL TEMPS WITH HIGH TEMPS EXPECTED TO BE IN
THE 50S. THIS WARMER AIR WILL BE RIDING ALONG SOME STRONG
SOUTHERLY WINDS...AS PRESSURE GRADIENT REALLY TIGHTENS UP AND
SPEEDS INCREASE INTO THE AFTERNOON. WITH MID/UPPER LEVEL TROUGH
PUSHING EAST THROUGH THE CENTRAL PLAINS DURING THE DAY...HIGH
LEVEL CLOUD COVER WILL BE ON THE INCREASE. FORECAST GUIDANCE IN
AGREEMENT WITH THIS MID LEVEL TROUGH TO SWING EAST JUST NORTH OF
THE CWA WEDNESDAY NIGHT...WITH BEST FORCING AND PRECIP TO STAY
NORTH OF THE CWA. HAVE KEPT THE CWA DRY BUT WILL NEED TO MONITOR
THE POTENTIAL FOR SOME WAA PRECIP TO POSSIBLE DEVELOP ACROSS
SOUTHERN WISCONSIN...WHICH COULD CLIP AREAS RIGHT ALONG THE BORDER
IN NORTHERN ILLINOIS. ATTENDANT SURFACE LOW WILL LIFT THROUGH
SOUTHERN WISCONSIN THURSDAY MORNING WHILE WEAKENING...BUT WITH
MOST OF THE CWA EXPECTED TO BE IN THE WARM SECTOR. IN THIS WARMER
AIR MASS...TEMPS WILL BE IN THE 50S AND LOW 60S ACROSS THE
SOUTHERN HALF OF THE CWA ON THURSDAY. IT DOES LOOK LIKE SOME
SLIGHT COOLING WILL OCCUR LATE IN THE DAY/EVENING AS A WEAK
FRONT/TROUGH MOVES THROUGH THE CWA. AS THIS IS
OCCURRING...APPROACHING LONGWAVE TROUGH WILL HELP USHER SOME WEAK
IMPULSES WHICH SHOULD AID IN THE DEVELOPMENT OF RAIN THURSDAY
EVENING/NIGHT. DID INCREASE POPS AND COVERAGE OF POPS THURSDAY
NIGHT AS PRECIP IS APPEARING TO BE MORE LIKELY...BUT WITH SOME
UNCERTAINTY AS TO THE EXACT PLACEMENT OF PRECIP AXIS. COLDER AIR
WILL BE TRYING TO WORK SOUTH ACROSS THE AREA THURSDAY NIGHT INTO
FRIDAY MORNING...WITH THE RAIN/SNOW LINE TRYING TO INCH ITS WAY
CLOSE TO THE CWA. ALTHOUGH...IT DOES APPEAR THAT THIS LINE WILL
REMAIN NORTH OF THE CWA...AS DEEPER MOISTURE MOISTURE/CRYSTALS
WILL BE LOST BY THE TIME THERMAL PROFILES WOULD BE SUPPORTIVE OF
SNOW. DRYING TREND WILL OCCUR DURING THE DAY FRIDAY WITH SLIGHTLY
COOLER TEMPS IN THE 40S AND 50S. EXPECT THIS RETURN TO COOLER
WEATHER TO BRIEF AS WARMING TREND IS EXPECTED INTO THE WEEKEND.

RODRIGUEZ

&&

.AVIATION...

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

* LIGHT WEST WINDS SHIFTING SOUTHEAST THIS EVENING.

* STRONG SOUTH WINDS WEDNESDAY...GUSTS 30-35 KT POSSIBLE IN THE
  AFTERNOON.

* POTENTIAL FOR LLWS LATE WEDNESDAY EVENING AS GUSTS
  DIMINISH...WITH WINDS 20045-50KT AROUND 2000 FT AGL.

RATZER

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

SURFACE HIGH PRESSURE RIDGE ALONG IL/IN BORDER AND OVER SOUTHERN
LAKE MICHIGAN WILL CONTINUE TO DRIFT EAST THIS EVENING WILL ALLOW
DECREASING WESTERLY WINDS TO SHIFT TO THE SOUTHEAST OVER THE NEXT
1-3 HRS. LAKE BREEZE HAD DEVELOPED AND MOVED AS FAR INLAND AS MDW
BEFORE RETREATING A BIT...BUT DEPARTURE OF RIDGE AXIS TO EAST
SHOULD ALLOW FOR A LARGE SCALE SHIFT TO SOUTHEAST WINDS ACROSS THE
AREA.

FOCUS THEN SHIFTS TO STRONG SOUTH WINDS EXPECTED WEDNESDAY IN
RESPONSE TO AN AREA OF LOW PRESSURE DEVELOPING INTO THE UPPER
MIDWEST. TIGHTENING PRESSURE GRADIENT APPEARS TO SUPPORT SUSTAINED
WINDS AROUND 20 KT BY AFTERNOON...WITH GUSTS INTO THE 30-35 KT
RANGE POSSIBLE PER FORECAST SOUNDINGS DEPICTING MIXING TO
4000-5000 FT AGL. SURFACE LOW LIFTS INTO WESTERN WISCONSIN
WEDNESDAY EVENING ALLOWING THE GRADIENT TO EASE SLIGHTLY. DEGREE
OF BOUNDARY LAYER DECOUPLING SOMEWHAT UNCERTAIN AFTER SUNSET WITH
STRONG WINDS CONTINUING...THOUGH BY LATE EVENING EXPECT DECREASED
GUSTS. THIS SETS UP THE POTENTIAL FOR NON-CONVECTIVE LOW LEVEL
WIND SHEAR HOWEVER...WITH MODELS DEPICTING LOW LEVEL JET FROM
ABOUT 200 DEGREES AT 45-50KT AT 2000 FT AGL.

OTHERWISE...CURRENT VFR STRATOCU DECK EXPECTED TO ERODE QUICKLY
EARLY THIS EVENING WITH STRONG SUBSIDENCE DEVELOPING AND DRY AIR
IN PLACE. MID/HIGH VFR CLOUDS ALREADY RACING SOUTHEAST ACROSS THE
NORTHERN PLAINS SHOULD RESULT IN INCREASING MID-CLOUDS LATER
TONIGHT. MODEL TIME/HEIGHT DEPICTIONS INDICATE VFR MID DECK WILL
REMAIN ACROSS AREA IN 10-15 KFT RANGE THROUGH WEDNESDAY. LOW
CLOUDS WILL BE ABSENT...WITH SOUTHERN PORTION OF SURFACE HIGH
PRESSURE RIDGE EFFECTIVELY BLOCKING MOISTURE RETURN FROM THE GULF
OF MEXICO.

RATZER

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

* MEDIUM CONFIDENCE IN TIMING WIND SHIFT FROM LIGHT WEST TO LIGHT
  SOUTHEAST THIS EVENING.

* MEDIUM CONFIDENCE IN GUSTS ABATING AND TRUE LLWS CONDITIONS
  DEVELOPING WEDNESDAY EVENING.

* HIGH CONFIDENCE ALL OTHER ELEMENTS.

RATZER

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

THURSDAY...CHC RA LATE AFTN/NGT. MAINLY VFR.

FRIDAY...CHC RA/MVFR EARLY...THEN VFR.

SATURDAY...VFR.

SUNDAY...CHC RA.

MONDAY...SLGT CHC RA.

RATZER

&&

.MARINE...
303 PM CDT

HIGH PRESSURE STRETCHED FROM MANITOBA TO THE WESTERN GULF COAST WILL
WORK EASTWARD TONIGHT AND CONSOLIDATE INTO A BETTER ORGANIZED AREA
OF HIGH PRESSURE OVER THE OHIO VALLEY INTO WEDNESDAY MORNING. SOME
RESIDUAL GUSTY WINDS ACROSS THE FAR EASTERN SECTION OF LAKE MICHIGAN
THIS AFTERNOON WILL DIMINISH INTO THE EVENING AS THE PRESSURE
GRADIENT WEAKENS. SHOULD SEE QUITE A BIT OF VARIABILITY IN WIND
DIRECTION THIS EVENING BEFORE A STEADIER SOUTH WIND DEVELOPS OVER
THE SOUTHERN TWO THIRDS OF THE LAKE OVERNIGHT...WITH AN EASTERLY
DIRECTION FAR NORTH THANKS TO A DEVELOPING WARM FRONTAL BOUNDARY.
SOUTH TO SOUTHEAST WINDS WILL INCREASE MARKEDLY WEDNESDAY MORNING
AND SHOULD EASILY GUSTS TO 30 KT ACROSS CENTRAL AND SOUTHERN
PORTIONS OF THE LAKE...ESPECIALLY OVER THE WESTERN HALF. DO SEE SOME
POTENTIAL FOR GALES THOUGH THEY MAY BE SHORT LIVED OR
INFREQUENT...OR CONFINED TO THE NEARSHORE WATERS GIVEN THE SHORE
PARALLEL FLOW SLIGHT ONSHORE COMPONENT SUGGESTING ANY LAKEWARD
EXTENT OF MIXING FROM LAND WOULD BE MINIMAL. IL/IN NEARSHORE WATERS
WILL SOLIDLY FALL INTO SMALL CRAFT CRITERIA. CANNOT RULE OUT GALES
THERE AS WELL BUT THE STRONGER WINDS JUST ABOVE THE SURFACE ARE
FOCUSED FURTHER WEST OF THE LAKE BUT WILL NEED TO MONITOR.

LOW PRESSURE WILL TRACK FROM NEBRASKA/SOUTH DAKOTA TO NORTHERN LAKE
MICHIGAN INTO THURSDAY BRINGING A COOL FRONT DOWN THE LAKE LATER
THURSDAY. THIS WILL SHIFT WINDS TO THE NORTH. THE LOW WILL BE
WEAKENING AS IT PASSES AND THE PRESSURE GRADIENT BETWEEN IT AND HIGH
PRESSURE TO THE NORTH WILL BE FAIRLY BAGGY. THIS COMBINED WITH A
FAIRLY WEAK PUSH OF COLDER AIR WILL RESULT IN RATHER MODEST WINDS
FOR A FRONTAL PASSAGE AND SPEEDS WILL LIKELY BE QUITE A BIT WEAKER
WITH THE FRONTAL PASSAGE LATER THURSDAY INTO FRIDAY. HIGH PRESSURE
RIDGING THEN WORKS EASTWARD ACROSS THE LAKE FRIDAY AND SATURDAY
KEEPING WINDS ON THE LIGHT SIDE. ANOTHER WEAK LOW MAY MOVE INTO THE
REGION LATER IN THE WEEKEND.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM WEDNESDAY TO 4 AM THURSDAY.

&&

$$

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

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







000
FXUS63 KLOT 152340
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
640 PM CDT TUE APR 15 2014

.DISCUSSION...
340 PM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH CLOUD COVER AND TEMPS
THIS EVENING...SOME UP AND DOWN WITH TEMPS OVER THE NEXT COUPLE OF
DAYS...AND THEN INCREASING CHANCES FOR PRECIP LATE IN THE WORK
WEEK.

IN THE NEAR TERM...CLOUD COVER REMAINS OVER THE CWA AND HAS
REMAINED ON THE THICKER SIDE FOR MOST OF THE DAY. THIS HAS LIMITED
DAYTIME WARMING TODAY...WITH TEMPS STRUGGLING TO GET INTO THE
UPPER 30S. ALTHOUGH CLOUD COVER IS ON A DIMINISHING TREND...DID
KEEP AT LEAST SOME PARTLY CLOUDY MENTION INTO EARLY THIS EVENING
WITH THIS STRATOCU DECK CONTINUING A SLOW DIMINISHING TREND. ANY
REMAINING ISOL FLURRIES ACROSS THE AREA WILL LIKEWISE
DIMINISH...BUT MORE LIKELY AT A QUICKER RATE THAN THE CLOUD COVER.
THEN WITH MID/HIGH LEVEL CLOUD COVER TO THE WEST/NORTHWEST
REMAINING OFF TO THE WEST...A PERIOD OF MOSTLY CLEAR SKIES WILL BE
OBSERVED TONIGHT. DESPITE WARMING ALOFT TONIGHT...SURFACE RIDGE
WITH RELAXED GRADIENT AND CLEAR SKIES SHOULD ALLOW FOR ANOTHER
COLD NIGHT TONIGHT WITH LOW TEMPS IN THE 20S EXPECTED FOR MOST OF
THE CWA. CONFIDENCE IS SOMEWHAT LOWER FOR LOW TEMPS ACROSS THE
WESTERN CWA TONIGHT...AS SOUTHERLY PICKS BACK UP WITH THE SURFACE
RIDGE QUICKLY SHIFTING TO THE EAST OF THE CWA.
NONETHELESS...ANOTHER NIGHT WITH TEMPS WELL BELOW NORMAL WILL
LIKELY BE OBSERVED.

EXPECT WEDNESDAY TO BE DRY...AS WAA PERSISTS AND HELPS START A
TREND TOWARDS MORE NORMAL TEMPS WITH HIGH TEMPS EXPECTED TO BE IN
THE 50S. THIS WARMER AIR WILL BE RIDING ALONG SOME STRONG
SOUTHERLY WINDS...AS PRESSURE GRADIENT REALLY TIGHTENS UP AND
SPEEDS INCREASE INTO THE AFTERNOON. WITH MID/UPPER LEVEL TROUGH
PUSHING EAST THROUGH THE CENTRAL PLAINS DURING THE DAY...HIGH
LEVEL CLOUD COVER WILL BE ON THE INCREASE. FORECAST GUIDANCE IN
AGREEMENT WITH THIS MID LEVEL TROUGH TO SWING EAST JUST NORTH OF
THE CWA WEDNESDAY NIGHT...WITH BEST FORCING AND PRECIP TO STAY
NORTH OF THE CWA. HAVE KEPT THE CWA DRY BUT WILL NEED TO MONITOR
THE POTENTIAL FOR SOME WAA PRECIP TO POSSIBLE DEVELOP ACROSS
SOUTHERN WISCONSIN...WHICH COULD CLIP AREAS RIGHT ALONG THE BORDER
IN NORTHERN ILLINOIS. ATTENDANT SURFACE LOW WILL LIFT THROUGH
SOUTHERN WISCONSIN THURSDAY MORNING WHILE WEAKENING...BUT WITH
MOST OF THE CWA EXPECTED TO BE IN THE WARM SECTOR. IN THIS WARMER
AIR MASS...TEMPS WILL BE IN THE 50S AND LOW 60S ACROSS THE
SOUTHERN HALF OF THE CWA ON THURSDAY. IT DOES LOOK LIKE SOME
SLIGHT COOLING WILL OCCUR LATE IN THE DAY/EVENING AS A WEAK
FRONT/TROUGH MOVES THROUGH THE CWA. AS THIS IS
OCCURRING...APPROACHING LONGWAVE TROUGH WILL HELP USHER SOME WEAK
IMPULSES WHICH SHOULD AID IN THE DEVELOPMENT OF RAIN THURSDAY
EVENING/NIGHT. DID INCREASE POPS AND COVERAGE OF POPS THURSDAY
NIGHT AS PRECIP IS APPEARING TO BE MORE LIKELY...BUT WITH SOME
UNCERTAINTY AS TO THE EXACT PLACEMENT OF PRECIP AXIS. COLDER AIR
WILL BE TRYING TO WORK SOUTH ACROSS THE AREA THURSDAY NIGHT INTO
FRIDAY MORNING...WITH THE RAIN/SNOW LINE TRYING TO INCH ITS WAY
CLOSE TO THE CWA. ALTHOUGH...IT DOES APPEAR THAT THIS LINE WILL
REMAIN NORTH OF THE CWA...AS DEEPER MOISTURE MOISTURE/CRYSTALS
WILL BE LOST BY THE TIME THERMAL PROFILES WOULD BE SUPPORTIVE OF
SNOW. DRYING TREND WILL OCCUR DURING THE DAY FRIDAY WITH SLIGHTLY
COOLER TEMPS IN THE 40S AND 50S. EXPECT THIS RETURN TO COOLER
WEATHER TO BRIEF AS WARMING TREND IS EXPECTED INTO THE WEEKEND.

RODRIGUEZ

&&

.AVIATION...

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

* LIGHT WEST WINDS SHIFTING SOUTHEAST THIS EVENING.

* STRONG SOUTH WINDS WEDNESDAY...GUSTS 30-35 KT POSSIBLE IN THE
  AFTERNOON.

* POTENTIAL FOR LLWS LATE WEDNESDAY EVENING AS GUSTS
  DIMINISH...WITH WINDS 20045-50KT AROUND 2000 FT AGL.

RATZER

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

SURFACE HIGH PRESSURE RIDGE ALONG IL/IN BORDER AND OVER SOUTHERN
LAKE MICHIGAN WILL CONTINUE TO DRIFT EAST THIS EVENING WILL ALLOW
DECREASING WESTERLY WINDS TO SHIFT TO THE SOUTHEAST OVER THE NEXT
1-3 HRS. LAKE BREEZE HAD DEVELOPED AND MOVED AS FAR INLAND AS MDW
BEFORE RETREATING A BIT...BUT DEPARTURE OF RIDGE AXIS TO EAST
SHOULD ALLOW FOR A LARGE SCALE SHIFT TO SOUTHEAST WINDS ACROSS THE
AREA.

FOCUS THEN SHIFTS TO STRONG SOUTH WINDS EXPECTED WEDNESDAY IN
RESPONSE TO AN AREA OF LOW PRESSURE DEVELOPING INTO THE UPPER
MIDWEST. TIGHTENING PRESSURE GRADIENT APPEARS TO SUPPORT SUSTAINED
WINDS AROUND 20 KT BY AFTERNOON...WITH GUSTS INTO THE 30-35 KT
RANGE POSSIBLE PER FORECAST SOUNDINGS DEPICTING MIXING TO
4000-5000 FT AGL. SURFACE LOW LIFTS INTO WESTERN WISCONSIN
WEDNESDAY EVENING ALLOWING THE GRADIENT TO EASE SLIGHTLY. DEGREE
OF BOUNDARY LAYER DECOUPLING SOMEWHAT UNCERTAIN AFTER SUNSET WITH
STRONG WINDS CONTINUING...THOUGH BY LATE EVENING EXPECT DECREASED
GUSTS. THIS SETS UP THE POTENTIAL FOR NON-CONVECTIVE LOW LEVEL
WIND SHEAR HOWEVER...WITH MODELS DEPICTING LOW LEVEL JET FROM
ABOUT 200 DEGREES AT 45-50KT AT 2000 FT AGL.

OTHERWISE...CURRENT VFR STRATOCU DECK EXPECTED TO ERODE QUICKLY
EARLY THIS EVENING WITH STRONG SUBSIDENCE DEVELOPING AND DRY AIR
IN PLACE. MID/HIGH VFR CLOUDS ALREADY RACING SOUTHEAST ACROSS THE
NORTHERN PLAINS SHOULD RESULT IN INCREASING MID-CLOUDS LATER
TONIGHT. MODEL TIME/HEIGHT DEPICTIONS INDICATE VFR MID DECK WILL
REMAIN ACROSS AREA IN 10-15 KFT RANGE THROUGH WEDNESDAY. LOW
CLOUDS WILL BE ABSENT...WITH SOUTHERN PORTION OF SURFACE HIGH
PRESSURE RIDGE EFFECTIVELY BLOCKING MOISTURE RETURN FROM THE GULF
OF MEXICO.

RATZER


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

* MEDIUM CONFIDENCE IN TIMING WIND SHIFT FROM LIGHT WEST TO LIGHT
  SOUTHEAST THIS EVENING.

* MEDIUM CONFIDENCE IN GUSTS ABATING AND TRUE LLWS CONDITIONS
  DEVELOPING WEDNESDAY EVENING.

* HIGH CONFIDENCE ALL OTHER ELEMENTS.

RATZER

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

THURSDAY...CHC RA LATE AFTN/NGT. MAINLY VFR.

FRIDAY...CHC RA/MVFR EARLY...THEN VFR.

SATURDAY...VFR.

SUNDAY...CHC RA.

MONDAY...SLGT CHC RA.

RATZER

&&

.MARINE...
303 PM CDT

HIGH PRESSURE STRETCHED FROM MANITOBA TO THE WESTERN GULF COAST WILL
WORK EASTWARD TONIGHT AND CONSOLIDATE INTO A BETTER ORGANIZED AREA
OF HIGH PRESSURE OVER THE OHIO VALLEY INTO WEDNESDAY MORNING. SOME
RESIDUAL GUSTY WINDS ACROSS THE FAR EASTERN SECTION OF LAKE MICHIGAN
THIS AFTERNOON WILL DIMINISH INTO THE EVENING AS THE PRESSURE
GRADIENT WEAKENS. SHOULD SEE QUITE A BIT OF VARIABILITY IN WIND
DIRECTION THIS EVENING BEFORE A STEADIER SOUTH WIND DEVELOPS OVER
THE SOUTHERN TWO THIRDS OF THE LAKE OVERNIGHT...WITH AN EASTERLY
DIRECTION FAR NORTH THANKS TO A DEVELOPING WARM FRONTAL BOUNDARY.
SOUTH TO SOUTHEAST WINDS WILL INCREASE MARKEDLY WEDNESDAY MORNING
AND SHOULD EASILY GUSTS TO 30 KT ACROSS CENTRAL AND SOUTHERN
PORTIONS OF THE LAKE...ESPECIALLY OVER THE WESTERN HALF. DO SEE SOME
POTENTIAL FOR GALES THOUGH THEY MAY BE SHORT LIVED OR
INFREQUENT...OR CONFINED TO THE NEARSHORE WATERS GIVEN THE SHORE
PARALLEL FLOW SLIGHT ONSHORE COMPONENT SUGGESTING ANY LAKEWARD
EXTENT OF MIXING FROM LAND WOULD BE MINIMAL. IL/IN NEARSHORE WATERS
WILL SOLIDLY FALL INTO SMALL CRAFT CRITERIA. CANNOT RULE OUT GALES
THERE AS WELL BUT THE STRONGER WINDS JUST ABOVE THE SURFACE ARE
FOCUSED FURTHER WEST OF THE LAKE BUT WILL NEED TO MONITOR.

LOW PRESSURE WILL TRACK FROM NEBRASKA/SOUTH DAKOTA TO NORTHERN LAKE
MICHIGAN INTO THURSDAY BRINGING A COOL FRONT DOWN THE LAKE LATER
THURSDAY. THIS WILL SHIFT WINDS TO THE NORTH. THE LOW WILL BE
WEAKENING AS IT PASSES AND THE PRESSURE GRADIENT BETWEEN IT AND HIGH
PRESSURE TO THE NORTH WILL BE FAIRLY BAGGY. THIS COMBINED WITH A
FAIRLY WEAK PUSH OF COLDER AIR WILL RESULT IN RATHER MODEST WINDS
FOR A FRONTAL PASSAGE AND SPEEDS WILL LIKELY BE QUITE A BIT WEAKER
WITH THE FRONTAL PASSAGE LATER THURSDAY INTO FRIDAY. HIGH PRESSURE
RIDGING THEN WORKS EASTWARD ACROSS THE LAKE FRIDAY AND SATURDAY
KEEPING WINDS ON THE LIGHT SIDE. ANOTHER WEAK LOW MAY MOVE INTO THE
REGION LATER IN THE WEEKEND.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM WEDNESDAY TO 4 AM THURSDAY.

&&

$$

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

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







000
FXUS63 KLOT 152202
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
502 PM CDT TUE APR 15 2014

.DISCUSSION...
340 PM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH CLOUD COVER AND TEMPS
THIS EVENING...SOME UP AND DOWN WITH TEMPS OVER THE NEXT COUPLE OF
DAYS...AND THEN INCREASING CHANCES FOR PRECIP LATE IN THE WORK
WEEK.

IN THE NEAR TERM...CLOUD COVER REMAINS OVER THE CWA AND HAS
REMAINED ON THE THICKER SIDE FOR MOST OF THE DAY. THIS HAS LIMITED
DAYTIME WARMING TODAY...WITH TEMPS STRUGGLING TO GET INTO THE
UPPER 30S. ALTHOUGH CLOUD COVER IS ON A DIMINISHING TREND...DID
KEEP AT LEAST SOME PARTLY CLOUDY MENTION INTO EARLY THIS EVENING
WITH THIS STRATOCU DECK CONTINUING A SLOW DIMINISHING TREND. ANY
REMAINING ISOL FLURRIES ACROSS THE AREA WILL LIKEWISE
DIMINISH...BUT MORE LIKELY AT A QUICKER RATE THAN THE CLOUD COVER.
THEN WITH MID/HIGH LEVEL CLOUD COVER TO THE WEST/NORTHWEST
REMAINING OFF TO THE WEST...A PERIOD OF MOSTLY CLEAR SKIES WILL BE
OBSERVED TONIGHT. DESPITE WARMING ALOFT TONIGHT...SURFACE RIDGE
WITH RELAXED GRADIENT AND CLEAR SKIES SHOULD ALLOW FOR ANOTHER
COLD NIGHT TONIGHT WITH LOW TEMPS IN THE 20S EXPECTED FOR MOST OF
THE CWA. CONFIDENCE IS SOMEWHAT LOWER FOR LOW TEMPS ACROSS THE
WESTERN CWA TONIGHT...AS SOUTHERLY PICKS BACK UP WITH THE SURFACE
RIDGE QUICKLY SHIFTING TO THE EAST OF THE CWA.
NONETHELESS...ANOTHER NIGHT WITH TEMPS WELL BELOW NORMAL WILL
LIKELY BE OBSERVED.

EXPECT WEDNESDAY TO BE DRY...AS WAA PERSISTS AND HELPS START A
TREND TOWARDS MORE NORMAL TEMPS WITH HIGH TEMPS EXPECTED TO BE IN
THE 50S. THIS WARMER AIR WILL BE RIDING ALONG SOME STRONG
SOUTHERLY WINDS...AS PRESSURE GRADIENT REALLY TIGHTENS UP AND
SPEEDS INCREASE INTO THE AFTERNOON. WITH MID/UPPER LEVEL TROUGH
PUSHING EAST THROUGH THE CENTRAL PLAINS DURING THE DAY...HIGH
LEVEL CLOUD COVER WILL BE ON THE INCREASE. FORECAST GUIDANCE IN
AGREEMENT WITH THIS MID LEVEL TROUGH TO SWING EAST JUST NORTH OF
THE CWA WEDNESDAY NIGHT...WITH BEST FORCING AND PRECIP TO STAY
NORTH OF THE CWA. HAVE KEPT THE CWA DRY BUT WILL NEED TO MONITOR
THE POTENTIAL FOR SOME WAA PRECIP TO POSSIBLE DEVELOP ACROSS
SOUTHERN WISCONSIN...WHICH COULD CLIP AREAS RIGHT ALONG THE BORDER
IN NORTHERN ILLINOIS. ATTENDANT SURFACE LOW WILL LIFT THROUGH
SOUTHERN WISCONSIN THURSDAY MORNING WHILE WEAKENING...BUT WITH
MOST OF THE CWA EXPECTED TO BE IN THE WARM SECTOR. IN THIS WARMER
AIR MASS...TEMPS WILL BE IN THE 50S AND LOW 60S ACROSS THE
SOUTHERN HALF OF THE CWA ON THURSDAY. IT DOES LOOK LIKE SOME
SLIGHT COOLING WILL OCCUR LATE IN THE DAY/EVENING AS A WEAK
FRONT/TROUGH MOVES THROUGH THE CWA. AS THIS IS
OCCURRING...APPROACHING LONGWAVE TROUGH WILL HELP USHER SOME WEAK
IMPULSES WHICH SHOULD AID IN THE DEVELOPMENT OF RAIN THURSDAY
EVENING/NIGHT. DID INCREASE POPS AND COVERAGE OF POPS THURSDAY
NIGHT AS PRECIP IS APPEARING TO BE MORE LIKELY...BUT WITH SOME
UNCERTAINTY AS TO THE EXACT PLACEMENT OF PRECIP AXIS. COLDER AIR
WILL BE TRYING TO WORK SOUTH ACROSS THE AREA THURSDAY NIGHT INTO
FRIDAY MORNING...WITH THE RAIN/SNOW LINE TRYING TO INCH ITS WAY
CLOSE TO THE CWA. ALTHOUGH...IT DOES APPEAR THAT THIS LINE WILL
REMAIN NORTH OF THE CWA...AS DEEPER MOISTURE MOISTURE/CRYSTALS
WILL BE LOST BY THE TIME THERMAL PROFILES WOULD BE SUPPORTIVE OF
SNOW. DRYING TREND WILL OCCUR DURING THE DAY FRIDAY WITH SLIGHTLY
COOLER TEMPS IN THE 40S AND 50S. EXPECT THIS RETURN TO COOLER
WEATHER TO BRIEF AS WARMING TREND IS EXPECTED INTO THE WEEKEND.

RODRIGUEZ

&&

.AVIATION...

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

* WEAK LAKE BREEZE HAS JUST MOVED INTO MDW AT 22Z.

* LAKE BREEZE MAY NOT IMPACT ORD...THOUGH WINDS WILL EVENTUALLY
  BECOME VRBL/LGT SE THIS EVE AS SFC HIGH MOVES EAST.

* VERY GUSTY SOUTH WINDS TO 30-35 KT WED.

RATZER

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

WEAK LAKE BREEZE HAS DRIFTED AS FAR WEST AS MDW AS OF 22Z.
WESTERLY SFC WINDS GRADUALLY DIMINISHING ELSEWHERE AS SURFACE HIGH
PRESSURE RIDGE MOVES ACROSS AREA. LAKE BREEZE STILL SEVERAL MILES
EAST OF ORD PER MESO-NET OBS AND SUSPECT IT WILL LIKELY NOT REACH
ORD BY 00Z. IN ANY CASE...WINDS EXPECTED TO BECOME LGT/VRBL AND
EVENTUALLY SE LATER THIS EVENING.

RATZER

PREVIOUS DISCUSSION FROM 18Z...

COMBINATION OF COLD AIR ALOFT AND DAYTIME HEATING HAS LEAD TO
DEVELOPMENT OF OVERALL SHALLOW STRATOCUMULUS FIELD ACROSS THE
AREA. A FEW WEAK RETURNS PAINTING ON RADAR AND FLURRIES HAVE BEEN REPORTED
AT SOME LOCATIONS. FLURRIES TO REMAIN POSSIBLE INTO MID AFTERNOON
UNTIL COLD AIR POOL ALOFT MOVES FURTHER EAST. CLOUDS TO THEN THIN
AND DISSIPATE LATE THIS AFTERNOON INTO EARLY EVENING.

LAKE BREEZE NOT EXPECTED TO PUSH TOO FAR INLAND AS CLOUD COVER TO
MINIMIZE LAND/LAKE TEMPERATURE CONTRAST AND ALLOW REGIONAL FLOW TO
DOMINATE.

AXIS OF A LARGE HIGH PRESSURE AREA STRETCHED OVER MINNESOTA TO
ACROSS MISSOURI AT MIDDAY. AXIS TO MOVE ACROSS THIS EVENING
CAUSING WIND TO BECOME LIGHT AND VARIABLE. WIND TO BECOME SOUTH BY
DAYBREAK WEDNESDAY AND STEADILY INCREASE WITH GUSTS AROUND 30KT BY
AFTERNOON AS NEXT LOW PRESSURE SYSTEM MOVES OUT OF THE PLAINS. DZ

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

* LOW CONFIDENCE IN LAKE BREEZE REACHING ORD PRIOR TO 00Z.

* HIGH CONFIDENCE IN ALL TAF ELEMENTS.

RATZER

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
303 PM CDT

HIGH PRESSURE STRETCHED FROM MANITOBA TO THE WESTERN GULF COAST WILL
WORK EASTWARD TONIGHT AND CONSOLIDATE INTO A BETTER ORGANIZED AREA
OF HIGH PRESSURE OVER THE OHIO VALLEY INTO WEDNESDAY MORNING. SOME
RESIDUAL GUSTY WINDS ACROSS THE FAR EASTERN SECTION OF LAKE MICHIGAN
THIS AFTERNOON WILL DIMINISH INTO THE EVENING AS THE PRESSURE
GRADIENT WEAKENS. SHOULD SEE QUITE A BIT OF VARIABILITY IN WIND
DIRECTION THIS EVENING BEFORE A STEADIER SOUTH WIND DEVELOPS OVER
THE SOUTHERN TWO THIRDS OF THE LAKE OVERNIGHT...WITH AN EASTERLY
DIRECTION FAR NORTH THANKS TO A DEVELOPING WARM FRONTAL BOUNDARY.
SOUTH TO SOUTHEAST WINDS WILL INCREASE MARKEDLY WEDNESDAY MORNING
AND SHOULD EASILY GUSTS TO 30 KT ACROSS CENTRAL AND SOUTHERN
PORTIONS OF THE LAKE...ESPECIALLY OVER THE WESTERN HALF. DO SEE SOME
POTENTIAL FOR GALES THOUGH THEY MAY BE SHORT LIVED OR
INFREQUENT...OR CONFINED TO THE NEARSHORE WATERS GIVEN THE SHORE
PARALLEL FLOW SLIGHT ONSHORE COMPONENT SUGGESTING ANY LAKEWARD
EXTENT OF MIXING FROM LAND WOULD BE MINIMAL. IL/IN NEARSHORE WATERS
WILL SOLIDLY FALL INTO SMALL CRAFT CRITERIA. CANNOT RULE OUT GALES
THERE AS WELL BUT THE STRONGER WINDS JUST ABOVE THE SURFACE ARE
FOCUSED FURTHER WEST OF THE LAKE BUT WILL NEED TO MONITOR.

LOW PRESSURE WILL TRACK FROM NEBRASKA/SOUTH DAKOTA TO NORTHERN LAKE
MICHIGAN INTO THURSDAY BRINGING A COOL FRONT DOWN THE LAKE LATER
THURSDAY. THIS WILL SHIFT WINDS TO THE NORTH. THE LOW WILL BE
WEAKENING AS IT PASSES AND THE PRESSURE GRADIENT BETWEEN IT AND HIGH
PRESSURE TO THE NORTH WILL BE FAIRLY BAGGY. THIS COMBINED WITH A
FAIRLY WEAK PUSH OF COLDER AIR WILL RESULT IN RATHER MODEST WINDS
FOR A FRONTAL PASSAGE AND SPEEDS WILL LIKELY BE QUITE A BIT WEAKER
WITH THE FRONTAL PASSAGE LATER THURSDAY INTO FRIDAY. HIGH PRESSURE
RIDGING THEN WORKS EASTWARD ACROSS THE LAKE FRIDAY AND SATURDAY
KEEPING WINDS ON THE LIGHT SIDE. ANOTHER WEAK LOW MAY MOVE INTO THE
REGION LATER IN THE WEEKEND.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM WEDNESDAY TO 4 AM THURSDAY.

&&

$$

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

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








000
FXUS63 KLOT 152042
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
342 PM CDT TUE APR 15 2014

.DISCUSSION...
340 PM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH CLOUD COVER AND TEMPS
THIS EVENING...SOME UP AND DOWN WITH TEMPS OVER THE NEXT COUPLE OF
DAYS...AND THEN INCREASING CHANCES FOR PRECIP LATE IN THE WORK
WEEK.

IN THE NEAR TERM...CLOUD COVER REMAINS OVER THE CWA AND HAS
REMAINED ON THE THICKER SIDE FOR MOST OF THE DAY. THIS HAS LIMITED
DAYTIME WARMING TODAY...WITH TEMPS STRUGGLING TO GET INTO THE
UPPER 30S. ALTHOUGH CLOUD COVER IS ON A DIMINISHING TREND...DID
KEEP AT LEAST SOME PARTLY CLOUDY MENTION INTO EARLY THIS EVENING
WITH THIS STRATOCU DECK CONTINUING A SLOW DIMINISHING TREND. ANY
REMAINING ISOL FLURRIES ACROSS THE AREA WILL LIKEWISE
DIMINISH...BUT MORE LIKELY AT A QUICKER RATE THAN THE CLOUD COVER.
THEN WITH MID/HIGH LEVEL CLOUD COVER TO THE WEST/NORTHWEST
REMAINING OFF TO THE WEST...A PERIOD OF MOSTLY CLEAR SKIES WILL BE
OBSERVED TONIGHT. DESPITE WARMING ALOFT TONIGHT...SURFACE RIDGE
WITH RELAXED GRADIENT AND CLEAR SKIES SHOULD ALLOW FOR ANOTHER
COLD NIGHT TONIGHT WITH LOW TEMPS IN THE 20S EXPECTED FOR MOST OF
THE CWA. CONFIDENCE IS SOMEWHAT LOWER FOR LOW TEMPS ACROSS THE
WESTERN CWA TONIGHT...AS SOUTHERLY PICKS BACK UP WITH THE SURFACE
RIDGE QUICKLY SHIFTING TO THE EAST OF THE CWA.
NONETHELESS...ANOTHER NIGHT WITH TEMPS WELL BELOW NORMAL WILL
LIKELY BE OBSERVED.

EXPECT WEDNESDAY TO BE DRY...AS WAA PERSISTS AND HELPS START A
TREND TOWARDS MORE NORMAL TEMPS WITH HIGH TEMPS EXPECTED TO BE IN
THE 50S. THIS WARMER AIR WILL BE RIDING ALONG SOME STRONG
SOUTHERLY WINDS...AS PRESSURE GRADIENT REALLY TIGHTENS UP AND
SPEEDS INCREASE INTO THE AFTERNOON. WITH MID/UPPER LEVEL TROUGH
PUSHING EAST THROUGH THE CENTRAL PLAINS DURING THE DAY...HIGH
LEVEL CLOUD COVER WILL BE ON THE INCREASE. FORECAST GUIDANCE IN
AGREEMENT WITH THIS MID LEVEL TROUGH TO SWING EAST JUST NORTH OF
THE CWA WEDNESDAY NIGHT...WITH BEST FORCING AND PRECIP TO STAY
NORTH OF THE CWA. HAVE KEPT THE CWA DRY BUT WILL NEED TO MONITOR
THE POTENTIAL FOR SOME WAA PRECIP TO POSSIBLE DEVELOP ACROSS
SOUTHERN WISCONSIN...WHICH COULD CLIP AREAS RIGHT ALONG THE BORDER
IN NORTHERN ILLINOIS. ATTENDANT SURFACE LOW WILL LIFT THROUGH
SOUTHERN WISCONSIN THURSDAY MORNING WHILE WEAKENING...BUT WITH
MOST OF THE CWA EXPECTED TO BE IN THE WARM SECTOR. IN THIS WARMER
AIR MASS...TEMPS WILL BE IN THE 50S AND LOW 60S ACROSS THE
SOUTHERN HALF OF THE CWA ON THURSDAY. IT DOES LOOK LIKE SOME
SLIGHT COOLING WILL OCCUR LATE IN THE DAY/EVENING AS A WEAK
FRONT/TROUGH MOVES THROUGH THE CWA. AS THIS IS
OCCURRING...APPROACHING LONGWAVE TROUGH WILL HELP USHER SOME WEAK
IMPULSES WHICH SHOULD AID IN THE DEVELOPMENT OF RAIN THURSDAY
EVENING/NIGHT. DID INCREASE POPS AND COVERAGE OF POPS THURSDAY
NIGHT AS PRECIP IS APPEARING TO BE MORE LIKELY...BUT WITH SOME
UNCERTAINTY AS TO THE EXACT PLACEMENT OF PRECIP AXIS. COLDER AIR
WILL BE TRYING TO WORK SOUTH ACROSS THE AREA THURSDAY NIGHT INTO
FRIDAY MORNING...WITH THE RAIN/SNOW LINE TRYING TO INCH ITS WAY
CLOSE TO THE CWA. ALTHOUGH...IT DOES APPEAR THAT THIS LINE WILL
REMAIN NORTH OF THE CWA...AS DEEPER MOISTURE MOISTURE/CRYSTALS
WILL BE LOST BY THE TIME THERMAL PROFILES WOULD BE SUPPORTIVE OF
SNOW. DRYING TREND WILL OCCUR DURING THE DAY FRIDAY WITH SLIGHTLY
COOLER TEMPS IN THE 40S AND 50S. EXPECT THIS RETURN TO COOLER
WEATHER TO BRIEF AS WARMING TREND IS EXPECTED INTO THE WEEKEND.

RODRIGUEZ

&&

.CLIMATE...

IT IS STILL POSSIBLE A RECORD LOW MAX MAY BE REACHED AT ROCKFORD
TODAY WITH THAT BEING 39 SET IN 1951...AS THE CURRENT TEMP IS
HOVERING AROUND 38.

MTF/RODRIGUEZ

&&

.AVIATION...

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

* POTENTIAL FOR LAKE BREEZE THIS AFTERNOON/EVENING

DZ

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

COMBINATION OF COLD AIR ALOFT AND DAYTIME HEATING HAS LEAD TO
DEVELOPMENT OF OVERALL SHALLOW STRATOCUMULUS FIELD ACROSS THE
AREA. A FEW WEAK RETURNS PAINTING ON RADAR AND FLURRIES HAVE BEEN REPORTED
AT SOME LOCATIONS. FLURRIES TO REMAIN POSSIBLE INTO MID AFTERNOON
UNTIL COLD AIR POOL ALOFT MOVES FURTHER EAST. CLOUDS TO THEN THIN
AND DISSIPATE LATE THIS AFTERNOON INTO EARLY EVENING.

LAKE BREEZE NOT EXPECTED TO PUSH TOO FAR INLAND AS CLOUD COVER TO
MINIMIZE LAND/LAKE TEMPERATURE CONTRAST AND ALLOW REGIONAL FLOW TO
DOMINATE.

AXIS OF A LARGE HIGH PRESSURE AREA STRETCHED OVER MINNESOTA TO
ACROSS MISSOURI AT MIDDAY. AXIS TO MOVE ACROSS THIS EVENING
CAUSING WIND TO BECOME LIGHT AND VARIABLE. WIND TO BECOME SOUTH BY
DAYBREAK WEDNESDAY AND STEADILY INCREASE WITH GUSTS AROUND 30KT BY
AFTERNOON AS NEXT LOW PRESSURE SYSTEM MOVES OUT OF THE PLAINS. DZ

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

* LOW CONFIDENCE LAKE BREEZE WILL MOVE ACROSS ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

DZ

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
303 PM CDT

HIGH PRESSURE STRETCHED FROM MANITOBA TO THE WESTERN GULF COAST WILL
WORK EASTWARD TONIGHT AND CONSOLIDATE INTO A BETTER ORGANIZED AREA
OF HIGH PRESSURE OVER THE OHIO VALLEY INTO WEDNESDAY MORNING. SOME
RESIDUAL GUSTY WINDS ACROSS THE FAR EASTERN SECTION OF LAKE MICHIGAN
THIS AFTERNOON WILL DIMINISH INTO THE EVENING AS THE PRESSURE
GRADIENT WEAKENS. SHOULD SEE QUITE A BIT OF VARIABILITY IN WIND
DIRECTION THIS EVENING BEFORE A STEADIER SOUTH WIND DEVELOPS OVER
THE SOUTHERN TWO THIRDS OF THE LAKE OVERNIGHT...WITH AN EASTERLY
DIRECTION FAR NORTH THANKS TO A DEVELOPING WARM FRONTAL BOUNDARY.
SOUTH TO SOUTHEAST WINDS WILL INCREASE MARKEDLY WEDNESDAY MORNING
AND SHOULD EASILY GUSTS TO 30 KT ACROSS CENTRAL AND SOUTHERN
PORTIONS OF THE LAKE...ESPECIALLY OVER THE WESTERN HALF. DO SEE SOME
POTENTIAL FOR GALES THOUGH THEY MAY BE SHORT LIVED OR
INFREQUENT...OR CONFINED TO THE NEARSHORE WATERS GIVEN THE SHORE
PARALLEL FLOW SLIGHT ONSHORE COMPONENT SUGGESTING ANY LAKEWARD
EXTENT OF MIXING FROM LAND WOULD BE MINIMAL. IL/IN NEARSHORE WATERS
WILL SOLIDLY FALL INTO SMALL CRAFT CRITERIA. CANNOT RULE OUT GALES
THERE AS WELL BUT THE STRONGER WINDS JUST ABOVE THE SURFACE ARE
FOCUSED FURTHER WEST OF THE LAKE BUT WILL NEED TO MONITOR.

LOW PRESSURE WILL TRACK FROM NEBRASKA/SOUTH DAKOTA TO NORTHERN LAKE
MICHIGAN INTO THURSDAY BRINGING A COOL FRONT DOWN THE LAKE LATER
THURSDAY. THIS WILL SHIFT WINDS TO THE NORTH. THE LOW WILL BE
WEAKENING AS IT PASSES AND THE PRESSURE GRADIENT BETWEEN IT AND HIGH
PRESSURE TO THE NORTH WILL BE FAIRLY BAGGY. THIS COMBINED WITH A
FAIRLY WEAK PUSH OF COLDER AIR WILL RESULT IN RATHER MODEST WINDS
FOR A FRONTAL PASSAGE AND SPEEDS WILL LIKELY BE QUITE A BIT WEAKER
WITH THE FRONTAL PASSAGE LATER THURSDAY INTO FRIDAY. HIGH PRESSURE
RIDGING THEN WORKS EASTWARD ACROSS THE LAKE FRIDAY AND SATURDAY
KEEPING WINDS ON THE LIGHT SIDE. ANOTHER WEAK LOW MAY MOVE INTO THE
REGION LATER IN THE WEEKEND.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM WEDNESDAY TO 4 AM THURSDAY.

&&

$$

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

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







000
FXUS63 KLOT 152004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
304 PM CDT TUE APR 15 2014

.DISCUSSION...
1138 AM CDT

MINOR UPDATES TO SKY COVER AND POP/WX THIS MORNING...TO ACCOUNT
FOR PARTLY SUNNY SKIES WITH SOME ISOL TO SCT FLURRIES THROUGH
EARLY THIS AFTERNOON. LATEST SATELLITE IMAGERY DEPICTING RAPID
STRATOCU DEVELOPMENT ACROSS THE REGION OVER THE LAST HOUR. THIS IS
OCCURRING AS CYCLONIC FLOW REMAINS IN PLACE WHILE LONGWAVE TROUGH
PROGRESSES THROUGH THE REGION...AND LOW LEVEL LAPSE RATES CONTINUE
TO STEEPEN. AS REMAINING SNOW MELTS OVER THE NEXT ONE TO TWO
HOURS...SHOULD OBSERVE ANY HOLES IN THE CLOUD DECK TO FILL WITH
SKIES BECOMING MORE PARTLY SUNNY WITH POSSIBLE BUT BRIEF OVERCAST
SKIES THIS AFTERNOON. RADAR IS SHOWING SOME LIGHT RETURNS AS
CU/STRATOCU FIELD CONTINUES TO BUBBLE...AND WOULD NOT BE OUT OF
THE QUESTION FOR SOME MOISTURE TO BE SQUEEZED OUT ESPECIALLY NEAR
BETTER LOW LEVEL CONVERGENCE. HAVE INCLUDED THE MENTION OF
FLURRIES IN THE GRIDS...BUT THIS SHOULD LIKELY PEAK OVER THE NEXT
COUPLE OF HOURS BEFORE DIMINISHING INTO THE REST OF THE AFTERNOON.

RODRIGUEZ

//PREV DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR LAKE BREEZE THIS AFTERNOON/EVENING

DZ

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

COMBINATION OF COLD AIR ALOFT AND DAYTIME HEATING HAS LEAD TO
DEVELOPMENT OF OVERALL SHALLOW STRATOCUMULUS FIELD ACROSS THE
AREA. A FEW WEAK RETURNS PAINTING ON RADAR AND FLURRIES HAVE BEEN REPORTED
AT SOME LOCATIONS. FLURRIES TO REMAIN POSSIBLE INTO MID AFTERNOON
UNTIL COLD AIR POOL ALOFT MOVES FURTHER EAST. CLOUDS TO THEN THIN
AND DISSIPATE LATE THIS AFTERNOON INTO EARLY EVENING.

LAKE BREEZE NOT EXPECTED TO PUSH TOO FAR INLAND AS CLOUD COVER TO
MINIMIZE LAND/LAKE TEMPERATURE CONTRAST AND ALLOW REGIONAL FLOW TO
DOMINATE.

AXIS OF A LARGE HIGH PRESSURE AREA STRETCHED OVER MINNESOTA TO
ACROSS MISSOURI AT MIDDAY. AXIS TO MOVE ACROSS THIS EVENING
CAUSING WIND TO BECOME LIGHT AND VARIABLE. WIND TO BECOME SOUTH BY
DAYBREAK WEDNESDAY AND STEADILY INCREASE WITH GUSTS AROUND 30KT BY
AFTERNOON AS NEXT LOW PRESSURE SYSTEM MOVES OUT OF THE PLAINS. DZ

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

* LOW CONFIDENCE LAKE BREEZE WILL MOVE ACROSS ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

DZ

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
303 PM CDT

HIGH PRESSURE STRETCHED FROM MANITOBA TO THE WESTERN GULF COAST WILL
WORK EASTWARD TONIGHT AND CONSOLIDATE INTO A BETTER ORGANIZED AREA
OF HIGH PRESSURE OVER THE OHIO VALLEY INTO WEDNESDAY MORNING. SOME
RESIDUAL GUSTY WINDS ACROSS THE FAR EASTERN SECTION OF LAKE MICHIGAN
THIS AFTERNOON WILL DIMINISH INTO THE EVENING AS THE PRESSURE
GRADIENT WEAKENS. SHOULD SEE QUITE A BIT OF VARIABILITY IN WIND
DIRECTION THIS EVENING BEFORE A STEADIER SOUTH WIND DEVELOPS OVER
THE SOUTHERN TWO THIRDS OF THE LAKE OVERNIGHT...WITH AN EASTERLY
DIRECTION FAR NORTH THANKS TO A DEVELOPING WARM FRONTAL BOUNDARY.
SOUTH TO SOUTHEAST WINDS WILL INCREASE MARKEDLY WEDNESDAY MORNING
AND SHOULD EASILY GUSTS TO 30 KT ACROSS CENTRAL AND SOUTHERN
PORTIONS OF THE LAKE...ESPECIALLY OVER THE WESTERN HALF. DO SEE SOME
POTENTIAL FOR GALES THOUGH THEY MAY BE SHORT LIVED OR
INFREQUENT...OR CONFINED TO THE NEARSHORE WATERS GIVEN THE SHORE
PARALLEL FLOW SLIGHT ONSHORE COMPONENT SUGGESTING ANY LAKEWARD
EXTENT OF MIXING FROM LAND WOULD BE MINIMAL. IL/IN NEARSHORE WATERS
WILL SOLIDLY FALL INTO SMALL CRAFT CRITERIA. CANNOT RULE OUT GALES
THERE AS WELL BUT THE STRONGER WINDS JUST ABOVE THE SURFACE ARE
FOCUSED FURTHER WEST OF THE LAKE BUT WILL NEED TO MONITOR.

LOW PRESSURE WILL TRACK FROM NEBRASKA/SOUTH DAKOTA TO NORTHERN LAKE
MICHIGAN INTO THURSDAY BRINGING A COOL FRONT DOWN THE LAKE LATER
THURSDAY. THIS WILL SHIFT WINDS TO THE NORTH. THE LOW WILL BE
WEAKENING AS IT PASSES AND THE PRESSURE GRADIENT BETWEEN IT AND HIGH
PRESSURE TO THE NORTH WILL BE FAIRLY BAGGY. THIS COMBINED WITH A
FAIRLY WEAK PUSH OF COLDER AIR WILL RESULT IN RATHER MODEST WINDS
FOR A FRONTAL PASSAGE AND SPEEDS WILL LIKELY BE QUITE A BIT WEAKER
WITH THE FRONTAL PASSAGE LATER THURSDAY INTO FRIDAY. HIGH PRESSURE
RIDGING THEN WORKS EASTWARD ACROSS THE LAKE FRIDAY AND SATURDAY
KEEPING WINDS ON THE LIGHT SIDE. ANOTHER WEAK LOW MAY MOVE INTO THE
REGION LATER IN THE WEEKEND.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM WEDNESDAY TO 4 AM THURSDAY.

&&

$$

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

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









000
FXUS63 KLOT 151825
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
125 PM CDT TUE APR 15 2014

.DISCUSSION...
1138 AM CDT

MINOR UPDATES TO SKY COVER AND POP/WX THIS MORNING...TO ACCOUNT
FOR PARTLY SUNNY SKIES WITH SOME ISOL TO SCT FLURRIES THROUGH
EARLY THIS AFTERNOON. LATEST SATELLITE IMAGERY DEPICTING RAPID
STRATOCU DEVELOPMENT ACROSS THE REGION OVER THE LAST HOUR. THIS IS
OCCURRING AS CYCLONIC FLOW REMAINS IN PLACE WHILE LONGWAVE TROUGH
PROGRESSES THROUGH THE REGION...AND LOW LEVEL LAPSE RATES CONTINUE
TO STEEPEN. AS REMAINING SNOW MELTS OVER THE NEXT ONE TO TWO
HOURS...SHOULD OBSERVE ANY HOLES IN THE CLOUD DECK TO FILL WITH
SKIES BECOMING MORE PARTLY SUNNY WITH POSSIBLE BUT BRIEF OVERCAST
SKIES THIS AFTERNOON. RADAR IS SHOWING SOME LIGHT RETURNS AS
CU/STRATOCU FIELD CONTINUES TO BUBBLE...AND WOULD NOT BE OUT OF
THE QUESTION FOR SOME MOISTURE TO BE SQUEEZED OUT ESPECIALLY NEAR
BETTER LOW LEVEL CONVERGENCE. HAVE INCLUDED THE MENTION OF
FLURRIES IN THE GRIDS...BUT THIS SHOULD LIKELY PEAK OVER THE NEXT
COUPLE OF HOURS BEFORE DIMINISHING INTO THE REST OF THE AFTERNOON.

RODRIGUEZ

//PREV DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR LAKE BREEZE THIS AFTERNOON/EVENING

DZ

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

COMBINATION OF COLD AIR ALOFT AND DAYTIME HEATING HAS LEAD TO
DEVELOPMENT OF OVERALL SHALLOW STRATOCUMULUS FIELD ACROSS THE
AREA. A FEW WEAK RETURNS PAINTING ON RADAR AND FLURRIES HAVE BEEN REPORTED
AT SOME LOCATIONS. FLURRIES TO REMAIN POSSIBLE INTO MID AFTERNOON
UNTIL COLD AIR POOL ALOFT MOVES FURTHER EAST. CLOUDS TO THEN THIN
AND DISSIPATE LATE THIS AFTERNOON INTO EARLY EVENING.

LAKE BREEZE NOT EXPECTED TO PUSH TOO FAR INLAND AS CLOUD COVER TO
MINIMIZE LAND/LAKE TEMPERATURE CONTRAST AND ALLOW REGIONAL FLOW TO
DOMINATE.

AXIS OF A LARGE HIGH PRESSURE AREA STRETCHED OVER MINNESOTA TO
ACROSS MISSOURI AT MIDDAY. AXIS TO MOVE ACROSS THIS EVENING
CAUSING WIND TO BECOME LIGHT AND VARIABLE. WIND TO BECOME SOUTH BY
DAYBREAK WEDNESDAY AND STEADILY INCREASE WITH GUSTS AROUND 30KT BY
AFTERNOON AS NEXT LOW PRESSURE SYSTEM MOVES OUT OF THE PLAINS. DZ

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

* LOW CONFIDENCE LAKE BREEZE WILL MOVE ACROSS ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

DZ


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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 151647
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1147 AM CDT TUE APR 15 2014

.DISCUSSION...
1138 AM CDT

MINOR UPDATES TO SKY COVER AND POP/WX THIS MORNING...TO ACCOUNT
FOR PARTLY SUNNY SKIES WITH SOME ISOL TO SCT FLURRIES THROUGH
EARLY THIS AFTERNOON. LATEST SATELLITE IMAGERY DEPICTING RAPID
STRATOCU DEVELOPMENT ACROSS THE REGION OVER THE LAST HOUR. THIS IS
OCCURRING AS CYCLONIC FLOW REMAINS IN PLACE WHILE LONGWAVE TROUGH
PROGRESSES THROUGH THE REGION...AND LOW LEVEL LAPSE RATES CONTINUE
TO STEEPEN. AS REMAINING SNOW MELTS OVER THE NEXT ONE TO TWO
HOURS...SHOULD OBSERVE ANY HOLES IN THE CLOUD DECK TO FILL WITH
SKIES BECOMING MORE PARTLY SUNNY WITH POSSIBLE BUT BRIEF OVERCAST
SKIES THIS AFTERNOON. RADAR IS SHOWING SOME LIGHT RETURNS AS
CU/STRATOCU FIELD CONTINUES TO BUBBLE...AND WOULD NOT BE OUT OF
THE QUESTION FOR SOME MOISTURE TO BE SQUEEZED OUT ESPECIALLY NEAR
BETTER LOW LEVEL CONVERGENCE. HAVE INCLUDED THE MENTION OF
FLURRIES IN THE GRIDS...BUT THIS SHOULD LIKELY PEAK OVER THE NEXT
COUPLE OF HOURS BEFORE DIMINISHING INTO THE REST OF THE AFTERNOON.

RODRIGUEZ

&&

.PREV DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR LAKE BREEZE THIS AFTERNOON/EVENING

DZ

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

HIGH PRESSURE STRETCHES FROM MINNESOTA INTO KANSAS EARLY THIS
MORNING WITH A MODEST N-NNW GRADIENT IN PLACE ACROSS NORTHERN
ILLINOIS. COLD ADVECTION INTO THE AREA IS RESULTING IN STEEP LOW
LEVEL LAPSE RATES...AND ESPECIALLY AS THE SUN RISES EXPECT WINDS
HOVERING AROUND OR SLIGHTLY ABOVE 10 KTS TODAY WITH A FEW OCCASIONAL
GUSTS INTO THE MID TEENS. WINDS WILL DIMINISH SLIGHTLY THIS
AFTERNOON ALLOWING A LAKE BREEZE TO DEVELOP. WINDS WILL TURN NE AT
GYY...AND THE BOUNDARY WILL TRY TO PUSH WEST TOWARDS MDW/ORD BUT
WITH WEAK TEMPERATURE CONTRAST AND AN OPPOSING SYNOPTIC WIND...NOT
CONFIDENT IT WILL MAKE IT THROUGH THE TERMINALS THIS AFTERNOON. AS
THE RIDGE AXIS MOVES OVERHEAD THIS EVENING...THE BOUNDARY MAY PUSH
THROUGH AS IT WASHES OUT...BUT EITHER WAY EXPECT WINDS TO GO LIGHT
AND VARIABLE AS THE SUN SETS. SSE WINDS WILL BEGIN TO PICK UP
TOMORROW MORNING AS LOW PRESSURE SKIRTS EAST ACROSS THE PLAINS.
GUSTS TO OR IN EXCESS OF 30 KTS ARE POSSIBLE MAINLY AFTER
18Z...THOUGH FOR NOW SUSPECT MODELS MAY BE OVERDOING THE WIND
POTENTIAL GIVEN THE STABLE CONDITIONS DUE TO WARM ADVECTION OVER
THE COLD GROUND.

BMD

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

* LOW CONFIDENCE IN LAKE BREEZE PUSHING THROUGH ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

DZ

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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








000
FXUS63 KLOT 151612
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1112 AM CDT TUE APR 15 2014

.DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR LAKE BREEZE THIS AFTERNOON/EVENING

DZ

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

HIGH PRESSURE STRETCHES FROM MINNESOTA INTO KANSAS EARLY THIS
MORNING WITH A MODEST N-NNW GRADIENT IN PLACE ACROSS NORTHERN
ILLINOIS. COLD ADVECTION INTO THE AREA IS RESULTING IN STEEP LOW
LEVEL LAPSE RATES...AND ESPECIALLY AS THE SUN RISES EXPECT WINDS
HOVERING AROUND OR SLIGHTLY ABOVE 10 KTS TODAY WITH A FEW OCCASIONAL
GUSTS INTO THE MID TEENS. WINDS WILL DIMINISH SLIGHTLY THIS
AFTERNOON ALLOWING A LAKE BREEZE TO DEVELOP. WINDS WILL TURN NE AT
GYY...AND THE BOUNDARY WILL TRY TO PUSH WEST TOWARDS MDW/ORD BUT
WITH WEAK TEMPERATURE CONTRAST AND AN OPPOSING SYNOPTIC WIND...NOT
CONFIDENT IT WILL MAKE IT THROUGH THE TERMINALS THIS AFTERNOON. AS
THE RIDGE AXIS MOVES OVERHEAD THIS EVENING...THE BOUNDARY MAY PUSH
THROUGH AS IT WASHES OUT...BUT EITHER WAY EXPECT WINDS TO GO LIGHT
AND VARIABLE AS THE SUN SETS. SSE WINDS WILL BEGIN TO PICK UP
TOMORROW MORNING AS LOW PRESSURE SKIRTS EAST ACROSS THE PLAINS.
GUSTS TO OR IN EXCESS OF 30 KTS ARE POSSIBLE MAINLY AFTER
18Z...THOUGH FOR NOW SUSPECT MODELS MAY BE OVERDOING THE WIND
POTENTIAL GIVEN THE STABLE CONDITIONS DUE TO WARM ADVECTION OVER
THE COLD GROUND.

BMD

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

* LOW CONFIDENCE IN LAKE BREEZE PUSHING THROUGH ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

DZ

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 151400
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
900 AM CDT TUE APR 15 2014

.DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...329 AM CDT

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR A LAKE BREEZE THIS AFTERNOON/EVENING

BMD/DZ

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

HIGH PRESSURE STRETCHES FROM MINNESOTA INTO KANSAS EARLY THIS
MORNING WITH A MODEST N-NNW GRADIENT IN PLACE ACROSS NORTHERN
ILLINOIS. COLD ADVECTION INTO THE AREA IS RESULTING IN STEEP LOW
LEVEL LAPSE RATES...AND ESPECIALLY AS THE SUN RISES EXPECT WINDS
HOVERING AROUND OR SLIGHTLY ABOVE 10 KTS TODAY WITH A FEW OCCASIONAL
GUSTS INTO THE MID TEENS. WINDS WILL DIMINISH SLIGHTLY THIS
AFTERNOON ALLOWING A LAKE BREEZE TO DEVELOP. WINDS WILL TURN NE AT
GYY...AND THE BOUNDARY WILL TRY TO PUSH WEST TOWARDS MDW/ORD BUT
WITH WEAK TEMPERATURE CONTRAST AND AN OPPOSING SYNOPTIC WIND...NOT
CONFIDENT IT WILL MAKE IT THROUGH THE TERMINALS THIS AFTERNOON. AS
THE RIDGE AXIS MOVES OVERHEAD THIS EVENING...THE BOUNDARY MAY PUSH
THROUGH AS IT WASHES OUT...BUT EITHER WAY EXPECT WINDS TO GO LIGHT
AND VARIABLE AS THE SUN SETS. SSE WINDS WILL BEGIN TO PICK UP
TOMORROW MORNING AS LOW PRESSURE SKIRTS EAST ACROSS THE PLAINS.
GUSTS TO OR IN EXCESS OF 30 KTS ARE POSSIBLE MAINLY AFTER
18Z...THOUGH FOR NOW SUSPECT MODELS MAY BE OVERDOING THE WIND
POTENTIAL GIVEN THE STABLE CONDITIONS DUE TO WARM ADVECTION OVER
THE COLD GROUND.

BMD

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

* LOW CONFIDENCE IN LAKE BREEZE PUSHING THROUGH ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

BMD/DZ

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 151138
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
638 AM CDT TUE APR 15 2014

.DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...
329 AM CDT

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR A LAKE BREEZE THIS AFTERNOON/EVENING

BMD

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

HIGH PRESSURE STRETCHES FROM MINNESOTA INTO KANSAS EARLY THIS
MORNING WITH A MODEST N-NNW GRADIENT IN PLACE ACROSS NORTHERN
ILLINOIS. COLD ADVECTION INTO THE AREA IS RESULTING IN STEEP LOW
LEVEL LAPSE RATES...AND ESPECIALLY AS THE SUN RISES EXPECT WINDS
HOVERING AROUND OR SLIGHTLY ABOVE 10 KTS TODAY WITH A FEW OCCASIONAL
GUSTS INTO THE MID TEENS. WINDS WILL DIMINISH SLIGHTLY THIS
AFTERNOON ALLOWING A LAKE BREEZE TO DEVELOP. WINDS WILL TURN NE AT
GYY...AND THE BOUNDARY WILL TRY TO PUSH WEST TOWARDS MDW/ORD BUT
WITH WEAK TEMPERATURE CONTRAST AND AN OPPOSING SYNOPTIC WIND...NOT
CONFIDENT IT WILL MAKE IT THROUGH THE TERMINALS THIS AFTERNOON. AS
THE RIDGE AXIS MOVES OVERHEAD THIS EVENING...THE BOUNDARY MAY PUSH
THROUGH AS IT WASHES OUT...BUT EITHER WAY EXPECT WINDS TO GO LIGHT
AND VARIABLE AS THE SUN SETS. SSE WINDS WILL BEGIN TO PICK UP
TOMORROW MORNING AS LOW PRESSURE SKIRTS EAST ACROSS THE PLAINS.
GUSTS TO OR IN EXCESS OF 30 KTS ARE POSSIBLE MAINLY AFTER
18Z...THOUGH FOR NOW SUSPECT MODELS MAY BE OVERDOING THE WIND
POTENTIAL GIVEN THE STABLE CONDITIONS DUE TO WARM ADVECTION OVER
THE COLD GROUND.

BMD


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

* LOW CONFIDENCE IN LAKE BREEZE PUSHING THROUGH ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

BMD

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 150901
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
401 AM CDT TUE APR 15 2014

.DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...
329 AM CDT

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR A LAKE BREEZE TUESDAY AFTERNOON/EVENING.

BMD

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

HIGH PRESSURE IS SLOWLY BUILDING EAST FROM THE MID-MISSOURI VALLEY
WITH MFVR CIGS AND LIGHT SNOW GRADUALLY ERODING AND SHIFTING EAST OF
THE TERMINALS TONIGHT. THE EXCEPTION WILL BE AT GARY WHERE SOME LAKE
EFFECT SNOW WILL BE AT OR NEAR THE TERMINAL FOR THE NEXT FEW HOURS.
OTHERWISE...VFR CONDITIONS ARE SETTING UP ACROSS THE REMAINDER OF
THE AREA WITH MODEST NORTHWEST WINDS. WINDS WILL BACK TOWARDS THE
WEST TUESDAY AFTERNOON AND DIMINISH SOME...ALLOWING A LAKE BREEZE TO
DEVELOP. WITH WEAK THERMAL CONTRAST BETWEEN THE LAKE AND LAND...AND
AN OPPOSING WEST FLOW...IT REMAINS DOUBTFUL THAT THE LAKE BREEZE
WILL MAKE IT THROUGH ORD/MDW SO FOR NOW WILL HOLD OFF ON ANY
WIND SHIFT BUT IT WILL NEED TO BE MONITORED. HIGH PRESSURE WILL BUILD
OVERHEAD MID TO LAKE EVENING TUESDAY WITH WINDS BECOMING LIGHT AND
VARIABLE OVERNIGHT...THEN BECOMING SOUTHEASTERLY EARLY WEDNESDAY.

BMD

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

* LOW CONFIDENCE THAT A LAKE BREEZE WILL REACH ORD/MDW.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

BMD

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 150829
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
329 AM CDT TUE APR 15 2014

.DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...
329 AM CDT

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

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

* POTENTIAL FOR A LAKE BREEZE TUESDAY AFTERNOON/EVENING.

BMD

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

HIGH PRESSURE IS SLOWLY BUILDING EAST FROM THE MID-MISSOURI VALLEY
WITH MFVR CIGS AND LIGHT SNOW GRADUALLY ERODING AND SHIFTING EAST OF
THE TERMINALS TONIGHT. THE EXCEPTION WILL BE AT GARY WHERE SOME LAKE
EFFECT SNOW WILL BE AT OR NEAR THE TERMINAL FOR THE NEXT FEW HOURS.
OTHERWISE...VFR CONDITIONS ARE SETTING UP ACROSS THE REMAINDER OF
THE AREA WITH MODEST NORTHWEST WINDS. WINDS WILL BACK TOWARDS THE
WEST TUESDAY AFTERNOON AND DIMINISH SOME...ALLOWING A LAKE BREEZE TO
DEVELOP. WITH WEAK THERMAL CONTRAST BETWEEN THE LAKE AND LAND...AND
AN OPPOSING WEST FLOW...IT REMAINS DOUBTFUL THAT THE LAKE BREEZE
WILL MAKE IT THROUGH ORD/MDW SO FOR NOW WILL HOLD OFF ON ANY
WIND SHIFT BUT IT WILL NEED TO BE MONITORED. HIGH PRESSURE WILL BUILD
OVERHEAD MID TO LAKE EVENING TUESDAY WITH WINDS BECOMING LIGHT AND
VARIABLE OVERNIGHT...THEN BECOMING SOUTHEASTERLY EARLY WEDNESDAY.

BMD

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

* LOW CONFIDENCE THAT A LAKE BREEZE WILL REACH ORD/MDW.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

BMD

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 150740
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
240 AM CDT TUE APR 15 2014

.DISCUSSION...
804 PM CDT

FOR EVENING UPDATE...

MADE SOME TWEAKS TO HOURLY POP/WX GRIDS TO SHARPEN UP THE TRAILING
EDGE AND TIGHTEN TIMING OF ENDING OF CURRENT SNOW. ALSO INCREASED
CHANCE POPS SOMEWHAT AND ADDED MENTION OF SOME ADDITIONAL MINOR
ACCUMULATION ACROSS NORTHWEST INDIANA BEYOND MIDNIGHT FOR LAKE
EFFECT SNOW SHOWERS.

UNWELCOME REMINDER THAT APRIL CAN STILL BE WINTER-LIKE IN THE
MIDWEST THIS AFTERNOON/EVENING...AS BAND OF LIGHT/MODERATE SNOW
CONTINUES TO SHIFT EAST ACROSS THE FORECAST AREA AT 730 PM CDT.
THIS BAND OF SNOW IS BEING DRIVEN BY A COMBINATION OF A MID-LEVEL
SHORT WAVE TROUGH LIFTING NORTHEAST FROM MISSOURI...THE APPROACH OF
A LONG WAVE UPPER TROUGH FROM THE WEST...WITH ENHANCEMENT INTO
STRONGER SOUTHWEST-NORTHEAST BANDS BY MID-LEVEL FRONTOGENESIS.
REGIONAL RADAR MOSAIC HAS CONSISTENTLY INDICATED A FAIRLY SHARP
TRAILING EDGE TO THE MORE INTENSE SNOW...ROUGHLY ALONG A SPRINGFIELD
TO STREATOR TO ARLINGTON HEIGHTS AND HIGHLAND PARK IL LINE AT THIS
TIME. FRONTOGENESIS MAXIMA AT 700 HPA DEPICTED NICELY BY THE RAP...
AND EVOLUTION OF THIS FEATURE OFF TO THE EAST SHOWS NICE CORRELATION
WITH RADAR TRENDS OVER THE PAST FEW HOURS AND INDICATES THAT SNOW
WILL TAPER TO FLURRIES AND LARGELY END FROM WEST TO EAST ACROSS MUCH
OF THE CHICAGO AREA BY 9 PM...AND PRIOR TO 11 PM FOR OUR NORTHWEST
INDIANA AND FAR EAST CENTRAL IL COUNTIES. TOTAL SNOWFALL REPORTS
HAVE RANGED FROM A HALF INCH TO NEAR 2 INCHES IN SPOTS THAT HAVE
BEEN AFFECTED BY THE ENHANCED HEAVIER BANDING.

NORTH WINDS AND COLD AIR DO LOOK TO MAINTAIN THE POTENTIAL FOR SOME
LAKE EFFECT SNOW SHOWERS ALONG THE SOUTH END OF THE LAKE THROUGH THE
OVERNIGHT HOURS...WITH LAKE EFFECT PARAMETERS FROM THE 18Z NAM
SUPPORTIVE OF ORGANIZED CONVECTIVE SNOW SHOWERS (DELTA T AROUND
16C...EQUILIBRIUM HEIGHTS OVER 8 KFT...UNIDIRECTIONAL NORTH FLOW
NEAR 20 KT THROUGH MARINE BOUNDARY LAYER). BASED ON THIS...HAVE
INCREASED CHANCE POPS ACROSS LAKE/PORTER COUNTY AFTER MIDNIGHT
TONIGHT AND INTO TUESDAY BEFORE APPROACHING SURFACE RIDGE MAKES THE
LOW LEVEL WIND FIELD INCREASINGLY LESS FAVORABLE.

OTHER CONCERN THIS EVENING WITH LUNAR ECLIPSE TO OCCUR AFTER
MIDNIGHT IS WITH CLEARING OF CLOUD COVER. THICKER/DEEPER CLOUD COVER
ASSOCIATED WITH MID-LEVEL TROUGH LOOKS TO CLEAR OUR EASTERN COUNTIES
AROUND OR SHORTLY AFTER MIDNIGHT BASED ON EXTRAPOLATION OF SATELLITE
IMAGES. WHILE SOME EROSION/DISSIPATION IS POSSIBLE...AREA OF
CLOSED-CELL STRATO-CU UPSTREAM ACROSS IA/MN WITH BASES 5000-7000 FT
MAY TEND TO PERSIST DUE TO FAIRLY STEEP LOW LEVEL LAPSE RATES IN
STRONG LOW LEVEL COLD ADVECTION REGIME. WILL MAINTAIN A BECOMING
PARTLY CLOUDY FORECAST AFTER MIDNIGHT...AND HOPEFULLY THE ECLIPSE
WILL BE VISIBLE BETWEEN PASSING PATCHES OF STRATOCU.

RATZER

//PREV DISCUSSION...
314 PM CDT

THE MAIN PERIOD OF ACTIVE WEATHER WILL BE THIS EVENING WITH A MORE
TRANQUIL PERIOD SETTING UP INTO TUESDAY AND CONTINUING THROUGH MUCH
OF THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS AN EXPANSIVE
LONGWAVE TROUGH OVER THE MID SECTION OF THE COUNTRY WITH THE TROUGH
AXIS SWINGING EASTWARD TOWARD THE LOCAL AREA. A SHARP BUT NARROW
RIDGE TRAILS THE BIG TROUGH OVER WEST COAST WITH A SERIES OF MORE
COMPACT UPPER LOWS SPINNING EASTWARD TOWARDS THE CANADIAN WEST
COAST. AT THE SURFACE...THE MAIN SURFACE LOW WHICH BROUGHT THE
ACTIVE WEATHER OVER THE PAST FEW DAYS IS NOW OVER EASTERN QUEBEC
WITH HIGH PRESSURE SPREADING SOUTHWARD ACROSS THE CANADIAN PRAIRIES
INTO THE CENTRAL AND NORTHERN PLANS.

TONIGHT...WATER VAPOR SHOWS AN EMBEDDED UPPER WAVE MOVING INTO THE
AREA FROM THE SOUTHWEST LATE THIS AFTERNOON. THIS IS TIGHTENING THE
MID LEVEL BAROCLINIC ZONE AND RESULTING IN INTENSIFYING
FRONTOGENESIS IN A CORRIDOR ACROSS THE NORTHWEST CWA WHICH IS
SHIFTING EASTWARD. COLDER AIR AT THE SURFACE AND ALOFT CONTINUES TO
SPREAD SOUTHEASTWARD AS WELL. PRECIP WILL CONTINUE TO INTENSIFY IN
CONJUNCTION WITH THE INCREASED FORCING WHILE THE ENTIRE BAND PIVOTS
EASTWARD AS THE LONGWAVE TROUGH AXIS PUSHES EASTWARD INTO THE
EVENING. FORECAST SOUNDINGS SHOW THAT THE BEST FORCING LINES UP WELL
WITH THE FAVORED SNOW GROWTH REGION SUPPORTING EFFICIENT SNOW GROWTH
WITH THE COLUMN COLD ENOUGH TO SUPPORT ALL SNOW WITHIN THE BAND.
AREAS TO THE SOUTH AND WEST OF THE HAVE BEEN REPORTING VSBY AS LOW
AS 1/4 TO 3/4 SM VSBY UNDER THE HEAVIER PRECIP ELEMENTS. SURFACE
TEMPS...WHILE STILL ABOVE FREEZING WILL COOL WITH TIME FAVORING
ACCUMULATING SNOW BUT GROUND TEMPS WILL BE THE LIMITING FACTOR
OVERALL. HOWEVER...SNOW INTENSITY WITHIN THE HEAVIEST BANDS WILL
LIKELY OVERCOME THE WARMER GROUND...ESPECIALLY ON GRASSY AND
ELEVATED SURFACES...WITH SLUSHY ACCUMULATION POSSIBLE ON ROADWAYS.
BASED ON LATEST TRENDS...AREAS FROM MENDOTA TO CHICAGO NORTHWEST
WILL BE THE FOCUS GOING THROUGH LATE AFTERNOON WITH AN EXPANSION
EXPECTED JUST TO THE SOUTHEAST OF THIS LINE TOWARDS A GARY TO
PONTIAC LINE BY EARLY EVENING. THIS WILL PUT THE CORRIDOR OF
HEAVIEST SNOW ACROSS THE CHICAGO METRO FOR MUCH OF IF NOT ALL OF THE
EVENING RUSH...WITH DEPARTURE FROM THE ROCKFORD AREA RIGHT AROUND
THE START. THE MAIN VORT RESPONSIBLE FOR THIS WILL ZIP NORTHEAST SO
THERE MAY BE A DECREASE IN INTENSITY OF THE BAND TOWARD MID EVENING
BUT BROADER SCALE FORCING WILL CONTINUE TO BRING PRECIP AT A LOWER
RATE THROUGH THE EVENING FROM THE GARY/CHICAGO AREA TO PONTIAC AND
POINTS EAST. ANOTHER WAVE WILL LIFT NORTHEAST INTO NORTH-CENTRAL
INDIANA THIS EVENING AND MAY BRING AN INCREASE IN SNOW TO NORTHWEST
INDIANA MID/LATE EVENING BUT THIS MAY REMAIN TO THE EAST. WILL
CONTINUE WITH ACCUMULATION AROUND AN INCH FOR MOST AREAS EXCEPT FAR
SOUTH WHERE SNOW WILL LIKELY BE LIGHTER AND TEMPS A LITTLE WARMER.
AM THINKING THAT THE CORRIDOR FROM MENDOTA UP TO THE NORTHERN
CHICAGO SUBURBS AND EVEN WAUKEGAN...THEN SOUTHEAST TO THE GARY AND
PONTIAC AREA MAY SEE THE MOST INTENSE SNOW OVERALL AS WELL AS
OVERLAP WITH COLDEST TEMPS GOING INTO THE EVENING. HOWEVER...JUST
ABOUT ANYONE WEST OF GARY-PONTIAC COULD SEE AN INCH GIVEN SNOW
INTENSITY SEEN SO FAR TODAY. DO NOT REALLY HAVE A GOOD FEEL FOR
ACCUMULATION GIVEN THE WARM GROUND ETC...AND CANNOT RULE OUT SOME 2
INCH AMOUNTS UNDER THE MOST PERSISTENT BANDS. SNOW WILL TAPER OFF
FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER TROUGH AXIS LATE
THIS EVENING AND EARLY TONIGHT.

ANOTHER CONCERN IS LAKE EFFECT POTENTIAL INTO THE OVERNIGHT. COLDER
AIR WILL CONTINUE TO SPREAD SOUTHWARD INTO THE AREA WITH A GOOD
NORTH FETCH DOWN LAKE MICHIGAN. H85 TEMPS FALL TO AROUND -14 C WHICH
IS ENOUGH TO SUPPORT LAKE EFFECT...WITH LAKE WATER TEMPS PROBABLY
/PERHAPS CONSERVATIVELY/ IN THE UPPER 30S ACROSS MUCH OF THE
SOUTHERN PART OF THE LAKE /WITH MID/UPPER 40S AT NEARSHORE OBS
SITES/ DELTA TS ARE AT LEAST IN THE UPPER TEENS. THE PASSAGE OF THE
UPPER TROUGH WILL BRING SOME SUPPRESSION AS WELL AS DEEP LAYER
DRYING INTO THE REGION BUT LAKE INDUCED EQUILIBRIUM LEVELS
MAY PUSH 6-7 KFT OVERNIGHT. WITH A GRADUALLY WEAKENING PRESSURE
GRADIENT TO THE WEST...WINDS WILL EASE UP FROM WEST TO EAST AND THIS
MAY LEAD TO CONVERGENCE NEAR OR OFF THE ILLINOIS SHORE. SO IF PRECIP
CAN DEVELOP...WHICH IS A BIT OF A WILD CARD...THEN SOUTHERN SECTIONS
OF COOK COUNTY AND WESTERN PORTIONS OF LAKE COUNTY INDIANA MAY SEE
SNOW SHOWERS OVERNIGHT. IT IS ALSO NOT OUT OF THE REALM OF
POSSIBILITY THAT A FURTHER INLAND PUSH TO THE WEST COULD OCCUR INTO
THE CHICAGO AND NORTH SHORE AREAS. WILL GO AHEAD AND CARRY LOW POPS
AT THE SHORELINE AND INTO FAR SOUTHEAST COOK AND WESTERN LAKE COUNTY
THROUGH THE OVERNIGHT. SHORELINE AREAS COULD STAY AT OR JUST ABOVE
FREEZING GIVEN THE LAKE SO ANY ACCUMULATION COULD BE SLUSHY OR EVEN
GRADUALLY MELT...BUT AREAS JUST INLAND WILL LIKELY BE IN THE UPPER
20S TO AROUND 30 SO ACCUMULATION IS A CONCERN. WILL SHARE CONCERN
WITH THE EVENING SHIFT FOR FURTHER MONITORING. OTHERWISE WINDS WILL
EASE INLAND WITH SKIES CLEARING ACROSS WESTERN AREAS ALLOWING TEMPS
TO FALL INTO THE LOWER TO MID 20S.

TUESDAY THROUGH FRIDAY...THE UPPER FLOW WILL FLATTEN BEHIND THE
DEPARTING UPPER TROUGH TUESDAY AS SURFACE HIGH PRESSURE CROSSES THE
AREA. MID LEVEL WARM ADVECTION WILL COMMENCE IN THE AFTERNOON. HIGH
TEMPS WILL BE TOUGH GIVEN THE HIGH SUN ANGLE BUT VERY COLD START AND
SLOW START TO MID LEVEL WAA. LOW LEVEL LAPSE RATES STEEPEN QUITE A
BIT BY AFTERNOON AND WITH THE CONTINUED CYCLONIC FLOW ALOFT WILL
LIKELY SEE SCT-BKN CU DEVELOP INTO THE MIDDAY THEN DISSIPATE FROM
WEST TO EAST DURING THE LATE AFTERNOON. THAT SAID...WE HAVE SEEN
SEVERAL DAYS IN RECENT WEEKS WHERE TEMPS WARMED NICELY IN SIMILAR
SITUATIONS. WILL STAY ON THE WARMER SIDE OF THINGS WITH LOWER TO MID
40S WEST AND UPPER 30S TO AROUND 40 EAST. MOISTURE LOOKS PRETTY
SHALLOW BUT CANNOT RULE OUT A FEW SHOWERS DURING THE AFTERNOON BUT
WILL KEEP THE FORECAST DRY FOR NOW. THE TROUGH OFF THE BRITISH
COLUMBIA COAST TODAY WILL WEAKEN AND MOVE SOUTHEAST ACROSS THE UPPER
MIDWEST WEDNESDAY. THIS WILL BRING A PUSH OF WARMER MID LEVEL AREA
WHICH WILL COMBINE WITH INCREASING SOUTHERLY WINDS BEHIND THE
DEPARTING SURFACE HIGH TO PROPEL TEMPS INTO THE 50S WEDNESDAY. A
SURFACE LOW WILL ACCOMPANY THE UPPER TROUGH WITH A WARM FRONT
DEVELOPING NORTH OF THE AREA. THIS SHOULD KEEP THE LOCAL AREA DRY
WEDNESDAY BUT THE ATTENDANT COLD FRONT WILL MOVE IN THURSDAY
POTENTIALLY BRINGING SOME PRECIP. THE FRONT STALLS OUT OVER OR NEAR
THE AREA THURSDAY EVENING AND A SECOND UPPER TROUGH DIGS INTO THE
CENTRAL AND SOUTHERN PLAINS. A NEW SURFACE LOW WILL TRACK NORTHEAST
AND ACROSS THE LOCAL AREA FRIDAY. PRECIP CHANCES LOOK TO RAMP UP
THURSDAY EVENING NORTHWEST OF THE FRONT...THEN EXPAND ACROSS THE
AREA SOME TIME FRIDAY AS THE SURFACE LOW PASSES. PROVIDED THE
BOUNDARY ARRIVES LATE ENOUGH THURSDAY HIGHS WILL LIKELY BE IN THE
60S...WITH FRIDAY BEING COOLER BUT ALSO SEEING A LARGER RANGE OF
TEMPS THANKS TO THE BOUNDARY. EXPECT LOWER 50S NORTH AND UPPER 50S
SOUTH.

SATURDAY AND BEYOND...THE LOW WILL CLEAR TO THE NORTHEAST SOME TIME
EARLY SATURDAY WITH HIGH PRESSURE BUILDING IN THROUGH THE DAY. WITH
THE UPPER FLOW NOT ALL THAT AMPLIFIED THERE WILL BE LITTLE IN THE
WAY OF COOLING ALOFT AND ENOUGH SUNSHINE SHOULD HELP PROPEL TEMPS
INTO THE 50S. ANOTHER TROUGH LOOKS TO CROSS THE AREA SUNDAY BRINGING
MORE CHANCES FOR RAIN BUT OVERALL MILD TEMPS IN THE 50S.

MDB

&&

.CLIMATE...
THE FOLLOWING ARE THE MOST RECENT APRIL DATES AND
AMOUNTS OF ACCUMULATING SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* POTENTIAL FOR A LAKE BREEZE TUESDAY AFTERNOON/EVENING.

BMD

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

HIGH PRESSURE IS SLOWLY BUILDING EAST FROM THE MID-MISSOURI VALLEY
WITH MFVR CIGS AND LIGHT SNOW GRADUALLY ERODING AND SHIFTING EAST OF
THE TERMINALS TONIGHT. THE EXCEPTION WILL BE AT GARY WHERE SOME LAKE
EFFECT SNOW WILL BE AT OR NEAR THE TERMINAL FOR THE NEXT FEW HOURS.
OTHERWISE...VFR CONDITIONS ARE SETTING UP ACROSS THE REMAINDER OF
THE AREA WITH MODEST NORTHWEST WINDS. WINDS WILL BACK TOWARDS THE
WEST TUESDAY AFTERNOON AND DIMINISH SOME...ALLOWING A LAKE BREEZE TO
DEVELOP. WITH WEAK THERMAL CONTRAST BETWEEN THE LAKE AND LAND...AND
AN OPPOSING WEST FLOW...IT REMAINS DOUBTFUL THAT THE LAKE BREEZE
WILL MAKE IT THROUGH ORD/MDW SO FOR NOW WILL HOLD OFF ON ANY
WIND SHIFT BUT IT WILL NEED TO BE MONITORED. HIGH PRESSURE WILL BUILD
OVERHEAD MID TO LAKE EVENING TUESDAY WITH WINDS BECOMING LIGHT AND
VARIABLE OVERNIGHT...THEN BECOMING SOUTHEASTERLY EARLY WEDNESDAY.

BMD

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

* LOW CONFIDENCE THAT A LAKE BREEZE WILL REACH ORD/MDW.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

BMD

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 150554
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1254 AM CDT TUE APR 15 2014

.DISCUSSION...
804 PM CDT

FOR EVENING UPDATE...

MADE SOME TWEAKS TO HOURLY POP/WX GRIDS TO SHARPEN UP THE TRAILING
EDGE AND TIGHTEN TIMING OF ENDING OF CURRENT SNOW. ALSO INCREASED
CHANCE POPS SOMEWHAT AND ADDED MENTION OF SOME ADDITIONAL MINOR
ACCUMULATION ACROSS NORTHWEST INDIANA BEYOND MIDNIGHT FOR LAKE
EFFECT SNOW SHOWERS.

UNWELCOME REMINDER THAT APRIL CAN STILL BE WINTER-LIKE IN THE
MIDWEST THIS AFTERNOON/EVENING...AS BAND OF LIGHT/MODERATE SNOW
CONTINUES TO SHIFT EAST ACROSS THE FORECAST AREA AT 730 PM CDT.
THIS BAND OF SNOW IS BEING DRIVEN BY A COMBINATION OF A MID-LEVEL
SHORT WAVE TROUGH LIFTING NORTHEAST FROM MISSOURI...THE APPROACH OF
A LONG WAVE UPPER TROUGH FROM THE WEST...WITH ENHANCEMENT INTO
STRONGER SOUTHWEST-NORTHEAST BANDS BY MID-LEVEL FRONTOGENESIS.
REGIONAL RADAR MOSAIC HAS CONSISTENTLY INDICATED A FAIRLY SHARP
TRAILING EDGE TO THE MORE INTENSE SNOW...ROUGHLY ALONG A SPRINGFIELD
TO STREATOR TO ARLINGTON HEIGHTS AND HIGHLAND PARK IL LINE AT THIS
TIME. FRONTOGENESIS MAXIMA AT 700 HPA DEPICTED NICELY BY THE RAP...
AND EVOLUTION OF THIS FEATURE OFF TO THE EAST SHOWS NICE CORRELATION
WITH RADAR TRENDS OVER THE PAST FEW HOURS AND INDICATES THAT SNOW
WILL TAPER TO FLURRIES AND LARGELY END FROM WEST TO EAST ACROSS MUCH
OF THE CHICAGO AREA BY 9 PM...AND PRIOR TO 11 PM FOR OUR NORTHWEST
INDIANA AND FAR EAST CENTRAL IL COUNTIES. TOTAL SNOWFALL REPORTS
HAVE RANGED FROM A HALF INCH TO NEAR 2 INCHES IN SPOTS THAT HAVE
BEEN AFFECTED BY THE ENHANCED HEAVIER BANDING.

NORTH WINDS AND COLD AIR DO LOOK TO MAINTAIN THE POTENTIAL FOR SOME
LAKE EFFECT SNOW SHOWERS ALONG THE SOUTH END OF THE LAKE THROUGH THE
OVERNIGHT HOURS...WITH LAKE EFFECT PARAMETERS FROM THE 18Z NAM
SUPPORTIVE OF ORGANIZED CONVECTIVE SNOW SHOWERS (DELTA T AROUND
16C...EQUILIBRIUM HEIGHTS OVER 8 KFT...UNIDIRECTIONAL NORTH FLOW
NEAR 20 KT THROUGH MARINE BOUNDARY LAYER). BASED ON THIS...HAVE
INCREASED CHANCE POPS ACROSS LAKE/PORTER COUNTY AFTER MIDNIGHT
TONIGHT AND INTO TUESDAY BEFORE APPROACHING SURFACE RIDGE MAKES THE
LOW LEVEL WIND FIELD INCREASINGLY LESS FAVORABLE.

OTHER CONCERN THIS EVENING WITH LUNAR ECLIPSE TO OCCUR AFTER
MIDNIGHT IS WITH CLEARING OF CLOUD COVER. THICKER/DEEPER CLOUD COVER
ASSOCIATED WITH MID-LEVEL TROUGH LOOKS TO CLEAR OUR EASTERN COUNTIES
AROUND OR SHORTLY AFTER MIDNIGHT BASED ON EXTRAPOLATION OF SATELLITE
IMAGES. WHILE SOME EROSION/DISSIPATION IS POSSIBLE...AREA OF
CLOSED-CELL STRATO-CU UPSTREAM ACROSS IA/MN WITH BASES 5000-7000 FT
MAY TEND TO PERSIST DUE TO FAIRLY STEEP LOW LEVEL LAPSE RATES IN
STRONG LOW LEVEL COLD ADVECTION REGIME. WILL MAINTAIN A BECOMING
PARTLY CLOUDY FORECAST AFTER MIDNIGHT...AND HOPEFULLY THE ECLIPSE
WILL BE VISIBLE BETWEEN PASSING PATCHES OF STRATOCU.

RATZER

//PREV DISCUSSION...
314 PM CDT

THE MAIN PERIOD OF ACTIVE WEATHER WILL BE THIS EVENING WITH A MORE
TRANQUIL PERIOD SETTING UP INTO TUESDAY AND CONTINUING THROUGH MUCH
OF THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS AN EXPANSIVE
LONGWAVE TROUGH OVER THE MID SECTION OF THE COUNTRY WITH THE TROUGH
AXIS SWINGING EASTWARD TOWARD THE LOCAL AREA. A SHARP BUT NARROW
RIDGE TRAILS THE BIG TROUGH OVER WEST COAST WITH A SERIES OF MORE
COMPACT UPPER LOWS SPINNING EASTWARD TOWARDS THE CANADIAN WEST
COAST. AT THE SURFACE...THE MAIN SURFACE LOW WHICH BROUGHT THE
ACTIVE WEATHER OVER THE PAST FEW DAYS IS NOW OVER EASTERN QUEBEC
WITH HIGH PRESSURE SPREADING SOUTHWARD ACROSS THE CANADIAN PRAIRIES
INTO THE CENTRAL AND NORTHERN PLANS.

TONIGHT...WATER VAPOR SHOWS AN EMBEDDED UPPER WAVE MOVING INTO THE
AREA FROM THE SOUTHWEST LATE THIS AFTERNOON. THIS IS TIGHTENING THE
MID LEVEL BAROCLINIC ZONE AND RESULTING IN INTENSIFYING
FRONTOGENESIS IN A CORRIDOR ACROSS THE NORTHWEST CWA WHICH IS
SHIFTING EASTWARD. COLDER AIR AT THE SURFACE AND ALOFT CONTINUES TO
SPREAD SOUTHEASTWARD AS WELL. PRECIP WILL CONTINUE TO INTENSIFY IN
CONJUNCTION WITH THE INCREASED FORCING WHILE THE ENTIRE BAND PIVOTS
EASTWARD AS THE LONGWAVE TROUGH AXIS PUSHES EASTWARD INTO THE
EVENING. FORECAST SOUNDINGS SHOW THAT THE BEST FORCING LINES UP WELL
WITH THE FAVORED SNOW GROWTH REGION SUPPORTING EFFICIENT SNOW GROWTH
WITH THE COLUMN COLD ENOUGH TO SUPPORT ALL SNOW WITHIN THE BAND.
AREAS TO THE SOUTH AND WEST OF THE HAVE BEEN REPORTING VSBY AS LOW
AS 1/4 TO 3/4 SM VSBY UNDER THE HEAVIER PRECIP ELEMENTS. SURFACE
TEMPS...WHILE STILL ABOVE FREEZING WILL COOL WITH TIME FAVORING
ACCUMULATING SNOW BUT GROUND TEMPS WILL BE THE LIMITING FACTOR
OVERALL. HOWEVER...SNOW INTENSITY WITHIN THE HEAVIEST BANDS WILL
LIKELY OVERCOME THE WARMER GROUND...ESPECIALLY ON GRASSY AND
ELEVATED SURFACES...WITH SLUSHY ACCUMULATION POSSIBLE ON ROADWAYS.
BASED ON LATEST TRENDS...AREAS FROM MENDOTA TO CHICAGO NORTHWEST
WILL BE THE FOCUS GOING THROUGH LATE AFTERNOON WITH AN EXPANSION
EXPECTED JUST TO THE SOUTHEAST OF THIS LINE TOWARDS A GARY TO
PONTIAC LINE BY EARLY EVENING. THIS WILL PUT THE CORRIDOR OF
HEAVIEST SNOW ACROSS THE CHICAGO METRO FOR MUCH OF IF NOT ALL OF THE
EVENING RUSH...WITH DEPARTURE FROM THE ROCKFORD AREA RIGHT AROUND
THE START. THE MAIN VORT RESPONSIBLE FOR THIS WILL ZIP NORTHEAST SO
THERE MAY BE A DECREASE IN INTENSITY OF THE BAND TOWARD MID EVENING
BUT BROADER SCALE FORCING WILL CONTINUE TO BRING PRECIP AT A LOWER
RATE THROUGH THE EVENING FROM THE GARY/CHICAGO AREA TO PONTIAC AND
POINTS EAST. ANOTHER WAVE WILL LIFT NORTHEAST INTO NORTH-CENTRAL
INDIANA THIS EVENING AND MAY BRING AN INCREASE IN SNOW TO NORTHWEST
INDIANA MID/LATE EVENING BUT THIS MAY REMAIN TO THE EAST. WILL
CONTINUE WITH ACCUMULATION AROUND AN INCH FOR MOST AREAS EXCEPT FAR
SOUTH WHERE SNOW WILL LIKELY BE LIGHTER AND TEMPS A LITTLE WARMER.
AM THINKING THAT THE CORRIDOR FROM MENDOTA UP TO THE NORTHERN
CHICAGO SUBURBS AND EVEN WAUKEGAN...THEN SOUTHEAST TO THE GARY AND
PONTIAC AREA MAY SEE THE MOST INTENSE SNOW OVERALL AS WELL AS
OVERLAP WITH COLDEST TEMPS GOING INTO THE EVENING. HOWEVER...JUST
ABOUT ANYONE WEST OF GARY-PONTIAC COULD SEE AN INCH GIVEN SNOW
INTENSITY SEEN SO FAR TODAY. DO NOT REALLY HAVE A GOOD FEEL FOR
ACCUMULATION GIVEN THE WARM GROUND ETC...AND CANNOT RULE OUT SOME 2
INCH AMOUNTS UNDER THE MOST PERSISTENT BANDS. SNOW WILL TAPER OFF
FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER TROUGH AXIS LATE
THIS EVENING AND EARLY TONIGHT.

ANOTHER CONCERN IS LAKE EFFECT POTENTIAL INTO THE OVERNIGHT. COLDER
AIR WILL CONTINUE TO SPREAD SOUTHWARD INTO THE AREA WITH A GOOD
NORTH FETCH DOWN LAKE MICHIGAN. H85 TEMPS FALL TO AROUND -14 C WHICH
IS ENOUGH TO SUPPORT LAKE EFFECT...WITH LAKE WATER TEMPS PROBABLY
/PERHAPS CONSERVATIVELY/ IN THE UPPER 30S ACROSS MUCH OF THE
SOUTHERN PART OF THE LAKE /WITH MID/UPPER 40S AT NEARSHORE OBS
SITES/ DELTA TS ARE AT LEAST IN THE UPPER TEENS. THE PASSAGE OF THE
UPPER TROUGH WILL BRING SOME SUPPRESSION AS WELL AS DEEP LAYER
DRYING INTO THE REGION BUT LAKE INDUCED EQUILIBRIUM LEVELS
MAY PUSH 6-7 KFT OVERNIGHT. WITH A GRADUALLY WEAKENING PRESSURE
GRADIENT TO THE WEST...WINDS WILL EASE UP FROM WEST TO EAST AND THIS
MAY LEAD TO CONVERGENCE NEAR OR OFF THE ILLINOIS SHORE. SO IF PRECIP
CAN DEVELOP...WHICH IS A BIT OF A WILD CARD...THEN SOUTHERN SECTIONS
OF COOK COUNTY AND WESTERN PORTIONS OF LAKE COUNTY INDIANA MAY SEE
SNOW SHOWERS OVERNIGHT. IT IS ALSO NOT OUT OF THE REALM OF
POSSIBILITY THAT A FURTHER INLAND PUSH TO THE WEST COULD OCCUR INTO
THE CHICAGO AND NORTH SHORE AREAS. WILL GO AHEAD AND CARRY LOW POPS
AT THE SHORELINE AND INTO FAR SOUTHEAST COOK AND WESTERN LAKE COUNTY
THROUGH THE OVERNIGHT. SHORELINE AREAS COULD STAY AT OR JUST ABOVE
FREEZING GIVEN THE LAKE SO ANY ACCUMULATION COULD BE SLUSHY OR EVEN
GRADUALLY MELT...BUT AREAS JUST INLAND WILL LIKELY BE IN THE UPPER
20S TO AROUND 30 SO ACCUMULATION IS A CONCERN. WILL SHARE CONCERN
WITH THE EVENING SHIFT FOR FURTHER MONITORING. OTHERWISE WINDS WILL
EASE INLAND WITH SKIES CLEARING ACROSS WESTERN AREAS ALLOWING TEMPS
TO FALL INTO THE LOWER TO MID 20S.

TUESDAY THROUGH FRIDAY...THE UPPER FLOW WILL FLATTEN BEHIND THE
DEPARTING UPPER TROUGH TUESDAY AS SURFACE HIGH PRESSURE CROSSES THE
AREA. MID LEVEL WARM ADVECTION WILL COMMENCE IN THE AFTERNOON. HIGH
TEMPS WILL BE TOUGH GIVEN THE HIGH SUN ANGLE BUT VERY COLD START AND
SLOW START TO MID LEVEL WAA. LOW LEVEL LAPSE RATES STEEPEN QUITE A
BIT BY AFTERNOON AND WITH THE CONTINUED CYCLONIC FLOW ALOFT WILL
LIKELY SEE SCT-BKN CU DEVELOP INTO THE MIDDAY THEN DISSIPATE FROM
WEST TO EAST DURING THE LATE AFTERNOON. THAT SAID...WE HAVE SEEN
SEVERAL DAYS IN RECENT WEEKS WHERE TEMPS WARMED NICELY IN SIMILAR
SITUATIONS. WILL STAY ON THE WARMER SIDE OF THINGS WITH LOWER TO MID
40S WEST AND UPPER 30S TO AROUND 40 EAST. MOISTURE LOOKS PRETTY
SHALLOW BUT CANNOT RULE OUT A FEW SHOWERS DURING THE AFTERNOON BUT
WILL KEEP THE FORECAST DRY FOR NOW. THE TROUGH OFF THE BRITISH
COLUMBIA COAST TODAY WILL WEAKEN AND MOVE SOUTHEAST ACROSS THE UPPER
MIDWEST WEDNESDAY. THIS WILL BRING A PUSH OF WARMER MID LEVEL AREA
WHICH WILL COMBINE WITH INCREASING SOUTHERLY WINDS BEHIND THE
DEPARTING SURFACE HIGH TO PROPEL TEMPS INTO THE 50S WEDNESDAY. A
SURFACE LOW WILL ACCOMPANY THE UPPER TROUGH WITH A WARM FRONT
DEVELOPING NORTH OF THE AREA. THIS SHOULD KEEP THE LOCAL AREA DRY
WEDNESDAY BUT THE ATTENDANT COLD FRONT WILL MOVE IN THURSDAY
POTENTIALLY BRINGING SOME PRECIP. THE FRONT STALLS OUT OVER OR NEAR
THE AREA THURSDAY EVENING AND A SECOND UPPER TROUGH DIGS INTO THE
CENTRAL AND SOUTHERN PLAINS. A NEW SURFACE LOW WILL TRACK NORTHEAST
AND ACROSS THE LOCAL AREA FRIDAY. PRECIP CHANCES LOOK TO RAMP UP
THURSDAY EVENING NORTHWEST OF THE FRONT...THEN EXPAND ACROSS THE
AREA SOME TIME FRIDAY AS THE SURFACE LOW PASSES. PROVIDED THE
BOUNDARY ARRIVES LATE ENOUGH THURSDAY HIGHS WILL LIKELY BE IN THE
60S...WITH FRIDAY BEING COOLER BUT ALSO SEEING A LARGER RANGE OF
TEMPS THANKS TO THE BOUNDARY. EXPECT LOWER 50S NORTH AND UPPER 50S
SOUTH.

SATURDAY AND BEYOND...THE LOW WILL CLEAR TO THE NORTHEAST SOME TIME
EARLY SATURDAY WITH HIGH PRESSURE BUILDING IN THROUGH THE DAY. WITH
THE UPPER FLOW NOT ALL THAT AMPLIFIED THERE WILL BE LITTLE IN THE
WAY OF COOLING ALOFT AND ENOUGH SUNSHINE SHOULD HELP PROPEL TEMPS
INTO THE 50S. ANOTHER TROUGH LOOKS TO CROSS THE AREA SUNDAY BRINGING
MORE CHANCES FOR RAIN BUT OVERALL MILD TEMPS IN THE 50S.

MDB

&&

.CLIMATE...
THE FOLLOWING ARE THE MOST RECENT APRIL DATES AND
AMOUNTS OF ACCUMULATING SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* POTENTIAL FOR A LAKE BREEZE TUESDAY AFTERNOON/EVENING.

BMD

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

HIGH PRESSURE IS SLOWLY BUILDING EAST FROM THE MID-MISSOURI VALLEY
WITH MFVR CIGS AND LIGHT SNOW GRADUALLY ERODING AND SHIFTING EAST OF
THE TERMINALS TONIGHT. THE EXCEPTION WILL BE AT GARY WHERE SOME LAKE
EFFECT SNOW WILL BE AT OR NEAR THE TERMINAL FOR THE NEXT FEW HOURS.
OTHERWISE...VFR CONDITIONS ARE SETTING UP ACROSS THE REMAINDER OF
THE AREA WITH MODEST NORTHWEST WINDS. WINDS WILL BACK TOWARDS THE
WEST TUESDAY AFTERNOON AND DIMINISH SOME...ALLOWING A LAKE BREEZE TO
DEVELOP. WITH WEAK THERMAL CONTRAST BETWEEN THE LAKE AND LAND...AND
AN OPPOSING WEST FLOW...IT REMAINS DOUBTFUL THAT THE LAKE BREEZE
WILL MAKE IT THROUGH ORD/MDW SO FOR NOW WILL HOLD OFF ON ANY
WIND SHIFT BUT IT WILL NEED TO BE MONITORED. HIGH PRESSURE WILL BUILD
OVERHEAD MID TO LAKE EVENING TUESDAY WITH WINDS BECOMING LIGHT AND
VARIABLE OVERNIGHT...THEN BECOMING SOUTHEASTERLY EARLY WEDNESDAY.

BMD

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

* LOW CONFIDENCE THAT A LAKE BREEZE WILL REACH ORD/MDW.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

BMD

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.MARINE...
313 PM CDT

LOW PRESSURE OVER QUEBEC DRAGGED A COLD FRONT OVER THE LAKE THIS
MORNING. NORTH GALES BEHIND THE FRONT HAVE PERSISTED INTO MID
AFTERNOON AND ARE EXPECTED TO EASE QUICKLY THIS EVENING...BUT EAST
SIDE OF THE ENTIRE LAKE IS STILL SEEING GUSTS INTO THE MID 30S TO
AROUND 40 KT RANGE...SO GALE WARNING HAS BEEN EXTENDED INTO THE
EVENING. TO THE WEST...HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TONIGHT THEN INTO THE WESTERN GREAT LAKES LATER TOMORROW. ANOTHER
LOW WILL DEVELOP ACROSS THE CENTRAL AND SOUTHERN PLAINS WEDNESDAY
WITH TROUGHING EXTENDING TO THE NORTHEAST WHICH WILL MOVE OVER
LAKE MICHIGAN WEDNESDAY NIGHT INTO THURSDAY. LOW PRESSURE WILL
THEN LIFT NORTHEAST ACROSS THE MIDWEST OVER THE WEEKEND.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 150320
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1020 PM CDT MON APR 14 2014

.DISCUSSION...
804 PM CDT

FOR EVENING UPDATE...

MADE SOME TWEAKS TO HOURLY POP/WX GRIDS TO SHARPEN UP THE TRAILING
EDGE AND TIGHTEN TIMING OF ENDING OF CURRENT SNOW. ALSO INCREASED
CHANCE POPS SOMEWHAT AND ADDED MENTION OF SOME ADDITIONAL MINOR
ACCUMULATION ACROSS NORTHWEST INDIANA BEYOND MIDNIGHT FOR LAKE
EFFECT SNOW SHOWERS.

UNWELCOME REMINDER THAT APRIL CAN STILL BE WINTER-LIKE IN THE
MIDWEST THIS AFTERNOON/EVENING...AS BAND OF LIGHT/MODERATE SNOW
CONTINUES TO SHIFT EAST ACROSS THE FORECAST AREA AT 730 PM CDT.
THIS BAND OF SNOW IS BEING DRIVEN BY A COMBINATION OF A MID-LEVEL
SHORT WAVE TROUGH LIFTING NORTHEAST FROM MISSOURI...THE APPROACH OF
A LONG WAVE UPPER TROUGH FROM THE WEST...WITH ENHANCEMENT INTO
STRONGER SOUTHWEST-NORTHEAST BANDS BY MID-LEVEL FRONTOGENESIS.
REGIONAL RADAR MOSAIC HAS CONSISTENTLY INDICATED A FAIRLY SHARP
TRAILING EDGE TO THE MORE INTENSE SNOW...ROUGHLY ALONG A SPRINGFIELD
TO STREATOR TO ARLINGTON HEIGHTS AND HIGHLAND PARK IL LINE AT THIS
TIME. FRONTOGENESIS MAXIMA AT 700 HPA DEPICTED NICELY BY THE RAP...
AND EVOLUTION OF THIS FEATURE OFF TO THE EAST SHOWS NICE CORRELATION
WITH RADAR TRENDS OVER THE PAST FEW HOURS AND INDICATES THAT SNOW
WILL TAPER TO FLURRIES AND LARGELY END FROM WEST TO EAST ACROSS MUCH
OF THE CHICAGO AREA BY 9 PM...AND PRIOR TO 11 PM FOR OUR NORTHWEST
INDIANA AND FAR EAST CENTRAL IL COUNTIES. TOTAL SNOWFALL REPORTS
HAVE RANGED FROM A HALF INCH TO NEAR 2 INCHES IN SPOTS THAT HAVE
BEEN AFFECTED BY THE ENHANCED HEAVIER BANDING.

NORTH WINDS AND COLD AIR DO LOOK TO MAINTAIN THE POTENTIAL FOR SOME
LAKE EFFECT SNOW SHOWERS ALONG THE SOUTH END OF THE LAKE THROUGH THE
OVERNIGHT HOURS...WITH LAKE EFFECT PARAMETERS FROM THE 18Z NAM
SUPPORTIVE OF ORGANIZED CONVECTIVE SNOW SHOWERS (DELTA T AROUND
16C...EQUILIBRIUM HEIGHTS OVER 8 KFT...UNIDIRECTIONAL NORTH FLOW
NEAR 20 KT THROUGH MARINE BOUNDARY LAYER). BASED ON THIS...HAVE
INCREASED CHANCE POPS ACROSS LAKE/PORTER COUNTY AFTER MIDNIGHT
TONIGHT AND INTO TUESDAY BEFORE APPROACHING SURFACE RIDGE MAKES THE
LOW LEVEL WIND FIELD INCREASINGLY LESS FAVORABLE.

OTHER CONCERN THIS EVENING WITH LUNAR ECLIPSE TO OCCUR AFTER
MIDNIGHT IS WITH CLEARING OF CLOUD COVER. THICKER/DEEPER CLOUD COVER
ASSOCIATED WITH MID-LEVEL TROUGH LOOKS TO CLEAR OUR EASTERN COUNTIES
AROUND OR SHORTLY AFTER MIDNIGHT BASED ON EXTRAPOLATION OF SATELLITE
IMAGES. WHILE SOME EROSION/DISSIPATION IS POSSIBLE...AREA OF
CLOSED-CELL STRATO-CU UPSTREAM ACROSS IA/MN WITH BASES 5000-7000 FT
MAY TEND TO PERSIST DUE TO FAIRLY STEEP LOW LEVEL LAPSE RATES IN
STRONG LOW LEVEL COLD ADVECTION REGIME. WILL MAINTAIN A BECOMING
PARTLY CLOUDY FORECAST AFTER MIDNIGHT...AND HOPEFULLY THE ECLIPSE
WILL BE VISIBLE BETWEEN PASSING PATCHES OF STRATOCU.

RATZER

//PREV DISCUSSION...
314 PM CDT

THE MAIN PERIOD OF ACTIVE WEATHER WILL BE THIS EVENING WITH A MORE
TRANQUIL PERIOD SETTING UP INTO TUESDAY AND CONTINUING THROUGH MUCH
OF THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS AN EXPANSIVE
LONGWAVE TROUGH OVER THE MID SECTION OF THE COUNTRY WITH THE TROUGH
AXIS SWINGING EASTWARD TOWARD THE LOCAL AREA. A SHARP BUT NARROW
RIDGE TRAILS THE BIG TROUGH OVER WEST COAST WITH A SERIES OF MORE
COMPACT UPPER LOWS SPINNING EASTWARD TOWARDS THE CANADIAN WEST
COAST. AT THE SURFACE...THE MAIN SURFACE LOW WHICH BROUGHT THE
ACTIVE WEATHER OVER THE PAST FEW DAYS IS NOW OVER EASTERN QUEBEC
WITH HIGH PRESSURE SPREADING SOUTHWARD ACROSS THE CANADIAN PRAIRIES
INTO THE CENTRAL AND NORTHERN PLANS.

TONIGHT...WATER VAPOR SHOWS AN EMBEDDED UPPER WAVE MOVING INTO THE
AREA FROM THE SOUTHWEST LATE THIS AFTERNOON. THIS IS TIGHTENING THE
MID LEVEL BAROCLINIC ZONE AND RESULTING IN INTENSIFYING
FRONTOGENESIS IN A CORRIDOR ACROSS THE NORTHWEST CWA WHICH IS
SHIFTING EASTWARD. COLDER AIR AT THE SURFACE AND ALOFT CONTINUES TO
SPREAD SOUTHEASTWARD AS WELL. PRECIP WILL CONTINUE TO INTENSIFY IN
CONJUNCTION WITH THE INCREASED FORCING WHILE THE ENTIRE BAND PIVOTS
EASTWARD AS THE LONGWAVE TROUGH AXIS PUSHES EASTWARD INTO THE
EVENING. FORECAST SOUNDINGS SHOW THAT THE BEST FORCING LINES UP WELL
WITH THE FAVORED SNOW GROWTH REGION SUPPORTING EFFICIENT SNOW GROWTH
WITH THE COLUMN COLD ENOUGH TO SUPPORT ALL SNOW WITHIN THE BAND.
AREAS TO THE SOUTH AND WEST OF THE HAVE BEEN REPORTING VSBY AS LOW
AS 1/4 TO 3/4 SM VSBY UNDER THE HEAVIER PRECIP ELEMENTS. SURFACE
TEMPS...WHILE STILL ABOVE FREEZING WILL COOL WITH TIME FAVORING
ACCUMULATING SNOW BUT GROUND TEMPS WILL BE THE LIMITING FACTOR
OVERALL. HOWEVER...SNOW INTENSITY WITHIN THE HEAVIEST BANDS WILL
LIKELY OVERCOME THE WARMER GROUND...ESPECIALLY ON GRASSY AND
ELEVATED SURFACES...WITH SLUSHY ACCUMULATION POSSIBLE ON ROADWAYS.
BASED ON LATEST TRENDS...AREAS FROM MENDOTA TO CHICAGO NORTHWEST
WILL BE THE FOCUS GOING THROUGH LATE AFTERNOON WITH AN EXPANSION
EXPECTED JUST TO THE SOUTHEAST OF THIS LINE TOWARDS A GARY TO
PONTIAC LINE BY EARLY EVENING. THIS WILL PUT THE CORRIDOR OF
HEAVIEST SNOW ACROSS THE CHICAGO METRO FOR MUCH OF IF NOT ALL OF THE
EVENING RUSH...WITH DEPARTURE FROM THE ROCKFORD AREA RIGHT AROUND
THE START. THE MAIN VORT RESPONSIBLE FOR THIS WILL ZIP NORTHEAST SO
THERE MAY BE A DECREASE IN INTENSITY OF THE BAND TOWARD MID EVENING
BUT BROADER SCALE FORCING WILL CONTINUE TO BRING PRECIP AT A LOWER
RATE THROUGH THE EVENING FROM THE GARY/CHICAGO AREA TO PONTIAC AND
POINTS EAST. ANOTHER WAVE WILL LIFT NORTHEAST INTO NORTH-CENTRAL
INDIANA THIS EVENING AND MAY BRING AN INCREASE IN SNOW TO NORTHWEST
INDIANA MID/LATE EVENING BUT THIS MAY REMAIN TO THE EAST. WILL
CONTINUE WITH ACCUMULATION AROUND AN INCH FOR MOST AREAS EXCEPT FAR
SOUTH WHERE SNOW WILL LIKELY BE LIGHTER AND TEMPS A LITTLE WARMER.
AM THINKING THAT THE CORRIDOR FROM MENDOTA UP TO THE NORTHERN
CHICAGO SUBURBS AND EVEN WAUKEGAN...THEN SOUTHEAST TO THE GARY AND
PONTIAC AREA MAY SEE THE MOST INTENSE SNOW OVERALL AS WELL AS
OVERLAP WITH COLDEST TEMPS GOING INTO THE EVENING. HOWEVER...JUST
ABOUT ANYONE WEST OF GARY-PONTIAC COULD SEE AN INCH GIVEN SNOW
INTENSITY SEEN SO FAR TODAY. DO NOT REALLY HAVE A GOOD FEEL FOR
ACCUMULATION GIVEN THE WARM GROUND ETC...AND CANNOT RULE OUT SOME 2
INCH AMOUNTS UNDER THE MOST PERSISTENT BANDS. SNOW WILL TAPER OFF
FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER TROUGH AXIS LATE
THIS EVENING AND EARLY TONIGHT.

ANOTHER CONCERN IS LAKE EFFECT POTENTIAL INTO THE OVERNIGHT. COLDER
AIR WILL CONTINUE TO SPREAD SOUTHWARD INTO THE AREA WITH A GOOD
NORTH FETCH DOWN LAKE MICHIGAN. H85 TEMPS FALL TO AROUND -14 C WHICH
IS ENOUGH TO SUPPORT LAKE EFFECT...WITH LAKE WATER TEMPS PROBABLY
/PERHAPS CONSERVATIVELY/ IN THE UPPER 30S ACROSS MUCH OF THE
SOUTHERN PART OF THE LAKE /WITH MID/UPPER 40S AT NEARSHORE OBS
SITES/ DELTA TS ARE AT LEAST IN THE UPPER TEENS. THE PASSAGE OF THE
UPPER TROUGH WILL BRING SOME SUPPRESSION AS WELL AS DEEP LAYER
DRYING INTO THE REGION BUT LAKE INDUCED EQUILIBRIUM LEVELS
MAY PUSH 6-7 KFT OVERNIGHT. WITH A GRADUALLY WEAKENING PRESSURE
GRADIENT TO THE WEST...WINDS WILL EASE UP FROM WEST TO EAST AND THIS
MAY LEAD TO CONVERGENCE NEAR OR OFF THE ILLINOIS SHORE. SO IF PRECIP
CAN DEVELOP...WHICH IS A BIT OF A WILD CARD...THEN SOUTHERN SECTIONS
OF COOK COUNTY AND WESTERN PORTIONS OF LAKE COUNTY INDIANA MAY SEE
SNOW SHOWERS OVERNIGHT. IT IS ALSO NOT OUT OF THE REALM OF
POSSIBILITY THAT A FURTHER INLAND PUSH TO THE WEST COULD OCCUR INTO
THE CHICAGO AND NORTH SHORE AREAS. WILL GO AHEAD AND CARRY LOW POPS
AT THE SHORELINE AND INTO FAR SOUTHEAST COOK AND WESTERN LAKE COUNTY
THROUGH THE OVERNIGHT. SHORELINE AREAS COULD STAY AT OR JUST ABOVE
FREEZING GIVEN THE LAKE SO ANY ACCUMULATION COULD BE SLUSHY OR EVEN
GRADUALLY MELT...BUT AREAS JUST INLAND WILL LIKELY BE IN THE UPPER
20S TO AROUND 30 SO ACCUMULATION IS A CONCERN. WILL SHARE CONCERN
WITH THE EVENING SHIFT FOR FURTHER MONITORING. OTHERWISE WINDS WILL
EASE INLAND WITH SKIES CLEARING ACROSS WESTERN AREAS ALLOWING TEMPS
TO FALL INTO THE LOWER TO MID 20S.

TUESDAY THROUGH FRIDAY...THE UPPER FLOW WILL FLATTEN BEHIND THE
DEPARTING UPPER TROUGH TUESDAY AS SURFACE HIGH PRESSURE CROSSES THE
AREA. MID LEVEL WARM ADVECTION WILL COMMENCE IN THE AFTERNOON. HIGH
TEMPS WILL BE TOUGH GIVEN THE HIGH SUN ANGLE BUT VERY COLD START AND
SLOW START TO MID LEVEL WAA. LOW LEVEL LAPSE RATES STEEPEN QUITE A
BIT BY AFTERNOON AND WITH THE CONTINUED CYCLONIC FLOW ALOFT WILL
LIKELY SEE SCT-BKN CU DEVELOP INTO THE MIDDAY THEN DISSIPATE FROM
WEST TO EAST DURING THE LATE AFTERNOON. THAT SAID...WE HAVE SEEN
SEVERAL DAYS IN RECENT WEEKS WHERE TEMPS WARMED NICELY IN SIMILAR
SITUATIONS. WILL STAY ON THE WARMER SIDE OF THINGS WITH LOWER TO MID
40S WEST AND UPPER 30S TO AROUND 40 EAST. MOISTURE LOOKS PRETTY
SHALLOW BUT CANNOT RULE OUT A FEW SHOWERS DURING THE AFTERNOON BUT
WILL KEEP THE FORECAST DRY FOR NOW. THE TROUGH OFF THE BRITISH
COLUMBIA COAST TODAY WILL WEAKEN AND MOVE SOUTHEAST ACROSS THE UPPER
MIDWEST WEDNESDAY. THIS WILL BRING A PUSH OF WARMER MID LEVEL AREA
WHICH WILL COMBINE WITH INCREASING SOUTHERLY WINDS BEHIND THE
DEPARTING SURFACE HIGH TO PROPEL TEMPS INTO THE 50S WEDNESDAY. A
SURFACE LOW WILL ACCOMPANY THE UPPER TROUGH WITH A WARM FRONT
DEVELOPING NORTH OF THE AREA. THIS SHOULD KEEP THE LOCAL AREA DRY
WEDNESDAY BUT THE ATTENDANT COLD FRONT WILL MOVE IN THURSDAY
POTENTIALLY BRINGING SOME PRECIP. THE FRONT STALLS OUT OVER OR NEAR
THE AREA THURSDAY EVENING AND A SECOND UPPER TROUGH DIGS INTO THE
CENTRAL AND SOUTHERN PLAINS. A NEW SURFACE LOW WILL TRACK NORTHEAST
AND ACROSS THE LOCAL AREA FRIDAY. PRECIP CHANCES LOOK TO RAMP UP
THURSDAY EVENING NORTHWEST OF THE FRONT...THEN EXPAND ACROSS THE
AREA SOME TIME FRIDAY AS THE SURFACE LOW PASSES. PROVIDED THE
BOUNDARY ARRIVES LATE ENOUGH THURSDAY HIGHS WILL LIKELY BE IN THE
60S...WITH FRIDAY BEING COOLER BUT ALSO SEEING A LARGER RANGE OF
TEMPS THANKS TO THE BOUNDARY. EXPECT LOWER 50S NORTH AND UPPER 50S
SOUTH.

SATURDAY AND BEYOND...THE LOW WILL CLEAR TO THE NORTHEAST SOME TIME
EARLY SATURDAY WITH HIGH PRESSURE BUILDING IN THROUGH THE DAY. WITH
THE UPPER FLOW NOT ALL THAT AMPLIFIED THERE WILL BE LITTLE IN THE
WAY OF COOLING ALOFT AND ENOUGH SUNSHINE SHOULD HELP PROPEL TEMPS
INTO THE 50S. ANOTHER TROUGH LOOKS TO CROSS THE AREA SUNDAY BRINGING
MORE CHANCES FOR RAIN BUT OVERALL MILD TEMPS IN THE 50S.

MDB

&&

.CLIMATE...
THE FOLLOWING ARE THE MOST RECENT APRIL DATES AND AMOUNTS OF
ACCUMULATING SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* LIGHT SNOW AND LINGERING MVFR CIGS MOVE OUT BY 06Z

IZZI

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

BAND OF SNOW AND ASSOCIATED IFR/LIFR VSBYS WILL SHIFT EAST OF THE
TERMINALS EARLY THIS EVENING WITH A RAPID IMPROVEMENT IN
CONDITIONS EXPECTED SHORTLY THERE AFTER. SHARP CLEARING LINE
NEARING THE MS RIVER JUST BEFORE 00Z IS MAKING QUICK PROGRESS
EASTWARD...THOUGH THERE COULD BE SOME LOWER CLOUDS THAT LINGER A
BIT LONGER AS THE HIGHER CLOUD DECK MOVES OUT. REGARDLESS...FIELD
OF STRATOCUMULUS UPSTREAM OVER MN/IA SHOULD ROTATE INTO THE AREA
AND MAINTAIN ITSELF INTO THE DAY TUESDAY GIVEN THE VERY COLD AIR
ALOFT AND RESULTANT STEEP LAPSE RATES. GUSTINESS OF WINDS SHOULD
ABATE WITH THE PARTIAL CLEARING WITH NORTHWEST WINDS CONTINUING
THROUGH THE DAY TUESDAY. EXPECT A LAKE BREEZE TO DEVELOP AND MOVE
THROUGH GYY IN THE AFTERNOON TUES AND COULD MAKE A RUN AT MDW
TOWARD EVENING...BUT CONFIDENCE IS LOW ENOUGH TO KEEP ANY WIND
SHIFT OUT OF ORD/MDW FOR NOW.

IZZI

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS

IZZI

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.MARINE...
313 PM CDT

LOW PRESSURE OVER QUEBEC DRAGGED A COLD FRONT OVER THE LAKE THIS
MORNING. NORTH GALES BEHIND THE FRONT HAVE PERSISTED INTO MID
AFTERNOON AND ARE EXPECTED TO EASE QUICKLY THIS EVENING...BUT EAST
SIDE OF THE ENTIRE LAKE IS STILL SEEING GUSTS INTO THE MID 30S TO
AROUND 40 KT RANGE...SO GALE WARNING HAS BEEN EXTENDED INTO THE
EVENING. TO THE WEST...HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TONIGHT THEN INTO THE WESTERN GREAT LAKES LATER TOMORROW. ANOTHER
LOW WILL DEVELOP ACROSS THE CENTRAL AND SOUTHERN PLAINS WEDNESDAY
WITH TROUGHING EXTENDING TO THE NORTHEAST WHICH WILL MOVE OVER
LAKE MICHIGAN WEDNESDAY NIGHT INTO THURSDAY. LOW PRESSURE WILL
THEN LIFT NORTHEAST ACROSS THE MIDWEST OVER THE WEEKEND.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 150104
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
804 PM CDT MON APR 14 2014

.DISCUSSION...
804 PM CDT

FOR EVENING UPDATE...

MADE SOME TWEAKS TO HOURLY POP/WX GRIDS TO SHARPEN UP THE TRAILING
EDGE AND TIGHTEN TIMING OF ENDING OF CURRENT SNOW. ALSO INCREASED
CHANCE POPS SOMEWHAT AND ADDED MENTION OF SOME ADDITIONAL MINOR
ACCUMULATION ACROSS NORTHWEST INDIANA BEYOND MIDNIGHT FOR LAKE
EFFECT SNOW SHOWERS.

UNWELCOME REMINDER THAT APRIL CAN STILL BE WINTER-LIKE IN THE
MIDWEST THIS AFTERNOON/EVENING...AS BAND OF LIGHT/MODERATE SNOW
CONTINUES TO SHIFT EAST ACROSS THE FORECAST AREA AT 730 PM CDT.
THIS BAND OF SNOW IS BEING DRIVEN BY A COMBINATION OF A MID-LEVEL
SHORT WAVE TROUGH LIFTING NORTHEAST FROM MISSOURI...THE APPROACH OF
A LONG WAVE UPPER TROUGH FROM THE WEST...WITH ENHANCEMENT INTO
STRONGER SOUTHWEST-NORTHEAST BANDS BY MID-LEVEL FRONTOGENESIS.
REGIONAL RADAR MOSAIC HAS CONSISTENTLY INDICATED A FAIRLY SHARP
TRAILING EDGE TO THE MORE INTENSE SNOW...ROUGHLY ALONG A SPRINGFIELD
TO STREATOR TO ARLINGTON HEIGHTS AND HIGHLAND PARK IL LINE AT THIS
TIME. FRONTOGENESIS MAXIMA AT 700 HPA DEPICTED NICELY BY THE RAP...
AND EVOLUTION OF THIS FEATURE OFF TO THE EAST SHOWS NICE CORRELATION
WITH RADAR TRENDS OVER THE PAST FEW HOURS AND INDICATES THAT SNOW
WILL TAPER TO FLURRIES AND LARGELY END FROM WEST TO EAST ACROSS MUCH
OF THE CHICAGO AREA BY 9 PM...AND PRIOR TO 11 PM FOR OUR NORTHWEST
INDIANA AND FAR EAST CENTRAL IL COUNTIES. TOTAL SNOWFALL REPORTS
HAVE RANGED FROM A HALF INCH TO NEAR 2 INCHES IN SPOTS THAT HAVE
BEEN AFFECTED BY THE ENHANCED HEAVIER BANDING.

NORTH WINDS AND COLD AIR DO LOOK TO MAINTAIN THE POTENTIAL FOR SOME
LAKE EFFECT SNOW SHOWERS ALONG THE SOUTH END OF THE LAKE THROUGH THE
OVERNIGHT HOURS...WITH LAKE EFFECT PARAMETERS FROM THE 18Z NAM
SUPPORTIVE OF ORGANIZED CONVECTIVE SNOW SHOWERS (DELTA T AROUND
16C...EQUILIBRIUM HEIGHTS OVER 8 KFT...UNIDIRECTIONAL NORTH FLOW
NEAR 20 KT THROUGH MARINE BOUNDARY LAYER). BASED ON THIS...HAVE
INCREASED CHANCE POPS ACROSS LAKE/PORTER COUNTY AFTER MIDNIGHT
TONIGHT AND INTO TUESDAY BEFORE APPROACHING SURFACE RIDGE MAKES THE
LOW LEVEL WIND FIELD INCREASINGLY LESS FAVORABLE.

OTHER CONCERN THIS EVENING WITH LUNAR ECLIPSE TO OCCUR AFTER
MIDNIGHT IS WITH CLEARING OF CLOUD COVER. THICKER/DEEPER CLOUD COVER
ASSOCIATED WITH MID-LEVEL TROUGH LOOKS TO CLEAR OUR EASTERN COUNTIES
AROUND OR SHORTLY AFTER MIDNIGHT BASED ON EXTRAPOLATION OF SATELLITE
IMAGES. WHILE SOME EROSION/DISSIPATION IS POSSIBLE...AREA OF
CLOSED-CELL STRATO-CU UPSTREAM ACROSS IA/MN WITH BASES 5000-7000 FT
MAY TEND TO PERSIST DUE TO FAIRLY STEEP LOW LEVEL LAPSE RATES IN
STRONG LOW LEVEL COLD ADVECTION REGIME. WILL MAINTAIN A BECOMING
PARTLY CLOUDY FORECAST AFTER MIDNIGHT...AND HOPEFULLY THE ECLIPSE
WILL BE VISIBLE BETWEEN PASSING PATCHES OF STRATOCU.

RATZER

&&

.PREV DISCUSSION...
314 PM CDT

THE MAIN PERIOD OF ACTIVE WEATHER WILL BE THIS EVENING WITH A MORE
TRANQUIL PERIOD SETTING UP INTO TUESDAY AND CONTINUING THROUGH MUCH
OF THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS AN EXPANSIVE
LONGWAVE TROUGH OVER THE MID SECTION OF THE COUNTRY WITH THE TROUGH
AXIS SWINGING EASTWARD TOWARD THE LOCAL AREA. A SHARP BUT NARROW
RIDGE TRAILS THE BIG TROUGH OVER WEST COAST WITH A SERIES OF MORE
COMPACT UPPER LOWS SPINNING EASTWARD TOWARDS THE CANADIAN WEST
COAST. AT THE SURFACE...THE MAIN SURFACE LOW WHICH BROUGHT THE
ACTIVE WEATHER OVER THE PAST FEW DAYS IS NOW OVER EASTERN QUEBEC
WITH HIGH PRESSURE SPREADING SOUTHWARD ACROSS THE CANADIAN PRAIRIES
INTO THE CENTRAL AND NORTHERN PLANS.

TONIGHT...WATER VAPOR SHOWS AN EMBEDDED UPPER WAVE MOVING INTO THE
AREA FROM THE SOUTHWEST LATE THIS AFTERNOON. THIS IS TIGHTENING THE
MID LEVEL BAROCLINIC ZONE AND RESULTING IN INTENSIFYING
FRONTOGENESIS IN A CORRIDOR ACROSS THE NORTHWEST CWA WHICH IS
SHIFTING EASTWARD. COLDER AIR AT THE SURFACE AND ALOFT CONTINUES TO
SPREAD SOUTHEASTWARD AS WELL. PRECIP WILL CONTINUE TO INTENSIFY IN
CONJUNCTION WITH THE INCREASED FORCING WHILE THE ENTIRE BAND PIVOTS
EASTWARD AS THE LONGWAVE TROUGH AXIS PUSHES EASTWARD INTO THE
EVENING. FORECAST SOUNDINGS SHOW THAT THE BEST FORCING LINES UP WELL
WITH THE FAVORED SNOW GROWTH REGION SUPPORTING EFFICIENT SNOW GROWTH
WITH THE COLUMN COLD ENOUGH TO SUPPORT ALL SNOW WITHIN THE BAND.
AREAS TO THE SOUTH AND WEST OF THE HAVE BEEN REPORTING VSBY AS LOW
AS 1/4 TO 3/4 SM VSBY UNDER THE HEAVIER PRECIP ELEMENTS. SURFACE
TEMPS...WHILE STILL ABOVE FREEZING WILL COOL WITH TIME FAVORING
ACCUMULATING SNOW BUT GROUND TEMPS WILL BE THE LIMITING FACTOR
OVERALL. HOWEVER...SNOW INTENSITY WITHIN THE HEAVIEST BANDS WILL
LIKELY OVERCOME THE WARMER GROUND...ESPECIALLY ON GRASSY AND
ELEVATED SURFACES...WITH SLUSHY ACCUMULATION POSSIBLE ON ROADWAYS.
BASED ON LATEST TRENDS...AREAS FROM MENDOTA TO CHICAGO NORTHWEST
WILL BE THE FOCUS GOING THROUGH LATE AFTERNOON WITH AN EXPANSION
EXPECTED JUST TO THE SOUTHEAST OF THIS LINE TOWARDS A GARY TO
PONTIAC LINE BY EARLY EVENING. THIS WILL PUT THE CORRIDOR OF
HEAVIEST SNOW ACROSS THE CHICAGO METRO FOR MUCH OF IF NOT ALL OF THE
EVENING RUSH...WITH DEPARTURE FROM THE ROCKFORD AREA RIGHT AROUND
THE START. THE MAIN VORT RESPONSIBLE FOR THIS WILL ZIP NORTHEAST SO
THERE MAY BE A DECREASE IN INTENSITY OF THE BAND TOWARD MID EVENING
BUT BROADER SCALE FORCING WILL CONTINUE TO BRING PRECIP AT A LOWER
RATE THROUGH THE EVENING FROM THE GARY/CHICAGO AREA TO PONTIAC AND
POINTS EAST. ANOTHER WAVE WILL LIFT NORTHEAST INTO NORTH-CENTRAL
INDIANA THIS EVENING AND MAY BRING AN INCREASE IN SNOW TO NORTHWEST
INDIANA MID/LATE EVENING BUT THIS MAY REMAIN TO THE EAST. WILL
CONTINUE WITH ACCUMULATION AROUND AN INCH FOR MOST AREAS EXCEPT FAR
SOUTH WHERE SNOW WILL LIKELY BE LIGHTER AND TEMPS A LITTLE WARMER.
AM THINKING THAT THE CORRIDOR FROM MENDOTA UP TO THE NORTHERN
CHICAGO SUBURBS AND EVEN WAUKEGAN...THEN SOUTHEAST TO THE GARY AND
PONTIAC AREA MAY SEE THE MOST INTENSE SNOW OVERALL AS WELL AS
OVERLAP WITH COLDEST TEMPS GOING INTO THE EVENING. HOWEVER...JUST
ABOUT ANYONE WEST OF GARY-PONTIAC COULD SEE AN INCH GIVEN SNOW
INTENSITY SEEN SO FAR TODAY. DO NOT REALLY HAVE A GOOD FEEL FOR
ACCUMULATION GIVEN THE WARM GROUND ETC...AND CANNOT RULE OUT SOME 2
INCH AMOUNTS UNDER THE MOST PERSISTENT BANDS. SNOW WILL TAPER OFF
FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER TROUGH AXIS LATE
THIS EVENING AND EARLY TONIGHT.

ANOTHER CONCERN IS LAKE EFFECT POTENTIAL INTO THE OVERNIGHT. COLDER
AIR WILL CONTINUE TO SPREAD SOUTHWARD INTO THE AREA WITH A GOOD
NORTH FETCH DOWN LAKE MICHIGAN. H85 TEMPS FALL TO AROUND -14 C WHICH
IS ENOUGH TO SUPPORT LAKE EFFECT...WITH LAKE WATER TEMPS PROBABLY
/PERHAPS CONSERVATIVELY/ IN THE UPPER 30S ACROSS MUCH OF THE
SOUTHERN PART OF THE LAKE /WITH MID/UPPER 40S AT NEARSHORE OBS
SITES/ DELTA TS ARE AT LEAST IN THE UPPER TEENS. THE PASSAGE OF THE
UPPER TROUGH WILL BRING SOME SUPPRESSION AS WELL AS DEEP LAYER
DRYING INTO THE REGION BUT LAKE INDUCED EQUILIBRIUM LEVELS
MAY PUSH 6-7 KFT OVERNIGHT. WITH A GRADUALLY WEAKENING PRESSURE
GRADIENT TO THE WEST...WINDS WILL EASE UP FROM WEST TO EAST AND THIS
MAY LEAD TO CONVERGENCE NEAR OR OFF THE ILLINOIS SHORE. SO IF PRECIP
CAN DEVELOP...WHICH IS A BIT OF A WILD CARD...THEN SOUTHERN SECTIONS
OF COOK COUNTY AND WESTERN PORTIONS OF LAKE COUNTY INDIANA MAY SEE
SNOW SHOWERS OVERNIGHT. IT IS ALSO NOT OUT OF THE REALM OF
POSSIBILITY THAT A FURTHER INLAND PUSH TO THE WEST COULD OCCUR INTO
THE CHICAGO AND NORTH SHORE AREAS. WILL GO AHEAD AND CARRY LOW POPS
AT THE SHORELINE AND INTO FAR SOUTHEAST COOK AND WESTERN LAKE COUNTY
THROUGH THE OVERNIGHT. SHORELINE AREAS COULD STAY AT OR JUST ABOVE
FREEZING GIVEN THE LAKE SO ANY ACCUMULATION COULD BE SLUSHY OR EVEN
GRADUALLY MELT...BUT AREAS JUST INLAND WILL LIKELY BE IN THE UPPER
20S TO AROUND 30 SO ACCUMULATION IS A CONCERN. WILL SHARE CONCERN
WITH THE EVENING SHIFT FOR FURTHER MONITORING. OTHERWISE WINDS WILL
EASE INLAND WITH SKIES CLEARING ACROSS WESTERN AREAS ALLOWING TEMPS
TO FALL INTO THE LOWER TO MID 20S.

TUESDAY THROUGH FRIDAY...THE UPPER FLOW WILL FLATTEN BEHIND THE
DEPARTING UPPER TROUGH TUESDAY AS SURFACE HIGH PRESSURE CROSSES THE
AREA. MID LEVEL WARM ADVECTION WILL COMMENCE IN THE AFTERNOON. HIGH
TEMPS WILL BE TOUGH GIVEN THE HIGH SUN ANGLE BUT VERY COLD START AND
SLOW START TO MID LEVEL WAA. LOW LEVEL LAPSE RATES STEEPEN QUITE A
BIT BY AFTERNOON AND WITH THE CONTINUED CYCLONIC FLOW ALOFT WILL
LIKELY SEE SCT-BKN CU DEVELOP INTO THE MIDDAY THEN DISSIPATE FROM
WEST TO EAST DURING THE LATE AFTERNOON. THAT SAID...WE HAVE SEEN
SEVERAL DAYS IN RECENT WEEKS WHERE TEMPS WARMED NICELY IN SIMILAR
SITUATIONS. WILL STAY ON THE WARMER SIDE OF THINGS WITH LOWER TO MID
40S WEST AND UPPER 30S TO AROUND 40 EAST. MOISTURE LOOKS PRETTY
SHALLOW BUT CANNOT RULE OUT A FEW SHOWERS DURING THE AFTERNOON BUT
WILL KEEP THE FORECAST DRY FOR NOW. THE TROUGH OFF THE BRITISH
COLUMBIA COAST TODAY WILL WEAKEN AND MOVE SOUTHEAST ACROSS THE UPPER
MIDWEST WEDNESDAY. THIS WILL BRING A PUSH OF WARMER MID LEVEL AREA
WHICH WILL COMBINE WITH INCREASING SOUTHERLY WINDS BEHIND THE
DEPARTING SURFACE HIGH TO PROPEL TEMPS INTO THE 50S WEDNESDAY. A
SURFACE LOW WILL ACCOMPANY THE UPPER TROUGH WITH A WARM FRONT
DEVELOPING NORTH OF THE AREA. THIS SHOULD KEEP THE LOCAL AREA DRY
WEDNESDAY BUT THE ATTENDANT COLD FRONT WILL MOVE IN THURSDAY
POTENTIALLY BRINGING SOME PRECIP. THE FRONT STALLS OUT OVER OR NEAR
THE AREA THURSDAY EVENING AND A SECOND UPPER TROUGH DIGS INTO THE
CENTRAL AND SOUTHERN PLAINS. A NEW SURFACE LOW WILL TRACK NORTHEAST
AND ACROSS THE LOCAL AREA FRIDAY. PRECIP CHANCES LOOK TO RAMP UP
THURSDAY EVENING NORTHWEST OF THE FRONT...THEN EXPAND ACROSS THE
AREA SOME TIME FRIDAY AS THE SURFACE LOW PASSES. PROVIDED THE
BOUNDARY ARRIVES LATE ENOUGH THURSDAY HIGHS WILL LIKELY BE IN THE
60S...WITH FRIDAY BEING COOLER BUT ALSO SEEING A LARGER RANGE OF
TEMPS THANKS TO THE BOUNDARY. EXPECT LOWER 50S NORTH AND UPPER 50S
SOUTH.

SATURDAY AND BEYOND...THE LOW WILL CLEAR TO THE NORTHEAST SOME TIME
EARLY SATURDAY WITH HIGH PRESSURE BUILDING IN THROUGH THE DAY. WITH
THE UPPER FLOW NOT ALL THAT AMPLIFIED THERE WILL BE LITTLE IN THE
WAY OF COOLING ALOFT AND ENOUGH SUNSHINE SHOULD HELP PROPEL TEMPS
INTO THE 50S. ANOTHER TROUGH LOOKS TO CROSS THE AREA SUNDAY BRINGING
MORE CHANCES FOR RAIN BUT OVERALL MILD TEMPS IN THE 50S.

MDB

&&

.CLIMATE...
THE FOLLOWING ARE THE MOST RECENT APRIL DATES AND
AMOUNTS OF ACCUMULATING SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* IFR AND SNOW END EARLY THIS EVENING

IZZI

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

BAND OF SNOW AND ASSOCIATED IFR/LIFR VSBYS WILL SHIFT EAST OF THE
TERMINALS EARLY THIS EVENING WITH A RAPID IMPROVEMENT IN
CONDITIONS EXPECTED SHORTLY THERE AFTER. SHARP CLEARING LINE
NEARING THE MS RIVER JUST BEFORE 00Z IS MAKING QUICK PROGRESS
EASTWARD...THOUGH THERE COULD BE SOME LOWER CLOUDS THAT LINGER A
BIT LONGER AS THE HIGHER CLOUD DECK MOVES OUT. REGARDLESS...FIELD
OF STRATOCUMULUS UPSTREAM OVER MN/IA SHOULD ROTATE INTO THE AREA
AND MAINTAIN ITSELF INTO THE DAY TUESDAY GIVEN THE VERY COLD AIR
ALOFT AND RESULTANT STEEP LAPSE RATES. GUSTINESS OF WINDS SHOULD
ABATE WITH THE PARTIAL CLEARING WITH NORTHWEST WINDS CONTINUING
THROUGH THE DAY TUESDAY. EXPECT A LAKE BREEZE TO DEVELOP AND MOVE
THROUGH GYY IN THE AFTERNOON TUES AND COULD MAKE A RUN AT MDW
TOWARD EVENING...BUT CONFIDENCE IS LOW ENOUGH TO KEEP ANY WIND
SHIFT OUT OF ORD/MDW FOR NOW.

IZZI

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS

IZZI

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.MARINE...
313 PM CDT

LOW PRESSURE OVER QUEBEC DRAGGED A COLD FRONT OVER THE LAKE THIS
MORNING. NORTH GALES BEHIND THE FRONT HAVE PERSISTED INTO MID
AFTERNOON AND ARE EXPECTED TO EASE QUICKLY THIS EVENING...BUT EAST
SIDE OF THE ENTIRE LAKE IS STILL SEEING GUSTS INTO THE MID 30S TO
AROUND 40 KT RANGE...SO GALE WARNING HAS BEEN EXTENDED INTO THE
EVENING. TO THE WEST...HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TONIGHT THEN INTO THE WESTERN GREAT LAKES LATER TOMORROW. ANOTHER
LOW WILL DEVELOP ACROSS THE CENTRAL AND SOUTHERN PLAINS WEDNESDAY
WITH TROUGHING EXTENDING TO THE NORTHEAST WHICH WILL MOVE OVER
LAKE MICHIGAN WEDNESDAY NIGHT INTO THURSDAY. LOW PRESSURE WILL
THEN LIFT NORTHEAST ACROSS THE MIDWEST OVER THE WEEKEND.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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








000
FXUS63 KLOT 142340
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
640 PM CDT MON APR 14 2014

.DISCUSSION...
314 PM CDT

THE MAIN PERIOD OF ACTIVE WEATHER WILL BE THIS EVENING WITH A MORE
TRANQUIL PERIOD SETTING UP INTO TUESDAY AND CONTINUING THROUGH MUCH
OF THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS AN EXPANSIVE
LONGWAVE TROUGH OVER THE MID SECTION OF THE COUNTRY WITH THE TROUGH
AXIS SWINGING EASTWARD TOWARD THE LOCAL AREA. A SHARP BUT NARROW
RIDGE TRAILS THE BIG TROUGH OVER WEST COAST WITH A SERIES OF MORE
COMPACT UPPER LOWS SPINNING EASTWARD TOWARDS THE CANADIAN WEST
COAST. AT THE SURFACE...THE MAIN SURFACE LOW WHICH BROUGHT THE
ACTIVE WEATHER OVER THE PAST FEW DAYS IS NOW OVER EASTERN QUEBEC
WITH HIGH PRESSURE SPREADING SOUTHWARD ACROSS THE CANADIAN PRAIRIES
INTO THE CENTRAL AND NORTHERN PLANS.

TONIGHT...WATER VAPOR SHOWS AN EMBEDDED UPPER WAVE MOVING INTO THE
AREA FROM THE SOUTHWEST LATE THIS AFTERNOON. THIS IS TIGHTENING THE
MID LEVEL BAROCLINIC ZONE AND RESULTING IN INTENSIFYING
FRONTOGENESIS IN A CORRIDOR ACROSS THE NORTHWEST CWA WHICH IS
SHIFTING EASTWARD. COLDER AIR AT THE SURFACE AND ALOFT CONTINUES TO
SPREAD SOUTHEASTWARD AS WELL. PRECIP WILL CONTINUE TO INTENSIFY IN
CONJUNCTION WITH THE INCREASED FORCING WHILE THE ENTIRE BAND PIVOTS
EASTWARD AS THE LONGWAVE TROUGH AXIS PUSHES EASTWARD INTO THE
EVENING. FORECAST SOUNDINGS SHOW THAT THE BEST FORCING LINES UP WELL
WITH THE FAVORED SNOW GROWTH REGION SUPPORTING EFFICIENT SNOW GROWTH
WITH THE COLUMN COLD ENOUGH TO SUPPORT ALL SNOW WITHIN THE BAND.
AREAS TO THE SOUTH AND WEST OF THE HAVE BEEN REPORTING VSBY AS LOW
AS 1/4 TO 3/4 SM VSBY UNDER THE HEAVIER PRECIP ELEMENTS. SURFACE
TEMPS...WHILE STILL ABOVE FREEZING WILL COOL WITH TIME FAVORING
ACCUMULATING SNOW BUT GROUND TEMPS WILL BE THE LIMITING FACTOR
OVERALL. HOWEVER...SNOW INTENSITY WITHIN THE HEAVIEST BANDS WILL
LIKELY OVERCOME THE WARMER GROUND...ESPECIALLY ON GRASSY AND
ELEVATED SURFACES...WITH SLUSHY ACCUMULATION POSSIBLE ON ROADWAYS.
BASED ON LATEST TRENDS...AREAS FROM MENDOTA TO CHICAGO NORTHWEST
WILL BE THE FOCUS GOING THROUGH LATE AFTERNOON WITH AN EXPANSION
EXPECTED JUST TO THE SOUTHEAST OF THIS LINE TOWARDS A GARY TO
PONTIAC LINE BY EARLY EVENING. THIS WILL PUT THE CORRIDOR OF
HEAVIEST SNOW ACROSS THE CHICAGO METRO FOR MUCH OF IF NOT ALL OF THE
EVENING RUSH...WITH DEPARTURE FROM THE ROCKFORD AREA RIGHT AROUND
THE START. THE MAIN VORT RESPONSIBLE FOR THIS WILL ZIP NORTHEAST SO
THERE MAY BE A DECREASE IN INTENSITY OF THE BAND TOWARD MID EVENING
BUT BROADER SCALE FORCING WILL CONTINUE TO BRING PRECIP AT A LOWER
RATE THROUGH THE EVENING FROM THE GARY/CHICAGO AREA TO PONTIAC AND
POINTS EAST. ANOTHER WAVE WILL LIFT NORTHEAST INTO NORTH-CENTRAL
INDIANA THIS EVENING AND MAY BRING AN INCREASE IN SNOW TO NORTHWEST
INDIANA MID/LATE EVENING BUT THIS MAY REMAIN TO THE EAST. WILL
CONTINUE WITH ACCUMULATION AROUND AN INCH FOR MOST AREAS EXCEPT FAR
SOUTH WHERE SNOW WILL LIKELY BE LIGHTER AND TEMPS A LITTLE WARMER.
AM THINKING THAT THE CORRIDOR FROM MENDOTA UP TO THE NORTHERN
CHICAGO SUBURBS AND EVEN WAUKEGAN...THEN SOUTHEAST TO THE GARY AND
PONTIAC AREA MAY SEE THE MOST INTENSE SNOW OVERALL AS WELL AS
OVERLAP WITH COLDEST TEMPS GOING INTO THE EVENING. HOWEVER...JUST
ABOUT ANYONE WEST OF GARY-PONTIAC COULD SEE AN INCH GIVEN SNOW
INTENSITY SEEN SO FAR TODAY. DO NOT REALLY HAVE A GOOD FEEL FOR
ACCUMULATION GIVEN THE WARM GROUND ETC...AND CANNOT RULE OUT SOME 2
INCH AMOUNTS UNDER THE MOST PERSISTENT BANDS. SNOW WILL TAPER OFF
FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER TROUGH AXIS LATE
THIS EVENING AND EARLY TONIGHT.

ANOTHER CONCERN IS LAKE EFFECT POTENTIAL INTO THE OVERNIGHT. COLDER
AIR WILL CONTINUE TO SPREAD SOUTHWARD INTO THE AREA WITH A GOOD
NORTH FETCH DOWN LAKE MICHIGAN. H85 TEMPS FALL TO AROUND -14 C WHICH
IS ENOUGH TO SUPPORT LAKE EFFECT...WITH LAKE WATER TEMPS PROBABLY
/PERHAPS CONSERVATIVELY/ IN THE UPPER 30S ACROSS MUCH OF THE
SOUTHERN PART OF THE LAKE /WITH MID/UPPER 40S AT NEARSHORE OBS
SITES/ DELTA TS ARE AT LEAST IN THE UPPER TEENS. THE PASSAGE OF THE
UPPER TROUGH WILL BRING SOME SUPPRESSION AS WELL AS DEEP LAYER
DRYING INTO THE REGION BUT LAKE INDUCED EQUILIBRIUM LEVELS
MAY PUSH 6-7 KFT OVERNIGHT. WITH A GRADUALLY WEAKENING PRESSURE
GRADIENT TO THE WEST...WINDS WILL EASE UP FROM WEST TO EAST AND THIS
MAY LEAD TO CONVERGENCE NEAR OR OFF THE ILLINOIS SHORE. SO IF PRECIP
CAN DEVELOP...WHICH IS A BIT OF A WILD CARD...THEN SOUTHERN SECTIONS
OF COOK COUNTY AND WESTERN PORTIONS OF LAKE COUNTY INDIANA MAY SEE
SNOW SHOWERS OVERNIGHT. IT IS ALSO NOT OUT OF THE REALM OF
POSSIBILITY THAT A FURTHER INLAND PUSH TO THE WEST COULD OCCUR INTO
THE CHICAGO AND NORTH SHORE AREAS. WILL GO AHEAD AND CARRY LOW POPS
AT THE SHORELINE AND INTO FAR SOUTHEAST COOK AND WESTERN LAKE COUNTY
THROUGH THE OVERNIGHT. SHORELINE AREAS COULD STAY AT OR JUST ABOVE
FREEZING GIVEN THE LAKE SO ANY ACCUMULATION COULD BE SLUSHY OR EVEN
GRADUALLY MELT...BUT AREAS JUST INLAND WILL LIKELY BE IN THE UPPER
20S TO AROUND 30 SO ACCUMULATION IS A CONCERN. WILL SHARE CONCERN
WITH THE EVENING SHIFT FOR FURTHER MONITORING. OTHERWISE WINDS WILL
EASE INLAND WITH SKIES CLEARING ACROSS WESTERN AREAS ALLOWING TEMPS
TO FALL INTO THE LOWER TO MID 20S.

TUESDAY THROUGH FRIDAY...THE UPPER FLOW WILL FLATTEN BEHIND THE
DEPARTING UPPER TROUGH TUESDAY AS SURFACE HIGH PRESSURE CROSSES THE
AREA. MID LEVEL WARM ADVECTION WILL COMMENCE IN THE AFTERNOON. HIGH
TEMPS WILL BE TOUGH GIVEN THE HIGH SUN ANGLE BUT VERY COLD START AND
SLOW START TO MID LEVEL WAA. LOW LEVEL LAPSE RATES STEEPEN QUITE A
BIT BY AFTERNOON AND WITH THE CONTINUED CYCLONIC FLOW ALOFT WILL
LIKELY SEE SCT-BKN CU DEVELOP INTO THE MIDDAY THEN DISSIPATE FROM
WEST TO EAST DURING THE LATE AFTERNOON. THAT SAID...WE HAVE SEEN
SEVERAL DAYS IN RECENT WEEKS WHERE TEMPS WARMED NICELY IN SIMILAR
SITUATIONS. WILL STAY ON THE WARMER SIDE OF THINGS WITH LOWER TO MID
40S WEST AND UPPER 30S TO AROUND 40 EAST. MOISTURE LOOKS PRETTY
SHALLOW BUT CANNOT RULE OUT A FEW SHOWERS DURING THE AFTERNOON BUT
WILL KEEP THE FORECAST DRY FOR NOW. THE TROUGH OFF THE BRITISH
COLUMBIA COAST TODAY WILL WEAKEN AND MOVE SOUTHEAST ACROSS THE UPPER
MIDWEST WEDNESDAY. THIS WILL BRING A PUSH OF WARMER MID LEVEL AREA
WHICH WILL COMBINE WITH INCREASING SOUTHERLY WINDS BEHIND THE
DEPARTING SURFACE HIGH TO PROPEL TEMPS INTO THE 50S WEDNESDAY. A
SURFACE LOW WILL ACCOMPANY THE UPPER TROUGH WITH A WARM FRONT
DEVELOPING NORTH OF THE AREA. THIS SHOULD KEEP THE LOCAL AREA DRY
WEDNESDAY BUT THE ATTENDANT COLD FRONT WILL MOVE IN THURSDAY
POTENTIALLY BRINGING SOME PRECIP. THE FRONT STALLS OUT OVER OR NEAR
THE AREA THURSDAY EVENING AND A SECOND UPPER TROUGH DIGS INTO THE
CENTRAL AND SOUTHERN PLAINS. A NEW SURFACE LOW WILL TRACK NORTHEAST
AND ACROSS THE LOCAL AREA FRIDAY. PRECIP CHANCES LOOK TO RAMP UP
THURSDAY EVENING NORTHWEST OF THE FRONT...THEN EXPAND ACROSS THE
AREA SOME TIME FRIDAY AS THE SURFACE LOW PASSES. PROVIDED THE
BOUNDARY ARRIVES LATE ENOUGH THURSDAY HIGHS WILL LIKELY BE IN THE
60S...WITH FRIDAY BEING COOLER BUT ALSO SEEING A LARGER RANGE OF
TEMPS THANKS TO THE BOUNDARY. EXPECT LOWER 50S NORTH AND UPPER 50S
SOUTH.

SATURDAY AND BEYOND...THE LOW WILL CLEAR TO THE NORTHEAST SOME TIME
EARLY SATURDAY WITH HIGH PRESSURE BUILDING IN THROUGH THE DAY. WITH
THE UPPER FLOW NOT ALL THAT AMPLIFIED THERE WILL BE LITTLE IN THE
WAY OF COOLING ALOFT AND ENOUGH SUNSHINE SHOULD HELP PROPEL TEMPS
INTO THE 50S. ANOTHER TROUGH LOOKS TO CROSS THE AREA SUNDAY BRINGING
MORE CHANCES FOR RAIN BUT OVERALL MILD TEMPS IN THE 50S.

MDB

&&

.CLIMATE...
THE FOLLOWING ARE THE MOST RECENT APRIL DATES AND AMOUNTS OF
ACCUMULATING SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* IFR AND SNOW END EARLY THIS EVENING

IZZI

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

BAND OF SNOW AND ASSOCIATED IFR/LIFR VSBYS WILL SHIFT EAST OF THE
TERMINALS EARLY THIS EVENING WITH A RAPID IMPROVEMENT IN
CONDITIONS EXPECTED SHORTLY THERE AFTER. SHARP CLEARING LINE
NEARING THE MS RIVER JUST BEFORE 00Z IS MAKING QUICK PROGRESS
EASTWARD...THOUGH THERE COULD BE SOME LOWER CLOUDS THAT LINGER A
BIT LONGER AS THE HIGHER CLOUD DECK MOVES OUT. REGARDLESS...FIELD
OF STRATOCUMULUS UPSTREAM OVER MN/IA SHOULD ROTATE INTO THE AREA
AND MAINTAIN ITSELF INTO THE DAY TUESDAY GIVEN THE VERY COLD AIR
ALOFT AND RESULTANT STEEP LAPSE RATES. GUSTINESS OF WINDS SHOULD
ABATE WITH THE PARTIAL CLEARING WITH NORTHWEST WINDS CONTINUING
THROUGH THE DAY TUESDAY. EXPECT A LAKE BREEZE TO DEVELOP AND MOVE
THROUGH GYY IN THE AFTERNOON TUES AND COULD MAKE A RUN AT MDW
TOWARD EVENING...BUT CONFIDENCE IS LOW ENOUGH TO KEEP ANY WIND
SHIFT OUT OF ORD/MDW FOR NOW.

IZZI


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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS

IZZI

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.MARINE...
313 PM CDT

LOW PRESSURE OVER QUEBEC DRAGGED A COLD FRONT OVER THE LAKE THIS
MORNING. NORTH GALES BEHIND THE FRONT HAVE PERSISTED INTO MID
AFTERNOON AND ARE EXPECTED TO EASE QUICKLY THIS EVENING...BUT EAST
SIDE OF THE ENTIRE LAKE IS STILL SEEING GUSTS INTO THE MID 30S TO
AROUND 40 KT RANGE...SO GALE WARNING HAS BEEN EXTENDED INTO THE
EVENING. TO THE WEST...HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TONIGHT THEN INTO THE WESTERN GREAT LAKES LATER TOMORROW. ANOTHER
LOW WILL DEVELOP ACROSS THE CENTRAL AND SOUTHERN PLAINS WEDNESDAY
WITH TROUGHING EXTENDING TO THE NORTHEAST WHICH WILL MOVE OVER
LAKE MICHIGAN WEDNESDAY NIGHT INTO THURSDAY. LOW PRESSURE WILL
THEN LIFT NORTHEAST ACROSS THE MIDWEST OVER THE WEEKEND.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 142229
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
529 PM CDT MON APR 14 2014

.DISCUSSION...
314 PM CDT

THE MAIN PERIOD OF ACTIVE WEATHER WILL BE THIS EVENING WITH A MORE
TRANQUIL PERIOD SETTING UP INTO TUESDAY AND CONTINUING THROUGH MUCH
OF THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS AN EXPANSIVE
LONGWAVE TROUGH OVER THE MID SECTION OF THE COUNTRY WITH THE TROUGH
AXIS SWINGING EASTWARD TOWARD THE LOCAL AREA. A SHARP BUT NARROW
RIDGE TRAILS THE BIG TROUGH OVER WEST COAST WITH A SERIES OF MORE
COMPACT UPPER LOWS SPINNING EASTWARD TOWARDS THE CANADIAN WEST
COAST. AT THE SURFACE...THE MAIN SURFACE LOW WHICH BROUGHT THE
ACTIVE WEATHER OVER THE PAST FEW DAYS IS NOW OVER EASTERN QUEBEC
WITH HIGH PRESSURE SPREADING SOUTHWARD ACROSS THE CANADIAN PRAIRIES
INTO THE CENTRAL AND NORTHERN PLANS.

TONIGHT...WATER VAPOR SHOWS AN EMBEDDED UPPER WAVE MOVING INTO THE
AREA FROM THE SOUTHWEST LATE THIS AFTERNOON. THIS IS TIGHTENING THE
MID LEVEL BAROCLINIC ZONE AND RESULTING IN INTENSIFYING
FRONTOGENESIS IN A CORRIDOR ACROSS THE NORTHWEST CWA WHICH IS
SHIFTING EASTWARD. COLDER AIR AT THE SURFACE AND ALOFT CONTINUES TO
SPREAD SOUTHEASTWARD AS WELL. PRECIP WILL CONTINUE TO INTENSIFY IN
CONJUNCTION WITH THE INCREASED FORCING WHILE THE ENTIRE BAND PIVOTS
EASTWARD AS THE LONGWAVE TROUGH AXIS PUSHES EASTWARD INTO THE
EVENING. FORECAST SOUNDINGS SHOW THAT THE BEST FORCING LINES UP WELL
WITH THE FAVORED SNOW GROWTH REGION SUPPORTING EFFICIENT SNOW GROWTH
WITH THE COLUMN COLD ENOUGH TO SUPPORT ALL SNOW WITHIN THE BAND.
AREAS TO THE SOUTH AND WEST OF THE HAVE BEEN REPORTING VSBY AS LOW
AS 1/4 TO 3/4 SM VSBY UNDER THE HEAVIER PRECIP ELEMENTS. SURFACE
TEMPS...WHILE STILL ABOVE FREEZING WILL COOL WITH TIME FAVORING
ACCUMULATING SNOW BUT GROUND TEMPS WILL BE THE LIMITING FACTOR
OVERALL. HOWEVER...SNOW INTENSITY WITHIN THE HEAVIEST BANDS WILL
LIKELY OVERCOME THE WARMER GROUND...ESPECIALLY ON GRASSY AND
ELEVATED SURFACES...WITH SLUSHY ACCUMULATION POSSIBLE ON ROADWAYS.
BASED ON LATEST TRENDS...AREAS FROM MENDOTA TO CHICAGO NORTHWEST
WILL BE THE FOCUS GOING THROUGH LATE AFTERNOON WITH AN EXPANSION
EXPECTED JUST TO THE SOUTHEAST OF THIS LINE TOWARDS A GARY TO
PONTIAC LINE BY EARLY EVENING. THIS WILL PUT THE CORRIDOR OF
HEAVIEST SNOW ACROSS THE CHICAGO METRO FOR MUCH OF IF NOT ALL OF THE
EVENING RUSH...WITH DEPARTURE FROM THE ROCKFORD AREA RIGHT AROUND
THE START. THE MAIN VORT RESPONSIBLE FOR THIS WILL ZIP NORTHEAST SO
THERE MAY BE A DECREASE IN INTENSITY OF THE BAND TOWARD MID EVENING
BUT BROADER SCALE FORCING WILL CONTINUE TO BRING PRECIP AT A LOWER
RATE THROUGH THE EVENING FROM THE GARY/CHICAGO AREA TO PONTIAC AND
POINTS EAST. ANOTHER WAVE WILL LIFT NORTHEAST INTO NORTH-CENTRAL
INDIANA THIS EVENING AND MAY BRING AN INCREASE IN SNOW TO NORTHWEST
INDIANA MID/LATE EVENING BUT THIS MAY REMAIN TO THE EAST. WILL
CONTINUE WITH ACCUMULATION AROUND AN INCH FOR MOST AREAS EXCEPT FAR
SOUTH WHERE SNOW WILL LIKELY BE LIGHTER AND TEMPS A LITTLE WARMER.
AM THINKING THAT THE CORRIDOR FROM MENDOTA UP TO THE NORTHERN
CHICAGO SUBURBS AND EVEN WAUKEGAN...THEN SOUTHEAST TO THE GARY AND
PONTIAC AREA MAY SEE THE MOST INTENSE SNOW OVERALL AS WELL AS
OVERLAP WITH COLDEST TEMPS GOING INTO THE EVENING. HOWEVER...JUST
ABOUT ANYONE WEST OF GARY-PONTIAC COULD SEE AN INCH GIVEN SNOW
INTENSITY SEEN SO FAR TODAY. DO NOT REALLY HAVE A GOOD FEEL FOR
ACCUMULATION GIVEN THE WARM GROUND ETC...AND CANNOT RULE OUT SOME 2
INCH AMOUNTS UNDER THE MOST PERSISTENT BANDS. SNOW WILL TAPER OFF
FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER TROUGH AXIS LATE
THIS EVENING AND EARLY TONIGHT.

ANOTHER CONCERN IS LAKE EFFECT POTENTIAL INTO THE OVERNIGHT. COLDER
AIR WILL CONTINUE TO SPREAD SOUTHWARD INTO THE AREA WITH A GOOD
NORTH FETCH DOWN LAKE MICHIGAN. H85 TEMPS FALL TO AROUND -14 C WHICH
IS ENOUGH TO SUPPORT LAKE EFFECT...WITH LAKE WATER TEMPS PROBABLY
/PERHAPS CONSERVATIVELY/ IN THE UPPER 30S ACROSS MUCH OF THE
SOUTHERN PART OF THE LAKE /WITH MID/UPPER 40S AT NEARSHORE OBS
SITES/ DELTA TS ARE AT LEAST IN THE UPPER TEENS. THE PASSAGE OF THE
UPPER TROUGH WILL BRING SOME SUPPRESSION AS WELL AS DEEP LAYER
DRYING INTO THE REGION BUT LAKE INDUCED EQUILIBRIUM LEVELS
MAY PUSH 6-7 KFT OVERNIGHT. WITH A GRADUALLY WEAKENING PRESSURE
GRADIENT TO THE WEST...WINDS WILL EASE UP FROM WEST TO EAST AND THIS
MAY LEAD TO CONVERGENCE NEAR OR OFF THE ILLINOIS SHORE. SO IF PRECIP
CAN DEVELOP...WHICH IS A BIT OF A WILD CARD...THEN SOUTHERN SECTIONS
OF COOK COUNTY AND WESTERN PORTIONS OF LAKE COUNTY INDIANA MAY SEE
SNOW SHOWERS OVERNIGHT. IT IS ALSO NOT OUT OF THE REALM OF
POSSIBILITY THAT A FURTHER INLAND PUSH TO THE WEST COULD OCCUR INTO
THE CHICAGO AND NORTH SHORE AREAS. WILL GO AHEAD AND CARRY LOW POPS
AT THE SHORELINE AND INTO FAR SOUTHEAST COOK AND WESTERN LAKE COUNTY
THROUGH THE OVERNIGHT. SHORELINE AREAS COULD STAY AT OR JUST ABOVE
FREEZING GIVEN THE LAKE SO ANY ACCUMULATION COULD BE SLUSHY OR EVEN
GRADUALLY MELT...BUT AREAS JUST INLAND WILL LIKELY BE IN THE UPPER
20S TO AROUND 30 SO ACCUMULATION IS A CONCERN. WILL SHARE CONCERN
WITH THE EVENING SHIFT FOR FURTHER MONITORING. OTHERWISE WINDS WILL
EASE INLAND WITH SKIES CLEARING ACROSS WESTERN AREAS ALLOWING TEMPS
TO FALL INTO THE LOWER TO MID 20S.

TUESDAY THROUGH FRIDAY...THE UPPER FLOW WILL FLATTEN BEHIND THE
DEPARTING UPPER TROUGH TUESDAY AS SURFACE HIGH PRESSURE CROSSES THE
AREA. MID LEVEL WARM ADVECTION WILL COMMENCE IN THE AFTERNOON. HIGH
TEMPS WILL BE TOUGH GIVEN THE HIGH SUN ANGLE BUT VERY COLD START AND
SLOW START TO MID LEVEL WAA. LOW LEVEL LAPSE RATES STEEPEN QUITE A
BIT BY AFTERNOON AND WITH THE CONTINUED CYCLONIC FLOW ALOFT WILL
LIKELY SEE SCT-BKN CU DEVELOP INTO THE MIDDAY THEN DISSIPATE FROM
WEST TO EAST DURING THE LATE AFTERNOON. THAT SAID...WE HAVE SEEN
SEVERAL DAYS IN RECENT WEEKS WHERE TEMPS WARMED NICELY IN SIMILAR
SITUATIONS. WILL STAY ON THE WARMER SIDE OF THINGS WITH LOWER TO MID
40S WEST AND UPPER 30S TO AROUND 40 EAST. MOISTURE LOOKS PRETTY
SHALLOW BUT CANNOT RULE OUT A FEW SHOWERS DURING THE AFTERNOON BUT
WILL KEEP THE FORECAST DRY FOR NOW. THE TROUGH OFF THE BRITISH
COLUMBIA COAST TODAY WILL WEAKEN AND MOVE SOUTHEAST ACROSS THE UPPER
MIDWEST WEDNESDAY. THIS WILL BRING A PUSH OF WARMER MID LEVEL AREA
WHICH WILL COMBINE WITH INCREASING SOUTHERLY WINDS BEHIND THE
DEPARTING SURFACE HIGH TO PROPEL TEMPS INTO THE 50S WEDNESDAY. A
SURFACE LOW WILL ACCOMPANY THE UPPER TROUGH WITH A WARM FRONT
DEVELOPING NORTH OF THE AREA. THIS SHOULD KEEP THE LOCAL AREA DRY
WEDNESDAY BUT THE ATTENDANT COLD FRONT WILL MOVE IN THURSDAY
POTENTIALLY BRINGING SOME PRECIP. THE FRONT STALLS OUT OVER OR NEAR
THE AREA THURSDAY EVENING AND A SECOND UPPER TROUGH DIGS INTO THE
CENTRAL AND SOUTHERN PLAINS. A NEW SURFACE LOW WILL TRACK NORTHEAST
AND ACROSS THE LOCAL AREA FRIDAY. PRECIP CHANCES LOOK TO RAMP UP
THURSDAY EVENING NORTHWEST OF THE FRONT...THEN EXPAND ACROSS THE
AREA SOME TIME FRIDAY AS THE SURFACE LOW PASSES. PROVIDED THE
BOUNDARY ARRIVES LATE ENOUGH THURSDAY HIGHS WILL LIKELY BE IN THE
60S...WITH FRIDAY BEING COOLER BUT ALSO SEEING A LARGER RANGE OF
TEMPS THANKS TO THE BOUNDARY. EXPECT LOWER 50S NORTH AND UPPER 50S
SOUTH.

SATURDAY AND BEYOND...THE LOW WILL CLEAR TO THE NORTHEAST SOME TIME
EARLY SATURDAY WITH HIGH PRESSURE BUILDING IN THROUGH THE DAY. WITH
THE UPPER FLOW NOT ALL THAT AMPLIFIED THERE WILL BE LITTLE IN THE
WAY OF COOLING ALOFT AND ENOUGH SUNSHINE SHOULD HELP PROPEL TEMPS
INTO THE 50S. ANOTHER TROUGH LOOKS TO CROSS THE AREA SUNDAY BRINGING
MORE CHANCES FOR RAIN BUT OVERALL MILD TEMPS IN THE 50S.

MDB

&&

.CLIMATE...
THE FOLLOWING ARE THE MOST RECENT APRIL DATES AND AMOUNTS OF
ACCUMULATING SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* A PERIOD OF IFR/LIFR SNOW THROUGH MID EVENING

* MVFR CIGS THROUGH THIS EVENING

* GUSTY NORTH/NORTHWEST WINDS

IZZI

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

COMPLEX FORECAST THIS PERIOD AS A WINTRY MIX IS LIKELY THIS
AFTERNOON INTO THE EVENING. LATEST RADAR IMAGERY DEPICTING
CONTINUED LIGHT DEVELOPMENT AT THIS HOUR WITH ALL SNOW BEING
REPORTED ACROSS NORTH/NORTHWEST ILLINOIS...AND THEN A RAIN SNOW
MIX BEING REPORTED OVER AREAS IN NORTHEAST ILLINOIS. THIS LIGHTER
DEVELOPMENT WILL LIKELY CONTINUE THROUGH MID AFTERNOON BEFORE A
HEAVIER/STEADIER BAND OF LIGHT TO MODERATE SNOW MOVES THROUGH LATE
THIS AFTERNOON INTO THE EARL EVENING...WITH ANY AREAS OBSERVING A
RAIN/SNOW MIX OBSERVING A QUICK TRANSITION TO ALL SNOW. VIS AND
CEILINGS WILL LIKELY LOWER UNDER THIS BETTER DEVELOPMENT...WITH
IFR VIS AND LOW END MVFR CEILINGS LIKELY. THIS STEADIER SNOW
SHOULD BEGIN TO SHIFT EAST OF THE TERMINALS LATER THIS
EVENING...BUT WITH LAKE EFFECT DEVELOPMENT POSSIBLY LINGERING
THROUGH THE MIDNIGHT TIME FRAME. CONFIDENCE IS LOW WITH REGARDS TO
LAKE EFFECT SNOW DEVELOPMENT THIS EVENING/TONIGHT...AND WILL NEED
TO MONITOR THIS POSSIBLE DEVELOPMENT. AREAS WILL THEN OBSERVE A
CLEARING TREND OVERNIGHT...WITH VFR CONDITIONS THEN LIKELY
TUESDAY. NORTHERLY WINDS MAY CONTINUE TO VARY BETWEEN NNW AND NNE
OVER THE NEXT SEVERAL HOURS...BUT WITH A TREND TOWARDS NNW. HAVE
CONTINUED TO LOWER SPEEDS/GUSTS THIS AFTERNOON WITH THE HIGHEST
GUSTS OF AROUND 21KT NOW LIKELY EARLY THIS AFTERNOON. NORTHWEST
WINDS WILL PREVAIL TONIGHT INTO TUESDAY...WITH SPEEDS DIMINISHING.

RODRIGUEZ

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

* MEDIUM-HIGH CONFIDENCE WITH CEILING TRENDS

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED

* HIGH CONFIDENCE IN SNOW TRENDS

* LOW CONFIDENCE WITH LAKE EFFECT SNOW SHOWERS

IZZI

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
313 PM CDT

LOW PRESSURE OVER QUEBEC DRAGGED A COLD FRONT OVER THE LAKE THIS
MORNING. NORTH GALES BEHIND THE FRONT HAVE PERSISTED INTO MID
AFTERNOON AND ARE EXPECTED TO EASE QUICKLY THIS EVENING...BUT EAST
SIDE OF THE ENTIRE LAKE IS STILL SEEING GUSTS INTO THE MID 30S TO
AROUND 40 KT RANGE...SO GALE WARNING HAS BEEN EXTENDED INTO THE
EVENING. TO THE WEST...HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TONIGHT THEN INTO THE WESTERN GREAT LAKES LATER TOMORROW. ANOTHER
LOW WILL DEVELOP ACROSS THE CENTRAL AND SOUTHERN PLAINS WEDNESDAY
WITH TROUGHING EXTENDING TO THE NORTHEAST WHICH WILL MOVE OVER
LAKE MICHIGAN WEDNESDAY NIGHT INTO THURSDAY. LOW PRESSURE WILL
THEN LIFT NORTHEAST ACROSS THE MIDWEST OVER THE WEEKEND.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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

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







000
FXUS63 KLOT 142016
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
316 PM CDT MON APR 14 2014

.DISCUSSION...
314 PM CDT

THE MAIN PERIOD OF ACTIVE WEATHER WILL BE THIS EVENING WITH A MORE
TRANQUIL PERIOD SETTING UP INTO TUESDAY AND CONTINUING THROUGH MUCH
OF THE WEEK. EARLY AFTERNOON WATER VAPOR IMAGERY SHOWS AN EXPANSIVE
LONGWAVE TROUGH OVER THE MID SECTION OF THE COUNTRY WITH THE TROUGH
AXIS SWINGING EASTWARD TOWARD THE LOCAL AREA. A SHARP BUT NARROW
RIDGE TRAILS THE BIG TROUGH OVER WEST COAST WITH A SERIES OF MORE
COMPACT UPPER LOWS SPINNING EASTWARD TOWARDS THE CANADIAN WEST
COAST. AT THE SURFACE...THE MAIN SURFACE LOW WHICH BROUGHT THE
ACTIVE WEATHER OVER THE PAST FEW DAYS IS NOW OVER EASTERN QUEBEC
WITH HIGH PRESSURE SPREADING SOUTHWARD ACROSS THE CANADIAN PRAIRIES
INTO THE CENTRAL AND NORTHERN PLANS.

TONIGHT...WATER VAPOR SHOWS AN EMBEDDED UPPER WAVE MOVING INTO THE
AREA FROM THE SOUTHWEST LATE THIS AFTERNOON. THIS IS TIGHTENING THE
MID LEVEL BAROCLINIC ZONE AND RESULTING IN INTENSIFYING
FRONTOGENESIS IN A CORRIDOR ACROSS THE NORTHWEST CWA WHICH IS
SHIFTING EASTWARD. COLDER AIR AT THE SURFACE AND ALOFT CONTINUES TO
SPREAD SOUTHEASTWARD AS WELL. PRECIP WILL CONTINUE TO INTENSIFY IN
CONJUNCTION WITH THE INCREASED FORCING WHILE THE ENTIRE BAND PIVOTS
EASTWARD AS THE LONGWAVE TROUGH AXIS PUSHES EASTWARD INTO THE
EVENING. FORECAST SOUNDINGS SHOW THAT THE BEST FORCING LINES UP WELL
WITH THE FAVORED SNOW GROWTH REGION SUPPORTING EFFICIENT SNOW GROWTH
WITH THE COLUMN COLD ENOUGH TO SUPPORT ALL SNOW WITHIN THE BAND.
AREAS TO THE SOUTH AND WEST OF THE HAVE BEEN REPORTING VSBY AS LOW
AS 1/4 TO 3/4 SM VSBY UNDER THE HEAVIER PRECIP ELEMENTS. SURFACE
TEMPS...WHILE STILL ABOVE FREEZING WILL COOL WITH TIME FAVORING
ACCUMULATING SNOW BUT GROUND TEMPS WILL BE THE LIMITING FACTOR
OVERALL. HOWEVER...SNOW INTENSITY WITHIN THE HEAVIEST BANDS WILL
LIKELY OVERCOME THE WARMER GROUND...ESPECIALLY ON GRASSY AND
ELEVATED SURFACES...WITH SLUSHY ACCUMULATION POSSIBLE ON ROADWAYS.
BASED ON LATEST TRENDS...AREAS FROM MENDOTA TO CHICAGO NORTHWEST
WILL BE THE FOCUS GOING THROUGH LATE AFTERNOON WITH AN EXPANSION
EXPECTED JUST TO THE SOUTHEAST OF THIS LINE TOWARDS A GARY TO
PONTIAC LINE BY EARLY EVENING. THIS WILL PUT THE CORRIDOR OF
HEAVIEST SNOW ACROSS THE CHICAGO METRO FOR MUCH OF IF NOT ALL OF THE
EVENING RUSH...WITH DEPARTURE FROM THE ROCKFORD AREA RIGHT AROUND
THE START. THE MAIN VORT RESPONSIBLE FOR THIS WILL ZIP NORTHEAST SO
THERE MAY BE A DECREASE IN INTENSITY OF THE BAND TOWARD MID EVENING
BUT BROADER SCALE FORCING WILL CONTINUE TO BRING PRECIP AT A LOWER
RATE THROUGH THE EVENING FROM THE GARY/CHICAGO AREA TO PONTIAC AND
POINTS EAST. ANOTHER WAVE WILL LIFT NORTHEAST INTO NORTH-CENTRAL
INDIANA THIS EVENING AND MAY BRING AN INCREASE IN SNOW TO NORTHWEST
INDIANA MID/LATE EVENING BUT THIS MAY REMAIN TO THE EAST. WILL
CONTINUE WITH ACCUMULATION AROUND AN INCH FOR MOST AREAS EXCEPT FAR
SOUTH WHERE SNOW WILL LIKELY BE LIGHTER AND TEMPS A LITTLE WARMER.
AM THINKING THAT THE CORRIDOR FROM MENDOTA UP TO THE NORTHERN
CHICAGO SUBURBS AND EVEN WAUKEGAN...THEN SOUTHEAST TO THE GARY AND
PONTIAC AREA MAY SEE THE MOST INTENSE SNOW OVERALL AS WELL AS
OVERLAP WITH COLDEST TEMPS GOING INTO THE EVENING. HOWEVER...JUST
ABOUT ANYONE WEST OF GARY-PONTIAC COULD SEE AN INCH GIVEN SNOW
INTENSITY SEEN SO FAR TODAY. DO NOT REALLY HAVE A GOOD FEEL FOR
ACCUMULATION GIVEN THE WARM GROUND ETC...AND CANNOT RULE OUT SOME 2
INCH AMOUNTS UNDER THE MOST PERSISTENT BANDS. SNOW WILL TAPER OFF
FROM WEST TO EAST WITH THE PASSAGE OF THE UPPER TROUGH AXIS LATE
THIS EVENING AND EARLY TONIGHT.

ANOTHER CONCERN IS LAKE EFFECT POTENTIAL INTO THE OVERNIGHT. COLDER
AIR WILL CONTINUE TO SPREAD SOUTHWARD INTO THE AREA WITH A GOOD
NORTH FETCH DOWN LAKE MICHIGAN. H85 TEMPS FALL TO AROUND -14 C WHICH
IS ENOUGH TO SUPPORT LAKE EFFECT...WITH LAKE WATER TEMPS PROBABLY
/PERHAPS CONSERVATIVELY/ IN THE UPPER 30S ACROSS MUCH OF THE
SOUTHERN PART OF THE LAKE /WITH MID/UPPER 40S AT NEARSHORE OBS
SITES/ DELTA TS ARE AT LEAST IN THE UPPER TEENS. THE PASSAGE OF THE
UPPER TROUGH WILL BRING SOME SUPPRESSION AS WELL AS DEEP LAYER
DRYING INTO THE REGION BUT LAKE INDUCED EQUILIBRIUM LEVELS
MAY PUSH 6-7 KFT OVERNIGHT. WITH A GRADUALLY WEAKENING PRESSURE
GRADIENT TO THE WEST...WINDS WILL EASE UP FROM WEST TO EAST AND THIS
MAY LEAD TO CONVERGENCE NEAR OR OFF THE ILLINOIS SHORE. SO IF PRECIP
CAN DEVELOP...WHICH IS A BIT OF A WILD CARD...THEN SOUTHERN SECTIONS
OF COOK COUNTY AND WESTERN PORTIONS OF LAKE COUNTY INDIANA MAY SEE
SNOW SHOWERS OVERNIGHT. IT IS ALSO NOT OUT OF THE REALM OF
POSSIBILITY THAT A FURTHER INLAND PUSH TO THE WEST COULD OCCUR INTO
THE CHICAGO AND NORTH SHORE AREAS. WILL GO AHEAD AND CARRY LOW POPS
AT THE SHORELINE AND INTO FAR SOUTHEAST COOK AND WESTERN LAKE COUNTY
THROUGH THE OVERNIGHT. SHORELINE AREAS COULD STAY AT OR JUST ABOVE
FREEZING GIVEN THE LAKE SO ANY ACCUMULATION COULD BE SLUSHY OR EVEN
GRADUALLY MELT...BUT AREAS JUST INLAND WILL LIKELY BE IN THE UPPER
20S TO AROUND 30 SO ACCUMULATION IS A CONCERN. WILL SHARE CONCERN
WITH THE EVENING SHIFT FOR FURTHER MONITORING. OTHERWISE WINDS WILL
EASE INLAND WITH SKIES CLEARING ACROSS WESTERN AREAS ALLOWING TEMPS
TO FALL INTO THE LOWER TO MID 20S.

TUESDAY THROUGH FRIDAY...THE UPPER FLOW WILL FLATTEN BEHIND THE
DEPARTING UPPER TROUGH TUESDAY AS SURFACE HIGH PRESSURE CROSSES THE
AREA. MID LEVEL WARM ADVECTION WILL COMMENCE IN THE AFTERNOON. HIGH
TEMPS WILL BE TOUGH GIVEN THE HIGH SUN ANGLE BUT VERY COLD START AND
SLOW START TO MID LEVEL WAA. LOW LEVEL LAPSE RATES STEEPEN QUITE A
BIT BY AFTERNOON AND WITH THE CONTINUED CYCLONIC FLOW ALOFT WILL
LIKELY SEE SCT-BKN CU DEVELOP INTO THE MIDDAY THEN DISSIPATE FROM
WEST TO EAST DURING THE LATE AFTERNOON. THAT SAID...WE HAVE SEEN
SEVERAL DAYS IN RECENT WEEKS WHERE TEMPS WARMED NICELY IN SIMILAR
SITUATIONS. WILL STAY ON THE WARMER SIDE OF THINGS WITH LOWER TO MID
40S WEST AND UPPER 30S TO AROUND 40 EAST. MOISTURE LOOKS PRETTY
SHALLOW BUT CANNOT RULE OUT A FEW SHOWERS DURING THE AFTERNOON BUT
WILL KEEP THE FORECAST DRY FOR NOW. THE TROUGH OFF THE BRITISH
COLUMBIA COAST TODAY WILL WEAKEN AND MOVE SOUTHEAST ACROSS THE UPPER
MIDWEST WEDNESDAY. THIS WILL BRING A PUSH OF WARMER MID LEVEL AREA
WHICH WILL COMBINE WITH INCREASING SOUTHERLY WINDS BEHIND THE
DEPARTING SURFACE HIGH TO PROPEL TEMPS INTO THE 50S WEDNESDAY. A
SURFACE LOW WILL ACCOMPANY THE UPPER TROUGH WITH A WARM FRONT
DEVELOPING NORTH OF THE AREA. THIS SHOULD KEEP THE LOCAL AREA DRY
WEDNESDAY BUT THE ATTENDANT COLD FRONT WILL MOVE IN THURSDAY
POTENTIALLY BRINGING SOME PRECIP. THE FRONT STALLS OUT OVER OR NEAR
THE AREA THURSDAY EVENING AND A SECOND UPPER TROUGH DIGS INTO THE
CENTRAL AND SOUTHERN PLAINS. A NEW SURFACE LOW WILL TRACK NORTHEAST
AND ACROSS THE LOCAL AREA FRIDAY. PRECIP CHANCES LOOK TO RAMP UP
THURSDAY EVENING NORTHWEST OF THE FRONT...THEN EXPAND ACROSS THE
AREA SOME TIME FRIDAY AS THE SURFACE LOW PASSES. PROVIDED THE
BOUNDARY ARRIVES LATE ENOUGH THURSDAY HIGHS WILL LIKELY BE IN THE
60S...WITH FRIDAY BEING COOLER BUT ALSO SEEING A LARGER RANGE OF
TEMPS THANKS TO THE BOUNDARY. EXPECT LOWER 50S NORTH AND UPPER 50S
SOUTH.

SATURDAY AND BEYOND...THE LOW WILL CLEAR TO THE NORTHEAST SOME TIME
EARLY SATURDAY WITH HIGH PRESSURE BUILDING IN THROUGH THE DAY. WITH
THE UPPER FLOW NOT ALL THAT AMPLIFIED THERE WILL BE LITTLE IN THE
WAY OF COOLING ALOFT AND ENOUGH SUNSHINE SHOULD HELP PROPEL TEMPS
INTO THE 50S. ANOTHER TROUGH LOOKS TO CROSS THE AREA SUNDAY BRINGING
MORE CHANCES FOR RAIN BUT OVERALL MILD TEMPS IN THE 50S.

MDB

&&

.CLIMATE...
THE FOLLOWING ARE THE MOST RECENT APRIL DATES AND AMOUNTS OF
ACCUMULATING SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* MVFR CEILINGS...LOWERING BACK TOWARDS LOW END MVFR LATER THIS
  AFTERNOON.

* GUSTY NORTH/NORTHWEST WINDS.

* RAIN/SNOW MIX...WITH BETTER SNOW DEVELOPMENT MOVING OVER THE
  TERMINAL LATE THIS AFTERNOON INTO THE EARLY EVENING.

* POSSIBLE LAKE EFFECT SNOW SHOWERS LINGERING INTO THE LATE
  EVENING.

RODRIGUEZ

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

COMPLEX FORECAST THIS PERIOD AS A WINTRY MIX IS LIKELY THIS
AFTERNOON INTO THE EVENING. LATEST RADAR IMAGERY DEPICTING
CONTINUED LIGHT DEVELOPMENT AT THIS HOUR WITH ALL SNOW BEING
REPORTED ACROSS NORTH/NORTHWEST ILLINOIS...AND THEN A RAIN SNOW
MIX BEING REPORTED OVER AREAS IN NORTHEAST ILLINOIS. THIS LIGHTER
DEVELOPMENT WILL LIKELY CONTINUE THROUGH MID AFTERNOON BEFORE A
HEAVIER/STEADIER BAND OF LIGHT TO MODERATE SNOW MOVES THROUGH LATE
THIS AFTERNOON INTO THE EARL EVENING...WITH ANY AREAS OBSERVING A
RAIN/SNOW MIX OBSERVING A QUICK TRANSITION TO ALL SNOW. VIS AND
CEILINGS WILL LIKELY LOWER UNDER THIS BETTER DEVELOPMENT...WITH
IFR VIS AND LOW END MVFR CEILINGS LIKELY. THIS STEADIER SNOW
SHOULD BEGIN TO SHIFT EAST OF THE TERMINALS LATER THIS
EVENING...BUT WITH LAKE EFFECT DEVELOPMENT POSSIBLY LINGERING
THROUGH THE MIDNIGHT TIME FRAME. CONFIDENCE IS LOW WITH REGARDS TO
LAKE EFFECT SNOW DEVELOPMENT THIS EVENING/TONIGHT...AND WILL NEED
TO MONITOR THIS POSSIBLE DEVELOPMENT. AREAS WILL THEN OBSERVE A
CLEARING TREND OVERNIGHT...WITH VFR CONDITIONS THEN LIKELY
TUESDAY. NORTHERLY WINDS MAY CONTINUE TO VARY BETWEEN NNW AND NNE
OVER THE NEXT SEVERAL HOURS...BUT WITH A TREND TOWARDS NNW. HAVE
CONTINUED TO LOWER SPEEDS/GUSTS THIS AFTERNOON WITH THE HIGHEST
GUSTS OF AROUND 21KT NOW LIKELY EARLY THIS AFTERNOON. NORTHWEST
WINDS WILL PREVAIL TONIGHT INTO TUESDAY...WITH SPEEDS DIMINISHING.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH CEILING TRENDS.

* MEDIUM HIGH CONFIDENCE IN WIND DIRECTION/SPEED.

* MEDIUM HIGH CONFIDENCE WITH RAIN/SNOW AND ALL SNOW TRENDS AND
  TIMING.

* LOW CONFIDENCE WITH LAKE EFFECT SNOW SHOWERS.

RODRIGUEZ

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
313 PM CDT

LOW PRESSURE OVER QUEBEC DRAGGED A COLD FRONT OVER THE LAKE THIS
MORNING. NORTH GALES BEHIND THE FRONT HAVE PERSISTED INTO MID
AFTERNOON AND ARE EXPECTED TO EASE QUICKLY THIS EVENING...BUT EAST
SIDE OF THE ENTIRE LAKE IS STILL SEEING GUSTS INTO THE MID 30S TO
AROUND 40 KT RANGE...SO GALE WARNING HAS BEEEN EXTENDED INTO THE
EVENING. TO THE WEST...HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
TONIGHT THEN INTO THE WESTERN GREAT LAKES LATER TOMORROW. ANOTHER
LOW WILL DEVELOP ACROSS THE CENTRAL AND SOUTHERN PLAINS WEDNESDAY
WITH TROUGHING EXTENDING TO THE NORTHEAST WHICH WILL MOVE OVER
LAKE MICHIGAN WEDNESDAY NIGHT INTO THURSDAY. LOW PRESSURE WILL
THEN LIFT NORTHEAST ACROSS THE MIDWEST OVER THE WEEKEND.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

     GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM MONDAY.

&&

$$

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

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









000
FXUS63 KLOT 141955
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
255 PM CDT MON APR 14 2014

.DISCUSSION...
1205 PM CDT

CHALLENGING FORECAST CONTINUES THROUGH THE EVENING WITH PRECIP
COVERAGE...INTENSITY...AND TYPE BEING THE MAIN FOCUS. LARGE SCALE
UPPER TROUGH COVERING THE MID SECTION OF THE COUNTRY CONTINUES TO
PIVOT EASTWARD PUSHING COLDER AIR INTO THE REGION. SUBTLE WAVES
TRAVERSING THE FLOW CONTINUE TO WORK WITH COLD ADVECTION TO BRING
PRECIP DEVELOPMENT. SURFACE TEMPS HAVE WARMED CENTRAL AND
SOUTHEAST WHICH IS SUPPORTIVE OF MORE RAIN BUT TEMPERATURES WILL
LIKELY COOL INTO THE AFTERNOON FROM THE NORTHWEST.
THEREFORE...PRECIP TYPE THROUGH EARLY AFTERNOON WILL LIKELY BE
RAIN OR SNOW EXCEPT FOR FAR SOUTHEAST AREAS THAT WOULD SEE
RAIN...THOUGH PRECIP CHANCES ARE LOWER THERE. WATER VAPOR SHOWS A
MORE ORGANIZED SHORTWAVE STARTING TO EJECT NORTHEAST FROM
SOUTHWEST MISSOURI AND EASTERN OKLAHOMA AND KANSAS. THIS WAVE WILL
LIFT INTO THE AREA LATE THIS AFTERNOON INTO THE EARLY EVENING AND
TIGHTEN THE MID LEVEL BAROCLINIC ZONE RESULTING IN INTENSIFYING
FRONTOGENESIS. RADAR MOSAIC SHOWS BANDS OF PRECIP DEVELOPING
NORTHEASTWARD IN CONJUNCTION WITH THIS FEATURE. WILL CONTINUE WITH
THE IDEA OF A MORE FOCUSED PERIOD OF PRECIPITATION LATE THIS
AFTERNOON INTO THE EVENING BUT HAVE TRIED TO REFINE DETAILS. WHILE
PRECIP WILL CONTINUE ON AND OFF THROUGH THE AFTERNOON...HAVE
SLOWED THE PERIOD OF BETTER COVERAGE/INTENSITY SLIGHTLY. FORECAST
SOUNDINGS/CONCEPTUAL MODELS SUPPORT ALL SNOW WITHIN THE MOST
INTENSE BAND THANKS TO WELL ALIGNED ASCENT WITHIN THE SNOW GROWTH
ZONE AND COOLING LOW LEVEL TEMP PROFILES. EXPECT THAT THERE WILL
BE A CORRIDOR OF MODERATE SNOW WITHIN A LARGER AREA OF LESS
INTENSE PRECIP THAT WILL DEVELOP NORTHWARD ALONG A LINE FROM
ROUGHLY CHICAGO TO MENDOTA...THEN PIVOT EASTWARD INTO THE EVENING.
MUCH OF THE EVENING RUSH HOUR IN THE CHICAGO METRO LOOKS TO FALL
INTO THE PERIOD OF MORE INTENSE SNOWFALL...WHICH MAY LAST A FEW
HOURS. THE VORT MAX LIFTS NORTHEAST WHICH MAY BRING A LULL IN THE
PRECIP EARLY THIS EVENING BUT LARGER SCALE FORCING INCREASES TO
THE EAST SO THERE MAY BE RE-INTENSIFICATION OVER NORTHWEST INDIANA
BY MID EVENING BEFORE PRECIP EXITS LATE EVENING. TEMPERATURES
WILL LIKELY COOL INTO THE MID 30S LATER TODAY AND SNOW SHOULD FALL
AT AN INTENSE ENOUGH RATE TO PROVIDE FOR ACCUMULATION ON GRASSY
SURFACES AND SLUSHY ACCUMULATION ON ROADS. WILL CONTINUE WITH THE
IDEA OF AROUND AN INCH OF ACCUMULATION.

MDB

//PREV DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* MVFR CEILINGS...LOWERING BACK TOWARDS LOW END MVFR LATER THIS
  AFTERNOON.

* GUSTY NORTH/NORTHWEST WINDS.

* RAIN/SNOW MIX...WITH BETTER SNOW DEVELOPMENT MOVING OVER THE
  TERMINAL LATE THIS AFTERNOON INTO THE EARLY EVENING.

* POSSIBLE LAKE EFFECT SNOW SHOWERS LINGERING INTO THE LATE
  EVENING.

RODRIGUEZ

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

COMPLEX FORECAST THIS PERIOD AS A WINTRY MIX IS LIKELY THIS
AFTERNOON INTO THE EVENING. LATEST RADAR IMAGERY DEPICTING
CONTINUED LIGHT DEVELOPMENT AT THIS HOUR WITH ALL SNOW BEING
REPORTED ACROSS NORTH/NORTHWEST ILLINOIS...AND THEN A RAIN SNOW
MIX BEING REPORTED OVER AREAS IN NORTHEAST ILLINOIS. THIS LIGHTER
DEVELOPMENT WILL LIKELY CONTINUE THROUGH MID AFTERNOON BEFORE A
HEAVIER/STEADIER BAND OF LIGHT TO MODERATE SNOW MOVES THROUGH LATE
THIS AFTERNOON INTO THE EARL EVENING...WITH ANY AREAS OBSERVING A
RAIN/SNOW MIX OBSERVING A QUICK TRANSITION TO ALL SNOW. VIS AND
CEILINGS WILL LIKELY LOWER UNDER THIS BETTER DEVELOPMENT...WITH
IFR VIS AND LOW END MVFR CEILINGS LIKELY. THIS STEADIER SNOW
SHOULD BEGIN TO SHIFT EAST OF THE TERMINALS LATER THIS
EVENING...BUT WITH LAKE EFFECT DEVELOPMENT POSSIBLY LINGERING
THROUGH THE MIDNIGHT TIME FRAME. CONFIDENCE IS LOW WITH REGARDS TO
LAKE EFFECT SNOW DEVELOPMENT THIS EVENING/TONIGHT...AND WILL NEED
TO MONITOR THIS POSSIBLE DEVELOPMENT. AREAS WILL THEN OBSERVE A
CLEARING TREND OVERNIGHT...WITH VFR CONDITIONS THEN LIKELY
TUESDAY. NORTHERLY WINDS MAY CONTINUE TO VARY BETWEEN NNW AND NNE
OVER THE NEXT SEVERAL HOURS...BUT WITH A TREND TOWARDS NNW. HAVE
CONTINUED TO LOWER SPEEDS/GUSTS THIS AFTERNOON WITH THE HIGHEST
GUSTS OF AROUND 21KT NOW LIKELY EARLY THIS AFTERNOON. NORTHWEST
WINDS WILL PREVAIL TONIGHT INTO TUESDAY...WITH SPEEDS DIMINISHING.

RODRIGUEZ

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

* MEDIUM HIGH CONFIDENCE WITH CEILING TRENDS.

* MEDIUM HIGH CONFIDENCE IN WIND DIRECTION/SPEED.

* MEDIUM HIGH CONFIDENCE WITH RAIN/SNOW AND ALL SNOW TRENDS AND
  TIMING.

* LOW CONFIDENCE WITH LAKE EFFECT SNOW SHOWERS.

RODRIGUEZ

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 141803
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
103 PM CDT MON APR 14 2014

.DISCUSSION...
1205 PM CDT

CHALLENGING FORECAST CONTINUES THROUGH THE EVENING WITH PRECIP
COVERAGE...INTENSITY...AND TYPE BEING THE MAIN FOCUS. LARGE SCALE
UPPER TROUGH COVERING THE MID SECTION OF THE COUNTRY CONTINUES TO
PIVOT EASTWARD PUSHING COLDER AIR INTO THE REGION. SUBTLE WAVES
TRAVERSING THE FLOW CONTINUE TO WORK WITH COLD ADVECTION TO BRING
PRECIP DEVELOPMENT. SURFACE TEMPS HAVE WARMED CENTRAL AND
SOUTHEAST WHICH IS SUPPORTIVE OF MORE RAIN BUT TEMPERATURES WILL
LIKELY COOL INTO THE AFTERNOON FROM THE NORTHWEST.
THEREFORE...PRECIP TYPE THROUGH EARLY AFTERNOON WILL LIKELY BE
RAIN OR SNOW EXCEPT FOR FAR SOUTHEAST AREAS THAT WOULD SEE
RAIN...THOUGH PRECIP CHANCES ARE LOWER THERE. WATER VAPOR SHOWS A
MORE ORGANIZED SHORTWAVE STARTING TO EJECT NORTHEAST FROM
SOUTHWEST MISSOURI AND EASTERN OKLAHOMA AND KANSAS. THIS WAVE WILL
LIFT INTO THE AREA LATE THIS AFTERNOON INTO THE EARLY EVENING AND
TIGHTEN THE MID LEVEL BAROCLINIC ZONE RESULTING IN INTENSIFYING
FRONTOGENESIS. RADAR MOSAIC SHOWS BANDS OF PRECIP DEVELOPING
NORTHEASTWARD IN CONJUNCTION WITH THIS FEATURE. WILL CONTINUE WITH
THE IDEA OF A MORE FOCUSED PERIOD OF PRECIPITATION LATE THIS
AFTERNOON INTO THE EVENING BUT HAVE TRIED TO REFINE DETAILS. WHILE
PRECIP WILL CONTINUE ON AND OFF THROUGH THE AFTERNOON...HAVE
SLOWED THE PERIOD OF BETTER COVERAGE/INTENSITY SLIGHTLY. FORECAST
SOUNDINGS/CONCEPTUAL MODELS SUPPORT ALL SNOW WITHIN THE MOST
INTENSE BAND THANKS TO WELL ALIGNED ASCENT WITHIN THE SNOW GROWTH
ZONE AND COOLING LOW LEVEL TEMP PROFILES. EXPECT THAT THERE WILL
BE A CORRIDOR OF MODERATE SNOW WITHIN A LARGER AREA OF LESS
INTENSE PRECIP THAT WILL DEVELOP NORTHWARD ALONG A LINE FROM
ROUGHLY CHICAGO TO MENDOTA...THEN PIVOT EASTWARD INTO THE EVENING.
MUCH OF THE EVENING RUSH HOUR IN THE CHICAGO METRO LOOKS TO FALL
INTO THE PERIOD OF MORE INTENSE SNOWFALL...WHICH MAY LAST A FEW
HOURS. THE VORT MAX LIFTS NORTHEAST WHICH MAY BRING A LULL IN THE
PRECIP EARLY THIS EVENING BUT LARGER SCALE FORCING INCREASES TO
THE EAST SO THERE MAY BE RE-INTENSIFICATION OVER NORTHWEST INDIANA
BY MID EVENING BEFORE PRECIP EXITS LATE EVENING. TEMPERATURES
WILL LIKELY COOL INTO THE MID 30S LATER TODAY AND SNOW SHOULD FALL
AT AN INTENSE ENOUGH RATE TO PROVIDE FOR ACCUMULATION ON GRASSY
SURFACES AND SLUSHY ACCUMULATION ON ROADS. WILL CONTINUE WITH THE
IDEA OF AROUND AN INCH OF ACCUMULATION.

MDB

//PREV DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* MVFR CEILINGS...LOWERING BACK TOWARDS LOW END MVFR LATER THIS
  AFTERNOON.

* GUSTY NORTHERLY WINDS.

* RAIN/SNOW MIX EARLY THIS AFTERNOON...WITH BETTER SNOW
  DEVELOPMENT MOVING OVER THE TERMINAL LATE THIS AFTERNOON INTO
  THE EARLY EVENING.

* POSSIBLE LAKE EFFECT SNOW SHOWERS LINGERING INTO THE LATE
  EVENING.

RODRIGUEZ

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

COMPLEX FORECAST THIS PERIOD AS A WINTRY MIX IS LIKELY THIS
AFTERNOON INTO THE EVENING. LATEST RADAR IMAGERY DEPICTING
CONTINUED LIGHT DEVELOPMENT AT THIS HOUR WITH ALL SNOW BEING
REPORTED ACROSS NORTH/NORTHWEST ILLINOIS...AND THEN A RAIN SNOW
MIX BEING REPORTED OVER AREAS IN NORTHEAST ILLINOIS. THIS LIGHTER
DEVELOPMENT WILL LIKELY CONTINUE THROUGH MID AFTERNOON BEFORE A
HEAVIER/STEADIER BAND OF LIGHT TO MODERATE SNOW MOVES THROUGH LATE
THIS AFTERNOON INTO THE EARL EVENING...WITH ANY AREAS OBSERVING A
RAIN/SNOW MIX OBSERVING A QUICK TRANSITION TO ALL SNOW. VIS AND
CEILINGS WILL LIKELY LOWER UNDER THIS BETTER DEVELOPMENT...WITH
IFR VIS AND LOW END MVFR CEILINGS LIKELY. THIS STEADIER SNOW
SHOULD BEGIN TO SHIFT EAST OF THE TERMINALS LATER THIS
EVENING...BUT WITH LAKE EFFECT DEVELOPMENT POSSIBLY LINGERING
THROUGH THE MIDNIGHT TIME FRAME. CONFIDENCE IS LOW WITH REGARDS TO
LAKE EFFECT SNOW DEVELOPMENT THIS EVENING/TONIGHT...AND WILL NEED
TO MONITOR THIS POSSIBLE DEVELOPMENT. AREAS WILL THEN OBSERVE A
CLEARING TREND OVERNIGHT...WITH VFR CONDITIONS THEN LIKELY
TUESDAY. NORTHERLY WINDS MAY CONTINUE TO VARY BETWEEN NNW AND NNE
OVER THE NEXT SEVERAL HOURS...BUT WITH A TREND TOWARDS NNW. HAVE
CONTINUED TO LOWER SPEEDS/GUSTS THIS AFTERNOON WITH THE HIGHEST
GUSTS OF AROUND 21KT NOW LIKELY EARLY THIS AFTERNOON. NORTHWEST
WINDS WILL PREVAIL TONIGHT INTO TUESDAY...WITH SPEEDS DIMINISHING.

RODRIGUEZ


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

* MEDIUM HIGH CONFIDENCE WITH CEILING TRENDS.

* MEDIUM HIGH CONFIDENCE IN WIND DIRECTION/SPEED.

* MEDIUM HIGH CONFIDENCE WITH RAIN/SNOW AND ALL SNOW TRENDS AND
  TIMING.

* LOW CONFIDENCE WITH LAKE EFFECT SNOW SHOWERS.

RODRIGUEZ

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 141710
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1210 PM CDT MON APR 14 2014

.DISCUSSION...
1205 PM CDT

CHALLENGING FORECAST CONTINUES THROUGH THE EVENING WITH PRECIP
COVERAGE...INTENSITY...AND TYPE BEING THE MAIN FOCUS. LARGE SCALE
UPPER TROUGH COVERING THE MID SECTION OF THE COUNTRY CONTINUES TO
PIVOT EASTWARD PUSHING COLDER AIR INTO THE REGION. SUBTLE WAVES
TRAVERSING THE FLOW CONTINUE TO WORK WITH COLD ADVECTION TO BRING
PRECIP DEVELOPMENT. SURFACE TEMPS HAVE WARMED CENTRAL AND
SOUTHEAST WHICH IS SUPPORTIVE OF MORE RAIN BUT TEMPERATURES WILL
LIKELY COOL INTO THE AFTERNOON FROM THE NORTHWEST.
THEREFORE...PRECIP TYPE THROUGH EARLY AFTERNOON WILL LIKELY BE
RAIN OR SNOW EXCEPT FOR FAR SOUTHEAST AREAS THAT WOULD SEE
RAIN...THOUGH PRECIP CHANCES ARE LOWER THERE. WATER VAPOR SHOWS A
MORE ORGANIZED SHORTWAVE STARTING TO EJECT NORTHEAST FROM
SOUTHWEST MISSOURI AND EASTERN OKLAHOMA AND KANSAS. THIS WAVE WILL
LIFT INTO THE AREA LATE THIS AFTERNOON INTO THE EARLY EVENING AND
TIGHTEN THE MID LEVEL BAROCLINIC ZONE RESULTING IN INTENSIFYING
FRONTOGENESIS. RADAR MOSAIC SHOWS BANDS OF PRECIP DEVELOPING
NORTHEASTWARD IN CONJUNCTION WITH THIS FEATURE. WILL CONTINUE WITH
THE IDEA OF A MORE FOCUSED PERIOD OF PRECIPITATION LATE THIS
AFTERNOON INTO THE EVENING BUT HAVE TRIED TO REFINE DETAILS. WHILE
PRECIP WILL CONTINUE ON AND OFF THROUGH THE AFTERNOON...HAVE
SLOWED THE PERIOD OF BETTER COVERAGE/INTENSITY SLIGHTLY. FORECAST
SOUNDINGS/CONCEPTUAL MODELS SUPPORT ALL SNOW WITHIN THE MOST
INTENSE BAND THANKS TO WELL ALIGNED ASCENT WITHIN THE SNOW GROWTH
ZONE AND COOLING LOW LEVEL TEMP PROFILES. EXPECT THAT THERE WILL
BE A CORRIDOR OF MODERATE SNOW WITHIN A LARGER AREA OF LESS
INTENSE PRECIP THAT WILL DEVELOP NORTHWARD ALONG A LINE FROM
ROUGHLY CHICAGO TO MENDOTA...THEN PIVOT EASTWARD INTO THE EVENING.
MUCH OF THE EVENING RUSH HOUR IN THE CHICAGO METRO LOOKS TO FALL
INTO THE PERIOD OF MORE INTENSE SNOWFALL...WHICH MAY LAST A FEW
HOURS. THE VORT MAX LIFTS NORTHEAST WHICH MAY BRING A LULL IN THE
PRECIP EARLY THIS EVENING BUT LARGER SCALE FORCING INCREASES TO
THE EAST SO THERE MAY BE RE-INTENSIFICATION OVER NORTHWEST INDIANA
BY MID EVENING BEFORE PRECIP EXITS LATE EVENING. TEMPERATURES
WILL LIKELY COOL INTO THE MID 30S LATER TODAY AND SNOW SHOULD FALL
AT AN INTENSE ENOUGH RATE TO PROVIDE FOR ACCUMULATION ON GRASSY
SURFACES AND SLUSHY ACCUMULATION ON ROADS. WILL CONTINUE WITH THE
IDEA OF AROUND AN INCH OF ACCUMULATION.

MDB

&&

.PREV DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* MVFR CIGS...LOWERING BACK TOWARDS LOW END MVFR LATER THIS
  AFTERNOON.
* GUSTY N WINDS THROUGH THE DAY...POSSIBLY TURNING NNE BY EARLY
  AFTERNOON.
* SNOW OVERSPREADING THE TERMINALS MID AFTERNOON WITH MINOR
  ACCUMULATIONS.

BMD

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

A COLD FRONT IS WORKING ACROSS NORTHEASTERN ILLINOIS EARLY THIS
MORNING WITH WINDS TURNING SHARPLY TO THE NNW WITH GUSTS TO AROUND
30 KT. AREA OBSERVATIONS SHOW A NARROW CORRIDOR OF IFR CIGS IN THE
VICINITY OF THE FRONT...WHICH HAS BEEN SHRINKING OVERNIGHT WITH
PRIMARILY MVFR CIGS EXPECTED THIS MORNING. PRECIP HAS ALSO DWINDLED
AND EXPECTED A COUPLE HOURS OF LIGHT RAIN/DRIZZLE EARLY THIS MORNING
THEN DRY CONDITIONS SHOULD PREVAIL THROUGH AROUND MID AFTERNOON. AT
THAT TIME...AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE AREA
WITH PRECIP OVERSPREADING THE AREA FROM THE SOUTHWEST. RFD MAY BE
CLIPPED BY THIS PRECIP...BUT THE CHICAGO TERMINALS ARE EXPECTED TO
TAKE A MORE DIRECT SHOT. AT THE ONSET...TEMPERATURES MAY BE WARM
ENOUGH FOR A MIX OF RAIN AND SNOW...PARTICULARLY AT MDW AND
GYY...BUT THE COLUMN WILL COOL AND EXPECT A TRANSITION TO ALL SNOW
WITH MINOR ACCUMULATIONS POSSIBLE...ESPECIALLY ON GRASSY SURFACES...
OF UP TO AROUND AND INCH. WINDS SHOULD PRIMARILY REMAIN IN THE
330-360 DIRECTION TODAY WITH GUSTS AROUND 30 KT THIS MORNING VERY
SLOWLY TAPERING THROUGH THE DAY.

BMD

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

* MEDIUM HIGH CONFIDENCE WITH CIGS.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* MEDIUM-HIGH CONFIDENCE IN SNOW TIMING THIS AFTERNOON.

BMD

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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









000
FXUS63 KLOT 141648
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1148 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* MVFR CIGS...LOWERING BACK TOWARDS LOW END MVFR LATER THIS
  AFTERNOON.
* GUSTY N WINDS THROUGH THE DAY...POSSIBLY TURNING NNE BY EARLY
  AFTERNOON.
* SNOW OVERSPREADING THE TERMINALS MID AFTERNOON WITH MINOR
  ACCUMULATIONS.

BMD

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

A COLD FRONT IS WORKING ACROSS NORTHEASTERN ILLINOIS EARLY THIS
MORNING WITH WINDS TURNING SHARPLY TO THE NNW WITH GUSTS TO AROUND
30 KT. AREA OBSERVATIONS SHOW A NARROW CORRIDOR OF IFR CIGS IN THE
VICINITY OF THE FRONT...WHICH HAS BEEN SHRINKING OVERNIGHT WITH
PRIMARILY MVFR CIGS EXPECTED THIS MORNING. PRECIP HAS ALSO DWINDLED
AND EXPECTED A COUPLE HOURS OF LIGHT RAIN/DRIZZLE EARLY THIS MORNING
THEN DRY CONDITIONS SHOULD PREVAIL THROUGH AROUND MID AFTERNOON. AT
THAT TIME...AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE AREA
WITH PRECIP OVERSPREADING THE AREA FROM THE SOUTHWEST. RFD MAY BE
CLIPPED BY THIS PRECIP...BUT THE CHICAGO TERMINALS ARE EXPECTED TO
TAKE A MORE DIRECT SHOT. AT THE ONSET...TEMPERATURES MAY BE WARM
ENOUGH FOR A MIX OF RAIN AND SNOW...PARTICULARLY AT MDW AND
GYY...BUT THE COLUMN WILL COOL AND EXPECT A TRANSITION TO ALL SNOW
WITH MINOR ACCUMULATIONS POSSIBLE...ESPECIALLY ON GRASSY SURFACES...
OF UP TO AROUND AND INCH. WINDS SHOULD PRIMARILY REMAIN IN THE
330-360 DIRECTION TODAY WITH GUSTS AROUND 30 KT THIS MORNING VERY
SLOWLY TAPERING THROUGH THE DAY.

BMD

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

* MEDIUM HIGH CONFIDENCE WITH CIGS.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* MEDIUM-HIGH CONFIDENCE IN SNOW TIMING THIS AFTERNOON.

BMD

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 141421
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* RAIN/SNOW/SLEET MIX EXITING THIS NEXT HALF HOUR...WITH MVFR
  CIGS REMAINING.
* GUSTY N WINDS THROUGH THE DAY...LIKELY TURNING NNE BY EARLY
  AFTERNOON.
* SNOW OVERSPREADING THE TERMINALS MID AFTERNOON WITH MINOR
  ACCUMULATIONS.

BMD

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

A COLD FRONT IS WORKING ACROSS NORTHEASTERN ILLINOIS EARLY THIS
MORNING WITH WINDS TURNING SHARPLY TO THE NNW WITH GUSTS TO AROUND
30 KT. AREA OBSERVATIONS SHOW A NARROW CORRIDOR OF IFR CIGS IN THE
VICINITY OF THE FRONT...WHICH HAS BEEN SHRINKING OVERNIGHT WITH
PRIMARILY MVFR CIGS EXPECTED THIS MORNING. PRECIP HAS ALSO DWINDLED
AND EXPECTED A COUPLE HOURS OF LIGHT RAIN/DRIZZLE EARLY THIS MORNING
THEN DRY CONDITIONS SHOULD PREVAIL THROUGH AROUND MID AFTERNOON. AT
THAT TIME...AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE AREA
WITH PRECIP OVERSPREADING THE AREA FROM THE SOUTHWEST. RFD MAY BE
CLIPPED BY THIS PRECIP...BUT THE CHICAGO TERMINALS ARE EXPECTED TO
TAKE A MORE DIRECT SHOT. AT THE ONSET...TEMPERATURES MAY BE WARM
ENOUGH FOR A MIX OF RAIN AND SNOW...PARTICULARLY AT MDW AND
GYY...BUT THE COLUMN WILL COOL AND EXPECT A TRANSITION TO ALL SNOW
WITH MINOR ACCUMULATIONS POSSIBLE...ESPECIALLY ON GRASSY SURFACES...
OF UP TO AROUND AND INCH. WINDS SHOULD PRIMARILY REMAIN IN THE
330-360 DIRECTION TODAY WITH GUSTS AROUND 30 KT THIS MORNING VERY
SLOWLY TAPERING THROUGH THE DAY.

BMD

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

* HIGH CONFIDENCE IN PRECIP TIMING AND CIG/VIS TRENDS.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* MEDIUM-HIGH CONFIDENCE IN SNOW TIMING THIS AFTERNOON.

BMD

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 141133
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
633 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* FRONT SWEEPING ACROSS THE AREA WITH RAIN/IFR IN THE VICINITY OF
  THE FRONT...THEN PRIMARILY MVFR CIGS.
* GUSTY NNW WINDS THROUGH THE DAY.
* SNOW OVERSPREADING THE TERMINALS MID AFTERNOON WITH MINOR
  ACCUMULATIONS.

BMD

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

A COLD FRONT IS WORKING ACROSS NORTHEASTERN ILLINOIS EARLY THIS
MORNING WITH WINDS TURNING SHARPLY TO THE NNW WITH GUSTS TO AROUND
30 KT. AREA OBSERVATIONS SHOW A NARROW CORRIDOR OF IFR CIGS IN THE
VICINITY OF THE FRONT...WHICH HAS BEEN SHRINKING OVERNIGHT WITH
PRIMARILY MVFR CIGS EXPECTED THIS MORNING. PRECIP HAS ALSO DWINDLED
AND EXPECTED A COUPLE HOURS OF LIGHT RAIN/DRIZZLE EARLY THIS MORNING
THEN DRY CONDITIONS SHOULD PREVAIL THROUGH AROUND MID AFTERNOON. AT
THAT TIME...AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE AREA
WITH PRECIP OVERSPREADING THE AREA FROM THE SOUTHWEST. RFD MAY BE
CLIPPED BY THIS PRECIP...BUT THE CHICAGO TERMINALS ARE EXPECTED TO
TAKE A MORE DIRECT SHOT. AT THE ONSET...TEMPERATURES MAY BE WARM
ENOUGH FOR A MIX OF RAIN AND SNOW...PARTICULARLY AT MDW AND
GYY...BUT THE COLUMN WILL COOL AND EXPECT A TRANSITION TO ALL SNOW
WITH MINOR ACCUMULATIONS POSSIBLE...ESPECIALLY ON GRASSY SURFACES...
OF UP TO AROUND AND INCH. WINDS SHOULD PRIMARILY REMAIN IN THE
330-360 DIRECTION TODAY WITH GUSTS AROUND 30 KT THIS MORNING VERY
SLOWLY TAPERING THROUGH THE DAY.

BMD


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

* MEDIUM CONFIDENCE IN PRECIP TIMING AND CIG/VIS TRENDS.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* MEDIUM-HIGH CONFIDENCE IN SNOW TIMING THIS AFTERNOON.

BMD

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

TUESDAY NIGHT...VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...CHC RAIN. MVFR/IFR PSBL.
SATURDAY...SLT CHC RAIN. MVFR/IFR PSBL.
SUNDAY...CHC RAIN. MVFR/IFR PSBL.

BMD

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 141127
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
627 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
625 AM CDT

THE FOLLOWING ARE THE LAST APRIL DATES AND AMOUNTS OF ACCUMULATING
SNOWFALL:

CHICAGO: APRIL 18 2011 (0.6 IN.)
ROCKFORD: APRIL 5 2009 (0.2 IN.)

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS THE MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

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

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD

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

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 140931
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
406 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT
FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT
TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
400 AM CDT

THE FOLLOWING ARE RECORD LOWS FOR THE MORNING OF APRIL 15TH. THE
CHICAGO ONE IS MOST LIKELY IN JEOPARDY.

CHICAGO:  25 (1943)
ROCKFORD: 16 (1928)

MTF

&&

.AVIATION...

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

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

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

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD

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

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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












000
FXUS63 KLOT 140906
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
406 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM
A SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW.
GRADUALLY BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE
SOMETIME LATE FRIDAY/THIS WEEKEND.

MTF

&&

.CLIMATE...
400 AM CDT

THE FOLLOWING ARE RECORD LOWS IN JEOPARDY FOR THE MORNING OF APRIL
15TH:

CHICAGO:  25 (1943)
ROCKFORD: 21 (1957)

MTF

&&

.AVIATION...

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

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

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

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD

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

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

&&

$$

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

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









000
FXUS63 KLOT 140830
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
330 AM CDT MON APR 14 2014

.DISCUSSION...
330 AM CDT

THE INFAMOUS WINTER 2013-2014 BEGAN IN OCTOBER WITH SNOW AND TODAY
IT WANTS TO MAKE SURE IT INCLUDES APRIL TO ENCOMPASS SEVEN MONTHS.
THIS UNFRIENDLY VERY LATE VISIT FROM WINTER WAS THE PRIMARY FORECAST
CHALLENGE...ALONG WITH TEMPERATURES THROUGHOUT THE WEEK AS WE WILL
BE WELL BELOW NORMAL TO START THIS WEEK...POTENTIALLY TO RECORD
LEVELS TONIGHT.

THIS MORNING...
THE 995MB SURFACE LOW IS PASSING OVER THE NORTH METRO OF CHICAGO
EARLY THIS MORNING AND 30 MILES EITHER SIDE OF ITS PATH SEPARATES
60S AND CONVECTIVE RAIN SHOWERS AND 30S AND DEFORMATION SNOW. THE
DEEPENING AND CLASSIC LOOKING UPPER WAVE WITH THIS IS ADVANCING
NORTHEAST FROM SOUTHWEST WI AND ITS DEFORMATION AND WRAPAROUND
MOISTURE WILL ONLY GRAZE THE AREA THIS MORNING. WHILE A MIX WITH WET
SNOW IS PROBABLE OVER PARTS OF NORTH CENTRAL IL...THE FORCING FOR
MODEST SNOW RATES IS LIKELY TO REMAIN TO THE NORTH IN THE A.M. HOURS
SO NOT EXPECTING ANY ACCUMULATIONS PRIOR TO NOON. WINDS ON THE
BACKSIDE OF THE LOW THIS MORNING LOOK TO GUST TO AROUND 40 MPH AT
TIMES...WHICH BESIDES ADDING QUITE A CHILL TO THE AIR...MAY REDUCE
VISIBILITY UP BY ROCKFORD IF SNOW CAN MATERIALIZE THIS MORNING.
OTHERWISE THOUGH...IMPACTS LOOK MINOR DURING THIS PERIOD.

THIS AFTERNOON AND TONIGHT...
A SECOND WELL-DEFINED UPPER CIRCULATION IS ADVANCING EASTWARD INTO
THE CENTRAL PLAINS EARLY THIS MORNING. THIS IS BASICALLY ROUNDING
THE BASE OF WHAT REALLY IS A MASSIVE LONGWAVE TROUGH ACROSS CENTRAL
NORTH AMERICA...WITH AN IMPRESSIVE JANUARY-LIKE -40C OBSERVED AT
500MB LAST NIGHT ALL THE WAY SOUTH TO CYQD IN SOUTHERN MANITOBA.
GIVEN THE UPPER FLOW...PV ANOMALY EVOLUTION...AND MID-LEVEL
BAROCLINICITY...THIS WAVE IS FORECAST TO TURN MORE NORTHEAST THIS
AFTERNOON AND ADVANCE INTO CENTRAL AND NORTHERN IL/IN DURING THE
MID-AFTERNOON INTO MID-EVE. THIS WILL BRING WITH IT FOCUSED OMEGA
AND FRONTOGENETIC SUPPORTED UPWARD MOTION DURING THAT PERIOD AND
WOULD EXPECT TO SEE MODERATE PRECIPITATION DEVELOPING FROM SOUTHWEST
TO NORTHEAST ACROSS THE HEART OF THE FORECAST AREA...LIKELY REACHING
THE CHICAGO AREA DURING THE 3-6 PM TIME. SO HAVE BUMPED UP POPS
CONSIDERABLY. IN ADDITION...THE MID-LEVEL TEMPERATURES WILL CONTINUE
TO COOL WITH THE FEATURE AND THE LOWER LEVELS THROUGH DIABATIC
EFFECTS. ITS QUITE RARE TO SEE SNOW HERE DURING APRIL /ESPECIALLY
MID-APRIL/ AFTERNOONS...BUT DO SEE PRECIPITATION STRUGGLING TO STAY
AS RAIN GIVEN RAP AND NAM FORECAST THERMAL PROFILES AND JUST THE
DEGREE OF FORCING. SO A QUICK TRANSITION TO A WET SNOW FROM NORTH TO
SOUTH ACROSS THE CHICAGO METRO AREA IS FAVORED DURING THE RUSH
HOUR...AND PROBABLY THE FIRST HALF AT THAT. SUPPRESSION ALOFT FOLLOWS
BEHIND THE UPPER WAVE LATE THIS EVE INTO OVERNIGHT AND WILL END THE
SNOW /FOR GOOD FINALLY?/.

ANY INITIAL SNOW WILL STRUGGLE TO STICK WITH 4-INCH SOIL TEMPS
AROUND 50 DEGREES AND THE WET GROUND IN PLACES...BUT THE FORCING
LIKELY IS TO WIN OUT FOR A LIGHT COATING ESPECIALLY ON GRASSY
SURFACES. THIS IS PRESENTLY MOST FAVORED ALONG AND SOUTH OF A
MENDOTA TO CHICAGO LINE...AS THAT IS THE AREA THAT LOOKS TO HAVE THE
BEST FORCING AS THE TEMPERATURES COOL LATE IN THE DAY AND THIS EVE.
THERE IS UNCERTAINTY WITH THIS PLACEMENT THOUGH...AS SOME MESOSCALE
PARAMETERS ARE AT PLAY. ACCUMULATION AROUND AN INCH TO A LITTLE OVER
MAY OCCUR IN THE AREA THAT DOES END UP SEEING THE BETTER FORCING
THANKS TO DECENT SNOWFALL RATES AT TIMES.

TEMPERATURES WILL HOLD FLAT-LINE AND EVEN DROP DURING THE AFTERNOON
AS PRECIPITATION EVOLVES INTO THE REGION. COLD AIR ADVECTION
CONTINUES TONIGHT WITH 850MB TEMPS DROPPING TO THE -10C ARENA. THIS
WILL SUPPORT CHICAGO CLOSING IN ON A RECORD LOW FOR TONIGHT
/CALENDAR DAY OF APRIL 15/. SEE CLIMATE SECTION BELOW FOR MORE.

TUESDAY THROUGH THURSDAY...
NOT TOO MANY CHANGES MADE TO THIS PERIOD WHICH LOOKS MAINLY QUIET. A
CHILLY TUESDAY IS EXPECTED WITH THE LOW STARTING POINT AND THE
850-925MB THERMAL TROUGH OVER US IN THE MORNING. A LAKE BREEZE
DEVELOPING THAT AFTERNOON WILL NOT HELP MATTERS EITHER. UPPER 30S TO
MID 40S ARE EXPECTED FROM NEAR THE LAKE TO THE REST OF THE FORECAST
AREA ON TUESDAY AFTERNOON. UNCERTAINTY EXISTS ON CLOUD COVER FOR
MUCH OF THIS TIME RANGE AND THAT WILL OF COURSE IMPACT TEMPERATURES
GREATLY. THIS INCLUDES HIGH CLOUDS TUESDAY NIGHT WHICH COULD PREVENT
ANOTHER CHILLY NIGHT IN THE 20S...AND HAVE INCHED UP FORECAST VALUES
SOME FAVORING A LITTLE MORE CLOUD COVER AT THIS TIME. IN
ADDITION...THURSDAY INTO THURSDAY NIGHT LOOKS TO HAVE SOUTHERLY FLOW
AND THERE ARE INDICATIONS OF LOW CLOUDS MOVING NORTH DURING THAT TIME
FRAME. WILL NEED TO WAIT TO THAT PERIOD GETS CLOSER TO GET TOO FANCY
WITH TEMPERATURES BUT HAVE GONE WITH A BLEND OF GUIDANCE INCLUDING
THE PREVIOUS FORECAST AT THIS TIME FOR TEMPS DURING THURSDAY.

FRIDAY AND BEYOND...
GIVEN A MASSIVE UPPER RIDGE OVER THE WESTERN TO NORTHERN
ATLANTIC...ANY SHARP ADVANCEMENT OF AN UPPER RIDGE FROM THE WEST
INTO OUR AREA LOOKS TO BE HALTED/SLOWED. WE WILL BUILD HEIGHTS
GRADUALLY THURSDAY BUT MODEL GUIDANCE IS IN DECENT AGREEMENT WITH
ADVANCING A PACIFIC SYSTEM INTO THE REGION BY FRIDAY AND PRODUCING
LIKELY RAIN IN THE GENERAL REGION. THIS COULD SLOW SOME GIVEN THE
BACKED UP FLOW TO OUR EAST...AND HAVE TAKEN THAT INTO ACCOUNT FROM A
SMART BLEND OF GUIDANCE POPS...SLOWING THEM SOMEWHAT. ONCE AGAIN
TEMPERATURES ON FRIDAY DEPEND HEAVILY ON WHETHER OR NOT CLOUDS AND
PRECIP ARE AS PROLIFIC AS MOST GUIDANCE IS INDICATING NOW. GRADUALLY
BUILDING HEIGHTS SHOULD FOLLOW THAT SYSTEM DEPARTURE SOMETIME LATE
FRIDAY/THIS WEEKEND.

MTF

&&

.AVIATION...

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

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

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

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD

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

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL
     4 AM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

     DENSE FOG ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 140741
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
241 AM CDT MON APR 14 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

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

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD

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

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
240 AM CDT

LOW PRESSURE IS MOVING ACROSS FAR SOUTHERN LAKE MICHIGAN EARLY THIS
MORNING WITH GALE FORCE NORTHERLY WINDS OVERSPREADING THE LAKE
BEHIND THE LOW AS IT BEGINS TO DEPART EAST. GALES ARE EXPECTED TO
PERSIST THROUGH THE AFTERNOON...THEN SHOULD VERY GRADUALLY DIMINISH
TO AROUND 30 KT THIS EVENING AND TONIGHT. FOG THAT WAS IN PLACE NEAR
THE FRONTAL BOUNDARY ACROSS FAR SOUTHERN LAKE MICHIGAN SHOULD
DIMINISH AS THE NORTHERLY WINDS OVERSPREAD THE LAKE. RIDGING WILL
TRANSLATE ACROSS LAKE MICHIGAN LATE IN THE DAY TUESDAY ALLOWING
WINDS TO BRIEFLY SUBSIDE...BUT SOUTH/SOUTHEAST WINDS PICK UP AGAIN
ON WEDNESDAY AS ANOTHER LOW DEVELOPS OVER THE CENTRAL PLAINS.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL
     4 AM MONDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4
     PM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874 UNTIL 3 PM
     MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878 UNTIL 3
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 140538
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1238 AM CDT MON APR 14 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* GUSTY SOUTHERLY WINDS TURNING SHARPLY TO THE NORTH OVERNIGHT
  WITH CIGS DROPPING NEAR OR TO IFR.
* OCCASIONAL CHANCES FOR RAIN SHOWERS OVERNIGHT...AND CHANCE FOR
  SNOW ACCUMULATIONS DURING THE DAY MONDAY.

BMD

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

LOW PRESSURE LIES NEAR MLI TONIGHT WITH A FRONTAL BOUNDARY EXTENDING
ACROSS FAR NORTHERN ILLINOIS. STRONG SOUTHERLY WINDS ARE OCCURRING
ON THE SOUTH SIDE OF THE FRONT AT THE CHICAGO TERMINALS...BUT AS THE
LOW MOVES EAST OVERNIGHT WINDS WILL TURN SHARPLY TO THE NORTH BEHIND
THE DEPARTING LOW. CIGS WILL DROP TO AROUND 007-010 BEHIND THE FRONT
AND WINDS WILL BECOME QUITE GUSTY...TO AROUND 30 KT OR SO AT TIMES
THROUGH THE MORNING...THEN TAPERING GRADUALLY IN THE AFTERNOON AND
EVENING. ALSO MONDAY AFTERNOON...AN UPPER LEVEL DISTURBANCE MOVING
OVER THE AREA WILL ALLOW PRECIPITATION TO ONCE AGAIN OVERSPREAD THE
TERMINALS. WITH MUCH COLDER AIR IN PLACE TOMORROW...IT DOES APPEAR
MUCH OF THE PRECIP WILL FALL AS SNOW AND CANNOT RULE OUT
ACCUMULATIONS TO AROUND AN INCH. SURFACE TEMPERATURES MAY INITIALLY
MAKE IT DIFFICULT FOR SNOW TO ACCUMULATE...BUT AS SURFACE TEMPS FALL
TO NEAR FREEZING IN THE EVENING CHANCES BECOME A BIT BETTER.

BMD


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

* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION/SPEED.
* LOW-MEDIUM CONFIDENCE IN CIGS OVERNIGHT.
* MEDIUM CONFIDENCE IN SNOW TIMING.

BMD

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL
     4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874 UNTIL 3 PM
     MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878 UNTIL 3
     PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 140340
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1040 PM CDT SUN APR 13 2014

.MESOSCALE DISCUSSION...
730 PM CDT

CLOSELY MONITORING A COUPLE ADDITIONAL SMALL MINI-SUPERCELLS THAT
HAVE DEVELOPED OVER NORTHWEST ILLINOIS. THE 00Z DVN SOUNDING
SAMPLED THE WARM SECTOR ENVIRONMENT WHICH FEATURES AMPLE SBCAPE
AND MORE IMPORTANTLY VERY LOW LCL HEIGHTS AND SUBSEQUENT LOW LEVEL
CAPE AND STRONG LOW LEVEL SHEAR. ALREADY HAD ONE MINI-SUPERCELL
PRODUCE A VERY PICTURESQUE TORNADO OVER EASTERN IOWA EARLIER THIS
EVENING. HAVE OBSERVED ROTATION ALREADY WITH THE CELL IN SOUTHERN
WHITESIDE COUNTY AND WILL CONTINUE TO CLOSELY WATCH THE SMALL
CELLS DEVELOPING AND MOVING INTO OUR SOUTHERN AND WESTERN CWA THE
NEXT FEW HOURS. GIVEN THE VERY SMALL T/TD DEPRESSIONS EXPECT
LITTLE OR NO BOUNDARY LAYER DESTABILIZATION AFTER SUNSET AND WITH
THE STRENGTHENING LOW LEVEL FLOW AND RESULTANT LOW LEVEL SHEAR A
LOW END TORNADO THREAT WILL EXIST WITH CELLS WITHIN THE WARM
SECTOR OVER OUR CWA THIS EVENING.

IZZI

&&

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* OCNL SHRA INTO THE OVERNIGHT
* WIND SHIFT TO STRONG NORTHERLY LATE TONIGHT...GUSTS 30-40KT
  MONDAY
* SNOW LIKELY MONDAY AFTERNOON/EVENING WITH ASSOCIATED IFR
  CONDITIONS

IZZI

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

STRONG LOW PRESSURE MOVING ACROSS THE REGION WILL PRODUCE THE NEXT
24 HOURS BRINGING A WIDE VARIETY OF ADVERSE WEATHER CONDITIONS.
STRONG WARM FRONT NEAR I-80 WILL LIKELY LIFT NORTHWARD ACROSS THE
TERMINALS THIS EVENING RESULTING IN WINDS SHIFTING BACK TO THE
SOUTH. AS WARM FRONT LIFTS NORTH LOOK FOR IFR CIGS TO LIFT QUICKLY
TO MVFR...POTENTIALLY EVEN A BIT EARLIER THAN THE WIND SHIFT.
ADDITIONAL RAIN AND POSSIBLE ISOLD TSRA EXPECTED THROUGH THE
EVENING INTO THE EARLY PORTIONS OF THE OVERNIGHT HOURS...LIKELY
DECREASING IN COVERAGE/INTENSITY LATE TONIGHT/EARLY MONDAY
MORNING. AS LOW PASSES BY TERMINALS LATE TONIGHT LOOK FOR WIND
SHIFT TO NORTH AND A FAIRLY QUICK INCREASE IN WIND SPEEDS/GUSTS.
NORTHERLY WINDS SHOULD EASILY GUST OVER 30KT WITH GUSTS UP TO 40KT
POSSIBLE. IN ADDITION...A PERIOD OF IFR CIGS LOOKS PLAUSIBLE EARLY
MONDAY MORNING ACCOMPANYING THE STRONG NORTHERLY WINDS. CIGS
SHOULD LIFT TO MVFR DURING THE MORNING BUT STRONG NORTHERLY WINDS
LOOK LIKELY TO CONTINUE. ANOTHER WAVE OF LOW PRESSURE IS EXPECTED
TO LIFT NORTHWARD MONDAY AFTERNOON BRINGING ANOTHER BOUT ROUND OF
SOME PRECIPITATION LATER MONDAY AFTERNOON AND EVENING. WHILE THERE
COULD BE A BRIEF MIX OF RAIN/SNOW...FORECAST THERMAL PROFILES
STRONGLY SUPPORT A QUICK CHANGE OVER TO WET SNOW WITH IFR
CONDITIONS LOOKING LIKELY AND EVEN SOME POTENTIAL FOR PERIODIC
LIFR VSBY IN SNOW. SNOW SHOULD MELT INITIALLY...BUT WITH TIME THE
THREAT OF SOME SNOW ACCUMULATION WILL INCREASE DURING THE EVENING
AS THE SUN SETS AND TEMPS DROP BELOW FREEZING.

IZZI

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

* MEDIUM CONFIDENCE ON SNOW CHANCES MONDAY AFTERNOON/EVENING
* MEDIUM CONFIDENCE ON CIGS LATE TONIGHT/EARLY MONDAY MORNING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL
     4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874 UNTIL 3 PM
     MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 140031
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
731 PM CDT SUN APR 13 2014

.MESOSCALE DISCUSSION...
730 PM CDT

CLOSELY MONITORING A COUPLE ADDITIONAL SMALL MINI-SUPERCELLS THAT
HAVE DEVELOPED OVER NORTHWEST ILLINOIS. THE 00Z DVN SOUNDING
SAMPLED THE WARM SECTOR ENVIRONMENT WHICH FEATURES AMPLE SBCAPE
AND MORE IMPORTANTLY VERY LOW LCL HEIGHTS AND SUBSEQUENT LOW LEVEL
CAPE AND STRONG LOW LEVEL SHEAR. ALREADY HAD ONE MINI-SUPERCELL
PRODUCE A VERY PICTURESQUE TORNADO OVER EASTERN IOWA EARLIER THIS
EVENING. HAVE OBSERVED ROTATION ALREADY WITH THE CELL IN SOUTHERN
WHITESIDE COUNTY AND WILL CONTINUE TO CLOSELY WATCH THE SMALL
CELLS DEVELOPING AND MOVING INTO OUR SOUTHERN AND WESTERN CWA THE
NEXT FEW HOURS. GIVEN THE VERY SMALL T/TD DEPRESSIONS EXPECT
LITTLE OR NO BOUNDARY LAYER DESTABILIZATION AFTER SUNSET AND WITH
THE STRENGTHENING LOW LEVEL FLOW AND RESULTANT LOW LEVEL SHEAR A
LOW END TORNADO THREAT WILL EXIST WITH CELLS WITHIN THE WARM
SECTOR OVER OUR CWA THIS EVENING.

IZZI

&&

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* IFR CIGS LIKELY EARLY THIS EVENING
* EAST WINDS SHIFT TO GUSTY SOUTH TOWARD MID EVENING
* OCNL RAIN MID EVENING INTO THE OVERNIGHT WITH SLIGHT CHANCE OF A
  TSRA
* WIND SHIFT TO STRONG NORTHERLY LATE TONIGHT...GUSTS 30-40KT
  MONDAY
* SNOW LIKELY MONDAY AFTERNOON/EVENING WITH ASSOCIATED IFR
  CONDITIONS

IZZI

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

STRONG LOW PRESSURE MOVING ACROSS THE REGION WILL PRODUCE THE NEXT
24 HOURS BRINGING A WIDE VARIETY OF ADVERSE WEATHER CONDITIONS.
STRONG WARM FRONT NEAR I-80 WILL LIKELY LIFT NORTHWARD ACROSS THE
TERMINALS THIS EVENING RESULTING IN WINDS SHIFTING BACK TO THE
SOUTH. AS WARM FRONT LIFTS NORTH LOOK FOR IFR CIGS TO LIFT QUICKLY
TO MVFR...POTENTIALLY EVEN A BIT EARLIER THAN THE WIND SHIFT.
ADDITIONAL RAIN AND POSSIBLE ISOLD TSRA EXPECTED THROUGH THE
EVENING INTO THE EARLY PORTIONS OF THE OVERNIGHT HOURS...LIKELY
DECREASING IN COVERAGE/INTENSITY LATE TONIGHT/EARLY MONDAY
MORNING. AS LOW PASSES BY TERMINALS LATE TONIGHT LOOK FOR WIND
SHIFT TO NORTH AND A FAIRLY QUICK INCREASE IN WIND SPEEDS/GUSTS.
NORTHERLY WINDS SHOULD EASILY GUST OVER 30KT WITH GUSTS UP TO 40KT
POSSIBLE. IN ADDITION...A PERIOD OF IFR CIGS LOOKS PLAUSIBLE EARLY
MONDAY MORNING ACCOMPANYING THE STRONG NORTHERLY WINDS. CIGS
SHOULD LIFT TO MVFR DURING THE MORNING BUT STRONG NORTHERLY WINDS
LOOK LIKELY TO CONTINUE. ANOTHER WAVE OF LOW PRESSURE IS EXPECTED
TO LIFT NORTHWARD MONDAY AFTERNOON BRINGING ANOTHER BOUT ROUND OF
SOME PRECIPITATION LATER MONDAY AFTERNOON AND EVENING. WHILE THERE
COULD BE A BRIEF MIX OF RAIN/SNOW...FORECAST THERMAL PROFILES
STRONGLY SUPPORT A QUICK CHANGE OVER TO WET SNOW WITH IFR
CONDITIONS LOOKING LIKELY AND EVEN SOME POTENTIAL FOR PERIODIC
LIFR VSBY IN SNOW. SNOW SHOULD MELT INITIALLY...BUT WITH TIME THE
THREAT OF SOME SNOW ACCUMULATION WILL INCREASE DURING THE EVENING
AS THE SUN SETS AND TEMPS DROP BELOW FREEZING.

IZZI

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

* LOW-MEDIUM CONFIDENCE ON TIMING OF CIGS LIFTING FROM IFR THIS
  EVENING
* MEDIUM-HIGH CONFIDENCE IN WIND SHIFT TO SOUTH THIS
  EVENING...LOW-MEDIUM CONFIDENCE ON TIMING
* MEDIUM-HIGH CONFIDENCE ON PRECIP TRENDS TONIGHT...BUT LOW-
  MEDIUM CONFIDENCE ON TSRA NOT OCCURRING AT TERMINALS
* HIGH CONFIDENCE ON STRONG NORTHERLY WINDS (GUSTS 30KT+)
  MONDAY...MEDIUM CONFIDENCE ON TIMING OF ONSET OF STRONG N WINDS
* MEDIUM CONFIDENCE IN SNOW FORECAST MONDAY

IZZI

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 8 PM SUNDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874 UNTIL 3 PM
     MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 132359
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
659 PM CDT SUN APR 13 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* IFR CIGS LIKELY EARLY THIS EVENING
* EAST WINDS SHIFT TO GUSTY SOUTH TOWARD MID EVENING
* OCNL RAIN MID EVENING INTO THE OVERNIGHT WITH SLIGHT CHANCE OF A
  TSRA
* WIND SHIFT TO STRONG NORTHERLY LATE TONIGHT...GUSTS 30-40KT
  MONDAY
* SNOW LIKELY MONDAY AFTERNOON/EVENING WITH ASSOCIATED IFR
  CONDITIONS

IZZI

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

STRONG LOW PRESSURE MOVING ACROSS THE REGION WILL PRODUCE THE NEXT
24 HOURS BRINGING A WIDE VARIETY OF ADVERSE WEATHER CONDITIONS.
STRONG WARM FRONT NEAR I-80 WILL LIKELY LIFT NORTHWARD ACROSS THE
TERMINALS THIS EVENING RESULTING IN WINDS SHIFTING BACK TO THE
SOUTH. AS WARM FRONT LIFTS NORTH LOOK FOR IFR CIGS TO LIFT QUICKLY
TO MVFR...POTENTIALLY EVEN A BIT EARLIER THAN THE WIND SHIFT.
ADDITIONAL RAIN AND POSSIBLE ISOLD TSRA EXPECTED THROUGH THE
EVENING INTO THE EARLY PORTIONS OF THE OVERNIGHT HOURS...LIKELY
DECREASING IN COVERAGE/INTENSITY LATE TONIGHT/EARLY MONDAY
MORNING. AS LOW PASSES BY TERMINALS LATE TONIGHT LOOK FOR WIND
SHIFT TO NORTH AND A FAIRLY QUICK INCREASE IN WIND SPEEDS/GUSTS.
NORTHERLY WINDS SHOULD EASILY GUST OVER 30KT WITH GUSTS UP TO 40KT
POSSIBLE. IN ADDITION...A PERIOD OF IFR CIGS LOOKS PLAUSIBLE EARLY
MONDAY MORNING ACCOMPANYING THE STRONG NORTHERLY WINDS. CIGS
SHOULD LIFT TO MVFR DURING THE MORNING BUT STRONG NORTHERLY WINDS
LOOK LIKELY TO CONTINUE. ANOTHER WAVE OF LOW PRESSURE IS EXPECTED
TO LIFT NORTHWARD MONDAY AFTERNOON BRINGING ANOTHER BOUT ROUND OF
SOME PRECIPITATION LATER MONDAY AFTERNOON AND EVENING. WHILE THERE
COULD BE A BRIEF MIX OF RAIN/SNOW...FORECAST THERMAL PROFILES
STRONGLY SUPPORT A QUICK CHANGE OVER TO WET SNOW WITH IFR
CONDITIONS LOOKING LIKELY AND EVEN SOME POTENTIAL FOR PERIODIC
LIFR VSBY IN SNOW. SNOW SHOULD MELT INITIALLY...BUT WITH TIME THE
THREAT OF SOME SNOW ACCUMULATION WILL INCREASE DURING THE EVENING
AS THE SUN SETS AND TEMPS DROP BELOW FREEZING.

IZZI

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

* LOW-MEDIUM CONFIDENCE ON TIMING OF CIGS LIFTING FROM IFR THIS
  EVENING
* MEDIUM-HIGH CONFIDENCE IN WIND SHIFT TO SOUTH THIS
  EVENING...LOW-MEDIUM CONFIDENCE ON TIMING
* MEDIUM-HIGH CONFIDENCE ON PRECIP TRENDS TONIGHT...BUT LOW-
  MEDIUM CONFIDENCE ON TSRA NOT OCCURRING AT TERMINALS
* HIGH CONFIDENCE ON STRONG NORTHERLY WINDS (GUSTS 30KT+)
  MONDAY...MEDIUM CONFIDENCE ON TIMING OF ONSET OF STRONG N WINDS
* MEDIUM CONFIDENCE IN SNOW FORECAST MONDAY

IZZI

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

TUESDAY THROUGH THURSDAY...PREDOMINANTLY VFR.

FRIDAY...CHANCE OF SHRA.

SATURDAY...VFR PROBABLE.

IZZI

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 8 PM SUNDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 132219
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
519 PM CDT SUN APR 13 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* IFR CIGS POSSIBLE THROUGH MID EVENING
* WIND SHIFT FROM EAST TO SOUTH PROBABLE MID-LATE EVENING
* OCNL SHRA/POSSIBLE BRIEF TSRA THROUGH TONIGHT
* WIND SHIFT TO NORTH WITH GUSTS 25-30KT LATE TONIGHT
* RAIN POSSIBLY MIXING WITH OR CHANGING TO SNOW MONDAY

RC/IZZI

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

MULTIFACETED AVIATION CONCERNS THROUGH THE PERIOD. DUE TO WEAKNESS
IN PRESSURE PATTERN OVER THE TERMINALS...A LAKE ENHANCED FRONT IS
SURGING SOUTHWESTWARD AND HAS PUSHED THROUGH ORD/MDW AND GYY WITH
A WIND SHIFT TO EAST AND NORTHEAST. WARM MOIST AIR ALOFT ABOVE THE
DENSE MOIST MARINE LAYER HAS RESULTED IN IFR CIGS AND LOWERING
VSBY...WITH DENSE FOG ALONG THE LAKEFRONT. EXPECTING IFR VSBY TO
REACH ORD/MDW BY AROUND 19Z...THOUGH CONFIDENCE IS STILL ONLY
MEDIUM IN EXACT TIMING AND OCCURRENCE BASED ON UPSTREAM TRENDS AT
PWK. A WAVE OF SHRA AND EMBEDDED TSRA ALSO CURRENTLY LIFTING
NORTHEAST...WITH ADDITIONAL WAVES OF SHRA AND TSRA LATE THIS
AFTERNOON AND EVENING AND AT LEAST OCNL IFR VSBY IN THE HEAVIER
RAIN. AS LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST...WINDS WILL PICK UP OUT OF THE SOUTH-SOUTHWEST SOUTH OF
THE FRONTAL BOUNDARY...BUT THE CONVECTION IS LIKELY TO KEEP WINDS
OUT OF THE EAST AT ORD/MDW/DPA...POSSIBLY GOING BACK TO SOUTH AT
GYY AROUND 00Z. WINDS ARE EXPECTED TO SHIFT BACK TO GUSTY SOUTH-
SOUTHWEST AT ORD/MDW AND DPA BY MID TO LATE EVENING...WHICH COULD
TEMPORARILY LIFT CIGS BACK ABOVE IFR...THOUGH THIS IS NOT
CURRENTLY INDICATED IN TAF.

MUCH COLDER AIR WILL SURGE INTO THE AREA ON GUSTY NORTHERLY WINDS
LATE TONIGHT WHILE PERIODS OF RA/SHRA CONTINUE AS WELL AS IFR CIGS AND
VSBY REDUCTIONS. THE RAIN MAY LIGHTEN IN INTENSITY AND CIGS LOWER
BY MID MORNING MONDAY...THOUGH NORTHERLY WIND GUSTS COULD STILL BE
AS HIGH AS 30 KT ESPECIALLY FOR THE EASTERN TERMINALS. THE NEXT
CONCERN IS FOR ANOTHER UPPER LEVEL DISTURBANCE MOVING IN FROM THE
SOUTHWEST TOWARD MIDDAY MONDAY AS EVEN COLDER AIR ARRIVES WHICH
COULD RESULT IN A RAIN/SNOW MIX OR A CHANGE TO SNOW. UNLESS PRECIP
RATES ARE HEAVY AND THERE IS AN ACTUAL CHANGEOVER TO ALL SNOW AT
THE TERMINALS...WOULD EXPECT IMPACTS TO PRIMARILY BE TO VSBY AND
POSSIBLY LOWER CIGS THAN CURRENTLY INDICATED. FOR NOW HAVE A PROB
30 RASN MENTION IN THE ORD AND RFD TAFS...WITH SUBSEQUENT UPDATES
LIKELY TO ADD SOME BETTER DETAIL TO THIS POTENTIAL ON MONDAY.
WINDS ARE EXPECTED TO REMAIN CLOSE TO DUE NORTHERLY AND GUSTY
THROUGH THE AFTERNOON...THOUGH A SLOW DIMINISHING TREND IN SPEEDS
AND GUST MAGNITUDES IS PROBABLE.

RC

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

* HIGH CONFIDENCE IN EAST WINDS THROUGH EARLY TO MID
  EVENING...MEDIUM CONFIDENCE IN TIMING OF SHIFT BACK TO SOUTH-
  SOUTHWEST MID TO LATE THIS EVENING.
* MEDIUM CONFIDENCE IN IFR CIGS EARLY THIS EVENING.
* MEDIUM CONFIDENCE IN PRECIP TRENDS TONIGHT AND LOW CONFIDENCE IN
  PRECIP FORECAST MONDAY
* HIGH CONFIDENCE IN STRONG NORTHERLY WINDS MONDAY

IZZI

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 8 PM SUNDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 132005
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
305 PM CDT SUN APR 13 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* EAST TO NORTHEAST WINDS OF 10 TO 15 KT THROUGH THE EARLY TO MID EVENING.

* IFR CIGS CONTINUING THROUGH THE NIGHT...WITH A BRIEF IMPROVEMENT
  POSSIBLE LATE THIS EVENING.

* PERIODS OF SHRA THIS...WITH TSRA POSSIBLY ARRIVING LATE
  AFTERNOON INTO EARLY EVENING EVENING...HEAVIEST SHRA COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE TONIGHT INTO MONDAY MORNING.

* RAIN POSSIBLY MIXING WITH OR CHANGING TO SNOW ON MONDAY AND
  ASSOCIATED CIG/VSBY IMPACTS.

RC

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

MULTIFACETED AVIATION CONCERNS THROUGH THE PERIOD. DUE TO WEAKNESS
IN PRESSURE PATTERN OVER THE TERMINALS...A LAKE ENHANCED FRONT IS
SURGING SOUTHWESTWARD AND HAS PUSHED THROUGH ORD/MDW AND GYY WITH
A WIND SHIFT TO EAST AND NORTHEAST. WARM MOIST AIR ALOFT ABOVE THE
DENSE MOIST MARINE LAYER HAS RESULTED IN IFR CIGS AND LOWERING
VSBY...WITH DENSE FOG ALONG THE LAKEFRONT. EXPECTING IFR VSBY TO
REACH ORD/MDW BY AROUND 19Z...THOUGH CONFIDENCE IS STILL ONLY
MEDIUM IN EXACT TIMING AND OCCURRENCE BASED ON UPSTREAM TRENDS AT
PWK. A WAVE OF SHRA AND EMBEDDED TSRA ALSO CURRENTLY LIFTING
NORTHEAST...WITH ADDITIONAL WAVES OF SHRA AND TSRA LATE THIS
AFTERNOON AND EVENING AND AT LEAST OCNL IFR VSBY IN THE HEAVIER
RAIN. AS LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST...WINDS WILL PICK UP OUT OF THE SOUTH-SOUTHWEST SOUTH OF
THE FRONTAL BOUNDARY...BUT THE CONVECTION IS LIKELY TO KEEP WINDS
OUT OF THE EAST AT ORD/MDW/DPA...POSSIBLY GOING BACK TO SOUTH AT
GYY AROUND 00Z. WINDS ARE EXPECTED TO SHIFT BACK TO GUSTY SOUTH-
SOUTHWEST AT ORD/MDW AND DPA BY MID TO LATE EVENING...WHICH COULD
TEMPORARILY LIFT CIGS BACK ABOVE IFR...THOUGH THIS IS NOT
CURRENTLY INDICATED IN TAF.

MUCH COLDER AIR WILL SURGE INTO THE AREA ON GUSTY NORTHERLY WINDS
LATE TONIGHT WHILE PERIODS OF RA/SHRA CONTINUE AS WELL AS IFR CIGS AND
VSBY REDUCTIONS. THE RAIN MAY LIGHTEN IN INTENSITY AND CIGS LOWER
BY MID MORNING MONDAY...THOUGH NORTHERLY WIND GUSTS COULD STILL BE
AS HIGH AS 30 KT ESPECIALLY FOR THE EASTERN TERMINALS. THE NEXT
CONCERN IS FOR ANOTHER UPPER LEVEL DISTURBANCE MOVING IN FROM THE
SOUTHWEST TOWARD MIDDAY MONDAY AS EVEN COLDER AIR ARRIVES WHICH
COULD RESULT IN A RAIN/SNOW MIX OR A CHANGE TO SNOW. UNLESS PRECIP
RATES ARE HEAVY AND THERE IS AN ACTUAL CHANGEOVER TO ALL SNOW AT
THE TERMINALS...WOULD EXPECT IMPACTS TO PRIMARILY BE TO VSBY AND
POSSIBLY LOWER CIGS THAN CURRENTLY INDICATED. FOR NOW HAVE A PROB
30 RASN MENTION IN THE ORD AND RFD TAFS...WITH SUBSEQUENT UPDATES
LIKELY TO ADD SOME BETTER DETAIL TO THIS POTENTIAL ON MONDAY.
WINDS ARE EXPECTED TO REMAIN CLOSE TO DUE NORTHERLY AND GUSTY
THROUGH THE AFTERNOON...THOUGH A SLOW DIMINISHING TREND IN SPEEDS
AND GUST MAGNITUDES IS PROBABLE.

RC

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

* HIGH CONFIDENCE IN EAST WINDS THROUGH EARLY TO MID
  EVENING...MEDIUM CONFIDENCE IN TIMING OF SHIFT BACK TO SOUTH-
  SOUTHWEST MID TO LATE THIS EVENING.

* HIGH CONFIDENCE IN IFR CIGS INTO THE EVENIG.

* MEDIUM IN VSBY LOWERING TO MVFR IN BR...AND MEDIUM IN POTENTIAL
  FOR IFR VSBY IN HEAVIEST SHRA/TSRA.

* MEDIUM CONFIDENCE IN OVERALL SHRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH MEDIUM CONFIDENCE THERE WILL BE AT
  LEAST OCNL TSRA AT THE TERMINALS LATE THIS AFTERNOON INTO THIS
  EVENING.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

* LOW CONFIDENCE IN POTENTIAL FOR RASN MIX OR CHANGE TO SN AND
  ASSOCIATED VSBY/CIG IMPACTS MONDAY AFTERNOON.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 8 PM SUNDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...8 PM SUNDAY TO 4
     AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
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000
FXUS63 KLOT 131925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
225 PM CDT SUN APR 13 2014

.DISCUSSION...
225 PM CDT

MAIN FORECAST CONCERNS ARE IN THE SHORT TERM...WITH RAIN/THUNDER
TRENDS AND PRECIP AMOUNTS THROUGH TONIGHT AND THEN THE POTENTIAL FOR
A RAIN/SNOW MIX TOMORROW AS PRECIPITATION WINDS DOWN AND SYSTEM
PULLS AWAY. TEMP TRENDS ALSO RECEIVING ATTENTION...WITH NORTHEAST
WINDS OFF LAKE PRODUCING FOG/COOL TEMPS NEAR THE LAKE.

WEAK AREA OF LOW PRESSURE WHICH ACCOMPANIED OUR EARLY MORNING
CONVECTION HAD LIFTED OFF TO THE EAST DURING THE MORNING...WITH ITS
TRAILING COLD FRONT SAGGING ACROSS PARTS OF FAR NORTHERN ILLINOIS
AND BACK-DOORING DOWN THE ILLINOIS LAKE MICHIGAN SHORE INTO THIS
AFTERNOON. WITH WINDS SHIFTING TO THE NORTHEAST OFF THE LAKE...TEMPS
HAVE FALLEN INTO THE LOW-MID 40S ALONG THE LAKE WITH AREAS OF FAIRLY
DENSE FOG PUSHING A FEW BLOCKS INLAND AS WELL. FORECAST OF THESE
MESO/MICRO SCALE DETAILS WILL BE FRAUGHT WITH DANGER THROUGH THIS
EVENING...AS NEXT AREA OF LOW PRESSURE LIFTS NORTHEAST ACROSS THE
AREA OVERNIGHT AND BRINGS WINDS BACK TO THE SOUTH ACROSS PARTS OF
THE CENTRAL CHICAGO METRO AREA POTENTIALLY BRINGING TEMPS BACK UP
WELL INTO THE 50S/NEAR 60 LATER THIS EVENING. BEYOND THESE EFFECTS
WILL ALSO BE THE EXPECTATION OF SEVERAL ROUNDS OF RAIN/SHRA/THUNDER
THROUGH THE OVERNIGHT HOURS...AS SHORT WAVE TROUGH EJECTING FROM THE
SOUTHERN PLAINS PROPAGATES INTO THE REGION OVERNIGHT. SOME THREAT
EXISTS FOR LOCALLY HEAVY RAINFALL WITH ADDITIONAL PRECIP TONIGHT...
WITH PRECIPITABLE WATER VALUES JUST ABOVE 1 INCH PER 12Z RAOBS AND
NEARLY 200 PERCENT OF NORMAL FOR THIS TIME OF YEAR. SO FAR...AREAS
ALONG THE WISCONSIN/ILLINOIS HAVE BORDER RECEIVED THE GREATEST
RAINFALL SINCE SATURDAY MORNING WITH A COUPLE OF ROUNDS OF
THUNDERSTORMS PRODUCING 3/4 TO 1 1/2 INCHES ESPECIALLY OVER
WINNEBAGO...BOONE AND MCHENRY COUNTIES. ANOTHER 1-2" ARE POSSIBLE
FOR THESE AREAS THROUGH TONIGHT AS ADDITIONAL ROUNDS OF
THUNDERSTORMS LIFT ACROSS THE AREA IN ADVANCE OF THE APPROACHING
UPPER TROUGH. SOME AREAS ESPECIALLY NORTH OF A SQI-UGN LINE COULD
ULTIMATELY SEE AROUND 2.5 INCH STORM TOTALS. SYSTEM BEGINS TO
ACCELERATE A BIT LATE TONIGHT/MONDAY...WITH PRECIP DECREASING FROM
THE WEST DURING THE EARLY/MID MORNING HOURS AND THE LOW QUICKLY
LIFTING AWAY TO THE NORTHEAST. COLDER AIR SPILLING IN BEHIND THE
DEPARTING LOW WILL DECREASE THICKNESSES ENOUGH TO PRESENT THE
POTENTIAL FOR SOME WET SNOW/RAIN MIX TO DEVELOP MAINLY ACROSS NORTH
CENTRAL IL MONDAY...THOUGH WITH SURFACE TEMPS EXPECTED IN THE LOW
40S IN MANY AREAS AM NOT ANTICIPATING ANY ACCUMULATION OF
CONSEQUENCE. AFTER SATURDAY/S 70S AND 80 DEGREE TEMPS...MONDAY WILL
SERVE AS A BLUSTERY AND CHILLY REMINDER THAT SPRING HASNT COMPLETELY
SPRUNG FOR US JUST YET. WHILE THE MAIN LOW LIFTS QUICKLY AWAY DURING
THE MORNING...THE LARGE SCALE UPPER TROUGH AXIS CONTINUES TO DIG
ACROSS THE MIDWEST INTO MONDAY NIGHT...MAINTAINING THE POTENTIAL FOR
SOME ADDITIONAL LIGHT SNOW SHOWERS INTO MAINLY MONDAY EVENING.

HIGH PRESSURE RIDGE BUILDS ACROSS THE AREA TUESDAY WITH COOL BUT DRY
CONDITIONS FOR THE CWA...BEFORE ANOTHER LOW DEVELOPS OVER THE UPPER
MIDWEST WEDNESDAY AND BRINGS SOMEWHAT MILDER AIR BACK INTO THE
REGION. MODEL GUIDANCE IN DECENT AGREEMENT IN MOVING INVERTED
TROUGH/LOW PRESSURE AREA SLOWLY EAST ACROSS THE AREA
THURSDAY-SATURDAY WITH AN ATTENDANT PERIODIC LIGHT RAIN THREAT.
TEMPS HOWEVER LOOK TO MODERATE BACK INTO THE 50S/60S FOR THE MOST
PART...THOUGH WITH SOME COOLER READINGS ALONG LAKE MICHIGAN WITH AT
LEAST PARTIAL ONSHORE FLOW. LONGER RANGE...SOME INDICATION OF
COOLING BEHIND UPPER TROUGH MONDAY...THEN PERHAPS A MILDER PERIOD
INTO MID NEXT WEEK WITH BOTH GFS/ECMWF DEVELOPING BROAD UPPER
RIDGING OVER THE CENTRAL CONUS.

RATZER

&&

.AVIATION...

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

* EAST WINDS OF 10 TO 15 KT THROUGH THE EARLY TO MID EVENING.

* IFR CIGS ARRIVING THIS HOUR AND VSBY EXPECTED TO LOWER TO IFR BY
  19Z...THOUGH TIMING COULD BE DELAYED.

* PERIODS OF SHRA/TSRA THIS AFTERNOON AND EVENING...HEAVIEST COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE TONIGHT INTO MONDAY MORNING.

* RAIN POSSIBLY MIXING WITH OR CHANGING TO SNOW ON MONDAY AND
  ASSOCIATED CIG/VSBY IMPACTS.

RC

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

MULTIFACETED AVIATION CONCERNS THROUGH THE PERIOD. DUE TO WEAKNESS
IN PRESSURE PATTERN OVER THE TERMINALS...A LAKE ENHANCED FRONT IS
SURGING SOUTHWESTWARD AND HAS PUSHED THROUGH ORD/MDW AND GYY WITH
A WIND SHIFT TO EAST AND NORTHEAST. WARM MOIST AIR ALOFT ABOVE THE
DENSE MOIST MARINE LAYER HAS RESULTED IN IFR CIGS AND LOWERING
VSBY...WITH DENSE FOG ALONG THE LAKEFRONT. EXPECTING IFR VSBY TO
REACH ORD/MDW BY AROUND 19Z...THOUGH CONFIDENCE IS STILL ONLY
MEDIUM IN EXACT TIMING AND OCCURRENCE BASED ON UPSTREAM TRENDS AT
PWK. A WAVE OF SHRA AND EMBEDDED TSRA ALSO CURRENTLY LIFTING
NORTHEAST...WITH ADDITIONAL WAVES OF SHRA AND TSRA LATE THIS
AFTERNOON AND EVENING AND AT LEAST OCNL IFR VSBY IN THE HEAVIER
RAIN. AS LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST...WINDS WILL PICK UP OUT OF THE SOUTH-SOUTHWEST SOUTH OF
THE FRONTAL BOUNDARY...BUT THE CONVECTION IS LIKELY TO KEEP WINDS
OUT OF THE EAST AT ORD/MDW/DPA...POSSIBLY GOING BACK TO SOUTH AT
GYY AROUND 00Z. WINDS ARE EXPECTED TO SHIFT BACK TO GUSTY SOUTH-
SOUTHWEST AT ORD/MDW AND DPA BY MID TO LATE EVENING...WHICH COULD
TEMPORARILY LIFT CIGS BACK ABOVE IFR...THOUGH THIS IS NOT
CURRENTLY INDICATED IN TAF.

MUCH COLDER AIR WILL SURGE INTO THE AREA ON GUSTY NORTHERLY WINDS
LATE TONIGHT WHILE PERIODS OF RA/SHRA CONTINUE AS WELL AS IFR CIGS AND
VSBY REDUCTIONS. THE RAIN MAY LIGHTEN IN INTENSITY AND CIGS LOWER
BY MID MORNING MONDAY...THOUGH NORTHERLY WIND GUSTS COULD STILL BE
AS HIGH AS 30 KT ESPECIALLY FOR THE EASTERN TERMINALS. THE NEXT
CONCERN IS FOR ANOTHER UPPER LEVEL DISTURBANCE MOVING IN FROM THE
SOUTHWEST TOWARD MIDDAY MONDAY AS EVEN COLDER AIR ARRIVES WHICH
COULD RESULT IN A RAIN/SNOW MIX OR A CHANGE TO SNOW. UNLESS PRECIP
RATES ARE HEAVY AND THERE IS AN ACTUAL CHANGEOVER TO ALL SNOW AT
THE TERMINALS...WOULD EXPECT IMPACTS TO PRIMARILY BE TO VSBY AND
POSSIBLY LOWER CIGS THAN CURRENTLY INDICATED. FOR NOW HAVE A PROB
30 RASN MENTION IN THE ORD AND RFD TAFS...WITH SUBSEQUENT UPDATES
LIKELY TO ADD SOME BETTER DETAIL TO THIS POTENTIAL ON MONDAY.
WINDS ARE EXPECTED TO REMAIN CLOSE TO DUE NORTHERLY AND GUSTY
THROUGH THE AFTERNOON...THOUGH A SLOW DIMINISHING TREND IN SPEEDS
AND GUST MAGNITUDES IS PROBABLE.

RC

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

* HIGH CONFIDENCE IN EAST WINDS THROUGH EARLY TO MID EVENING...MEDIUM
  CONFIDENCE IN TIMING OF SHIFT BACK TO SOUTH-SOUTHWEST THIS
  EVENING.

* HIGH CONFIDENCE IN IFR CIGS MOVING IN BY 19Z.

* MEDIUM IN VSBY LOWERING TO MVFR OR IFR IN BR...MEDIUM IN
  TIMING...AND MEDIUM HIGH IN POTENTIAL FOR IFR VSBY IN HEAVIEST
  SHRA/TSRA.

* MEDIUM CONFIDENCE IN OVERALL SHRA/TSRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH HIGH CONFIDENCE THERE WILL BE AT
  LEAST OCNL TSRA AT THE TERMINALS THIS AFTERNOON AND EVENING.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

* LOW CONFIDENCE IN POTENTIAL FOR RASN MIX OR CHANGE TO SN AND
  ASSOCIATED VSBY/CIG IMPACTS MONDAY AFTERNOON.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 PM SUNDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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








000
FXUS63 KLOT 131921
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
221 PM CDT SUN APR 13 2014

.DISCUSSION...
1153 AM CDT

FOR MORNING UPDATE...

HAVE MADE SOME ADJUSTMENTS TO FORECAST THROUGH THIS AFTERNOON BASED
ON OBS/RADAR TRENDS THIS MORNING. MOST NOTABLY...COLD FRONTAL
BOUNDARY HAS SETTLED ACROSS FAR NORTHERN/NORTHEAST IL ESPECIALLY
NEAR LAKE MICHIGAN IN THE WAKE OF WEAK LOW PRESSURE WAVE MOVING OUT
OF LOWER MICHIGAN. WINDS VEERING TO NORTHEAST OFF THE CHILLY LAKE
WATERS WERE DROPPING TEMPS INTO THE MID-40S ALONG THE SHORE AND
PRODUCING AREAS OF FOG WITH VISIBILITY DROPPING BELOW A MILE. HAVE
THEREFORE ADJUSTED MAX TEMPS DOWN ACROSS FAR NORTHEAST IL AND HAVE
TRIED TO CAPTURE THE EXPECTED STEADY/COOLING TREND IN THE HOURLY
TEMP FORECAST ALONG THE LAKE THROUGH THIS AFTERNOON.

OTHERWISE...HAVE ALSO BEEN MONITORING AREA OF RAIN/EMBEDDED THUNDER
ACROSS A GOOD PORTION OF IA/MO AND WESTERN IL. AFTER EARLY
SUBSIDENCE IN THE WAKE OF EARLY MORNING SHORT WAVE AND MCS...THIS
AREA OF PRECIP SHOULD CONTINUE TO SPREAD SLOWLY NORTHEAST ACROSS THE
CWA THIS AFTERNOON BRINGING RAIN BACK TO THE AREA. MID-LEVEL LAPSE
RATES ARE A LITTLE MUSHY...THOUGH EMBEDDED THUNDER EXPECTED AT TIMES
ESPECIALLY LATER THIS AFTERNOON/TONIGHT AS LARGE SCALE FORCING
BECOMES STRONGER WITH APPROACH OF MID-LEVEL SHORT WAVE FROM THE
OK/KS PLAINS REGION. PERIODS OF RAIN/THUNDER AND POTENTIALLY SOME
HEAVY RAINFALL STILL LOOKS TO BE ON TRACK FOR TONIGHT AS SFC LOW AND
FRONTAL SYSTEM MOVE THROUGH THE AREA ALONG WITH MID-LEVEL TROUGH.

RATZER

//PREV DISCUSSION...
417 AM CDT

TODAY...
EARLY THIS MORNING LOW PRESSURE LIES OVER IOWA WITH A WARM FRONT
EXTENDING EAST ACROSS FAR NORTHERN ILLINOIS. THE BOUNDARY WAS DRIVEN
SOUTH OVERNIGHT BY CONVECTION/OUTFLOW. ON THE WARM SIDE OF THE
FRONT...TEMPERATURES REMAINED IN THE 60S OVERNIGHT...BUT NORTH OF
THE FRONT TEMPS QUICKLY FALL OFF INTO THE 40S AND THIS TIGHT THERMAL
GRADIENT WILL HOVER ACROSS NORTHERN COUNTIES OF THE STATE THIS
MORNING. AS FOR CONVECTION THIS MORNING...THUNDERSTORMS HAVE MOVED
EAST OVER LAKE MICHIGAN THIS MORNING WITH STABLE CONDITIONS IN THEIR
WAKE AND EXPECT QUIET CONDITIONS TO PERSIST THROUGH THE REMAINDER OF
THE MORNING AND EARLY AFTERNOON. COUPLED JET STILL PROGGED TO
DEVELOP THIS AFTERNOON WITH MODERATE TO STRONG UPPER LEVEL
DIVERGENCE RESULTING IN CYCLOGENENSIS ALONG THE MID MISSISSIPPI
VALLEY. ISENTROPIC ASCENT WILL INCREASE THROUGH THE LATE MORNING
INTO THE AFTERNOON WITH PRECIP OVERSPREADING NORTHERN ILLINOIS FROM
THE WEST. SOUNDINGS STILL INDICATE DEEP SATURATED LAYER WITH PWATS
PUSHING TO AROUND 1.4-1.5 INCHES. MODELS IN DECENT AGREEMENT ON
PLACEMENT OF AXIS OF HEAVIEST RAIN THIS EVENING AND TONIGHT...
STRETCHING FROM EASTERN IOWA TO EAST-CENTRAL WISCONSIN AND CLIPPING
NORTH CENTRAL ILLINOIS INCLUDING THE ROCKFORD AREA. HEAVY PRECIP
REMAINS A CONCERN THOUGH PRECIP SO FAR HAS UNDERPERFORMED FROM PRIOR
EXPECTATIONS AND A PROLONGED PERIOD OF DRY WEATHER OVER NORTH
CENTRAL ILLINOIS THE PAST SEVERAL WEEKS WILL HELP MITIGATE THE FLOOD
THREAT TO SOME DEGREE.

MONDAY...
LONGWAVE TROUGH AXIS WILL TRANSLATE EAST ACROSS THE PLAINS MONDAY
REACHING THE MISSISSIPPI VALLEY BY THE EVENING. MEANWHILE...COLD
ADVECTION INTO THE AREA WILL DRIVE H85 TEMPS DOWN TO AROUND -11C AND
SEVERAL SMALLER SCALE DISTURBANCES LIFTING UP THE LEE SIDE OF THE
TROUGH WILL RESULT IN RAIN CHANGING OVER TO SNOW ACROSS THE AREA.
MODELS HAVE TRENDED MORE BULLISH WITH QPF MONDAY AND CANNOT RULE OUT
LIGHT ACCUMULATIONS AT THIS TIME...MAINLY DURING THE LATE AFTERNOON
INTO THE EVENING WHEN THE AREA IS BETTER ENTRENCHED IN THE COLD AIR.
HIGHS MAY STRUGGLE TO REACH INTO THE LOW 40S FOR MUCH OF THE CWA AND
A GUSTY NORTH WIND WILL MAKE IT FEEL CLOSER TO THE FREEZING MARK.

TUESDAY THROUGH SATURDAY...
GENERALLY QUIET WEATHER EXPECTED TUESDAY AND WEDNESDAY UNDER THE
INFLUENCE OF HIGH PRESSURE. BY WEDNESDAY...LOW PRESSURE OVER THE
PLAINS WILL HELP SPREAD WARM AIR BACK INTO THE MIDWEST WITH A
WARMING TREND THROUGH THURSDAY WHEN TEMPERATURE SHOULD BE CLOSER TO
NORMAL. MORE ACTIVE WEATHER MAY RETURN LATE IN THE WEEK INTO THE
WEEKEND AS ANOTHER SOUTHWEST LOW LIFTS ACROSS THE MIDWEST BRINGING
CHANCES FOR PRECIP AND FLUCTUATING TEMPERATURES.

BMD

&&

.AVIATION...

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

* EAST WINDS OF 10 TO 15 KT THROUGH THE EARLY TO MID EVENING.

* IFR CIGS ARRIVING THIS HOUR AND VSBY EXPECTED TO LOWER TO IFR BY
  19Z...THOUGH TIMING COULD BE DELAYED.

* PERIODS OF SHRA/TSRA THIS AFTERNOON AND EVENING...HEAVIEST COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE TONIGHT INTO MONDAY MORNING.

* RAIN POSSIBLY MIXING WITH OR CHANGING TO SNOW ON MONDAY AND
  ASSOCIATED CIG/VSBY IMPACTS.

RC

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

MULTIFACETED AVIATION CONCERNS THROUGH THE PERIOD. DUE TO WEAKNESS
IN PRESSURE PATTERN OVER THE TERMINALS...A LAKE ENHANCED FRONT IS
SURGING SOUTHWESTWARD AND HAS PUSHED THROUGH ORD/MDW AND GYY WITH
A WIND SHIFT TO EAST AND NORTHEAST. WARM MOIST AIR ALOFT ABOVE THE
DENSE MOIST MARINE LAYER HAS RESULTED IN IFR CIGS AND LOWERING
VSBY...WITH DENSE FOG ALONG THE LAKEFRONT. EXPECTING IFR VSBY TO
REACH ORD/MDW BY AROUND 19Z...THOUGH CONFIDENCE IS STILL ONLY
MEDIUM IN EXACT TIMING AND OCCURRENCE BASED ON UPSTREAM TRENDS AT
PWK. A WAVE OF SHRA AND EMBEDDED TSRA ALSO CURRENTLY LIFTING
NORTHEAST...WITH ADDITIONAL WAVES OF SHRA AND TSRA LATE THIS
AFTERNOON AND EVENING AND AT LEAST OCNL IFR VSBY IN THE HEAVIER
RAIN. AS LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST...WINDS WILL PICK UP OUT OF THE SOUTH-SOUTHWEST SOUTH OF
THE FRONTAL BOUNDARY...BUT THE CONVECTION IS LIKELY TO KEEP WINDS
OUT OF THE EAST AT ORD/MDW/DPA...POSSIBLY GOING BACK TO SOUTH AT
GYY AROUND 00Z. WINDS ARE EXPECTED TO SHIFT BACK TO GUSTY SOUTH-
SOUTHWEST AT ORD/MDW AND DPA BY MID TO LATE EVENING...WHICH COULD
TEMPORARILY LIFT CIGS BACK ABOVE IFR...THOUGH THIS IS NOT
CURRENTLY INDICATED IN TAF.

MUCH COLDER AIR WILL SURGE INTO THE AREA ON GUSTY NORTHERLY WINDS
LATE TONIGHT WHILE PERIODS OF RA/SHRA CONTINUE AS WELL AS IFR CIGS AND
VSBY REDUCTIONS. THE RAIN MAY LIGHTEN IN INTENSITY AND CIGS LOWER
BY MID MORNING MONDAY...THOUGH NORTHERLY WIND GUSTS COULD STILL BE
AS HIGH AS 30 KT ESPECIALLY FOR THE EASTERN TERMINALS. THE NEXT
CONCERN IS FOR ANOTHER UPPER LEVEL DISTURBANCE MOVING IN FROM THE
SOUTHWEST TOWARD MIDDAY MONDAY AS EVEN COLDER AIR ARRIVES WHICH
COULD RESULT IN A RAIN/SNOW MIX OR A CHANGE TO SNOW. UNLESS PRECIP
RATES ARE HEAVY AND THERE IS AN ACTUAL CHANGEOVER TO ALL SNOW AT
THE TERMINALS...WOULD EXPECT IMPACTS TO PRIMARILY BE TO VSBY AND
POSSIBLY LOWER CIGS THAN CURRENTLY INDICATED. FOR NOW HAVE A PROB
30 RASN MENTION IN THE ORD AND RFD TAFS...WITH SUBSEQUENT UPDATES
LIKELY TO ADD SOME BETTER DETAIL TO THIS POTENTIAL ON MONDAY.
WINDS ARE EXPECTED TO REMAIN CLOSE TO DUE NORTHERLY AND GUSTY
THROUGH THE AFTERNOON...THOUGH A SLOW DIMINISHING TREND IN SPEEDS
AND GUST MAGNITUDES IS PROBABLE.

RC

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

* HIGH CONFIDENCE IN EAST WINDS THROUGH EARLY TO MID EVENING...MEDIUM
  CONFIDENCE IN TIMING OF SHIFT BACK TO SOUTH-SOUTHWEST THIS
  EVENING.

* HIGH CONFIDENCE IN IFR CIGS MOVING IN BY 19Z.

* MEDIUM IN VSBY LOWERING TO MVFR OR IFR IN BR...MEDIUM IN
  TIMING...AND MEDIUM HIGH IN POTENTIAL FOR IFR VSBY IN HEAVIEST
  SHRA/TSRA.

* MEDIUM CONFIDENCE IN OVERALL SHRA/TSRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH HIGH CONFIDENCE THERE WILL BE AT
  LEAST OCNL TSRA AT THE TERMINALS THIS AFTERNOON AND EVENING.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

* LOW CONFIDENCE IN POTENTIAL FOR RASN MIX OR CHANGE TO SN AND
  ASSOCIATED VSBY/CIG IMPACTS MONDAY AFTERNOON.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
218 PM CDT

A FRONTAL BOUNDARY IN CURRENTLY IN PLACE ACROSS THE SOUTHERN TIP OF
LAKE MICHIGAN EARLY THIS AFTERNOON. LAKE INFLUENCES HAVE ALLOWED THE
WINDS TO SHIFT ONSHORE ACROSS THE INDIANA AND ILLINOIS NEAR
SHORES...WITH DENSE FOG ALSO RESULTING DUE TO THE HIGH DEW POINT AIR
ACROSS THE SOUTHERN END OF THE LAKE IN THE VICINITY OF THE FRONTAL
BOUNDARY.

WINDS WILL SHIFT BACK OUT OF THE SOUTH ACROSS FAR SOUTHERN TIP OF
THE LAKE EARLY THIS EVENING...AND THIS SHOULD IMPACT MAINLY THE
INDIANA NEAR SHORE WATERS. THIS WILL HAPPEN IN RESPONSE TO THE
APPROACHING SURFACE LOW...NOW IN PLACE ACROSS KANSAS AND OKLAHOMA.
SO...ALTHOUGH WINDS ARE CURRENTLY LIGHT OUT OF THE NORTH ACROSS THE
INDIANA NEAR SHORES...EXPECT THAT TO CHANGE EARLY THIS
EVENING...WITH WINDS LIKELY TO BECOME GUSTY FOR A PERIOD UP TO 30 KT
OUT OF THE SOUTH. WE CURRENTLY HAVE A SMALL CRAFT ADVISORY IN PLACE
TO COVER THESE STRONGER SOUTHERLY WINDS...HOWEVER...I DID PUSH OFF
THE START TIME OF THE SMALL CRAFT ADVISORY A FEW HOURS UNTIL THIS
EVENING WHEN THE WINDS ARE EXPECTED TO SHIFT.

AREAS OF FOG WILL LIKELY CONTINUE TO IMPACT SOUTHERN PORTIONS OF
THE LAKE THROUGH MUCH OF TONIGHT AS THE FRONTAL BOUNDARY CONTINUES
TO MEANDER ACROSS THIS AREA. WITH THIS IN MIND I WILL CONTINUE THE
DENSE FOG ADVISORY THROUGH LATE TONIGHT.

OTHERWISE...EXPECT WINDS TO INCREASE OUT OF THE NORTH...FIRST ACROSS
THE NORTHERN 1/2 OR SO OF THE LAKE THIS EVENING...WITH NORTHERLY
GALES LIKELY DEVELOPING BY LATE THIS EVENING. THESE NORTHERLY GALES
WILL THEN OVERSPREAD THE REST OF THE LAKE BY DAYBREAK MONDAY.
OVERALL...IT STILL APPEARS THAT THE MAGNITUDES OF THE WINDS WILL BE
UP AROUND 40 KT...WITH A FEW SHORT PERIODS OF SOME SLIGHTLY HIGHER
WINDS POSSIBLE TOWARDS DAYBREAK MONDAY. THESE GALES WILL GRADUALLY
EASE TO AROUND 30 KT BY EARLY MONDAY EVENING AND MONDAY NIGHT.

A PERIOD OF LIGHTER WINDS ARE EXPECTED TUESDAY INTO EARLY WEDNESDAY
AS A SURFACE RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE.
HOWEVER...THE WINDS ARE EXPECTED TO INCREASE AGAIN OUT OF THE
SOUTHEAST BY THE MIDDLE OF NEXT WEEK AS OUR NEXT AREA OF LOW
PRESSURE BEGINS TO MOVE ACROSS THE MIDWEST.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 PM SUNDAY.

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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000
FXUS63 KLOT 131823
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
123 PM CDT SUN APR 13 2014

.DISCUSSION...
1153 AM CDT

FOR MORNING UPDATE...

HAVE MADE SOME ADJUSTMENTS TO FORECAST THROUGH THIS AFTERNOON BASED
ON OBS/RADAR TRENDS THIS MORNING. MOST NOTABLY...COLD FRONTAL
BOUNDARY HAS SETTLED ACROSS FAR NORTHERN/NORTHEAST IL ESPECIALLY
NEAR LAKE MICHIGAN IN THE WAKE OF WEAK LOW PRESSURE WAVE MOVING OUT
OF LOWER MICHIGAN. WINDS VEERING TO NORTHEAST OFF THE CHILLY LAKE
WATERS WERE DROPPING TEMPS INTO THE MID-40S ALONG THE SHORE AND
PRODUCING AREAS OF FOG WITH VISIBILITY DROPPING BELOW A MILE. HAVE
THEREFORE ADJUSTED MAX TEMPS DOWN ACROSS FAR NORTHEAST IL AND HAVE
TRIED TO CAPTURE THE EXPECTED STEADY/COOLING TREND IN THE HOURLY
TEMP FORECAST ALONG THE LAKE THROUGH THIS AFTERNOON.

OTHERWISE...HAVE ALSO BEEN MONITORING AREA OF RAIN/EMBEDDED THUNDER
ACROSS A GOOD PORTION OF IA/MO AND WESTERN IL. AFTER EARLY
SUBSIDENCE IN THE WAKE OF EARLY MORNING SHORT WAVE AND MCS...THIS
AREA OF PRECIP SHOULD CONTINUE TO SPREAD SLOWLY NORTHEAST ACROSS THE
CWA THIS AFTERNOON BRINGING RAIN BACK TO THE AREA. MID-LEVEL LAPSE
RATES ARE A LITTLE MUSHY...THOUGH EMBEDDED THUNDER EXPECTED AT TIMES
ESPECIALLY LATER THIS AFTERNOON/TONIGHT AS LARGE SCALE FORCING
BECOMES STRONGER WITH APPROACH OF MID-LEVEL SHORT WAVE FROM THE
OK/KS PLAINS REGION. PERIODS OF RAIN/THUNDER AND POTENTIALLY SOME
HEAVY RAINFALL STILL LOOKS TO BE ON TRACK FOR TONIGHT AS SFC LOW AND
FRONTAL SYSTEM MOVE THROUGH THE AREA ALONG WITH MID-LEVEL TROUGH.

RATZER

//PREV DISCUSSION...
417 AM CDT

TODAY...
EARLY THIS MORNING LOW PRESSURE LIES OVER IOWA WITH A WARM FRONT
EXTENDING EAST ACROSS FAR NORTHERN ILLINOIS. THE BOUNDARY WAS DRIVEN
SOUTH OVERNIGHT BY CONVECTION/OUTFLOW. ON THE WARM SIDE OF THE
FRONT...TEMPERATURES REMAINED IN THE 60S OVERNIGHT...BUT NORTH OF
THE FRONT TEMPS QUICKLY FALL OFF INTO THE 40S AND THIS TIGHT THERMAL
GRADIENT WILL HOVER ACROSS NORTHERN COUNTIES OF THE STATE THIS
MORNING. AS FOR CONVECTION THIS MORNING...THUNDERSTORMS HAVE MOVED
EAST OVER LAKE MICHIGAN THIS MORNING WITH STABLE CONDITIONS IN THEIR
WAKE AND EXPECT QUIET CONDITIONS TO PERSIST THROUGH THE REMAINDER OF
THE MORNING AND EARLY AFTERNOON. COUPLED JET STILL PROGGED TO
DEVELOP THIS AFTERNOON WITH MODERATE TO STRONG UPPER LEVEL
DIVERGENCE RESULTING IN CYCLOGENENSIS ALONG THE MID MISSISSIPPI
VALLEY. ISENTROPIC ASCENT WILL INCREASE THROUGH THE LATE MORNING
INTO THE AFTERNOON WITH PRECIP OVERSPREADING NORTHERN ILLINOIS FROM
THE WEST. SOUNDINGS STILL INDICATE DEEP SATURATED LAYER WITH PWATS
PUSHING TO AROUND 1.4-1.5 INCHES. MODELS IN DECENT AGREEMENT ON
PLACEMENT OF AXIS OF HEAVIEST RAIN THIS EVENING AND TONIGHT...
STRETCHING FROM EASTERN IOWA TO EAST-CENTRAL WISCONSIN AND CLIPPING
NORTH CENTRAL ILLINOIS INCLUDING THE ROCKFORD AREA. HEAVY PRECIP
REMAINS A CONCERN THOUGH PRECIP SO FAR HAS UNDERPERFORMED FROM PRIOR
EXPECTATIONS AND A PROLONGED PERIOD OF DRY WEATHER OVER NORTH
CENTRAL ILLINOIS THE PAST SEVERAL WEEKS WILL HELP MITIGATE THE FLOOD
THREAT TO SOME DEGREE.

MONDAY...
LONGWAVE TROUGH AXIS WILL TRANSLATE EAST ACROSS THE PLAINS MONDAY
REACHING THE MISSISSIPPI VALLEY BY THE EVENING. MEANWHILE...COLD
ADVECTION INTO THE AREA WILL DRIVE H85 TEMPS DOWN TO AROUND -11C AND
SEVERAL SMALLER SCALE DISTURBANCES LIFTING UP THE LEE SIDE OF THE
TROUGH WILL RESULT IN RAIN CHANGING OVER TO SNOW ACROSS THE AREA.
MODELS HAVE TRENDED MORE BULLISH WITH QPF MONDAY AND CANNOT RULE OUT
LIGHT ACCUMULATIONS AT THIS TIME...MAINLY DURING THE LATE AFTERNOON
INTO THE EVENING WHEN THE AREA IS BETTER ENTRENCHED IN THE COLD AIR.
HIGHS MAY STRUGGLE TO REACH INTO THE LOW 40S FOR MUCH OF THE CWA AND
A GUSTY NORTH WIND WILL MAKE IT FEEL CLOSER TO THE FREEZING MARK.

TUESDAY THROUGH SATURDAY...
GENERALLY QUIET WEATHER EXPECTED TUESDAY AND WEDNESDAY UNDER THE
INFLUENCE OF HIGH PRESSURE. BY WEDNESDAY...LOW PRESSURE OVER THE
PLAINS WILL HELP SPREAD WARM AIR BACK INTO THE MIDWEST WITH A
WARMING TREND THROUGH THURSDAY WHEN TEMPERATURE SHOULD BE CLOSER TO
NORMAL. MORE ACTIVE WEATHER MAY RETURN LATE IN THE WEEK INTO THE
WEEKEND AS ANOTHER SOUTHWEST LOW LIFTS ACROSS THE MIDWEST BRINGING
CHANCES FOR PRECIP AND FLUCTUATING TEMPERATURES.

BMD

&&

.AVIATION...

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

* EAST WINDS OF 10 TO 15 KT THROUGH THE EARLY TO MID EVENING.

* IFR CIGS ARRIVING THIS HOUR AND VSBY EXPECTED TO LOWER TO IFR BY
  19Z...THOUGH TIMING COULD BE DELAYED.

* PERIODS OF SHRA/TSRA THIS AFTERNOON AND EVENING...HEAVIEST COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE TONIGHT INTO MONDAY MORNING.

* RAIN POSSIBLY MIXING WITH OR CHANGING TO SNOW ON MONDAY AND
  ASSOCIATED CIG/VSBY IMPACTS.


RC

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

MULTIFACETED AVIATION CONCERNS THROUGH THE PERIOD. DUE TO WEAKNESS
IN PRESSURE PATTERN OVER THE TERMINALS...A LAKE ENHANCED FRONT IS
SURGING SOUTHWESTWARD AND HAS PUSHED THROUGH ORD/MDW AND GYY WITH
A WIND SHIFT TO EAST AND NORTHEAST. WARM MOIST AIR ALOFT ABOVE THE
DENSE MOIST MARINE LAYER HAS RESULTED IN IFR CIGS AND LOWERING
VSBY...WITH DENSE FOG ALONG THE LAKEFRONT. EXPECTING IFR VSBY TO
REACH ORD/MDW BY AROUND 19Z...THOUGH CONFIDENCE IS STILL ONLY
MEDIUM IN EXACT TIMING AND OCCURRENCE BASED ON UPSTREAM TRENDS AT
PWK. A WAVE OF SHRA AND EMBEDDED TSRA ALSO CURRENTLY LIFTING
NORTHEAST...WITH ADDITIONAL WAVES OF SHRA AND TSRA LATE THIS
AFTERNOON AND EVENING AND AT LEAST OCNL IFR VSBY IN THE HEAVIER
RAIN. AS LOW PRESSURE OVER THE SOUTHERN PLAINS LIFTS
NORTHEAST...WINDS WILL PICK UP OUT OF THE SOUTH-SOUTHWEST SOUTH OF
THE FRONTAL BOUNDARY...BUT THE CONVECTION IS LIKELY TO KEEP WINDS
OUT OF THE EAST AT ORD/MDW/DPA...POSSIBLY GOING BACK TO SOUTH AT
GYY AROUND 00Z. WINDS ARE EXPECTED TO SHIFT BACK TO GUSTY SOUTH-
SOUTHWEST AT ORD/MDW AND DPA BY MID TO LATE EVENING...WHICH COULD
TEMPORARILY LIFT CIGS BACK ABOVE IFR...THOUGH THIS IS NOT
CURRENTLY INDICATED IN TAF.

MUCH COLDER AIR WILL SURGE INTO THE AREA ON GUSTY NORTHERLY WINDS
LATE TONIGHT WHILE PERIODS OF RA/SHRA CONTINUE AS WELL AS IFR CIGS AND
VSBY REDUCTIONS. THE RAIN MAY LIGHTEN IN INTENSITY AND CIGS LOWER
BY MID MORNING MONDAY...THOUGH NORTHERLY WIND GUSTS COULD STILL BE
AS HIGH AS 30 KT ESPECIALLY FOR THE EASTERN TERMINALS. THE NEXT
CONCERN IS FOR ANOTHER UPPER LEVEL DISTURBANCE MOVING IN FROM THE
SOUTHWEST TOWARD MIDDAY MONDAY AS EVEN COLDER AIR ARRIVES WHICH
COULD RESULT IN A RAIN/SNOW MIX OR A CHANGE TO SNOW. UNLESS PRECIP
RATES ARE HEAVY AND THERE IS AN ACTUAL CHANGEOVER TO ALL SNOW AT
THE TERMINALS...WOULD EXPECT IMPACTS TO PRIMARILY BE TO VSBY AND
POSSIBLY LOWER CIGS THAN CURRENTLY INDICATED. FOR NOW HAVE A PROB
30 RASN MENTION IN THE ORD AND RFD TAFS...WITH SUBSEQUENT UPDATES
LIKELY TO ADD SOME BETTER DETAIL TO THIS POTENTIAL ON MONDAY.
WINDS ARE EXPECTED TO REMAIN CLOSE TO DUE NORTHERLY AND GUSTY
THROUGH THE AFTERNOON...THOUGH A SLOW DIMINISHING TREND IN SPEEDS
AND GUST MAGNITUDES IS PROBABLE.

RC


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

* HIGH CONFIDENCE IN EAST WINDS THROUGH EARLY TO MID EVENING...MEDIUM
  CONFIDENCE IN TIMING OF SHIFT BACK TO SOUTH-SOUTHWEST THIS
  EVENING.

* HIGH CONFIDENCE IN IFR CIGS MOVING IN BY 19Z.

* MEDIUM IN VSBY LOWERING TO MVFR OR IFR IN BR...MEDIUM IN
  TIMING...AND MEDIUM HIGH IN POTENTIAL FOR IFR VSBY IN HEAVIEST
  SHRA/TSRA.

* MEDIUM CONFIDENCE IN OVERALL SHRA/TSRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH HIGH CONFIDENCE THERE WILL BE AT
  LEAST OCNL TSRA AT THE TERMINALS THIS AFTERNOON AND EVENING.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

* LOW CONFIDENCE IN POTENTIAL FOR RASN MIX OR CHANGE TO SN AND
  ASSOCIATED VSBY/CIG IMPACTS MONDAY AFTERNOON.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
317 AM CDT

HEADLINES...WILL UPGRADE THE GALE WATCHES TO WARNINGS AS GALES ARE
STILL EXPECTED.

LOW PRESSURE IS OVER THE OK PANHANDLE EARLY THIS MORNING WITH A
BROAD TROUGH EXTENDING ALL THE WAY THROUGH THE IL/WI STATE LINE.
THERE IS A FRONT IN THE TROUGH BUT IT HOLDS A VARIETY OF FORMS AKA
COLD/STATIONARY/WARM AS YOU MOVE ALONG IT...SO WILL REFER TO IT AS A
TROUGH FOR SIMPLICITY.  THE FRONT WILL MEANDER OVER THE FAR SOUTHERN
END OF THE LAKE THIS MORNING WHILE THE LOW MOVES UP THE TROUGH AND
PASSES OVER THE SOUTHERN END OF THE LAKE THIS EVENING.  NORTH GALES
WILL DEVELOP BEHIND THE LOW AND EXTEND THROUGH THE NSH WATERS
TONIGHT AND THROUGH MID AFTN MONDAY.  WINDS CONTINUE TO DIMINISH
THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE
TUESDAY NIGHT.  WINDS TURN SOUTH BEHIND THE RIDGE AND INCREASE TO 30
KT AS A WEAKENING TROUGH OF LOW PRESSURE APPROACHES WEDNESDAY.  THE
TROUGH PASSES OVER THE LAKE THURSDAY WITH NORTHEAST TO EAST WINDS
BEHIND IT.  GUIDANCE THEN FEATURES EXTREME DIFFERENCES IN THE
PATTERN LATE IN THE WEEK SO HAVE LOW CONFIDENCE IN THE FORECAST PAST
THURSDAY.  FOR REFERENCE THE ECMWF FEATURES A HIGH MOVING OVER THE
LAKE LATE THIS WEEK WHILE THE GFS HAS A LOW MOVING UP THE LAKE AT
THE SAME TIME.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 PM SUNDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 PM SUNDAY TO 4
     AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 131653
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1153 AM CDT SUN APR 13 2014

.DISCUSSION...
1153 AM CDT

FOR MORNING UPDATE...

HAVE MADE SOME ADJUSTMENTS TO FORECAST THROUGH THIS AFTERNOON BASED
ON OBS/RADAR TRENDS THIS MORNING. MOST NOTABLY...COLD FRONTAL
BOUNDARY HAS SETTLED ACROSS FAR NORTHERN/NORTHEAST IL ESPEICALLY
NEAR LAKE MICHIGAN IN THE WAKE OF WEAK LOW PRESSURE WAVE MOVING OUT
OF LOWER MICHIGAN. WINDS VEERING TO NORTHEAST OFF THE CHILLY LAKE
WATERS WERE DROPPING TEMPS INTO THE MID-40S ALONG THE SHORE AND
PRODUCING AREAS OF FOG WITH VISIBILITY DROPPING BELOW A MILE. HAVE
THEREFORE ADJUSTED MAX TEMPS DOWN ACROSS FAR NORTHEAST IL AND HAVE
TRIED TO CAPTURE THE EXPECTED STEADY/COOLING TREND IN THE HOURLY
TEMP FORECAST ALONG THE LAKE THROUGH THIS AFTERNOON.

OTHERWISE...HAVE ALSO BEEN MONITORING AREA OF RAIN/EMBEDDED THUNDER
ACROSS A GOOD PORTION OF IA/MO AND WESTERN IL. AFTER EARLY
SUBSIDENCE IN THE WAKE OF EARLY MORNING SHORT WAVE AND MCS...THIS
AREA OF PRECIP SHOULD CONTNUE TO SPREAD SLOWLY NORTHEAST ACROSS THE
CWA THIS AFTERNOON BRINGING RAIN BACK TO THE AREA. MID-LEVEL LASPE
RATES ARE A LITTLE MUSHY...THOUGH EMBEDDED THUNDER EXPECTED AT TIMES
ESPECIALLY LATER THIS AFTERNOON/TONIGHT AS LARGE SCALE FORCING
BECOMES STRONGER WITH APPROACH OF MID-LEVEL SHORT WAVE FROM THE
OK/KS PLAINS REGION. PERIODS OF RAIN/THUNDER AND POTENTIALLY SOME
HEAVY RAINFALL STILL LOOKS TO BE ON TRACK FOR TONIGHT AS SFC LOW AND
FRONTAL SYSTEM MOVE THROUGH THE AREA ALONG WITH MID-LEVEL TROUGH.

RATZER

&&

.PREV DISCUSSION...
417 AM CDT

TODAY...
EARLY THIS MORNING LOW PRESSURE LIES OVER IOWA WITH A WARM FRONT
EXTENDING EAST ACROSS FAR NORTHERN ILLINOIS. THE BOUNDARY WAS DRIVEN
SOUTH OVERNIGHT BY CONVECTION/OUTFLOW. ON THE WARM SIDE OF THE
FRONT...TEMPERATURES REMAINED IN THE 60S OVERNIGHT...BUT NORTH OF
THE FRONT TEMPS QUICKLY FALL OFF INTO THE 40S AND THIS TIGHT THERMAL
GRADIENT WILL HOVER ACROSS NORTHERN COUNTIES OF THE STATE THIS
MORNING. AS FOR CONVECTION THIS MORNING...THUNDERSTORMS HAVE MOVED
EAST OVER LAKE MICHIGAN THIS MORNING WITH STABLE CONDITIONS IN THEIR
WAKE AND EXPECT QUIET CONDITIONS TO PERSIST THROUGH THE REMAINDER OF
THE MORNING AND EARLY AFTERNOON. COUPLED JET STILL PROGGED TO
DEVELOP THIS AFTERNOON WITH MODERATE TO STRONG UPPER LEVEL
DIVERGENCE RESULTING IN CYCLOGENENSIS ALONG THE MID MISSISSIPPI
VALLEY. ISENTROPIC ASCENT WILL INCREASE THROUGH THE LATE MORNING
INTO THE AFTERNOON WITH PRECIP OVERSPREADING NORTHERN ILLINOIS FROM
THE WEST. SOUNDINGS STILL INDICATE DEEP SATURATED LAYER WITH PWATS
PUSHING TO AROUND 1.4-1.5 INCHES. MODELS IN DECENT AGREEMENT ON
PLACEMENT OF AXIS OF HEAVIEST RAIN THIS EVENING AND TONIGHT...
STRETCHING FROM EASTERN IOWA TO EAST-CENTRAL WISCONSIN AND CLIPPING
NORTH CENTRAL ILLINOIS INCLUDING THE ROCKFORD AREA. HEAVY PRECIP
REMAINS A CONCERN THOUGH PRECIP SO FAR HAS UNDERPERFORMED FROM PRIOR
EXPECTATIONS AND A PROLONGED PERIOD OF DRY WEATHER OVER NORTH
CENTRAL ILLINOIS THE PAST SEVERAL WEEKS WILL HELP MITIGATE THE FLOOD
THREAT TO SOME DEGREE.

MONDAY...
LONGWAVE TROUGH AXIS WILL TRANSLATE EAST ACROSS THE PLAINS MONDAY
REACHING THE MISSISSIPPI VALLEY BY THE EVENING. MEANWHILE...COLD
ADVECTION INTO THE AREA WILL DRIVE H85 TEMPS DOWN TO AROUND -11C AND
SEVERAL SMALLER SCALE DISTURBANCES LIFTING UP THE LEE SIDE OF THE
TROUGH WILL RESULT IN RAIN CHANGING OVER TO SNOW ACROSS THE AREA.
MODELS HAVE TRENDED MORE BULLISH WITH QPF MONDAY AND CANNOT RULE OUT
LIGHT ACCUMULATIONS AT THIS TIME...MAINLY DURING THE LATE AFTERNOON
INTO THE EVENING WHEN THE AREA IS BETTER ENTRENCHED IN THE COLD AIR.
HIGHS MAY STRUGGLE TO REACH INTO THE LOW 40S FOR MUCH OF THE CWA AND
A GUSTY NORTH WIND WILL MAKE IT FEEL CLOSER TO THE FREEZING MARK.

TUESDAY THROUGH SATURDAY...
GENERALLY QUIET WEATHER EXPECTED TUESDAY AND WEDNESDAY UNDER THE
INFLUENCE OF HIGH PRESSURE. BY WEDNESDAY...LOW PRESSURE OVER THE
PLAINS WILL HELP SPREAD WARM AIR BACK INTO THE MIDWEST WITH A
WARMING TREND THROUGH THURSDAY WHEN TEMPERATURE SHOULD BE CLOSER TO
NORMAL. MORE ACTIVE WEATHER MAY RETURN LATE IN THE WEEK INTO THE
WEEKEND AS ANOTHER SOUTHWEST LOW LIFTS ACROSS THE MIDWEST BRINGING
CHANCES FOR PRECIP AND FLUCTUATING TEMPERATURES.

BMD

&&

.AVIATION...

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

* WIND SHIFT TO NORTHEAST AROUND 10 KT ARRIVING BY 1630-17Z.

* IFR CIGS ARRIVING BY 18Z AND VSBY LOWERING TO AT LEAST MVFR AND
  POSSIBLY IFR BY 19Z.

* PERIODS OF SHRA/TSRA THIS AFTERNOON AND EVENING...HEAVIEST COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE THIS EVENING/OVERNIGHT.

RC

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

VERY COMPLEX FORECAST. WEAK PRESSURE PATTERN OVER AREA AT THE
MOMENT...WITH WEAK LOW PRESSURE OVER LOWER MICHIGAN AND FRONTAL
BOUNDARY SAGGING SOUTHWARD. MAIN CHANGE IN TAF WAS TO BRING SHIFT
TO EAST OR NORTHEAST WINDS TO ORD SOONER THAN PREVIOUS FCST AND
ALSO INCLUDE MDW IN WIND SHIFT. IT IS POSSIBLE THAT THIS SHIFT
COULD OCCUR AS SOON AS 17 OR 18Z. CONFIDENCE IS LOWER IN GYY
SEEING SHIFT TO NORTHEAST. IFR CIGS BEHIND THE FRONT ACROSS WI SO
THESE SHOULD DEVELOP SOMETIME AFTER THE SHIFT TO EASTERLY WINDS.
ITS POSSIBLE THAT WINDS WILL REMAIN EASTERLY UNTIL EARLY EVENING
NOW AT ORD/MDW. OTHER CHALLENGE IS WITH SHRA/TSRA TRENDS...AS A
COMPLEX LIFTS NORTHEAST FROM IOWA. IT APPEARS THAT THE SHOWERS AND
AT LEAST OCNL EMBEDDED THUNDER WILL ARRIVE A BIT SOONER AT THE
EASTERN TERMINALS...BUT DURATION COULD BE SHORTER THAN INDICATED
IN TEMPO GROUP IN TAF. WILL CONTINUE TO ASSESS OBSERVATIONAL AND
RADAR TRENDS FOR UPDATES TO WIND/CIG/AND SHRA/TSRA FORECAST.

FROM 12Z...

LOW PRESSURE IS OVER THE SOUTHERN PLAINS WITH A FRONT EXTENDING
THROUGH NORTHERN IL/SOUTHERN WI. THE FRONT WILL MEANDER TODAY AND
THINKING IT WILL IMPACT RFD...ORD...AND DPA. WINDS WILL TURN N TO
NE BEHIND THE FRONT...AND BE SOUTH AHEAD OF THE FRONT. RAIN AND
STORMS SPREAD NORTH ACROSS THE TERMINALS EARLY THIS AFTN WITH
CHANCES OF THUNDERSTORMS INCREASING LATE THIS AFTN INTO THIS
EVENING. CIGS WILL LOWER THIS EVENING TO IFR AND THE STRONGEST
SHOWERS AND TSRA WILL LIKELY PRODUCE IFR VSBY.

INSTABILITY WEAKENS AND SHIFTS SE AS THE LOW MOVES THROUGH THE
REGION LATE THIS EVENING. THEREFORE EXPECTING LIMITED TSRA LATE
THIS EVENING AND JUST SHRA OVERNIGHT. WINDS WILL ALSO TURN NORTH
BEHIND THE LOW AND BEGIN GUSTING. THE HIGHEST GUSTS WILL BE SEEN
AT GYY WITH MAX GUSTS OVER 35 KT PSBL. THE OTHER TERMINALS SHOULD
SEE GUSTS BTWN 25 AND 30 KT. THE LOWER ATMOSPHERE BEGINS TO DRY
MID MONDAY MORNING AND CIGS LIFT TO MVFR.

JEE

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

* HIGH CONFIDENCE IN WIND SHIFT TO NORTHEAST...LOW-MEDIUM CONFIDENCE IN
  TIMING OF SHIFT BACK TO SOUTH-SOUTHWEST THIS EVENING.

* HIGH CONFIDENCE IN IFR CIGS...MEDIUM-HIGH IN ARRIVAL BY
  1730-18Z.

* HIGH IN VSBY LOWERING TO MVFR IN BR...MEDIUM IN TIMING...AND
  MEDIUM IN POTENTIAL FOR IFR VSBY IN BR AND HEAVIEST SHRA/TSRA.

* MEDIUM CONFIDENCE IN OVERALL SHRA/TSRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH MEDIUM-HIGH CONFIDENCE THERE WILL
  BE AT LEAST OCNL TSRA AT THE TERMINALS BY MID AFTERNOON.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
317 AM CDT

HEADLINES...WILL UPGRADE THE GALE WATCHES TO WARNINGS AS GALES ARE
STILL EXPECTED.

LOW PRESSURE IS OVER THE OK PANHANDLE EARLY THIS MORNING WITH A
BROAD TROUGH EXTENDING ALL THE WAY THROUGH THE IL/WI STATE LINE.
THERE IS A FRONT IN THE TROUGH BUT IT HOLDS A VARIETY OF FORMS AKA
COLD/STATIONARY/WARM AS YOU MOVE ALONG IT...SO WILL REFER TO IT AS A
TROUGH FOR SIMPLICITY.  THE FRONT WILL MEANDER OVER THE FAR SOUTHERN
END OF THE LAKE THIS MORNING WHILE THE LOW MOVES UP THE TROUGH AND
PASSES OVER THE SOUTHERN END OF THE LAKE THIS EVENING.  NORTH GALES
WILL DEVELOP BEHIND THE LOW AND EXTEND THROUGH THE NSH WATERS
TONIGHT AND THROUGH MID AFTN MONDAY.  WINDS CONTINUE TO DIMINISH
THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE
TUESDAY NIGHT.  WINDS TURN SOUTH BEHIND THE RIDGE AND INCREASE TO 30
KT AS A WEAKENING TROUGH OF LOW PRESSURE APPROACHES WEDNESDAY.  THE
TROUGH PASSES OVER THE LAKE THURSDAY WITH NORTHEAST TO EAST WINDS
BEHIND IT.  GUIDANCE THEN FEATURES EXTREME DIFFERENCES IN THE
PATTERN LATE IN THE WEEK SO HAVE LOW CONFIDENCE IN THE FORECAST PAST
THURSDAY.  FOR REFERENCE THE ECMWF FEATURES A HIGH MOVING OVER THE
LAKE LATE THIS WEEK WHILE THE GFS HAS A LOW MOVING UP THE LAKE AT
THE SAME TIME.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...INDIANA NEARSHORE WATERS UNTIL 4 PM SUNDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 PM SUNDAY TO 4
     AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     DENSE FOG ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 131621
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1121 AM CDT SUN APR 13 2014

.DISCUSSION...
417 AM CDT

TODAY...
EARLY THIS MORNING LOW PRESSURE LIES OVER IOWA WITH A WARM FRONT
EXTENDING EAST ACROSS FAR NORTHERN ILLINOIS. THE BOUNDARY WAS DRIVEN
SOUTH OVERNIGHT BY CONVECTION/OUTFLOW. ON THE WARM SIDE OF THE
FRONT...TEMPERATURES REMAINED IN THE 60S OVERNIGHT...BUT NORTH OF
THE FRONT TEMPS QUICKLY FALL OFF INTO THE 40S AND THIS TIGHT THERMAL
GRADIENT WILL HOVER ACROSS NORTHERN COUNTIES OF THE STATE THIS
MORNING. AS FOR CONVECTION THIS MORNING...THUNDERSTORMS HAVE MOVED
EAST OVER LAKE MICHIGAN THIS MORNING WITH STABLE CONDITIONS IN THEIR
WAKE AND EXPECT QUIET CONDITIONS TO PERSIST THROUGH THE REMAINDER OF
THE MORNING AND EARLY AFTERNOON. COUPLED JET STILL PROGGED TO
DEVELOP THIS AFTERNOON WITH MODERATE TO STRONG UPPER LEVEL
DIVERGENCE RESULTING IN CYCLOGENENSIS ALONG THE MID MISSISSIPPI
VALLEY. ISENTROPIC ASCENT WILL INCREASE THROUGH THE LATE MORNING
INTO THE AFTERNOON WITH PRECIP OVERSPREADING NORTHERN ILLINOIS FROM
THE WEST. SOUNDINGS STILL INDICATE DEEP SATURATED LAYER WITH PWATS
PUSHING TO AROUND 1.4-1.5 INCHES. MODELS IN DECENT AGREEMENT ON
PLACEMENT OF AXIS OF HEAVIEST RAIN THIS EVENING AND TONIGHT...
STRETCHING FROM EASTERN IOWA TO EAST-CENTRAL WISCONSIN AND CLIPPING
NORTH CENTRAL ILLINOIS INCLUDING THE ROCKFORD AREA. HEAVY PRECIP
REMAINS A CONCERN THOUGH PRECIP SO FAR HAS UNDERPERFORMED FROM PRIOR
EXPECTATIONS AND A PROLONGED PERIOD OF DRY WEATHER OVER NORTH
CENTRAL ILLINOIS THE PAST SEVERAL WEEKS WILL HELP MITIGATE THE FLOOD
THREAT TO SOME DEGREE.

MONDAY...
LONGWAVE TROUGH AXIS WILL TRANSLATE EAST ACROSS THE PLAINS MONDAY
REACHING THE MISSISSIPPI VALLEY BY THE EVENING. MEANWHILE...COLD
ADVECTION INTO THE AREA WILL DRIVE H85 TEMPS DOWN TO AROUND -11C AND
SEVERAL SMALLER SCALE DISTURBANCES LIFTING UP THE LEE SIDE OF THE
TROUGH WILL RESULT IN RAIN CHANGING OVER TO SNOW ACROSS THE AREA.
MODELS HAVE TRENDED MORE BULLISH WITH QPF MONDAY AND CANNOT RULE OUT
LIGHT ACCUMULATIONS AT THIS TIME...MAINLY DURING THE LATE AFTERNOON
INTO THE EVENING WHEN THE AREA IS BETTER ENTRENCHED IN THE COLD AIR.
HIGHS MAY STRUGGLE TO REACH INTO THE LOW 40S FOR MUCH OF THE CWA AND
A GUSTY NORTH WIND WILL MAKE IT FEEL CLOSER TO THE FREEZING MARK.

TUESDAY THROUGH SATURDAY...
GENERALLY QUIET WEATHER EXPECTED TUESDAY AND WEDNESDAY UNDER THE
INFLUENCE OF HIGH PRESSURE. BY WEDNESDAY...LOW PRESSURE OVER THE
PLAINS WILL HELP SPREAD WARM AIR BACK INTO THE MIDWEST WITH A
WARMING TREND THROUGH THURSDAY WHEN TEMPERATURE SHOULD BE CLOSER TO
NORMAL. MORE ACTIVE WEATHER MAY RETURN LATE IN THE WEEK INTO THE
WEEKEND AS ANOTHER SOUTHWEST LOW LIFTS ACROSS THE MIDWEST BRINGING
CHANCES FOR PRECIP AND FLUCTUATING TEMPERATURES.

BMD

&&

.AVIATION...

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

* WIND SHIFT TO NORTHEAST AROUND 10 KT ARRIVING BY 1630-17Z.

* IFR CIGS ARRIVING BY 18Z AND VSBY LOWERING TO AT LEAST MVFR AND
  POSSIBLY IFR BY 19Z.

* PERIODS OF SHRA/TSRA THIS AFTERNOON AND EVENING...HEAVIEST COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE THIS EVENING/OVERNIGHT.

RC

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

VERY COMPLEX FORECAST. WEAK PRESSURE PATTERN OVER AREA AT THE
MOMENT...WITH WEAK LOW PRESSURE OVER LOWER MICHIGAN AND FRONTAL
BOUNDARY SAGGING SOUTHWARD. MAIN CHANGE IN TAF WAS TO BRING SHIFT
TO EAST OR NORTHEAST WINDS TO ORD SOONER THAN PREVIOUS FCST AND
ALSO INCLUDE MDW IN WIND SHIFT. IT IS POSSIBLE THAT THIS SHIFT
COULD OCCUR AS SOON AS 17 OR 18Z. CONFIDENCE IS LOWER IN GYY
SEEING SHIFT TO NORTHEAST. IFR CIGS BEHIND THE FRONT ACROSS WI SO
THESE SHOULD DEVELOP SOMETIME AFTER THE SHIFT TO EASTERLY WINDS.
ITS POSSIBLE THAT WINDS WILL REMAIN EASTERLY UNTIL EARLY EVENING
NOW AT ORD/MDW. OTHER CHALLENGE IS WITH SHRA/TSRA TRENDS...AS A
COMPLEX LIFTS NORTHEAST FROM IOWA. IT APPEARS THAT THE SHOWERS AND
AT LEAST OCNL EMBEDDED THUNDER WILL ARRIVE A BIT SOONER AT THE
EASTERN TERMINALS...BUT DURATION COULD BE SHORTER THAN INDICATED
IN TEMPO GROUP IN TAF. WILL CONTINUE TO ASSESS OBSERVATIONAL AND
RADAR TRENDS FOR UPDATES TO WIND/CIG/AND SHRA/TSRA FORECAST.

FROM 12Z...

LOW PRESSURE IS OVER THE SOUTHERN PLAINS WITH A FRONT EXTENDING
THROUGH NORTHERN IL/SOUTHERN WI. THE FRONT WILL MEANDER TODAY AND
THINKING IT WILL IMPACT RFD...ORD...AND DPA. WINDS WILL TURN N TO
NE BEHIND THE FRONT...AND BE SOUTH AHEAD OF THE FRONT. RAIN AND
STORMS SPREAD NORTH ACROSS THE TERMINALS EARLY THIS AFTN WITH
CHANCES OF THUNDERSTORMS INCREASING LATE THIS AFTN INTO THIS
EVENING. CIGS WILL LOWER THIS EVENING TO IFR AND THE STRONGEST
SHOWERS AND TSRA WILL LIKELY PRODUCE IFR VSBY.

INSTABILITY WEAKENS AND SHIFTS SE AS THE LOW MOVES THROUGH THE
REGION LATE THIS EVENING. THEREFORE EXPECTING LIMITED TSRA LATE
THIS EVENING AND JUST SHRA OVERNIGHT. WINDS WILL ALSO TURN NORTH
BEHIND THE LOW AND BEGIN GUSTING. THE HIGHEST GUSTS WILL BE SEEN
AT GYY WITH MAX GUSTS OVER 35 KT PSBL. THE OTHER TERMINALS SHOULD
SEE GUSTS BTWN 25 AND 30 KT. THE LOWER ATMOSPHERE BEGINS TO DRY
MID MONDAY MORNING AND CIGS LIFT TO MVFR.

JEE

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

* HIGH CONFIDENCE IN WIND SHIFT TO NORTHEAST...LOW-MEDIUM CONFIDENCE IN
  TIMING OF SHIFT BACK TO SOUTH-SOUTHWEST THIS EVENING.

* HIGH CONFIDENCE IN IFR CIGS...MEDIUM-HIGH IN ARRIVAL BY
  1730-18Z.

* HIGH IN VSBY LOWERING TO MVFR IN BR...MEDIUM IN TIMING...AND
  MEDIUM IN POTENTIAL FOR IFR VSBY IN BR AND HEAVIEST SHRA/TSRA.

* MEDIUM CONFIDENCE IN OVERALL SHRA/TSRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH MEDIUM-HIGH CONFIDENCE THERE WILL
  BE AT LEAST OCNL TSRA AT THE TERMINALS BY MID AFTERNOON.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
317 AM CDT

HEADLINES...WILL UPGRADE THE GALE WATCHES TO WARNINGS AS GALES ARE
STILL EXPECTED.

LOW PRESSURE IS OVER THE OK PANHANDLE EARLY THIS MORNING WITH A
BROAD TROUGH EXTENDING ALL THE WAY THROUGH THE IL/WI STATE LINE.
THERE IS A FRONT IN THE TROUGH BUT IT HOLDS A VARIETY OF FORMS AKA
COLD/STATIONARY/WARM AS YOU MOVE ALONG IT...SO WILL REFER TO IT AS A
TROUGH FOR SIMPLICITY.  THE FRONT WILL MEANDER OVER THE FAR SOUTHERN
END OF THE LAKE THIS MORNING WHILE THE LOW MOVES UP THE TROUGH AND
PASSES OVER THE SOUTHERN END OF THE LAKE THIS EVENING.  NORTH GALES
WILL DEVELOP BEHIND THE LOW AND EXTEND THROUGH THE NSH WATERS
TONIGHT AND THROUGH MID AFTN MONDAY.  WINDS CONTINUE TO DIMINISH
THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE
TUESDAY NIGHT.  WINDS TURN SOUTH BEHIND THE RIDGE AND INCREASE TO 30
KT AS A WEAKENING TROUGH OF LOW PRESSURE APPROACHES WEDNESDAY.  THE
TROUGH PASSES OVER THE LAKE THURSDAY WITH NORTHEAST TO EAST WINDS
BEHIND IT.  GUIDANCE THEN FEATURES EXTREME DIFFERENCES IN THE
PATTERN LATE IN THE WEEK SO HAVE LOW CONFIDENCE IN THE FORECAST PAST
THURSDAY.  FOR REFERENCE THE ECMWF FEATURES A HIGH MOVING OVER THE
LAKE LATE THIS WEEK WHILE THE GFS HAS A LOW MOVING UP THE LAKE AT
THE SAME TIME.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 PM SUNDAY TO 4
     AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 131435
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
935 AM CDT SUN APR 13 2014

.DISCUSSION...
417 AM CDT

TODAY...
EARLY THIS MORNING LOW PRESSURE LIES OVER IOWA WITH A WARM FRONT
EXTENDING EAST ACROSS FAR NORTHERN ILLINOIS. THE BOUNDARY WAS DRIVEN
SOUTH OVERNIGHT BY CONVECTION/OUTFLOW. ON THE WARM SIDE OF THE
FRONT...TEMPERATURES REMAINED IN THE 60S OVERNIGHT...BUT NORTH OF
THE FRONT TEMPS QUICKLY FALL OFF INTO THE 40S AND THIS TIGHT THERMAL
GRADIENT WILL HOVER ACROSS NORTHERN COUNTIES OF THE STATE THIS
MORNING. AS FOR CONVECTION THIS MORNING...THUNDERSTORMS HAVE MOVED
EAST OVER LAKE MICHIGAN THIS MORNING WITH STABLE CONDITIONS IN THEIR
WAKE AND EXPECT QUIET CONDITIONS TO PERSIST THROUGH THE REMAINDER OF
THE MORNING AND EARLY AFTERNOON. COUPLED JET STILL PROGGED TO
DEVELOP THIS AFTERNOON WITH MODERATE TO STRONG UPPER LEVEL
DIVERGENCE RESULTING IN CYCLOGENENSIS ALONG THE MID MISSISSIPPI
VALLEY. ISENTROPIC ASCENT WILL INCREASE THROUGH THE LATE MORNING
INTO THE AFTERNOON WITH PRECIP OVERSPREADING NORTHERN ILLINOIS FROM
THE WEST. SOUNDINGS STILL INDICATE DEEP SATURATED LAYER WITH PWATS
PUSHING TO AROUND 1.4-1.5 INCHES. MODELS IN DECENT AGREEMENT ON
PLACEMENT OF AXIS OF HEAVIEST RAIN THIS EVENING AND TONIGHT...
STRETCHING FROM EASTERN IOWA TO EAST-CENTRAL WISCONSIN AND CLIPPING
NORTH CENTRAL ILLINOIS INCLUDING THE ROCKFORD AREA. HEAVY PRECIP
REMAINS A CONCERN THOUGH PRECIP SO FAR HAS UNDERPERFORMED FROM PRIOR
EXPECTATIONS AND A PROLONGED PERIOD OF DRY WEATHER OVER NORTH
CENTRAL ILLINOIS THE PAST SEVERAL WEEKS WILL HELP MITIGATE THE FLOOD
THREAT TO SOME DEGREE.

MONDAY...
LONGWAVE TROUGH AXIS WILL TRANSLATE EAST ACROSS THE PLAINS MONDAY
REACHING THE MISSISSIPPI VALLEY BY THE EVENING. MEANWHILE...COLD
ADVECTION INTO THE AREA WILL DRIVE H85 TEMPS DOWN TO AROUND -11C AND
SEVERAL SMALLER SCALE DISTURBANCES LIFTING UP THE LEE SIDE OF THE
TROUGH WILL RESULT IN RAIN CHANGING OVER TO SNOW ACROSS THE AREA.
MODELS HAVE TRENDED MORE BULLISH WITH QPF MONDAY AND CANNOT RULE OUT
LIGHT ACCUMULATIONS AT THIS TIME...MAINLY DURING THE LATE AFTERNOON
INTO THE EVENING WHEN THE AREA IS BETTER ENTRENCHED IN THE COLD AIR.
HIGHS MAY STRUGGLE TO REACH INTO THE LOW 40S FOR MUCH OF THE CWA AND
A GUSTY NORTH WIND WILL MAKE IT FEEL CLOSER TO THE FREEZING MARK.

TUESDAY THROUGH SATURDAY...
GENERALLY QUIET WEATHER EXPECTED TUESDAY AND WEDNESDAY UNDER THE
INFLUENCE OF HIGH PRESSURE. BY WEDNESDAY...LOW PRESSURE OVER THE
PLAINS WILL HELP SPREAD WARM AIR BACK INTO THE MIDWEST WITH A
WARMING TREND THROUGH THURSDAY WHEN TEMPERATURE SHOULD BE CLOSER TO
NORMAL. MORE ACTIVE WEATHER MAY RETURN LATE IN THE WEEK INTO THE
WEEKEND AS ANOTHER SOUTHWEST LOW LIFTS ACROSS THE MIDWEST BRINGING
CHANCES FOR PRECIP AND FLUCTUATING TEMPERATURES.

BMD

&&

.AVIATION...

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

* SHIFT TO EAST OR NORTHEAST WINDS UP TO 10 KT EARLY THIS
  AFTERNOON CONTINUING UNTIL EARLY EVENING. CURRENT TIMING COULD
  BE A FEW HRS EARLIER.

* IFR CIGS BEHIND WIND SHIFT.

* PERIODS OF SHRA/TSRA THIS AFTERNOON AND EVENING...HEAVIEST COULD PRODUCE
  IFR VSBY.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE THIS EVENING/OVERNIGHT.

RC

//DISCUSSION...UPDATED 14Z...

VERY COMPLEX FORECAST. WEAK PRESSURE PATTERN OVER AREA AT THE
MOMENT...WITH WEAK LOW PRESSURE OVER LOWER MICHIGAN AND FRONTAL
BOUNDARY SAGGING SOUTHWARD. MAIN CHANGE IN TAF WAS TO BRING SHIFT
TO EAST OR NORTHEAST WINDS TO ORD SOONER THAN PREVIOUS FCST AND
ALSO INCLUDE MDW IN WIND SHIFT. IT IS POSSIBLE THAT THIS SHIFT
COULD OCCUR AS SOON AS 17 OR 18Z. CONFIDENCE IS LOWER IN GYY
SEEING SHIFT TO NORTHEAST. IFR CIGS BEHIND THE FRONT ACROSS WI SO
THESE SHOULD DEVELOP SOMETIME AFTER THE SHIFT TO EASTERLY WINDS.
ITS POSSIBLE THAT WINDS WILL REMAIN EASTERLY UNTIL EARLY EVENING
NOW AT ORD/MDW. OTHER CHALLENGE IS WITH SHRA/TSRA TRENDS...AS A
COMPLEX LIFTS NORTHEAST FROM IOWA. IT APPEARS THAT THE SHOWERS AND
AT LEAST OCNL EMBEDDED THUNDER WILL ARRIVE A BIT SOONER AT THE
EASTERN TERMINALS...BUT DURATION COULD BE SHORTER THAN INDICATED
IN TEMPO GROUP IN TAF. WILL CONTINUE TO ASSESS OBSERVATIONAL AND
RADAR TRENDS FOR UPDATES TO WIND/CIG/AND SHRA/TSRA FORECAST.

FROM 12Z...

LOW PRESSURE IS OVER THE SOUTHERN PLAINS WITH A FRONT EXTENDING
THROUGH NORTHERN IL/SOUTHERN WI. THE FRONT WILL MEANDER TODAY AND
THINKING IT WILL IMPACT RFD...ORD...AND DPA. WINDS WILL TURN N TO
NE BEHIND THE FRONT...AND BE SOUTH AHEAD OF THE FRONT. RAIN AND
STORMS SPREAD NORTH ACROSS THE TERMINALS EARLY THIS AFTN WITH
CHANCES OF THUNDERSTORMS INCREASING LATE THIS AFTN INTO THIS
EVENING. CIGS WILL LOWER THIS EVENING TO IFR AND THE STRONGEST
SHOWERS AND TSRA WILL LIKELY PRODUCE IFR VSBY.

INSTABILITY WEAKENS AND SHIFTS SE AS THE LOW MOVES THROUGH THE
REGION LATE THIS EVENING. THEREFORE EXPECTING LIMITED TSRA LATE
THIS EVENING AND JUST SHRA OVERNIGHT. WINDS WILL ALSO TURN NORTH
BEHIND THE LOW AND BEGIN GUSTING. THE HIGHEST GUSTS WILL BE SEEN
AT GYY WITH MAX GUSTS OVER 35 KT PSBL. THE OTHER TERMINALS SHOULD
SEE GUSTS BTWN 25 AND 30 KT. THE LOWER ATMOSPHERE BEGINS TO DRY
MID MONDAY MORNING AND CIGS LIFT TO MVFR.

JEE

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

* MEDIUM CONFIDENCE IN SHIFT TO EAST OR NORTHEAST WINDS AT BOTH
  ORD AND MDW...LOW CONFIDENCE IN EXACT TIMING OF SHIFT TO
  EAST/NORTHEAST AND BACK TO SOUTH-SOUTHWEST EARLY THIS EVENING.

* MEDIUM CONFIDENCE IN IFR CIGS MOVING IN AFTER WIND SHIFT...LOW-
  MEDIUM CONFIDENCE IN TIMING.

* MEDIUM CONFIDENCE IN OVERALL SHRA/TSRA TRENDS AND TIMING THIS
  AFTERNOON AND EVENING...WITH HIGH CONFIDENCE THERE WILL BE AT
  LEAST OCNL TSRA AT THE TERMINALS.

* MEDIUM CONFIDENCE IN IFR VSBY WITH HEAVIEST SHRA/TSRA.

* HIGH CONFIDENCE IN SHIFT TO GUSTY NORTHERLY WINDS LATE
  TONIGHT...MEDIUM IN TIMING.

RC

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
317 AM CDT

HEADLINES...WILL UPGRADE THE GALE WATCHES TO WARNINGS AS GALES ARE
STILL EXPECTED.

LOW PRESSURE IS OVER THE OK PANHANDLE EARLY THIS MORNING WITH A
BROAD TROUGH EXTENDING ALL THE WAY THROUGH THE IL/WI STATE LINE.
THERE IS A FRONT IN THE TROUGH BUT IT HOLDS A VARIETY OF FORMS AKA
COLD/STATIONARY/WARM AS YOU MOVE ALONG IT...SO WILL REFER TO IT AS A
TROUGH FOR SIMPLICITY.  THE FRONT WILL MEANDER OVER THE FAR SOUTHERN
END OF THE LAKE THIS MORNING WHILE THE LOW MOVES UP THE TROUGH AND
PASSES OVER THE SOUTHERN END OF THE LAKE THIS EVENING.  NORTH GALES
WILL DEVELOP BEHIND THE LOW AND EXTEND THROUGH THE NSH WATERS
TONIGHT AND THROUGH MID AFTN MONDAY.  WINDS CONTINUE TO DIMINISH
THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE
TUESDAY NIGHT.  WINDS TURN SOUTH BEHIND THE RIDGE AND INCREASE TO 30
KT AS A WEAKENING TROUGH OF LOW PRESSURE APPROACHES WEDNESDAY.  THE
TROUGH PASSES OVER THE LAKE THURSDAY WITH NORTHEAST TO EAST WINDS
BEHIND IT.  GUIDANCE THEN FEATURES EXTREME DIFFERENCES IN THE
PATTERN LATE IN THE WEEK SO HAVE LOW CONFIDENCE IN THE FORECAST PAST
THURSDAY.  FOR REFERENCE THE ECMWF FEATURES A HIGH MOVING OVER THE
LAKE LATE THIS WEEK WHILE THE GFS HAS A LOW MOVING UP THE LAKE AT
THE SAME TIME.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 PM SUNDAY TO 4
     AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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

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







000
FXUS63 KLOT 131207
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
707 AM CDT SUN APR 13 2014

.DISCUSSION...
417 AM CDT

TODAY...
EARLY THIS MORNING LOW PRESSURE LIES OVER IOWA WITH A WARM FRONT
EXTENDING EAST ACROSS FAR NORTHERN ILLINOIS. THE BOUNDARY WAS DRIVEN
SOUTH OVERNIGHT BY CONVECTION/OUTFLOW. ON THE WARM SIDE OF THE
FRONT...TEMPERATURES REMAINED IN THE 60S OVERNIGHT...BUT NORTH OF
THE FRONT TEMPS QUICKLY FALL OFF INTO THE 40S AND THIS TIGHT THERMAL
GRADIENT WILL HOVER ACROSS NORTHERN COUNTIES OF THE STATE THIS
MORNING. AS FOR CONVECTION THIS MORNING...THUNDERSTORMS HAVE MOVED
EAST OVER LAKE MICHIGAN THIS MORNING WITH STABLE CONDITIONS IN THEIR
WAKE AND EXPECT QUIET CONDITIONS TO PERSIST THROUGH THE REMAINDER OF
THE MORNING AND EARLY AFTERNOON. COUPLED JET STILL PROGGED TO
DEVELOP THIS AFTERNOON WITH MODERATE TO STRONG UPPER LEVEL
DIVERGENCE RESULTING IN CYCLOGENENSIS ALONG THE MID MISSISSIPPI
VALLEY. ISENTROPIC ASCENT WILL INCREASE THROUGH THE LATE MORNING
INTO THE AFTERNOON WITH PRECIP OVERSPREADING NORTHERN ILLINOIS FROM
THE WEST. SOUNDINGS STILL INDICATE DEEP SATURATED LAYER WITH PWATS
PUSHING TO AROUND 1.4-1.5 INCHES. MODELS IN DECENT AGREEMENT ON
PLACEMENT OF AXIS OF HEAVIEST RAIN THIS EVENING AND TONIGHT...
STRETCHING FROM EASTERN IOWA TO EAST-CENTRAL WISCONSIN AND CLIPPING
NORTH CENTRAL ILLINOIS INCLUDING THE ROCKFORD AREA. HEAVY PRECIP
REMAINS A CONCERN THOUGH PRECIP SO FAR HAS UNDERPERFORMED FROM PRIOR
EXPECTATIONS AND A PROLONGED PERIOD OF DRY WEATHER OVER NORTH
CENTRAL ILLINOIS THE PAST SEVERAL WEEKS WILL HELP MITIGATE THE FLOOD
THREAT TO SOME DEGREE.

MONDAY...
LONGWAVE TROUGH AXIS WILL TRANSLATE EAST ACROSS THE PLAINS MONDAY
REACHING THE MISSISSIPPI VALLEY BY THE EVENING. MEANWHILE...COLD
ADVECTION INTO THE AREA WILL DRIVE H85 TEMPS DOWN TO AROUND -11C AND
SEVERAL SMALLER SCALE DISTURBANCES LIFTING UP THE LEE SIDE OF THE
TROUGH WILL RESULT IN RAIN CHANGING OVER TO SNOW ACROSS THE AREA.
MODELS HAVE TRENDED MORE BULLISH WITH QPF MONDAY AND CANNOT RULE OUT
LIGHT ACCUMULATIONS AT THIS TIME...MAINLY DURING THE LATE AFTERNOON
INTO THE EVENING WHEN THE AREA IS BETTER ENTRENCHED IN THE COLD AIR.
HIGHS MAY STRUGGLE TO REACH INTO THE LOW 40S FOR MUCH OF THE CWA AND
A GUSTY NORTH WIND WILL MAKE IT FEEL CLOSER TO THE FREEZING MARK.

TUESDAY THROUGH SATURDAY...
GENERALLY QUIET WEATHER EXPECTED TUESDAY AND WEDNESDAY UNDER THE
INFLUENCE OF HIGH PRESSURE. BY WEDNESDAY...LOW PRESSURE OVER THE
PLAINS WILL HELP SPREAD WARM AIR BACK INTO THE MIDWEST WITH A
WARMING TREND THROUGH THURSDAY WHEN TEMPERATURE SHOULD BE CLOSER TO
NORMAL. MORE ACTIVE WEATHER MAY RETURN LATE IN THE WEEK INTO THE
WEEKEND AS ANOTHER SOUTHWEST LOW LIFTS ACROSS THE MIDWEST BRINGING
CHANCES FOR PRECIP AND FLUCTUATING TEMPERATURES.

BMD

&&

.AVIATION...

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

* SECOND ROUND OF SHRA/TSRA ARRIVES EARLY THIS AFTN...WITH BEST
  CHANCE OF TSRA IN THE LATE AFTN/EVENING.

* POTENTIAL FOR MULTIPLE WIND SHIFTS OVERNIGHT THROUGH THIS
  EVENING.

* HEAVIER SHRA/TSRA MAY PRODUCE IFR VSBY.

* IFR CIGS EXPECTED LATE THIS AFTN/EARLY EVENING.

* WINDS TURN NORTH AND GUST TO 25-30 KT LATE THIS EVENING/OVERNIGHT.

JEE

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

LOW PRESSURE IS OVER THE SOUTHERN PLAINS WITH A FRONT EXTENDING
THROUGH NORTHERN IL/SOUTHERN WI. THE FRONT WILL MEANDER TODAY AND
THINKING IT WILL IMPACT RFD...ORD...AND DPA. WINDS WILL TURN N TO
NE BEHIND THE FRONT...AND BE SOUTH AHEAD OF THE FRONT. RAIN AND
STORMS SPREAD NORTH ACROSS THE TERMINALS EARLY THIS AFTN WITH
CHANCES OF THUNDERSTORMS INCREASING LATE THIS AFTN INTO THIS
EVENING. CIGS WILL LOWER THIS EVENING TO IFR AND THE STRONGEST
SHOWERS AND TSRA WILL LIKELY PRODUCE IFR VSBY.

INSTABILITY WEAKENS AND SHIFTS SE AS THE LOW MOVES THROUGH THE
REGION LATE THIS EVENING. THEREFORE EXPECTING LIMITED TSRA LATE
THIS EVENING AND JUST SHRA OVERNIGHT. WINDS WILL ALSO TURN NORTH
BEHIND THE LOW AND BEGIN GUSTING. THE HIGHEST GUSTS WILL BE SEEN
AT GYY WITH MAX GUSTS OVER 35 KT PSBL. THE OTHER TERMINALS SHOULD
SEE GUSTS BTWN 25 AND 30 KT. THE LOWER ATMOSPHERE BEGINS TO DRY
MID MONDAY MORNING AND CIGS LIFT TO MVFR.

JEE


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

* MEDIUM-HIGH CONFIDENCE IN WINDS REMAINING SOUTHERLY THROUGH THIS
  MORNING.

* HIGH CONFIDENCE IN WINDS SHIFTING DURING THE DAY...LOW
  CONFIDENCE IN WHEN AND HOW MANY WIND SHIFTS THERE WILL BE
  THROUGH THIS EVENING.

* MEDIUM-HIGH CONFIDENCE IN PRECIP CHANCES INCREASING LATE TODAY INTO
  THIS EVENING.

* HIGH CONFIDENCE IFR CONDITIONS DEVELOPING LATE TODAY OR THIS
  EVENING...BUT MEDIUM CONFIDENCE ON TIMING.

JEE

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

MONDAY NIGHT...-RASN PSBLY BCMG -SN AFTER MIDNIGHT. MVFR TO IFR
CIGS IMPROVING TO VFR.

TUESDAY...VFR.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF RAIN OVERNIGHT...MVFR/IFR CIGS PSBL OVERNIGHT.

FRIDAY...CHANCE OF RAIN...MVFR TO IFR CIGS PSBL.

SATURDAY...CHANCE OF RAIN.

JEE

&&

.MARINE...
317 AM CDT

HEADLINES...WILL UPGRADE THE GALE WATCHES TO WARNINGS AS GALES ARE
STILL EXPECTED.

LOW PRESSURE IS OVER THE OK PANHANDLE EARLY THIS MORNING WITH A
BROAD TROUGH EXTENDING ALL THE WAY THROUGH THE IL/WI STATE LINE.
THERE IS A FRONT IN THE TROUGH BUT IT HOLDS A VARIETY OF FORMS AKA
COLD/STATIONARY/WARM AS YOU MOVE ALONG IT...SO WILL REFER TO IT AS A
TROUGH FOR SIMPLICITY.  THE FRONT WILL MEANDER OVER THE FAR SOUTHERN
END OF THE LAKE THIS MORNING WHILE THE LOW MOVES UP THE TROUGH AND
PASSES OVER THE SOUTHERN END OF THE LAKE THIS EVENING.  NORTH GALES
WILL DEVELOP BEHIND THE LOW AND EXTEND THROUGH THE NSH WATERS
TONIGHT AND THROUGH MID AFTN MONDAY.  WINDS CONTINUE TO DIMINISH
THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE
TUESDAY NIGHT.  WINDS TURN SOUTH BEHIND THE RIDGE AND INCREASE TO 30
KT AS A WEAKENING TROUGH OF LOW PRESSURE APPROACHES WEDNESDAY.  THE
TROUGH PASSES OVER THE LAKE THURSDAY WITH NORTHEAST TO EAST WINDS
BEHIND IT.  GUIDANCE THEN FEATURES EXTREME DIFFERENCES IN THE
PATTERN LATE IN THE WEEK SO HAVE LOW CONFIDENCE IN THE FORECAST PAST
THURSDAY.  FOR REFERENCE THE ECMWF FEATURES A HIGH MOVING OVER THE
LAKE LATE THIS WEEK WHILE THE GFS HAS A LOW MOVING UP THE LAKE AT
THE SAME TIME.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...4 PM SUNDAY TO 4
     AM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

&&

$$

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FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 130920
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
420 AM CDT SUN APR 13 2014

.DISCUSSION...
417 AM CDT

TODAY...
EARLY THIS MORNING LOW PRESSURE LIES OVER IOWA WITH A WARM FRONT
EXTENDING EAST ACROSS FAR NORTHERN ILLINOIS. THE BOUNDARY WAS DRIVEN
SOUTH OVERNIGHT BY CONVECTION/OUTFLOW. ON THE WARM SIDE OF THE
FRONT...TEMPERATURES REMAINED IN THE 60S OVERNIGHT...BUT NORTH OF
THE FRONT TEMPS QUICKLY FALL OFF INTO THE 40S AND THIS TIGHT THERMAL
GRADIENT WILL HOVER ACROSS NORTHERN COUNTIES OF THE STATE THIS
MORNING. AS FOR CONVECTION THIS MORNING...THUNDERSTORMS HAVE MOVED
EAST OVER LAKE MICHIGAN THIS MORNING WITH STABLE CONDITIONS IN THEIR
WAKE AND EXPECT QUIET CONDITIONS TO PERSIST THROUGH THE REMAINDER OF
THE MORNING AND EARLY AFTERNOON. COUPLED JET STILL PROGGED TO
DEVELOP THIS AFTERNOON WITH MODERATE TO STRONG UPPER LEVEL
DIVERGENCE RESULTING IN CYCLOGENENSIS ALONG THE MID MISSISSIPPI
VALLEY. ISENTROPIC ASCENT WILL INCREASE THROUGH THE LATE MORNING
INTO THE AFTERNOON WITH PRECIP OVERSPREADING NORTHERN ILLINOIS FROM
THE WEST. SOUNDINGS STILL INDICATE DEEP SATURATED LAYER WITH PWATS
PUSHING TO AROUND 1.4-1.5 INCHES. MODELS IN DECENT AGREEMENT ON
PLACEMENT OF AXIS OF HEAVIEST RAIN THIS EVENING AND TONIGHT...
STRETCHING FROM EASTERN IOWA TO EAST-CENTRAL WISCONSIN AND CLIPPING
NORTH CENTRAL ILLINOIS INCLUDING THE ROCKFORD AREA. HEAVY PRECIP
REMAINS A CONCERN THOUGH PRECIP SO FAR HAS UNDERPERFORMED FROM PRIOR
EXPECTATIONS AND A PROLONGED PERIOD OF DRY WEATHER OVER NORTH
CENTRAL ILLINOIS THE PAST SEVERAL WEEKS WILL HELP MITIGATE THE FLOOD
THREAT TO SOME DEGREE.

MONDAY...
LONGWAVE TROUGH AXIS WILL TRANSLATE EAST ACROSS THE PLAINS MONDAY
REACHING THE MISSISSIPPI VALLEY BY THE EVENING. MEANWHILE...COLD
ADVECTION INTO THE AREA WILL DRIVE H85 TEMPS DOWN TO AROUND -11C AND
SEVERAL SMALLER SCALE DISTURBANCES LIFTING UP THE LEE SIDE OF THE
TROUGH WILL RESULT IN RAIN CHANGING OVER TO SNOW ACROSS THE AREA.
MODELS HAVE TRENDED MORE BULLISH WITH QPF MONDAY AND CANNOT RULE OUT
LIGHT ACCUMULATIONS AT THIS TIME...MAINLY DURING THE LATE AFTERNOON
INTO THE EVENING WHEN THE AREA IS BETTER ENTRENCHED IN THE COLD AIR.
HIGHS MAY STRUGGLE TO REACH INTO THE LOW 40S FOR MUCH OF THE CWA AND
A GUSTY NORTH WIND WILL MAKE IT FEEL CLOSER TO THE FREEZING MARK.

TUESDAY THROUGH SATURDAY...
GENERALLY QUIET WEATHER EXPECTED TUESDAY AND WEDNESDAY UNDER THE
INFLUENCE OF HIGH PRESSURE. BY WEDNESDAY...LOW PRESSURE OVER THE
PLAINS WILL HELP SPREAD WARM AIR BACK INTO THE MIDWEST WITH A
WARMING TREND THROUGH THURSDAY WHEN TEMPERATURE SHOULD BE CLOSER TO
NORMAL. MORE ACTIVE WEATHER MAY RETURN LATE IN THE WEEK INTO THE
WEEKEND AS ANOTHER SOUTHWEST LOW LIFTS ACROSS THE MIDWEST BRINGING
CHANCES FOR PRECIP AND FLUCTUATING TEMPERATURES.

BMD

&&

.AVIATION...

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

* SECOND ROUND OF SHRA/TSRA ARRIVES MID-DAY...WITH BEST CHANCE OF
  TSRA IN THE LATE AFTN/EVENING.

* POTENTIAL FOR MULTIPLE WIND SHIFTS OVERNIGHT THROUGH THIS
  EVENING

* INCREASING POTENTIAL FOR LOW MVFR-IFR CIGS VSBY LATE TODAY INTO
  TONIGHT WITH MVFR OR LOWER VSBY.

JEE

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

LINE OF TSRA STRETCHES ACROSS SOUTHERN WI AND THROUGH FAR EASTERN
IOWA. THE STORMS ARE WEAKENING SLOWER THAN ORIGINALLY
EXPECTED...BUT FINALLY STARTING TO LOOK LESS ORGANIZED. THE
TRAJECTORY OF THE STORMS WOULD BRING THE WEAKENED LINE ACROSS ALL
OF THE TERMINALS EXCEPT GYY. THINKING THE TSRA/SHRA WILL DISSIPATE
BEFORE REACHING GYY. LATEST WIND GUSTS BEHIND THE LINE ARE N TO NW
ARND 30 KT SO LEFT NORTH GUSTS IN AT RFD. BEHIND THE LINE WINDS
SHOULD GO VARIABLE FOR A FEW HOURS.

THE COLD FRONT HAS SHIFTED A BIT NORTH WITH UGN SHOWING A SOUTH
WIND. AS THE PREVIOUS FORECAST DISCUSSED...VERY VERY VERY LOW
CONFIDENCE IN WIND DIRECTION FOR THE EASTERN TERMINALS. THE COLD
FRONT COULD STILL SHIFT SOUTH IF THE LINE OF STORMS MOVES THROUGH.
THE MAJORITY OF GUIDANCE CONTINUES TO FEATURE SOUTH WINDS. SOME OF
THE HI-RES GUIDANCE ALSO CONTINUES TO INDICATE THE COLD FRONT
COULD MOVE AROUND TOMORROW AND TEMPORARILY SHIFT WINDS AT ORD NE.
WITH VERY LOW CONFIDENCE AND NO GOOD REASON TO MAKE CHANGES...LEFT
WINDS IN THE TAFS ALONE.

NEXT ROUND OF SHRA/TSRA MOVES IN EARLY IN THE AFTN WITH TSRA AND
HEAVY RAIN PSBL. PREVIOUS TIMING IN THE GRIDS LOOKED GOOD AND
THINKING A PROB30 FOR TSRA WAS THE BEST WAY TO HANDLE THE
SITUATION. MOVED THE POSSIBILITY OF IFR CIGS UP AS WELL AND
EXTENDED THE IFR CIGS THROUGH THE OVERNIGHT HOURS AS WELL.

JEE

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

* MEDIUM-HIGH CONFIDENCE IN WINDS REMAINING SOUTHERLY THROUGH THIS
  MORNING.

* ABSOLUTELY NO CONFIDENCE IN WIND DIRECTION FORECAST TODAY INTO
  THIS EVENING.

* MEDIUM CONFIDENCE IN PRECIP CHANCES INCREASING LATE TODAY INTO
  THIS EVENING.

* MEDIUM-HIGH CONFIDENCE IFR CONDITIONS DEVELOPING LATE TODAY OR
  THIS EVENING...BUT LOW CONFIDENCE ON TIMING.

JEE

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

MONDAY...RAIN LIKELY EARLY. IFR LIKELY. CHANCE OF RAIN OR SNOW MON
AFTERNOON AND EVENING. MODERATELY STRONG NORTH WINDS.

TUESDAY...MVFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY AND THURSDAY...VFR PROBABLE.

FRIDAY...CHANCE OF RAIN. IFR POSSIBLE.

IZZI

&&

.MARINE...
317 AM CDT

HEADLINES...WILL UPGRADE THE GALE WATCHES TO WARNINGS AS GALES ARE
STILL EXPECTED.

LOW PRESSURE IS OVER THE OK PANHANDLE EARLY THIS MORNING WITH A
BROAD TROUGH EXTENDING ALL THE WAY THROUGH THE IL/WI STATE LINE.
THERE IS A FRONT IN THE TROUGH BUT IT HOLDS A VARIETY OF FORMS AKA
COLD/STATIONARY/WARM AS YOU MOVE ALONG IT...SO WILL REFER TO IT AS A
TROUGH FOR SIMPLICITY.  THE FRONT WILL MEANDER OVER THE FAR SOUTHERN
END OF THE LAKE THIS MORNING WHILE THE LOW MOVES UP THE TROUGH AND
PASSES OVER THE SOUTHERN END OF THE LAKE THIS EVENING.  NORTH GALES
WILL DEVELOP BEHIND THE LOW AND EXTEND THROUGH THE NSH WATERS
TONIGHT AND THROUGH MID AFTN MONDAY.  WINDS CONTINUE TO DIMINISH
THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE
TUESDAY NIGHT.  WINDS TURN SOUTH BEHIND THE RIDGE AND INCREASE TO 30
KT AS A WEAKENING TROUGH OF LOW PRESSURE APPROACHES WEDNESDAY.  THE
TROUGH PASSES OVER THE LAKE THURSDAY WITH NORTHEAST TO EAST WINDS
BEHIND IT.  GUIDANCE THEN FEATURES EXTREME DIFFERENCES IN THE
PATTERN LATE IN THE WEEK SO HAVE LOW CONFIDENCE IN THE FORECAST PAST
THURSDAY.  FOR REFERENCE THE ECMWF FEATURES A HIGH MOVING OVER THE
LAKE LATE THIS WEEK WHILE THE GFS HAS A LOW MOVING UP THE LAKE AT
THE SAME TIME.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ673-LMZ868-LMZ870-LMZ872-LMZ874...10 PM
     SUNDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ080-LMZ675-LMZ777-LMZ779-LMZ876-LMZ878...3 AM
     MONDAY TO 3 PM MONDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

&&

$$

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

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
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000
FXUS63 KLOT 130817
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 AM CDT SUN APR 13 2014

.DISCUSSION...
843 PM CDT

LAKE/OUTFLOW ENHANCE COLD FRONT HAS SEEPED SOUTHWARD INTO FAR NE
IL THIS EVENING AND STRETCHES WEST-NORTHWEST ACROSS SOUTHERN
WISCONSIN. THE 00Z DVN AND ILX SOUNDINGS CONFIRMED THE PRESENCE OF
A STRONG CAPPING INVERSION BETWEEN 700-800MB THAT HAD BEEN OBSERVED
ON ACARS SOUNDINGS LATE THIS AFTERNOON IN THE WARM SECTOR. THUS
FAR CONVECTION HAS REMAINED CONFINED TO AREAS NORTH OF THE FRONT
WHERE ISENTROPIC ASCENT IS LIFTING PARCELS TO THEIR LFC. FRONT MAY
MEANDER AROUND A BIT THROUGH THE NIGHT BUT NOT EXPECTED TO
GENERALLY REMAIN QUASI-STATIONARY TONIGHT...MEANING THE BEST FOCUS
FOR CONVECTION SHOULD REMAIN ACROSS WISCONSIN AND JUST NORTH OF
OUR CWA. SURFACE BASED WARM SECTOR CONVECTION HAS BEEN INCREASING
IN COVERAGE OVER WESTERN/CENTRAL IOWA THIS EVENING AND IT IS THIS
CONVECTION THAT STANDS THE BEST CHANCE TO BRING OUR AREA RAIN
OVERNIGHT. GIVEN THE PRESENCE OF CAP AND LACK OF SIGNIFICANT LARGE
SCALE ASCENT TO ELIMINATE THE CINH IN THE WARM SECTOR...OUR BEST
THREAT OF RAIN WOULD BE THE CONVECTION IN IOWA CONGEALING INTO AN
MCS AND ROLLING EAST ACROSS THE AREA. SOME OF THE SHORT RANGE
GUIDANCE IS HINTING AT THIS POTENTIAL...BUT ALSO SEEMS TO SUGGEST
A WEAKENING TREND AS CONVECTION MOVES INTO NORTHERN ILLINOIS
OVERNIGHT. EXACT EVOLUTION OF CONVECTION OVERNIGHT IS SOMEWHAT
UNCLEAR...BUT CERTAINLY WOULD APPEAR THE BEST THREAT OF RAIN WOULD
BE NORTHWESTERN CWA WITH CHANCES TAPERING OFF SOUTH AND EAST FROM
THERE. HAVE MADE SOME MAINLY COSMETIC CHANGES TO POPS/WEATHER
OVERNIGHT.

IZZI

//PREV DISCUSSION...
359 PM CDT

A ROUND OF SEVERE THUNDERSTORMS RUMBLING ACROSS THE NORTHERN
PORTIONS OF THE CWA PRODUCED STRONG WINDS AND HAIL UP TO 2 INCHES
IN DIAMETER.

HOWEVER...FOR THE REMAINDER OF THE AFTERNOON CONDITIONS WILL BE
WINDY AS WARM AS THE WARM FRONT BLASTED NORTH OF THE REGION.  DO NOT
EXPECT ANY MORE THUNDERSTORMS FOR THE REMAINDER OF THE
AFTERNOON...AND THE MAIN CONCERNS WILL BE THE CONTINUED STRONG SOUTH
TO SOUTHWESTERLY WINDS AND THEN THE TIMING OF MORE SHOWERS AND
THUNDERSTORMS MOVING BACK INTO THE REGION OVERNIGHT TONIGHT.  THE
LATEST VISIBLE SATELLITE IMAGERY AND SFC OBS SHOW THAT THE CWA IS
WELL ENTRENCHED IN WARM SECTOR AIR WITH FILTERED
SUNSHINE...DEWPOINTS IN THE MIDDLE TO UPPER 50S AND TEMPERATURES
PEGGING 80 F.  LATEST RADAR IMAGERY SHOWS THAT SHOWERS AND
THUNDERSTORMS ARE CURRENTLY FOCUSED ALONG AN ELEVATED WARM FRONT
OVER CENTRAL WISCONSIN.  WHILE THERE WILL BE A SLIGHT CHANCE FOR
SOME ISOLATED ACTIVITY FORMING IN THE WARM SECTOR LATE THIS
AFTERNOON THROUGH EARLY THIS EVENING...THE FLAT APPEARANCE TO THE CU
FIELD WOULD INDICATE THAT THE THE ATMOSPHERE IS STILL SLIGHTLY
STABLE AND MODEL SOUNDING SHOW THAT THERE IS STILL SOME WEAK
CONVECTIVE INHIBITION TO THE ATMOSPHERE.  THROUGH THE EVENING...THE
INHIBITION WILL ERODE AND THERE WILL BE A CHANCE FOR SOME SHOWER OR
THUNDERSTORM ACTIVITY TO DEVELOP IN THE WARM SECTOR.  HOWEVER...THE
MAIN SHOW WILL BEGIN LATE THIS EVENING AS THE WHOLE SYNOPTIC SCALE
FRONTAL SYSTEM SLOWLY SAGS SOUTHEASTWARD WHILE SHORT WAVE ENERGY
ALOFT RIPPLES ALONG THE BAROCLINIC ZONE.  SFC WAVE DEVELOPMENT WILL
HAVE A TWO-FOLD EFFECT.  ONE IMPACT WILL BE TO FOCUS AND ENHANCE
THUNDERSTORM ACTIVITY WHILE SLOWING THE PROGRESSION OF THE
BOUNDARY.  CURRENTLY ANTICIPATE THAT PCPN WILL MOVE INTO THE FAR
NWRN PORTIONS OF THE CWA...INCLUDING THE ROCKFORD METRO AREA...NEAR
OR SHORTLY BEFORE MIDNIGHT AND THEN SLOWLY SAG SEWD...REACHING THE
CHICAGO METRO AREA AT OR SHORTLY BEFORE DAYBREAK.

THROUGH THE EVENING AND OVERNIGHT HOURS EXPECT THAT THE FRONTAL
BOUNDARY WILL BE STRUNG OUT FROM THE ERN GREAT LAKES BACK TO THE
MAIN SFC LOW OVER THE CNTRL PLAINS.  THERE MAY BE A CHANCE FOR SFC
BASED CONVECTION IN THE WARM SECTOR SOUTH OF THE FRONTAL BOUNDARY
WITH EMBEDDED THUNDERSTORMS IN THE OVERRUNNING REGION NORTH OF THE
SFC BOUNDARY.  THE ENVIRONMENT WILL CONTINUE TO MOISTEN THROUGH A
DEEP LAYER.  THE 12Z SOUNDING FROM ILX INDICATED CLOSE TO 1 INCH
PWAT AND THE HIGH RES SHORT RANGE GUIDANCE INDICATES THAT PWATS
WILL ONLY INCREASE THROUGH THE EVENING AND OVERNIGHT WITH A
PERSISTENT FETCH OFF OF A WIDE OPEN GULF OF MEXICO. GIVEN THE HIGH
AMOUNT OF DEEP LAYER MOISTURE IN THE ATMOSPHERE AND THE SLOW
PROGRESSIVE OF THE SYNOPTIC SCALE SYSTEM...THUNDERSTORMS SHOULD BE
EFFICIENT RAIN PRODUCERS...AND PCPN EVEN IN THE OVERRUNNING REGION
NORTH OF THE FRONTAL BOUNDARY SHOULD BE HEAVY AT TIMES.  ANTICIPATE
SOME SWD PROGRESSION TO THE BOUNDARY OVERNIGHT...BUT THEN ANTICIPATE
THAT THE BOUNDARY WILL STALL OUT THROUGH THE DAY TOMORROW...PIVOTING
AROUND SFC WAVE DEVELOPMENT OVER THE MIDDLE MISSISSIPPI VALLEY
DEVELOPING IN RESPONSE TO SHORT WAVE ENERGY RIPPLING ALONG THE
BAROCLINIC ZONE ALOFT.  DURING THE PERIOD FROM SUNDAY AFTERNOON
THROUGH MONDAY NIGHT...PWATS INVOF THE FRONT ARE EXPECTED TO
INCREASE TO NEAR 1.5 INCHES PER THE LATEST MODEL GUIDANCE.  FOR
QPF...ANTICIPATE THAT THERE SHOULD BE AREAL AVERAGE PCPN AMOUNTS OF
AROUND 1 INCH PER 6 HOURS...WITH LOCALLY HIGHER AMOUNTS LIKELY NEAR
HEAVIER THUNDERSTORMS OR IN AREAS OF ECHO TRAINING.  THE BOUNDARY
WILL HAVE THE SLOWEST PROGRESSION FOR THE PERIOD FROM EARLY SUNDAY
MORNING THROUGH LATE SUNDAY NIGHT AND THERE IS RELATIVELY HIGH
CONFIDENCE IN A BAND OF PCPN OF AROUND 2 INCHES IN THE 18-24 HOUR
PERIOD WHEN THE FRONT IS QUASISTATIONARY OVER NRN IL.

THE LARGER SCALE PATTERN SHOULD BECOME MORE QUICKLY PROGRESSIVE BY
MONDAY MORNING AS THE LONGWAVE TROUGH ACCELERATES ACROSS THE
MISSISSIPPI VALLEY IN RESPONSE TO A STRONG JET STREAM DIGGING SOUTH
INTO THE CENTRAL PLAINS AS THE LONG WAVE PATTERN ALONG UNDERGOES
SIGNIFICANT AMPLIFICATION.  A DEEPENING TROUGH OVER THE MISSISSIPPI
VALLEY COMBINED WITH AN BUILDING RIDGE OVER THE WEST COAST WILL SET
UP FAST NWLY FLOW ALOFT...ALLOWING FOR A PERIOD OF EXTENDED COLD
ADVECTION FOLLOWING THE PASSAGE OF THE FRONTAL SYSTEMS.
TEMPERATURES WILL DROP OFF FROM HIGHS AROUND 80F TODAY AND MIDDLE
70S TOMORROW TO ONLY THE LOWER TO MIDDLE 40S ON MONDAY.  CONTINUED
COLD ADVECTION WILL DROP HIGHS EVEN LOWER FOR TUESDAY WITH TEMPS
TOPPING OUT IN THE UPPER 30S TO LOWER 40S.  AS CANADIAN HIGH
PRESSURE BUILDS ACROSS THE REGION MONDAY NIGHT AND TUESDAY...WINDS
WILL DROP OFF AND CLOUD COVER SHOULD DIMINISH.  CONDITIONS FOR
TUESDAY MORNING SHOULD BE QUITE CHILLY WITH LOWS ACROSS THE CWA ONLY
IN THE 20S.  EVEN DOWNTOWN CHICAGO SHOULD DROP TO AROUND 30F.  WITH
THE COLDER AIR FILTERING INTO THE REGION FOLLOWING THE FRONTAL
PASSAGE...THERE WILL BE A CHANCE FOR SOME MEASURABLE SNOW MONDAY
EVENING INTO EARLY TUESDAY.  HOWEVER...CONFIDENCE IS LOW AT THE
CURRENT TIME AS TO HOW MUCH SNOW MAY ACCUMULATE...OTHER THAN TO
MENTION THAT THERE IS A CHANCE FOR SOME ACCUMULATION.

LOOKING INTO THE LONGER TERM...THERE SHOULD BE A GENERAL WARMING
TREND FROM  WEDNESDAY THROUGH NEXT SATURDAY.  THE LONGER RANGE
GUIDANCE IS INDICATING SLOW PROGRESSION TO THE UPPER LEVEL LONG WAVE
PATTERN WHILE BECOMING MUCH LESS AMPLIFIED THROUGH WEDNESDAY NIGHT.
SIGNIFICANT DIFFERENCES DEVELOP WITH WITH THE LONGER RANGE GUIDANCE
BY THURSDAY...LEADING TO LOWER THAN AVERAGE CONFIDENCE IN THE
FORECAST DETAILS FROM THURSDAY THROUGH SATURDAY.  THE GFS WANTS TO
DEVELOP SPLIT FLOW OVER THE CENTRAL PLAINS WITH A CLOSED NRN STREAM
LOW OVER THE ND/SCNTRL CANADA BORDER AND A CLOSED SRN STREAM LOW
OVER THE CNTRL PLAINS.  THIS SCENARIO IS REFLECTED AT THE SFC
STRONG CYCLOGENESIS OVER THE UPPER MISSOURI VALLEY. ON THE OTHER
HAND...THE ECMWF HAS A PHASED OPEN TROUGH FROM THE GREAT LAKES
THROUGH THE MISSISSIPPI VALLEY AND UPPER RIDGING FROM THE NRN PLAINS
TOWARD CENTRAL CANADA.  ESSENTIALLY...THE OPERATIONAL RUNS OF THE
GFS AND ECMWF ARE ABOUT 180 DEGREES OUT OF PHASE BY LATE NEXT WEEK.
THE GFS SEEMS OVERLY DEVELOPED WHEN COMPARED TO THE ECMWF...AND HAVE
TRENDED THE LONGER RANGE FORECAST CLOSER TO THE ECMWF...WHICH WOULD
SUPPORT THE SLOW WARMING TREND WITH LOW POPS.  ADMITTEDLY...THERE IS
LOW CONFIDENCE IN THE LONGER RANGE FORECAST GIVEN THE MODEL
DIFFERENCES.

KREIN

&&

.AVIATION...

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

* CHANCE OF TSRA/SHRA LATE.

* SECOND ROUND OF SHRA/TSRA ARRIVES MID-DAY...WITH BEST CHANCE OF
  TSRA IN THE LATE AFTN/EVENING.

* POTENTIAL FOR MULTIPLE WIND SHIFTS OVERNIGHT THROUGH SUNDAY
  EVENING

* INCREASING POTENTIAL FOR LOW MVFR-IFR CIGS VSBY LATE SUNDAY INTO
  SUNDAY NIGHT WITH MVFR OR LOWER VSBY.

JEE

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

LINE OF TSRA STRETCHES ACROSS SOUTHERN WI AND THROUGH FAR EASTERN
IOWA. THE STORMS ARE WEAKENING SLOWER THAN ORIGINALLY
EXPECTED...BUT FINALLY STARTING TO LOOK LESS ORGANIZED. THE
TRAJECTORY OF THE STORMS WOULD BRING THE WEAKENED LINE ACROSS ALL
OF THE TERMINALS EXCEPT GYY. THINKING THE TSRA/SHRA WILL DISSIPATE
BEFORE REACHING GYY. LATEST WIND GUSTS BEHIND THE LINE ARE N TO NW
ARND 30 KT SO LEFT NORTH GUSTS IN AT RFD. BEHIND THE LINE WINDS
SHOULD GO VARIABLE FOR A FEW HOURS.

THE COLD FRONT HAS SHIFTED A BIT NORTH WITH UGN SHOWING A SOUTH
WIND. AS THE PREVIOUS FORECAST DISCUSSED...VERY VERY VERY LOW
CONFIDENCE IN WIND DIRECTION FOR THE EASTERN TERMINALS. THE COLD
FRONT COULD STILL SHIFT SOUTH IF THE LINE OF STORMS MOVES THROUGH.
THE MAJORITY OF GUIDANCE CONTINUES TO FEATURE SOUTH WINDS. SOME OF
THE HI-RES GUIDANCE ALSO CONTINUES TO INDICATE THE COLD FRONT
COULD MOVE AROUND TOMORROW AND TEMPORARILY SHIFT WINDS AT ORD NE.
WITH VERY LOW CONFIDENCE AND NO GOOD REASON TO MAKE CHANGES...LEFT
WINDS IN THE TAFS ALONE.

NEXT ROUND OF SHRA/TSRA MOVES IN EARLY IN THE AFTN WITH TSRA AND
HEAVY RAIN PSBL. PREVIOUS TIMING IN THE GRIDS LOOKED GOOD AND
THINKING A PROB30 FOR TSRA WAS THE BEST WAY TO HANDLE THE
SITUATION. MOVED THE POSSIBILITY OF IFR CIGS UP AS WELL AND
EXTENDED THE IFR CIGS THROUGH THE OVERNIGHT HOURS AS WELL.

JEE

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

* MEDIUM CONFIDENCE IN SHRA/TSRA IMPACTING ORD/MDW OVERNIGHT.

* MEDIUM-HIGH CONFIDENCE IN WINDS REMAINING SOUTHERLY THROUGH LATE
  TONIGHT.

* ABSOLUTELY NO CONFIDENCE IN WIND DIRECTION FORECAST SUNDAY INTO
  SUNDAY EVENING.

* MEDIUM CONFIDENCE IN PRECIP CHANCES INCREASING LATE SUNDAY INTO
  SUNDAY EVENING.

* MEDIUM-HIGH CONFIDENCE IFR CONDITIONS DEVELOPING LATE SUNDAY OR
  SUNDAY EVENING...BUT LOW CONFIDENCE ON TIMING.

JEE

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

MONDAY...RAIN LIKELY EARLY. IFR LIKELY. CHANCE OF RAIN OR SNOW MON
AFTERNOON AND EVENING. MODERATELY STRONG NORTH WINDS.

TUESDAY...MVFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY AND THURSDAY...VFR PROBABLE.

FRIDAY...CHANCE OF RAIN. IFR POSSIBLE.

IZZI

&&

.MARINE...
317 AM CDT

HEADLINES...WILL UPGRADE THE GALE WATCHES TO WARNINGS AS GALES ARE
STILL EXPECTED.

LOW PRESSURE IS OVER THE OK PANHANDLE EARLY THIS MORNING WITH A
BROAD TROUGH EXTENDING ALL THE WAY THROUGH THE IL/WI STATE LINE.
THERE IS A FRONT IN THE TROUGH BUT IT HOLDS A VARIETY OF FORMS AKA
COLD/STATIONARY/WARM AS YOU MOVE ALONG IT...SO WILL REFER TO IT AS A
TROUGH FOR SIMPLICITY.  THE FRONT WILL MEANDER OVER THE FAR SOUTHERN
END OF THE LAKE THIS MORNING WHILE THE LOW MOVES UP THE TROUGH AND
PASSES OVER THE SOUTHERN END OF THE LAKE THIS EVENING.  NORTH GALES
WILL DEVELOP BEHIND THE LOW AND EXTEND THROUGH THE NSH WATERS
TONIGHT AND THROUGH MID AFTN MONDAY.  WINDS CONTINUE TO DIMINISH
THROUGH TUESDAY AS A RIDGE OF HIGH PRESSURE MOVES OVER THE LAKE
TUESDAY NIGHT.  WINDS TURN SOUTH BEHIND THE RIDGE AND INCREASE TO 30
KT AS A WEAKENING TROUGH OF LOW PRESSURE APPROACHES WEDNESDAY.  THE
TROUGH PASSES OVER THE LAKE THURSDAY WITH NORTHEAST TO EAST WINDS
BEHIND IT.  GUIDANCE THEN FEATURES EXTREME DIFFERENCES IN THE
PATTERN LATE IN THE WEEK SO HAVE LOW CONFIDENCE IN THE FORECAST PAST
THURSDAY.  FOR REFERENCE THE ECMWF FEATURES A HIGH MOVING OVER THE
LAKE LATE THIS WEEK WHILE THE GFS HAS A LOW MOVING UP THE LAKE AT
THE SAME TIME.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL
     4 AM SUNDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ868-LMZ870-LMZ872...10 PM SUNDAY TO 3 PM
     MONDAY.

     GALE WATCH...LMZ080-LMZ673-LMZ675-LMZ777-LMZ779-LMZ874-LMZ876-
     LMZ878...3 AM MONDAY TO 3 PM MONDAY.

&&

$$

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000
FXUS63 KLOT 130612
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
112 AM CDT SUN APR 13 2014

.DISCUSSION...
843 PM CDT

LAKE/OUTFLOW ENHANCE COLD FRONT HAS SEEPED SOUTHWARD INTO FAR NE
IL THIS EVENING AND STRETCHES WEST-NORTHWEST ACROSS SOUTHERN
WISCONSIN. THE 00Z DVN AND ILX SOUNDINGS CONFIRMED THE PRESENCE OF
A STRONG CAPPING INVERSION BETWEEN 700-800MB THAT HAD BEEN OBSERVED
ON ACARS SOUNDINGS LATE THIS AFTERNOON IN THE WARM SECTOR. THUS
FAR CONVECTION HAS REMAINED CONFINED TO AREAS NORTH OF THE FRONT
WHERE ISENTROPIC ASCENT IS LIFTING PARCELS TO THEIR LFC. FRONT MAY
MEANDER AROUND A BIT THROUGH THE NIGHT BUT NOT EXPECTED TO
GENERALLY REMAIN QUASI-STATIONARY TONIGHT...MEANING THE BEST FOCUS
FOR CONVECTION SHOULD REMAIN ACROSS WISCONSIN AND JUST NORTH OF
OUR CWA. SURFACE BASED WARM SECTOR CONVECTION HAS BEEN INCREASING
IN COVERAGE OVER WESTERN/CENTRAL IOWA THIS EVENING AND IT IS THIS
CONVECTION THAT STANDS THE BEST CHANCE TO BRING OUR AREA RAIN
OVERNIGHT. GIVEN THE PRESENCE OF CAP AND LACK OF SIGNIFICANT LARGE
SCALE ASCENT TO ELIMINATE THE CINH IN THE WARM SECTOR...OUR BEST
THREAT OF RAIN WOULD BE THE CONVECTION IN IOWA CONGEALING INTO AN
MCS AND ROLLING EAST ACROSS THE AREA. SOME OF THE SHORT RANGE
GUIDANCE IS HINTING AT THIS POTENTIAL...BUT ALSO SEEMS TO SUGGEST
A WEAKENING TREND AS CONVECTION MOVES INTO NORTHERN ILLINOIS
OVERNIGHT. EXACT EVOLUTION OF CONVECTION OVERNIGHT IS SOMEWHAT
UNCLEAR...BUT CERTAINLY WOULD APPEAR THE BEST THREAT OF RAIN WOULD
BE NORTHWESTERN CWA WITH CHANCES TAPERING OFF SOUTH AND EAST FROM
THERE. HAVE MADE SOME MAINLY COSMETIC CHANGES TO POPS/WEATHER
OVERNIGHT.

IZZI

//PREV DISCUSSION...
359 PM CDT

A ROUND OF SEVERE THUNDERSTORMS RUMBLING ACROSS THE NORTHERN
PORTIONS OF THE CWA PRODUCED STRONG WINDS AND HAIL UP TO 2 INCHES
IN DIAMETER.

HOWEVER...FOR THE REMAINDER OF THE AFTERNOON CONDITIONS WILL BE
WINDY AS WARM AS THE WARM FRONT BLASTED NORTH OF THE REGION.  DO NOT
EXPECT ANY MORE THUNDERSTORMS FOR THE REMAINDER OF THE
AFTERNOON...AND THE MAIN CONCERNS WILL BE THE CONTINUED STRONG SOUTH
TO SOUTHWESTERLY WINDS AND THEN THE TIMING OF MORE SHOWERS AND
THUNDERSTORMS MOVING BACK INTO THE REGION OVERNIGHT TONIGHT.  THE
LATEST VISIBLE SATELLITE IMAGERY AND SFC OBS SHOW THAT THE CWA IS
WELL ENTRENCHED IN WARM SECTOR AIR WITH FILTERED
SUNSHINE...DEWPOINTS IN THE MIDDLE TO UPPER 50S AND TEMPERATURES
PEGGING 80 F.  LATEST RADAR IMAGERY SHOWS THAT SHOWERS AND
THUNDERSTORMS ARE CURRENTLY FOCUSED ALONG AN ELEVATED WARM FRONT
OVER CENTRAL WISCONSIN.  WHILE THERE WILL BE A SLIGHT CHANCE FOR
SOME ISOLATED ACTIVITY FORMING IN THE WARM SECTOR LATE THIS
AFTERNOON THROUGH EARLY THIS EVENING...THE FLAT APPEARANCE TO THE CU
FIELD WOULD INDICATE THAT THE THE ATMOSPHERE IS STILL SLIGHTLY
STABLE AND MODEL SOUNDING SHOW THAT THERE IS STILL SOME WEAK
CONVECTIVE INHIBITION TO THE ATMOSPHERE.  THROUGH THE EVENING...THE
INHIBITION WILL ERODE AND THERE WILL BE A CHANCE FOR SOME SHOWER OR
THUNDERSTORM ACTIVITY TO DEVELOP IN THE WARM SECTOR.  HOWEVER...THE
MAIN SHOW WILL BEGIN LATE THIS EVENING AS THE WHOLE SYNOPTIC SCALE
FRONTAL SYSTEM SLOWLY SAGS SOUTHEASTWARD WHILE SHORT WAVE ENERGY
ALOFT RIPPLES ALONG THE BAROCLINIC ZONE.  SFC WAVE DEVELOPMENT WILL
HAVE A TWO-FOLD EFFECT.  ONE IMPACT WILL BE TO FOCUS AND ENHANCE
THUNDERSTORM ACTIVITY WHILE SLOWING THE PROGRESSION OF THE
BOUNDARY.  CURRENTLY ANTICIPATE THAT PCPN WILL MOVE INTO THE FAR
NWRN PORTIONS OF THE CWA...INCLUDING THE ROCKFORD METRO AREA...NEAR
OR SHORTLY BEFORE MIDNIGHT AND THEN SLOWLY SAG SEWD...REACHING THE
CHICAGO METRO AREA AT OR SHORTLY BEFORE DAYBREAK.

THROUGH THE EVENING AND OVERNIGHT HOURS EXPECT THAT THE FRONTAL
BOUNDARY WILL BE STRUNG OUT FROM THE ERN GREAT LAKES BACK TO THE
MAIN SFC LOW OVER THE CNTRL PLAINS.  THERE MAY BE A CHANCE FOR SFC
BASED CONVECTION IN THE WARM SECTOR SOUTH OF THE FRONTAL BOUNDARY
WITH EMBEDDED THUNDERSTORMS IN THE OVERRUNNING REGION NORTH OF THE
SFC BOUNDARY.  THE ENVIRONMENT WILL CONTINUE TO MOISTEN THROUGH A
DEEP LAYER.  THE 12Z SOUNDING FROM ILX INDICATED CLOSE TO 1 INCH
PWAT AND THE HIGH RES SHORT RANGE GUIDANCE INDICATES THAT PWATS
WILL ONLY INCREASE THROUGH THE EVENING AND OVERNIGHT WITH A
PERSISTENT FETCH OFF OF A WIDE OPEN GULF OF MEXICO. GIVEN THE HIGH
AMOUNT OF DEEP LAYER MOISTURE IN THE ATMOSPHERE AND THE SLOW
PROGRESSIVE OF THE SYNOPTIC SCALE SYSTEM...THUNDERSTORMS SHOULD BE
EFFICIENT RAIN PRODUCERS...AND PCPN EVEN IN THE OVERRUNNING REGION
NORTH OF THE FRONTAL BOUNDARY SHOULD BE HEAVY AT TIMES.  ANTICIPATE
SOME SWD PROGRESSION TO THE BOUNDARY OVERNIGHT...BUT THEN ANTICIPATE
THAT THE BOUNDARY WILL STALL OUT THROUGH THE DAY TOMORROW...PIVOTING
AROUND SFC WAVE DEVELOPMENT OVER THE MIDDLE MISSISSIPPI VALLEY
DEVELOPING IN RESPONSE TO SHORT WAVE ENERGY RIPPLING ALONG THE
BAROCLINIC ZONE ALOFT.  DURING THE PERIOD FROM SUNDAY AFTERNOON
THROUGH MONDAY NIGHT...PWATS INVOF THE FRONT ARE EXPECTED TO
INCREASE TO NEAR 1.5 INCHES PER THE LATEST MODEL GUIDANCE.  FOR
QPF...ANTICIPATE THAT THERE SHOULD BE AREAL AVERAGE PCPN AMOUNTS OF
AROUND 1 INCH PER 6 HOURS...WITH LOCALLY HIGHER AMOUNTS LIKELY NEAR
HEAVIER THUNDERSTORMS OR IN AREAS OF ECHO TRAINING.  THE BOUNDARY
WILL HAVE THE SLOWEST PROGRESSION FOR THE PERIOD FROM EARLY SUNDAY
MORNING THROUGH LATE SUNDAY NIGHT AND THERE IS RELATIVELY HIGH
CONFIDENCE IN A BAND OF PCPN OF AROUND 2 INCHES IN THE 18-24 HOUR
PERIOD WHEN THE FRONT IS QUASISTATIONARY OVER NRN IL.

THE LARGER SCALE PATTERN SHOULD BECOME MORE QUICKLY PROGRESSIVE BY
MONDAY MORNING AS THE LONGWAVE TROUGH ACCELERATES ACROSS THE
MISSISSIPPI VALLEY IN RESPONSE TO A STRONG JET STREAM DIGGING SOUTH
INTO THE CENTRAL PLAINS AS THE LONG WAVE PATTERN ALONG UNDERGOES
SIGNIFICANT AMPLIFICATION.  A DEEPENING TROUGH OVER THE MISSISSIPPI
VALLEY COMBINED WITH AN BUILDING RIDGE OVER THE WEST COAST WILL SET
UP FAST NWLY FLOW ALOFT...ALLOWING FOR A PERIOD OF EXTENDED COLD
ADVECTION FOLLOWING THE PASSAGE OF THE FRONTAL SYSTEMS.
TEMPERATURES WILL DROP OFF FROM HIGHS AROUND 80F TODAY AND MIDDLE
70S TOMORROW TO ONLY THE LOWER TO MIDDLE 40S ON MONDAY.  CONTINUED
COLD ADVECTION WILL DROP HIGHS EVEN LOWER FOR TUESDAY WITH TEMPS
TOPPING OUT IN THE UPPER 30S TO LOWER 40S.  AS CANADIAN HIGH
PRESSURE BUILDS ACROSS THE REGION MONDAY NIGHT AND TUESDAY...WINDS
WILL DROP OFF AND CLOUD COVER SHOULD DIMINISH.  CONDITIONS FOR
TUESDAY MORNING SHOULD BE QUITE CHILLY WITH LOWS ACROSS THE CWA ONLY
IN THE 20S.  EVEN DOWNTOWN CHICAGO SHOULD DROP TO AROUND 30F.  WITH
THE COLDER AIR FILTERING INTO THE REGION FOLLOWING THE FRONTAL
PASSAGE...THERE WILL BE A CHANCE FOR SOME MEASURABLE SNOW MONDAY
EVENING INTO EARLY TUESDAY.  HOWEVER...CONFIDENCE IS LOW AT THE
CURRENT TIME AS TO HOW MUCH SNOW MAY ACCUMULATE...OTHER THAN TO
MENTION THAT THERE IS A CHANCE FOR SOME ACCUMULATION.

LOOKING INTO THE LONGER TERM...THERE SHOULD BE A GENERAL WARMING
TREND FROM  WEDNESDAY THROUGH NEXT SATURDAY.  THE LONGER RANGE
GUIDANCE IS INDICATING SLOW PROGRESSION TO THE UPPER LEVEL LONG WAVE
PATTERN WHILE BECOMING MUCH LESS AMPLIFIED THROUGH WEDNESDAY NIGHT.
SIGNIFICANT DIFFERENCES DEVELOP WITH WITH THE LONGER RANGE GUIDANCE
BY THURSDAY...LEADING TO LOWER THAN AVERAGE CONFIDENCE IN THE
FORECAST DETAILS FROM THURSDAY THROUGH SATURDAY.  THE GFS WANTS TO
DEVELOP SPLIT FLOW OVER THE CENTRAL PLAINS WITH A CLOSED NRN STREAM
LOW OVER THE ND/SCNTRL CANADA BORDER AND A CLOSED SRN STREAM LOW
OVER THE CNTRL PLAINS.  THIS SCENARIO IS REFLECTED AT THE SFC
STRONG CYCLOGENESIS OVER THE UPPER MISSOURI VALLEY. ON THE OTHER
HAND...THE ECMWF HAS A PHASED OPEN TROUGH FROM THE GREAT LAKES
THROUGH THE MISSISSIPPI VALLEY AND UPPER RIDGING FROM THE NRN PLAINS
TOWARD CENTRAL CANADA.  ESSENTIALLY...THE OPERATIONAL RUNS OF THE
GFS AND ECMWF ARE ABOUT 180 DEGREES OUT OF PHASE BY LATE NEXT WEEK.
THE GFS SEEMS OVERLY DEVELOPED WHEN COMPARED TO THE ECMWF...AND HAVE
TRENDED THE LONGER RANGE FORECAST CLOSER TO THE ECMWF...WHICH WOULD
SUPPORT THE SLOW WARMING TREND WITH LOW POPS.  ADMITTEDLY...THERE IS
LOW CONFIDENCE IN THE LONGER RANGE FORECAST GIVEN THE MODEL
DIFFERENCES.

KREIN

&&

.AVIATION...

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

* CHANCE OF TSRA/SHRA LATE.

* SECOND ROUND OF SHRA/TSRA ARRIVES MID-DAY...WITH BEST CHANCE OF
  TSRA IN THE LATE AFTN/EVENING.

* POTENTIAL FOR MULTIPLE WIND SHIFTS OVERNIGHT THROUGH SUNDAY
  EVENING

* INCREASING POTENTIAL FOR LOW MVFR-IFR CIGS VSBY LATE SUNDAY INTO
  SUNDAY NIGHT WITH MVFR OR LOWER VSBY.

JEE

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

LINE OF TSRA STRETCHES ACROSS SOUTHERN WI AND THROUGH FAR EASTERN
IOWA. THE STORMS ARE WEAKENING SLOWER THAN ORIGINALLY
EXPECTED...BUT FINALLY STARTING TO LOOK LESS ORGANIZED. THE
TRAJECTORY OF THE STORMS WOULD BRING THE WEAKENED LINE ACROSS ALL
OF THE TERMINALS EXCEPT GYY. THINKING THE TSRA/SHRA WILL DISSIPATE
BEFORE REACHING GYY. LATEST WIND GUSTS BEHIND THE LINE ARE N TO NW
ARND 30 KT SO LEFT NORTH GUSTS IN AT RFD. BEHIND THE LINE WINDS
SHOULD GO VARIABLE FOR A FEW HOURS.

THE COLD FRONT HAS SHIFTED A BIT NORTH WITH UGN SHOWING A SOUTH
WIND. AS THE PREVIOUS FORECAST DISCUSSED...VERY VERY VERY LOW
CONFIDENCE IN WIND DIRECTION FOR THE EASTERN TERMINALS. THE COLD
FRONT COULD STILL SHIFT SOUTH IF THE LINE OF STORMS MOVES THROUGH.
THE MAJORITY OF GUIDANCE CONTINUES TO FEATURE SOUTH WINDS. SOME OF
THE HI-RES GUIDANCE ALSO CONTINUES TO INDICATE THE COLD FRONT
COULD MOVE AROUND TOMORROW AND TEMPORARILY SHIFT WINDS AT ORD NE.
WITH VERY LOW CONFIDENCE AND NO GOOD REASON TO MAKE CHANGES...LEFT
WINDS IN THE TAFS ALONE.

NEXT ROUND OF SHRA/TSRA MOVES IN EARLY IN THE AFTN WITH TSRA AND
HEAVY RAIN PSBL. PREVIOUS TIMING IN THE GRIDS LOOKED GOOD AND
THINKING A PROB30 FOR TSRA WAS THE BEST WAY TO HANDLE THE
SITUATION. MOVED THE POSSIBILITY OF IFR CIGS UP AS WELL AND
EXTENDED THE IFR CIGS THROUGH THE OVERNIGHT HOURS AS WELL.

JEE


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

* MEDIUM CONFIDENCE IN SHRA/TSRA IMPACTING ORD/MDW OVERNIGHT.

* MEDIUM-HIGH CONFIDENCE IN WINDS REMAINING SOUTHERLY THROUGH LATE
  TONIGHT.

* ABSOLUTELY NO CONFIDENCE IN WIND DIRECTION FORECAST SUNDAY INTO
  SUNDAY EVENING.

* MEDIUM CONFIDENCE IN PRECIP CHANCES INCREASING LATE SUNDAY INTO
  SUNDAY EVENING.

* MEDIUM-HIGH CONFIDENCE IFR CONDITIONS DEVELOPING LATE SUNDAY OR
  SUNDAY EVENING...BUT LOW CONFIDENCE ON TIMING.

JEE

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

MONDAY...RAIN LIKELY EARLY. IFR LIKELY. CHANCE OF RAIN OR SNOW MON
AFTERNOON AND EVENING. MODERATELY STRONG NORTH WINDS.

TUESDAY...MVFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY AND THURSDAY...VFR PROBABLE.

FRIDAY...CHANCE OF RAIN. IFR POSSIBLE.

IZZI

&&

.MARINE...
215 PM CDT

A VERY ACTIVE WEATHER PERIOD IS STILL EXPECTED OVER THE LAKE THROUGH
MONDAY. A STORM SYSTEM...CURRENT ACROSS THE PLAINS...IS EXPECTED TO
MOVE ACROSS THE CENTRAL PORTION OF THE LAKE LATE TONIGHT. THIS LOW
WILL DRAPE A FRONTAL BOUNDARY ACROSS THE SOUTHERN SECTIONS OF THE
LAKE ON SUNDAY...JUST PRIOR TO ANOTHER AREA OF LOW PRESSURE
TRANSITIONING NORTHEASTWARD ACROSS SOUTHERN LAKE MICHIGAN ALONG THIS
FRONTAL BOUNDARY SUNDAY NIGHT INTO MONDAY.

OVERALL...THIS WILL RESULT IN A RATHER COMPLEX WIND FORECAST ACROSS
THE LAKE OVER THE NEXT COUPLE OF DAYS. THIS WILL CREATE
LARGE VARIATIONS IN WIND SPEEDS AND DIRECTIONS ACROSS DIFFERENT
SECTIONS OF THE LAKE. EASTERLY WINDS WILL GRADUALLY SHIFT OUT OF THE
NORTH ACROSS THE NORTHERN 1/3 OF THE LAKE TONIGHT INTO SUNDAY AS
THIS FIRST LOW PASSES OVER THE LAKE. THE TRAILING FRONTAL BOUNDARY
WILL THEN SLOWLY SHIFT SOUTHWARD ACROSS THE SOUTHERN TIP OF THE LAKE
SUNDAY NIGHT...THEN SHIFT OVER THE ENTIRE LAKE BY MONDAY MORNING AS
THE SECOND LOW PASSES.

THE MAIN CONCERNS THROUGH THE DAY SUNDAY...AS FAR AS HEADLINE
CRITERIA WINDS...WILL BE THE THREAT FOR SMALL CRAFT ADVISORY WINDS
CONTINUING ON SUNDAY...ESPECIALLY ACROSS THE INDIANA NEAR SHORE
WATERS. STRONG SOUTH WINDS MAY CONTINUE HERE AS THE FRONTAL BOUNDARY
LOOKS TO REMAIN FARTHER NORTH FOR MUCH OF THE DAY. THIS COULD AGAIN
RESULT IN GUSTS UP TO 25 TO 30 KT DURING THE SUNDAY...POSSIBLY
REQUIRING THE CURRENT SMALL CRAFT TO BE EXTENDED INTO SUNDAY.
HOWEVER...AT THIS TIME I WILL HOLD OFF ON DOING THIS.

CONCERNS WILL QUICKLY TRANSITION TO THE GOOD POTENTIAL FOR NORTHERLY
GALES IN THE WAKE OF THIS SECOND LOW SUNDAY NIGHT INTO MONDAY. MUCH
COLD AIR IS EXPECTED TO SPILL OVER THE LAKE ALONG THE BACK SIDE OF
THE IS LOW. IN ADDITION...A RATHER STOUT SURFACE RIDGE OF HIGH
PRESSURE IS EXPECTED TO QUICKLY BUILD IN ACROSS THE UPPER MIDWEST
LATE SUNDAY NIGHT IN THE WAKE OF THIS LOW. THIS SHOULD RESULT IN A
STRENGTHENING PRESSURE GRADIENT...WHICH COULD SUPPORT AROUND 40 KT
NORTHERLY GALES FOR A PERIOD LATE SUNDAY NIGHT INTO MONDAY. I HAVE
OPTED TO ISSUE A GALE WATCH FOR THIS PERIOD DUE TO THE RELATIVELY
HIGH CONFIDENCE IN A PERIOD OF GALE FORCE WINDS.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WILMETTE HARBOR TO MICHIGAN CITY IN UNTIL
     4 AM SUNDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...4 AM
     MONDAY TO 4 PM MONDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ671-LMZ868-LMZ870-LMZ872...10 PM SUNDAY TO 3 PM
     MONDAY.

     GALE WATCH...LMZ080-LMZ673-LMZ675-LMZ777-LMZ779-LMZ874-LMZ876-
     LMZ878...3 AM MONDAY TO 3 PM MONDAY.

&&

$$

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