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000
FXUS63 KLOT 210535
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1235 AM CDT TUE MAY 21 2013

.DISCUSSION...
257 PM CDT

SHORT TERM (TONIGHT)...

POTENTIAL WILL EXIST FOR CONVECTION TO DEVELOP THIS EVENING OVER
SOUTHEASTERN CWA...BUT BETTER CHANCES FOR THUNDERSTORMS TONIGHT
LOOKS TO BE LATER THIS EVENING INTO THE OVERNIGHT HOURS OF LEFT OVER
CONVECTION THAT DEVELOPS OVER THE EASTERN PLAINS SPILLS EASTWARD
INTO THE AREA. SUBSIDENCE IN THE WAKE OF THIS EVENING`S MCV WILL
LIKELY RESULT IN MUCH OF THE EVENING HOURS REMAINING DRY NORTHWEST
OF INTERSTATE 55 WITH PRECIP CHANCES LIKELY HOLDING OFF UNTIL LATE
EVENING OR MORE LIKELY AFTER MIDNIGHT.

IZZI

LONG TERM (TUESDAY AND BEYOND)...

TUESDAY AND TUESDAY NIGHT...TRYING TO TIME THE MOST LIKELY
PERIODS FOR THUNDERSTORMS WILL BE THE MAIN CHALLENGE THROUGH
WEDNESDAY. THE UPPER LOW WILL CONTINUE TO SPIN OVER WESTERN
MINNESOTA AND SURROUNDING AREAS TUESDAY. CONVECTION MAY BE ONGOING
TUESDAY MORNING BUT SHOULD PRIMARILY BE SHIFTING OFF TO THE NORTH
AND EAST. IT APPEARS THAT SOME MID LEVEL DRYING WILL WORK INTO THE
AREA WHICH SHOULD ALLOW FOR A BREAK IN ORGANIZED CONVECTIVE
CHANCES THROUGH EARLY IF NOT LATE AFTERNOON. HOWEVER...AFTERNOON
HEATING MAY BE ENOUGH TO ENHANCE THE THREAT FOR STORM DEVELOPMENT
AS WILL ANY WEAK WAVE THAT CAN COME THROUGH THE FLOW...WHICH AT
THIS TIME IS INDISCERNIBLE. IN ADDITION...SHOULD CONVECTION CROSS
THE AREA TONIGHT THEN OUTFLOW BOUNDARIES LEFT BEHIND MAY SERVE AS
A TRIGGER DURING THE AFTERNOON AS WELL. HAVE BETTER CONFIDENCE IN
POPS TUESDAY EVENING AND TUESDAY NIGHT. A CLOSER LOOK AT CURRENT
WATER VAPOR IMAGERY SHOWS A TROUGH PIVOTING SOUTHWARD INTO THE
FOUR CORNERS. THIS IS EXPECTED TO ROUND THE BASE OF THE UPPER LOW
AND TRACK NORTHEASTWARD ACROSS THE LOCAL AREA TUESDAY NIGHT. THIS
WILL HELP NEW SURFACE LOW PRESSURE TO DEVELOP AHEAD OF THE UPPER
TROUGH ACROSS CENTRAL ILLINOIS AND MOVE RIGHT ACROSS THE AREA
EARLY WEDNESDAY MORNING. WILL TIE THE HIGHEST POPS WITH THE
PASSAGE OF THIS FEATURE...GIVEN THAT IT IS THE MOST COHERENT. THIS
MAY LEAVE MUCH OF THE EVENING WITH MINIMAL PRECIP COVERAGE BEFORE
MORE WIDESPREAD ACTIVITY ARRIVES FROM SOUTH TO NORTH LATE EVENING
OR AFTER. WITH THE EXPECTATION OF LOWER PRECIP COVERAGE DURING THE
DAY HAVE RAISED HIGHS SEVERAL DEGREES AND MAY NEED TO GO HIGHER IF
ENOUGH SUNSHINE CAN DEVELOP AND MIXING CAN DEEPEN ENOUGH.

WEDNESDAY AND THURSDAY...THE UPPER TROUGH NOW APPROACHING THE
BRITISH COLUMBIA COAST WILL DROP SOUTHWARD AND CLOSE OFF OVER THE
PACIFIC NORTHWEST AND HELP TO PUSH THE MINNESOTA UPPER LOW EASTWARD.
THE LOW WILL OPEN UP IN TO MORE OF A TROUGH WITH THE AXIS CROSSING
THE AREA WEDNESDAY NIGHT. EXPECT THAT SHOWERS/THUNDERSTORMS WILL BE
EXITING THE AREA WEDNESDAY MORNING WITH A POTENTIAL BREAK IN THE
ACTIVITY BEFORE ANOTHER ROUND OF SHOWERS AND MAYBE SOME STORMS
ARRIVE WEDNESDAY EVENING/NIGHT WITH THE TROUGH AXIS. THESE LOOK TO
EXIT QUICKLY THURSDAY MORNING. BY THIS TIME THE UPPER AIR PATTERN
WILL HAVE EVOLVED INTO A LONGWAVE OVER THE AREA WITH A SHARP RIDGE
OVER THE HIGH PLAINS INTO THE CANADIAN PRAIRIES AND A BIG CLOSED
UPPER LOW OVER THE FAR WESTERN U.S. THE PASSAGE OF THE TROUGH WILL
MARK THE ARRIVAL OF NOTICEABLY COOLER AIR AS LOW LEVEL FLOW TURNS
NORTHERLY AND HIGH PRESSURE BUILDS IN.

FRIDAY THROUGH MONDAY...QUIET WEATHER IS EXPECTED FRIDAY AND AT
LEAST EARLY SATURDAY AS HIGH PRESSURE REMAINS IN CONTROL THEN SHIFTS
EAST. THE UPPER RIDGE WILL PUSH EASTWARD ALLOWING WARM ADVECTION TO
RETURN SOMETIME SATURDAY WHICH MAY RESULT IN SOME PRECIPITATION
THROUGH THE WEEKEND. TEMPERATURES WILL SLOWLY MODERATE THROUGH THE
WEEKEND...WITH HIGHS MAINLY IN THE LOW TO MID 60S FRIDAY AND WARMING
A FEW DEGREES EACH DAY...WITH 70S BY MONDAY. HIGHS ALONG THE LAKE
WILL LIKELY BE HELD IN THE 50S THROUGH THE WEEKEND.

MDB

&&

.AVIATION...

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

* SHOWERS AND A FEW EMBEDDED THUNDERSTORMS NEXT FEW HOURS.

* STRONG GUSTY SSW WINDS DEVELOPING DURING THE DAY TUESDAY.

* ANOTHER ROUND OF THUNDERSTORMS LIKELY TUESDAY NIGHT.

ALLSOPP

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

MAIN LINE OF THUNDERSTORMS HAS MOVED EAST INTO NORTHWEST INDIANA
AND EAST CENTRAL ILLINOIS. LINGERING SHOWERS BACK THROUGH CENTRAL
ILLINOIS WILL CONTINUE TO SPREAD NNE THROUGH THE CHICAGO METRO AREA
FOR NEXT FEW HOURS WITH SOME EMBEDDED THUNDER. MVFR CIGS/VSBYS AT
TIMES IN HEAVIER SHOWERS BUT EXPECT VFR CONDITIONS IN BREAKS AND
LIGHTER SHOWERS. THIS ENTIRE AREA SHOULD DISSIPATE AND MOVE OUT OF
THE AREA BEFORE DAYBREAK. A SECOND NARROW LINE OF SHOWERS AND
THUNDERSTORMS OVER EASTERN IOWA APPEARS TO BE WEAKENING AND DON`T
EXPECT THIS TO HOLD TOGETHER LONG ENOUGH TO IMPACT CHICAGO.

WINDS MAY FLOP AROUND A BIT NEXT HOUR OR TWO IN THE WAKE OF THE
MAIN BAND OF THUNDERSTORMS BUT EXPECT PREVAILING WINDS TO BE SOUTH
AROUND 10 KTS THROUGH THE OVERNIGHT HOURS.

IN THE WAKE OF THESE SHOWERS AND THUNDERSTORMS...EXPECT
SUBSIDENCE/DRYING THROUGH THE MORNING. SCATTERED THUNDERSTORMS ARE
NOT OUT OF THE QUESTION DURING THE DAY TUESDAY BUT EXPECT THE
MAIN ACTION TO BE ASSOCIATED WITH A SHORT WAVE TROF MOVING THROUGH
NEW MEXICO...THIS WILL BE ROUNDING THE BASE OF THE LARGE PLAINS
TROF TUESDAY AFTERNOON AND MOVING RAPIDLY NORTHEAST TUESDAY NIGHT.
HAVE MAINTAINED TEMPO THUNDER AFTER 03Z WED.

ALLSOPP


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

* MEDIUM-LOW CONFIDENCE IN CIG/VSBY NEXT FEW HOURS IN SHOWERS.

* MEDIUM-HIGH CONFIDENCE IN VFR CONDITIONS PREVAILING THROUGH THE DAY TUESDAY.

* MEDIUM CONFIDENCE IN WIND FORECAST NEXT FEW HOURS.

* HIGH CONFIDENCE  IN WIND FORECAST TUESDAY.

ALLSOPP

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

WEDNESDAY...SCT SHRA/TSRA AND POSSIBLE MVFR CONDITIONS.
THURSDAY...CHC OF SHRA. GUSTY NE WINDS.
FRIDAY...VFR LIKELY.
SATURDAY...SLT CHC OF TSRA.
SUNDAY...CHC OF TSRA.

MTF

&&

.MARINE...
314 PM CDT

LOW PRESSURE OVER THE NORTHERN PLAINS WILL MOVE VERY LITTLE
TONIGHT BEFORE SLOWLY SHIFTING EAST TOWARDS THE UPPER MIDWEST AND
WESTERN GREAT LAKES ON TUESDAY. WITH THIS IN PLACE...STRONGER
SOUTHERLY WINDS WILL OCCUR OVER MUCH OF THE LAKE TONIGHT BEFORE
DIMINISHING ON TUESDAY WITH THIS LOW WEAKENING WHILE MOVING ACROSS
THE GREAT LAKES. LIGHTER WINDS WILL BE IN PLACE BRIEFLY TUESDAY
NIGHT AS THE LOW MOVES OVERHEAD BUT THEN INCREASE ONCE AGAIN ON
WEDNESDAY WHILE TURNING MORE NORTHERLY. EXPECT BOTH WINDS AND
WAVES TO INCREASE/BUILD WEDNESDAY NIGHT INTO THURSDAY...BEFORE
HIGH PRESSURE DROPS SOUTH THROUGH THE PLAINS AND UPPER MIDWEST
INTO THURSDAY NIGHT AND WINDS DIMINISH ONCE AGAIN INTO FRIDAY.

RODRIGUEZ

&&

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

$$

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