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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1236 PM CDT TUE MAY 14 2013

.DISCUSSION...
307 AM CDT

FORECAST CHALLENGES THIS MORNING INCLUDE TEMPS TODAY...THEN LAKE
BREEZE COOLING WEDNESDAY AFTERNOON/EVENING...AND FINALLY THE
TRANSITION TOWARD A MORE ACTIVE PATTERN NEXT WEEKEND.

FORECAST FOR THE NEXT 24 HOURS IS RIGHT ON TRACK AND SAW LITTLE
REASON TO TWEAK ANYTHING WITH MID TO UPPER 80S STILL EXPECTED ACROSS
MOST OF THE CWA TODAY. MODELS CONTINUE TO HANDLE BOUNDARY TEMP/TD
HORRIBLY WITH MONDAY EVENING`S WRF-NAM RUN WAS 10F+ TOO MOIST WITH
TDS OVER IA/NORTHERN MO/EASTERN NE/SOUTHERN MN AND 5-10F TOO COOL
WITH TEMPS MONDAY AFTERNOON. IN FACT...EVEN THE 18Z MON RUN OF THE
WRF-NAM WAS OFF BY 6-10F IN TD AND 4-8F IN TEMP 3 HOURS INTO THE
RUN...WHICH SUGGESTS THE MODELS ARE HANDLING EVAPOTRANSPIRATION
HORRIBLY. NAM LOW LEVEL TRAJECTORIES SUGGEST THAT THIS AFTERNOONS
AIR MASS OVER OUR AREA ORIGINATED FROM THE EASTERN DAKOTAS AND
EASTERN NEBRASKA MONDAY AFTERNOON...WHERE HIGHS CLIMBED INTO THE
UPPER 80S TO LOWER 90S. SUNNY SKIES AND DRY AIR SHOULD ALLOW TEMPS
TO BE OFF TO THE RACES RIGHT AFTER SUNRISE AND STILL THINK GUIDANCE
IS TOO COLD WITH MID TO UPPER 80S MOST AREAS TODAY WITH A SPOTTY 90
OR TWO NOT OUT OF THE QUESTION. FOR WHAT ITS WORTH...87 IS THE
MAGIC NUMBER FOR BOTH ORD AND RFD TO BREAK THE RECORD FOR THE
LARGEST SINGLE DAY WARM UP FOR THE MONTH OF MAY (SEE YESTERDAY`S
PNS OR WEATHER.GOV/LOT TOP NEWS STORY). GRADIENT IS PROGGED TO
WEAKEN SOMEWHAT THIS AFTERNOON WHICH COULD ALLOW A WEAK LAKE
BREEZE TO FORM...ESPECIALLY NORTH SHORE AREAS RIGHT ALONG THE
IMMEDIATE LAKE FRONT.

NOT TERRIBLY CONFIDENT ONE WAY OR ANOTHER IF THIS LAKE BREEZE
WILL OCCUR OR NOT...BUT IF IT DOES IT WOULD ONLY BE TEMPORARY
COOLING AS GRADIENT QUICKLY TIGHTENS THIS EVENING AHEAD OF WEAK
COLD FRONT. IN FACT...LOOKS LIKE IT COULD BE A DOWNRIGHT WINDY
NIGHT...PARTICULARLY IN THE URBAN HEAT ISLAND AREA WHERE LESS
DECOUPLING WILL OCCUR AND WE COULD BLOW 15-25 MPH FROM MID EVENING
INTO THE OVERNIGHT HOURS. THE STRONG SOUTHWEST WINDS WILL HELP
HOLD TEMPS UP WITH LOWS IN THE MID-UPPER 60S...EXCEPT PROBABLY
HOLDING IN THE LOW 70S DOWNTOWN CHICAGO.

WEAK COLD FRONT SLIPS SOUTH THROUGH THE AREA WEDNESDAY BUT EVEN WITH
MODELS WAY OVER-ESTIMATING DEWPOINTS MOST BRING THE FRONT THROUGH
DRY OR BREAK OUT A SPOTTY LIGHT QPF. GIVEN THE POOR REPRESENTATION
OF LOW LEVEL MOISTURE HAVE OPTED TO HOLD ONTO A DRY FROPA MOST
AREAS...BUT DID LEAVE IN A LOW CHANCE POPS FAR SOUTHERN CWA WED PM
AS SOME WEAK MOISTURE POOLING ALONG THE BOUNDARY COULD BE ENOUGH FOR
SOME ISOLD-SCT STORMS TO FIRE DURING PEAK HEATING.

BIGGER STORY WEDNESDAY WILL PROBABLY BE THE FAIRLY IMPRESSIVE LAKE
BREEZE THAT PLOWS INLAND DURING THE AFTERNOON OVER NW INDIANA AND
THEN INTO NE IL LATE WEDNESDAY AFTERNOON INTO WEDNESDAY EVENING AS
GRADIENT RELAXES AND VEERS MORE NORTHWESTERLY. COULD EASILY SEE
TEMPS CRASH 20 DEGREES BEHIND THAT LAKE BREEZE SENDING LAKESHORE
AREAS TUMBLING FROM NEAR 80 INTO THE 50S.

BOUNDARY SETTLES SOUTH OF THE CWA WEDNESDAY NIGHT THROUGH THURSDAY
NIGHT WITH HIGH PRESSURE KEEPING MOST OF THE AREA DRY...BUT DID HANG
ONTO LOW POPS FAR SOUTHERN CWA DUE TO PROXIMITY OF THE BOUNDARY.
OVER MOST OF THE AREA PARTIAL SUNSHINE AND WARM TEMPS WILL BE THE
RULE...THOUGH LIGHT GRADIENT WILL ALLOW FOR HEALTHY LAKE BREEZE TO
DEVELOP AND KEEP LAKE FRONT IN THE 50S THURSDAY AFTERNOON.

FRIDAY INTO THE WEEKEND THE LARGE SCALE PATTERN WILL FEATURE A
GRADUAL RE-AMPLIFICATION OF UPPER RIDGE OVER OUR AREA AS SEVERAL
SHORTWAVE TROUGHS DIG INTO AND HELP DEEPEN A WESTERN CONUS LONGWAVE
TROUGH. AS THIS OCCURS FRONTAL BOUNDARY WILL TEND TO LIFT BACK
NORTHWARD ACROSS THE AREA AND LIKELY PUT OUR CWA BACK INTO THE WARM
SECTOR NEXT WEEKEND. COULD EASILY SEE TEMPS CLIMB BACK INTO THE 80S
BUT KEPT GRIDS A BIT MORE CONSERVATIVE SINCE CLOUDS AND OCNL
SHRA/TSRA COULD KEEP TEMPS IN CHECK A BIT.

REGARDING PRECIP...CERTAINLY COULD BE A ROUND OF TWO OF SHOWERS AND
THUNDERSTORMS FRIDAY THROUGH SUNDAY BUT TIMING THIS IS IMPOSSIBLE AT
THIS POINT. THIS MEANS DAY AFTER DAY OF CHANCE POPS IN THE FORECAST
THROUGH THE WEEKEND WHICH CAN BE TERRIBLY MISLEADING SINCE I`D
EXPECT DRY HOURS FRIDAY THROUGH SUNDAY TO OUTNUMBER RAINY HOURS 10
TO 1...BUT SINCE THERE COULD BE PRECIP AT ANY POINT IN TIME AM STUCK
CARRYING CHANCES POPS EVERY PERIOD. DEEP LONG WAVE TROUGH WILL
LIKELY MAKE SLOW PROGRESS EASTWARD INTO THE PLAINS THEN UPPER
MISSISSIPPI VALLEY LATE IN THE WEEKEND OR MORE LIKELY EARLY NEXT
WEEK WHICH WILL RESULT IN HIGHER PRECIP CHANCES WHEN IT DOES
EVENTUALLY LIFT OUT. WOULD NOT BE AT ALL SURPRISED TO SEE MODELS
SLOW DOWN THE PROGRESSION OF THIS DEEP TROUGH WITH LATER RUNS AND
GFS ALREADY SEEMS TO BE SKIPPING MERRILY DOWN THIS PATH PUSHING
FROPA BACK TO MONDAY NOW.

IZZI

&&

.AVIATION...

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

* SOUTHWEST TO WEST WINDS...GUSTY AT TIMES. SPEEDS INCREASING THIS
  EVENING.

* LOW LEVEL WIND SHEAR LIKELY OVERNIGHT.

PAW

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

SOUTHWESTERLY WINDS CONTINUING THIS AFTERNOON AHEAD OF A COLD
FRONT APPROACHING FROM THE WEST. WIND SPEEDS INCREASING THIS
EVENING AND GUSTS PERSISTING OVERNIGHT AS THE FRONT GETS CLOSER.
THEN THE COLD FRONT WILL MOVE ACROSS THE TERMINALS LATE TONIGHT
THROUGH WEDNESDAY MORNING. LITTLE MOISTURE TO WORK WITH...SO LOOKS
LIKE A DRY FRONTAL PASSAGE WITH JUST SOME VFR-LEVEL CLOUDS. MODELS
SHOW A CORE OF STRONGER WINDS AT AROUND 2 TO 3 THOUSAND FEET
PASSING ACROSS NORTHERN ILLINOIS AND NORTHWEST INDIANA
OVERNIGHT...GIVING THE POTENTIAL FOR LOW LEVEL WIND SHEAR UNTIL
AROUND SUNRISE.

PAW

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

* HIGH CONFIDENCE IN WIND TREND...MEDIUM CONFIDENCE IN DETAILS.

* MEDIUM CONFIDENCE IN LOW LEVEL WIND SHEAR.

PAW

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

WEDNESDAY NIGHT...VFR.

THURSDAY...VFR.

FRIDAY...CHANCE OF TSRA...OTHERWISE VFR.

SATURDAY...CHANCE OF TSRA...OTHERWISE VFR.

SUNDAY...CHANCE OF TSRA...OTHERWISE VFR.

MONDAY...CHANCE OF TSRA...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
414 AM CDT

AS LARGE HIGH PRESSURE DEPARTS TO THE ATLANTIC COAST TODAY...A
TROUGH OF LOW PRESSURE CONTINUES TO MOVE EAST TOWARDS THE WESTERN
GREAT LAKES. THIS IS RESULTING IN SOUTHERLY WINDS INCREASING OVER
THE LENGTH OF THE LAKE THIS MORNING...AND IS EXPECTED TO CONTINUE
THROUGH MID MORNING WITH WINDS TOPPING OFF AT 15 TO 25 KT.
ALTHOUGH...THE PRESSURE GRADIENT OVER THE LAKE WILL RELAX THROUGH
THE AFTERNOON WITH WINDS DIMINISHING AS WELL. WITH THE LOW PUSHING
THROUGH THE CENTRAL GREAT LAKES REGION TONIGHT...THE PRESSURE
FIELD WILL BECOME MORE ORGANIZED WITH WINDS ONCE AGAIN INCREASING
AS THEY BECOME MORE SOUTHWEST AND THEN WEST LATE TONIGHT. WINDS
WILL DIMINISH AS THEY BECOME MORE NORTHERLY ON WEDNESDAY...WITH
FURTHER DIMINISHING EXPECTED TO OCCUR THROUGH THE REST OF THE WORK
WEEK.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$


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