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000
FXUS63 KLSX 220454
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1154 PM CDT TUE MAY 21 2013

.UPDATE...
ISSUED AT 943 PM CDT TUE MAY 21 2013

MOST OF THE SHOWER AND THUNDERSTORM ACTIVITY HAS REMAINED TO OUR
S AND E SO FAR THIS EVNG. STILL THINKING THAT ADDITIONAL
CONVECTION WILL LIKELY DEVELOP AND MOVE THROUGH PORTIONS OF SERN
MO AND SWRN IL LATE TGT...MAINLY S AND E OF STL AS THE STRONG
SHORTWAVE MOVING E-NEWD THROUGH ERN OK MOVES THROUGH NRN AR AND
INTO SERN MO BY 12Z WED. MODELS STILL DEPICTING UPPER LEVEL
DIVERGENCE TGT ACROSS MAINLY SERN MO AND SWRN IL AHEAD OF THE
APPROACHING UPPER LEVEL TROUGH. A S-SWLY LOW LEVEL JET WILL BRING
LOW LEVEL MOISTURE CONVERGENCE ACROSS SERN MO AND SWRN IL. THE
BEST LOW LEVEL MOISTURE AND INSTABILITY WILL ALSO EXIST OVER THIS
AREA AHEAD OF THE WEAK COLD FRONT EXTENDING FROM ERN IA AND NERN
MO SW THROUGH SWRN MO AND SERN KS. LOW TEMPERATURES TGT AHEAD OF
THIS WEAK COLD FRONT SHOULD CONTINUE ABOVE NORMAL DUE TO THE CLOUD
COVER AND RELATIVELY HIGH SFC DEW POINTS.

GKS

&&

.SHORT TERM...(THROUGH LATE TONIGHT)
ISSUED AT 314 PM CDT TUE MAY 21 2013

THE OVERALL SEVERE WEATHER THREAT HAS DIMINISHED SIGNIFICANTLY
FROM EARLIER THINKING OWING TO A SERIES OF MCS`S TRACKING TO OUR
SOUTH FROM OKLAHOMA TO ARKANSAS INTO THE TN VALLEY. THESE SYSTEMS
HAVE PRODUCED A GOOD DEAL OF CLOUD COVER WHICH HAS LIMITED HEATING
AND THAT COMBINED WITH MUCH WEAKER LAPSE RATES HAS LIMITED THE
INSTABILITY. THE HIGHEST VALUES OF SBCAPE PRESENTLY ARE FROM
1000-2000 J/KG EXTENDING FROM METRO ST LOUIS INTO EAST CENTRAL
IL...THIS HALF OR LESS THE AMOUNT OF THE PREVIOUS FEW DAYS. ALL
THIS SAID THE PRECIPITATION CHANCES STILL LOOK PRETTY HIGH TONIGHT
ACROSS EASTERN MO INTO SRN IL. WE MIGHT SEE SOME ISOLATED STORMS
DEVELOP IN THIS HIGHER CAPE AIR THRU SUNSET AND WE WILL ALSO SEE
THE NORTHERN PORTION OF THE STRATI FORM RAIN REGION OF THE AR MCS
IMPACT SE MO INTO SRN IL. THE MAIN THREAT OF PRECIPITATION HOWEVER
APPEARS TO BE LATER THIS EVENING INTO THE OVERNIGHT HOURS. WATER
VAPOR IMAGERY AND VWP DATA IS SHOWING A POWERFUL SHORT WAVE ACROSS
EXTREME WRN OK AND THIS WILL EJECT ENEWD TONIGHT AND BE CENTERED
THRU ERN MO AT DAYBREAK ON WED. DEEP LARGE SCALE ASCENT ASSOCIATED
WITH THIS SHORT WAVE SHOULD LEAD TO AN UPSWING IN SHOWERS AND
THUNDERSTORMS LATER THIS EVENING. I CANT RULE OUT AN ISOLATED
SEVERE THREAT BUT AGAIN THE MARGINAL INSTABILITY WOULD SUGGEST THE
CHANCE IS LOW. RAINFALL AMOUNTS WILL BE SUBSTANTIALLY LESS THAN
LAST NIGHT...LESS THAN AN INCH.

GLASS

.LONG TERM...(WEDNESDAY THROUGH NEXT TUESDAY)
ISSUED AT 314 PM CDT TUE MAY 21 2013

THE MAJORITY OF THE PRECIPITATION SHOULD BE EAST OF THE MS RIVER
IN ILLINOIS OR FURTHER EAST AT DAYBREAK AND CONTINUE TO MOVE
EASTWARD AS THE SHORTWAVE TROF AND ATTENDANT COLD FRONT MOVE EAST.
COOLER AND DRIER AIR WILL OVERSPREAD THE REGION IN THE WAKE OF THE
FRONT AND ANY ADDITIONAL PRECIPITATION THREAT AFTER MID-MORNING
SHOULD BE FROM ISOLATED DIURNAL SHOWERS. ANOTHER SECONDARY COLD
FRONT WILL PUSH THROUGH THE AREA WED NIGHT USHERING HIGH PRESSURE
AND EVEN COOLER AIR INTO THE AREA. THIS LARGE HIGH WILL DOMINATE
THE AREA THURSDAY INTO FRIDAY.

NOT MUCH HAS CHANGED IN THE EXTENDED RANGES OF THE FORECAST. AN
UPPER RIDGE WILL DOMINATE THE CENTRAL U.S. WITH THE RIDGE AXIS
REMAINING JUST WEST OF MISSOURI SAT-MON. THIS WILL PLACE US JUST
DOWNSTREAM OF THE RIDGE CREST AND SUBJECT TO WEAK SHORT WAVES
TOPPING THE RIDGE. THESE DISTURBANCES COMBINED WITH RETURN FLOW
AND LOW LEVEL WAA ON THE BACKSIDE OF THE RETREATING LOW LEVEL HIGH
PRESSURE SYSTEM WILL BRING A PROLONGED THREAT OF SHOWERS AND
THUNDERSTORMS TO PRIMARILY THE NORTHERN HALF OF THE CWA FROM SAT
THROUGH MON NIGHT. THEREAFTER THE UPPER RIDGE AXIS MOVES TO OUR
EAST...PRECIPITATION CHANCES DIMINISH AND TEMPERATURES WARM.

GLASS

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1148 PM CDT TUE MAY 21 2013

RECENT RADAR IMAGERY IS SHOWING RAIN DEVELOPING IN FAR SOUTHWEST
MISSOURI THAT WILL MOVE NORTHEAST AND IMPACT THE ST. LOUIS METRO
TAF SITES BEFORE 12Z. A WEAK STORM SYSTEM WILL MOVE ACROSS NORTHERN
MISSOURI ON WEDNESDAY WHICH MAY BRING LIGHT SHOWERS TO KUIN DURING
THE AFTERNOON. EXPECT MANY VFR CONDITIONS THROUGH THE PERIOD
EXCEPT FOR MVFR CONDITIONS WITH SHOWERS.

SPECIFICS FOR KSTL...RAIN DEVELOPING OVER SOUTHWEST MISSOURI WILL
MOVE NORTHEAST THE NEXT FEW HOURS AND MOVE INTO THE TERMINAL
BEFORE 12Z. OTHERWISE...DRY AND VFR CONDITIONS ARE EXPECTED.

BRITT

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

$$

WFO LSX