Area Forecast Discussion
Issued by NWS Chicago, IL

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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.

&&

$$

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