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000
FXUS63 KLOT 190557
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1257 AM CDT SUN MAY 19 2013

.DISCUSSION...

252 PM...MULTIPLE FORECAST CONCERNS AND CHALLENGES CONTINUE
THROUGH THE MIDDLE OF NEXT WEEK INCLUDING SEVERE POTENTIAL SUNDAY
AFTERNOON THROUGH MONDAY NIGHT...HEAVY RAIN POTENTIAL ESPECIALLY
MONDAY NIGHT THROUGH TUESDAY NIGHT ALONG WITH ASSOCIATED CLOUD
COVER...WINDS OFF THE LAKE/LAKE BREEZES AND THEIR AFFECTS ON
TEMPERATURES.

IN THE SHORT TERM...LOW LEVELS ARE NOW QUITE MOIST WITH DEWPOINTS
GENERALLY IN THE LOWER 60S WEST OF THE LAKE BREEZE. BROKEN TO AT
TIMES OVERCAST CU FIELD DEVELOPED EARLIER THIS MORNING WHICH
HELPED BUT THE BRAKES ON TEMPS MAKING IT INTO THE LOWER 80S...
THOUGH STILL A FEW LOCATIONS TAGGING 80. LACK OF INSTABILITY
HOWEVER HAS LIMITED SHOWER DEVELOPMENT WITH ISOLATED SHOWERS NOW
DEVELOPING SOUTH OF THE KANKAKEE RIVER. OTHER THAN AN ISOLATED
SPRINKLE/SHOWER...DRY WEATHER EXPECTED THROUGH SUNDAY MORNING.
WITH CONTINUED LIGHT WINDS AND CLEARING SKIES AS THE CU DISSIPATE
THIS EVENING...EXPECT AT LEAST SOME PATCHY FOG DEVELOPMENT AS
TEMPS COOL INTO THE LOWER 60S DEWPOINTS. THOUGH CONFIDENCE
REGARDING FOG DEVELOPMENT IS LOW.

CONVECTIVE TRENDS/POTENTIAL FROM SUNDAY AFTERNOON THROUGH MONDAY
NIGHT ARE FAIRLY UNCERTAIN. HOWEVER THERE APPEARS TO BE INCREASING
CONSENSUS...BOTH WITH TIMING AND LOCATION...OF A SHORTWAVE LIFTING
NORTHEAST ACROSS IOWA INTO SOUTHERN WISCONSIN SUNDAY AFTERNOON
INTO SUNDAY EVENING WITH INCREASING CHANCES FOR THUNDERSTORMS
SUNDAY AFTERNOON/EVENING. HOW FAR EAST THIS ACTIVITY MAY SPREAD
APPEARS TO BE THE MOST UNCERTAIN AND POPS MAY NEED TO BE ADJUSTED
AS WELL AS INCREASED AS TRENDS EMERGE. WITH THE UPPER RIDGE
BUILDING ACROSS THE REGION LATE TONIGHT...EXPECT HIGH TEMPS
SUNDAY TO BE WELL INTO THE MID/UPPER 80S WITH PERHAPS A FEW
LOCATIONS TAGGING 90. THESE TEMPS COMBINED WITH DEWPOINTS CREEPING
INTO THE UPPER 60S...PERHAPS EVEN 70 IN SOME LOCATIONS...WILL
PROVIDE PLENTY OF INSTABILITY IF THUNDERSTORMS ARE ABLE TO SPREAD
INTO THE CWA.

AS TIME GOES ON...CONFIDENCE DECREASES REGARDING CONVECTIVE
TRENDS AS TIMING DIFFERENCES AND LOCATIONS OF VARIOUS WAVES THEN
IMPACT FUTURE POTENTIAL CONVECTIVE TIME PERIODS. WITH ENOUGH
SUNSHINE AND ENOUGH OF A DRY PERIOD MIDDAY...EXPECT MONDAY COULD
BE AS WARM PERHAPS A FEW DEGREES WARMER THAN SUNDAY WITH HIGHS
BACK IN THE MID/UPPER 80S. ALSO STILL LOOKS BREEZY WHICH COULD
LOWER DEWPOINTS SOME IN THE AFTERNOON. SHOULD CONVECTION BE ABLE
TO FIRE...ATMOSPHERE REMAINS UNSTABLE AND SHEAR WOULD SUPPORT
CONTINUED SEVERE THREAT.

AS THE UPPER LOW OVER THE PLAINS SLOWLY SPINS EAST INTO THE
WESTERN LAKES TUESDAY AND WEDNESDAY...THIS SEEMS TO BE THE BEST
TIMING FOR A MORE PROLONGED/CONTINUED HEAVY RAIN THREAT. ANY OF
THE STORMS THAT FORM THROUGH THE MIDDLE OF NEXT WEEK WILL HAVE THE
POTENTIAL TO PRODUCE HEAVY RAIN...BUT WAVES OF MORE WIDESPREAD
STORMS WITH HEAVY RAIN APPEAR TO BE POSSIBLE LATE MONDAY NIGHT
INTO TUESDAY AND THEN AGAIN TUESDAY NIGHT INTO WEDNESDAY.
CONFIDENCE REGARDING RAINFALL AMOUNTS REMAINS LOW HOWEVER WITH
MODEL QPF STORM TOTAL AMOUNTS LOWER THAN 24 HOURS AGO. OF
COURSE...THIS DOESN/T DOWNPLAY THE POTENTIAL FOR WHAT COULD END UP
BEING SEVERAL INCHES OF RAIN IN PARTS OF THE AREA BY MIDWEEK...
JUST ADDS TO LOW CONFIDENCE REGARDING LOCATION/AMOUNTS.

LOW TEMPS APPEAR TO BE RATHER WARM IN THE 60S INTO WEDNESDAY
MORNING WITH HIGHS POTENTIALLY IN THE UPPER 70S/LOWER 80S BOTH
TUESDAY AND WEDNESDAY THOUGH CLOUD COVER/PRECIP DURATION/AMOUNTS
WILL DETERMINE JUST HOW WARM TEMPS ARE ABLE TO GO. LAKE BREEZES
AND OUTFLOWS FROM CONVECTIVE WAVES WILL ALSO MAKE TEMPERATURE
FORECASTS DIFFICULT. AS THE MAIN SURFACE LOW PASSES EAST OF THE
AREA THURSDAY/THURSDAY NIGHT...A COLD FRONT WILL PASS THROUGH THE
REGION...ENDING THE PRECIP WITH MUCH COOLER AND DRIER AIR EXPECTED
TO SPREAD ACROSS THE GREAT LAKES REGION INTO THE BEGINNING OF THE
HOLIDAY WEEKEND. CMS

&&

.AVIATION...

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

* PSBL PATCHY FOG/HAZE DEVELOPING BY 09-10Z. SLIGHT VSBY REDUCTION
  AT ORD/MDW TO ARND 5SM. PATCHY STARTUS CLOUDS ARND 1KFT AGL MAY
  DEVELOP...SHUD REMAIN FEW/SCT IN COVERAGE.

* LIGHT E WINDS ARND 5KT OR LESS THRU DAYBREAK. WINDS SLOWLY TURN
  SE...THEN INCREASE SHORTLY AFT DAYBREAK TO 10-13KT WITH
  OCCASIONAL GUSTS TO 16-18KT.

* DRY WEATHER SHUD HOLD MUCH OF THE DAY...PSBL TSRA LATE THIS
  EVENING. MAY BRING PATCHY MVFR CIGS WITH PRECIP.

BEACHLER

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

IR IMAGERY EARLY THIS MORNING INDICATES QUIET WEATHER FOR MUCH OF
THE AREA...HOWEVER TO THE WEST A LARGE AREA OF THUNDERSTORMS
EXISTS. IT APPEARS BASED ON THE LATEST GUIDANCE THAT DRY CONDS
WILL CONTINUE THRU TONIGHT...AND POSSIBLY THRU MUCH OF THE DAY
TODAY. WITH ABUNDANT LLVL MOISTURE STEADILY LIFTING NORTH ACROSS
THE AREA...AIRFIELDS MAY BEGIN TO SEE A SLIGHT REDUCTION IN VSBYS
AS A RESULT IN THE COMBINED MOISTURE AND LIGHT WINDS. WINDS WILL
GENERALLY REMAIN LIGHT FROM THE EAST...HOWEVER THEY MAY BECOME VRB
FOR A FEW HOURS. THEN ARND DAYBREAK WINDS WILL SOLIDIFY FROM THE
SOUTHEAST AND BEGIN TO INCREASE. AT THIS TIME IT APPEARS SPEEDS
WILL GENERALLY BE 10-12KT LATE THIS MORNIGN...WITH OCCASIONAL
GUSTS BETWEEN 16-19KT. HIGH BASED CLOUDS WILL BEGIN TO ARRIVE FROM
THE COMPLEX OF THUNDERSTORMS TO THE WEST OF IL. FOR THE BULK OF
TODAY IT WILL REMAIN DRY...HOWEVER AS THE MID-LVL FEATURE THAT
CONTINUES TO PROVIDE A BLOCK TO THE STORMS OVER NORTHERN
IL/NORTHWEST IN DRIFTS EAST...THE CHANCES FOR CONVECTION INCREASE.
THE TIMING FOR THIS TO OCCUR CONTINUES TO FLUCTUATE...ALTHOUGH
GENERAL CONSENSUS HAS BEEN ARND A 3-5Z MON TIMEFRAME. LCL GUIDANCE
INDICATES EVEN LATER THAN THIS. AS THUNDERSTORMS DEVELOP AND
APPROACH THE REGION...THEY WILL MOST LIKELY PRODUCE REDUCED
VSBYS/CIGS TO MVFR CONDS. WINDS WILL STEADILY TURN TO THE SOUTH.

BEACHLER


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

* HIGH CONFIDENCE IN WIND DIR/SPEED THRU MID-MORNING.
* MEDIUM CONFIDENCE IN WIND FORECAST FROM MIDDAY THRU TONIGHT.
* LOW CONFIDENCE IN TIMING OF PRECIPITATION/THUNDERSTORMS THIS
  EVENING.

BEACHLER

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

MONDAY-TUESDAY...PERIODS OF TSRA. GUSTY SSW WINDS ON MONDAY.

WEDNESDAY...LIKELY TSRA DURING THE DAY. CHANCE OF SHRA AT NIGHT.

THURSDAY...CHANCE OF SHRA.

FRIDAY...VFR LIKELY.

MTF

&&

.MARINE...
151 PM CDT

A SURFACE RIDGE OF HIGH PRESSURE CONTINUES TO BUILD
EASTWARD ACROSS EASTERN QUEBEC AND THE NORTHEASTERN CONUS THIS
AFTERNOON. HOWEVER...ATTENTION IS QUICKLY TURNING OUT WEST ACROSS
THE CENTRAL HIGH PLAINS...WHERE AN AREA OF LOW PRESSURE IS TAKING
SHAPE THIS AFTERNOON. THIS STORM SYSTEM IS EXPECTED TO MOVE
EAST-NORTHEASTWARD TOWARDS THE MID MISSOURI VALLEY BY SUNDAY
EVENING. AN ASSOCIATED SURFACE WARM FRONT...EXTENDING EASTWARD
ACROSS THE MID MISSISSIPPI VALLEY...WILL MOVE NORTHWARD ACROSS AT
LEAST THE SOUTHERN HALF TO TWO THIRDS OF THE LAKE SUNDAY NIGHT AND
MONDAY. BEHIND THIS FRONT WINDS LOOKS TO INCREASE OUT
OF THE SOUTH IN THE 15 TO 25 KT RANGE SUNDAY NIGHT INTO MONDAY.
HOWEVER...TO THE NORTH OF THIS FRONT...WINDS WILL PRIMARILY BE
MORE EASTERLY. THERE IS SOME UNCERTAINTY IN HOW FAR NORTH UP THE LAKE
THIS WARM FRONT WILL REACH. IT IS POSSIBLE THAT IT NEVER REACHES THE
NORTHERN THIRD OF THE LAKE...WHICH WOULD RESULT IN EASTERLY WINDS
REMAINING IN PLACE THERE DURING THE PERIOD.

THE OTHER CONCERN WILL BE THE THREAT FOR PERIODS OF DENSE MARINE FOG
SUNDAY NIGHT AND INTO AT LEAST THE FIRST PART OF THE COMING WEEK. AS
THIS WARM FRONT LIFTS OVER THE LAKE...MUCH HIGHER DEW POINTS WILL
MOVE OVER THE RELATIVELY COLD WATER...POSSIBLY RESULTING IN SOME
FOG DEVELOPMENT.

IT APPEARS THAT THE SURFACE LOW WILL SLOWLY MOVE EASTWARD ACROSS THE
MID MISSISSIPPI VALLEY THROUGH MID WEEK AND THEN ACROSS THE SOUTHERN
LAKES AND THE OHIO VALLEY LATER IN THE WEEK. THIS SHOULD ALLOW WARM
FRONT TO SHIFT BACK SOUTHWARD WITH TIME DURING THE WEEK. DURING THIS
TIME...THE WIND DIRECTIONS WILL PRIMARILY BECOME EAST NORTHEASTWARD
15 TO 25 KT NORTH OF THE FRONT. LATER IN THE WEEK...AS THE SURFACE
LOW PASSES EAST OF LAKE MICHIGAN...THE WINDS LOOK TO BE RATHER STOUT
UP TO 25 TO POSSIBLY AS HIGH AS 30 KT OUT OF THE NORTH FOR A PERIOD
AS A GOOD AREA OF HIGH PRESSURE BUILDS EASTWARD ACROSS ONTARIO AND
THE UPPER GREAT LAKES REGION.

KJB

&&

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

$$

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