Area Forecast Discussion
Issued by NWS Chicago, IL

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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.

&&

$$

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