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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1235 PM CDT SUN MAY 12 2013

.DISCUSSION...
327 AM CDT

MAIN FORECAST CHALLENGES/CONCERNS ARE WITH THE COLD TEMPS AND
FROST TONIGHT WITH A FROST ADVISORY NOW IN PLACE FOR ALL OF THE
CWA TONIGHT...THE ANTICIPATED WARM UP THIS WEEK...AND SIGNS OF A
MORE ACTIVE WEATHER PATTERN BEGINNING TO APPEAR IN THE EXTENDED.

IN THE NEAR TERM...QUIET WEATHER ONGOING ACROSS THE CWA WITH
MOSTLY CLEAR SKIES IN PLACE OVER MUCH OF NORTHEAST ILLINOIS AND
NORTHWEST INDIANA. THE EXCEPTION IS NEAR THE WISCONSIN BORDER
WHERE MID LEVEL CLOUDS ARE TRYING TO SPILL INTO THE AREA THIS
MORNING. THIS IS IN RESPONSE TO SEVERAL WAVES OF ENERGY DROPPING
SOUTHEAST AROUND THE BASE OF THE STRONG UPPER LEVEL LOW TO THE
NORTHEAST. STEEP LOW/MID LEVEL LAPSE RATES STILL IN PLACE EARLY
THIS MORNING WITHIN THIS CYCLONIC WILL CONTINUE TO ALLOW FOR SOME
SCATTERED CLOUD DEVELOPMENT BUT PRIMARILY FOR AREAS IN FAR
NORTHEAST ILLINOIS...AS THIS LOCATION NORTHWARD IS WHERE THE BEST
FORCING/STEEPER LAPSE CURRENTLY RESIDE. ALTHOUGH THERE MAY BE
PERIODS OF THIS SCATTERED MID DECK OR EVEN AN ISOLATED AND BRIEF
CEILING...THINK SKIES SHOULD REMAIN MORE ON THE CLEARER SIDE
THROUGH MID MORNING. TEMPERATURES RIGHT NOW ARE STILL HOLDING
AROUND 40 DEGREES DESPITE THE CLEAR SKIES AND MUCH COLDER AIRMASS
IN PLACE. AS WAS EXPECTED...THE SURFACE LOW TO THE NORTHEAST WITH
TIGHT PRESSURE GRADIENT OVER THE CWA HAS ALLOWED FOR SURFACE WINDS
TO STAY UP NEAR THE 10KT RANGE. SO ONLY EXPECT TEMPS TO FALL A
COUPLE OF MORE DEGREES HERE THIS MORNING BEFORE RISING TO WELL
BELOW NORMAL MAX TEMPS IN THE LOW TO MID 50S TODAY. SHOULD BE A
RATHER QUIET DAY TODAY...ALTHOUGH LOW LEVEL LAPSE RATES REALLY
STEEPEN UP ONCE AGAIN TODAY ACROSS THE CWA. ONCE AGAIN...THESE
LAPSE RATES WITHIN THIS CYCLONIC FLOW WILL PROVIDE FOR SOME
STRATOCU DEVELOPMENT BY MID TO LATE MORNING WITH ANY CLEAR SKIES
BECOMING BROKEN/PARTLY SUNNY. EXPECT THIS TO BE THE CASE THROUGH
THE AFTERNOON AND INTO THE EARLY EVENING. ALTHOUGH CONDITIONS
APPEAR DRY AT THE MOMENT FOR THIS AFTERNOON...LATEST SHORT TERM
GUIDANCE IS TRYING TO INDICATE SOME ISOLATED SHOWER DEVELOPMENT
ACROSS NORTHEAST ILLINOIS LATER THIS AFTERNOON. NOT COMPLETELY
SOLD ON ANY WIDESPREAD DEVELOPMENT LATER THIS AFTERNOON AND SO
HAVE REMAINED DRY...BUT IT WOULD NOT BE OUT OF THE QUESTION FOR
SOME ISOLATED SHOWERS ACROSS NORTHEAST ILLINOIS...ESPECIALLY IF
ANY LOW LEVEL CONVERGENCE COULD DEVELOP WHICH THE RAP IS BEGINNING
TO SHOW.

ATTENTION SHIFTS TOWARDS ANOTHER COLD NIGHT TONIGHT AS FORECAST
TEMPS IN THE LOW TO MID 30S ARE FORECAST AS WELL AS A FROST
EXPECTED FOR THE ENTIRE CWA...MINUS THE WARMER METRO AREA. AS THE
LARGE UPPER LEVEL LOW AND ATTENDANT SURFACE LOW/TROUGH EXIT TO THE
EAST TONIGHT...SURFACE RIDGE SETTLES IN. WITH THIS IN PLACE EXPECT
SURFACE WINDS TO RAPIDLY DROP OFF THIS EVENING WITH TEMPS COOLING.
THERE IS SOME CONCERN THAT CLOUD COVER AND THE BEGINNING STAGES OF
WAA COULD AFFECT NIGHT TIME LOWS...BUT STILL FEEL THAT THESE
SHOULD NOT PLAY TOO MUCH OF A ROLE WITH TEMPS FALLING TONIGHT.
CLOUD DEVELOPMENT COULD POSSIBLY HANG ON INTO THE EVENING AT LEAST
TOWARDS 3Z TONIGHT BUT THEN BEGIN TO ERODE AND SHIFT TO THE EAST
TOWARDS MIDNIGHT...WITH ANY HIGH LEVEL CLOUD COVER APPROACHING
FROM THE WEST REMAINING TO THE WEST. ALSO...ALTHOUGH STRONG WAA
WILL BE OCCURRING TO THE WEST OVER IOWA...THIS SHOULD NOT AFFECT
AREAS IN NORTHERN ILLINOIS AND NORTHWEST INDIANA TONIGHT. IN THE
END...SETTING THE STAGE FOR GOOD RADIATIONAL COOLING. SO HAVE
ISSUED A FROST ADVISORY FOR THE ENTIRE CWA...FROM 6Z TONIGHT TO
12Z MONDAY.

TEMPS WILL BEGIN TO RECOVER ON MONDAY AS THE PREVIOUSLY MENTIONED
WAA SHIFTS EAST TOWARDS THE CWA ON MONDAY...WITH TEMPS RISING BACK
INTO THE LOW TO MID 60S. HAVE MAINTAINED CHANCES FOR PRECIP MONDAY
NIGHT INTO EARLY TUESDAY AS THE WAA WING SHOULD SWING SOME
MOISTURE ACROSS PRIMARILY THE NORTHERN HALF OF THE CWA. SHOULD
REMAIN JUST SHOWERS WITH THUNDER NOT EXPECTED AS INSTABILITY IS
APPEARING TO REMAIN TO THE WEST. WITH STRONG WAA STILL OCCURRING
ACROSS THE AREA MONDAY NIGHT INTO TUESDAY...A RATHER WARM DAY IS
APPEARING TO BE LIKELY ON TUESDAY. HAVE RAISED MAX TEMPS FURTHER
FOR TUESDAY AND HAVE HIGHS IN THE MID TO UPPER 80S...AS THERMAL
AXIS WITH 850MB TEMPS NEAR 20C MOVING OVERHEAD. HAVE NOT PUT IN 90
DEGREE TEMPS FOR TUESDAY JUST QUITE YET AS THERE IS STILL SOME
UNCERTAINTY WITH THE EXTENT OF THIS THERMAL AXIS...BUT COULD
EASILY SEE THAT 90 DEGREE WEATHER INCLUDED IN THE FORECAST FOR
TUESDAY AT A LATER TIME. WEDNESDAY LOOKS WARM AGAIN WITH TEMPS
RISING TO THE 80S ONCE AGAIN...BUT WITH CONFIDENCE LOWERING EVEN
FURTHER. GUIDANCE BEGINS TO DIVERGE WITH HANDLING AN APPROACHING
SURFACE LOW AND FRONTAL BOUNDARY. THIS WILL IMPACT HIGHS FOR
WEDNESDAY AS WELL AS PRECIP CHANCES. A SLIGHT CHANCE FOR
THUNDERSTORMS HAS BEEN MAINTAINED DURING THE DAY WEDNESDAY...BUT
IT APPEARS THAT THERE WILL BE BETTER CHANCES FOR THUNDERSTORMS
WEDNESDAY NIGHT. BEYOND THIS POINT FROM THURSDAY INTO
SATURDAY...MODELS BEGIN TO DIVERGE FURTHER. DESPITE THIS MODEL
VARIABILITY...MODELS ARE AGREEING ON A WARMER AND MORE MOIST
AIRMASS REMAINING IN PLACE WITH 850MB DEWPOINTS REALLY INCREASING
ACROSS THE REGION AS WELL AS THE POTENTIAL SETUP FOR LINGERING
BOUNDARIES. THIS WILL HAVE TO BE RESOLVED ONCE GUIDANCE COMES INTO
BETTER AGREEMENT...BUT WITH THE GENERAL PATTERN IS BEGINNING TO
APPEAR MORE ACTIVE WITH PERIODS OF SHOWERS/THUNDERSTORMS POSSIBLE
INTO THE END OF THIS WEEK.

RODRIGUEZ

&&

.AVIATION...

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

* NORTHWEST WINDS GUSTING TO 18-20KT THIS AFTERNOON.

KREIN

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

A VERY QUIET WEATHER SETUP FOR AVIATION CONCERNS FOR THE PERIOD.
MAIN CONCERN WILL CONTINUE TO BE WIND DIRECTION AS WINDS CONTINUE
TO BE BRISK. HOWEVER...SUSTAINED WINDS AND GUSTS ARE DIMINISHING
THIS AFTERNOON AS HIGH PRESSURE CONTINUES TO BUILD ACROSS THE
MISSISSIPPI VALLEY. ALSO...LATEST SATELITE IMAGERY SHOWER DIURNAL
STRATOCU DEVELOPMENT...WITH A BKN DECK EXPECTED TO DEVELOP EARLY
THIS AFTERNOON...WHICH WILL ALSO HELP LIMIT MIXING. SO...THE
GENERAL TREND FOR WINDS WILL BE TO DECREASE THROUGH THE
AFTERNOON...WHILE BACKING SLIGHTLY TO OUT OF 300 DEGREES. WINDS
WILL THEN GO CALM AND SKIES WILL GO SKC OVERNIGHT.

KREIN

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS

KREIN

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

MONDAY NIGHT AND TUESDAY...VFR.

WEDNESDAY...SLIGHT CHANCE OF SHRA/TSRA.

THURSDAY THROUGH SATURDAY...A PERIOD OR TWO OF SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
255 AM CDT

SOME SHIP OBS AND COASTAL OBS ON EASTERN SHORE SUPPORT MAINTAINING
THE GALE WARNING AS IS THIS MORNING WITH CONTINUED UNSTABLE
CONDITIONS LIKELY TO ALLOW GALES TO LINGER INTO THE MORNING HOURS.
FAR NORTHERN LAKE MICHIGAN COULD SEE GALES LINGER INTO THE EARLY
AFTERNOON DUE TO TIGHTER GRADIENT BUT WINDS ACROSS THE LAKE SHOULD
BE TRENDING DOWNWARD THIS AFTERNOON INTO TONIGHT AS RIDGE AXIS
APPROACHES FROM THE WEST. RIDGE WILL MOVE ACROSS THE LAKE TONIGHT
INTO MONDAY WITH SOUTHERLY WINDS DEVELOPING AND STRENGTHENING AS
SEASONABLY STRONG LOW PRESSURE DEVELOPS OVER THE SOUTHERN CANADIAN
PLAINS TUESDAY. DESPITE FAIRLY TIGHT GRADIENT...SURGE OF VERY WARM
AIR OVER VERY COLD LAKE SHOULD KEEP WINDS AND WAVES SOMEWHAT IN
CHECK TUESDAY INTO WEDNESDAY.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...1 AM MONDAY TO 7 AM MONDAY.

IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019...1 AM
     MONDAY TO 7 AM MONDAY.

LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563 UNTIL 3 PM SUNDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 3 PM SUNDAY
.

&&

$$


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