Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 272342
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
642 PM CDT THU AUG 27 2015

.SHORT TERM:  (THROUGH LATE TONIGHT)
ISSUED AT 251 PM CDT THU AUG 27 2015

THUNDERSTORMS OVER NORTHWEST MISSOURI HAVE BEGUN TO DIMINISH AT
MIDDAY IN AREAL COVERAGE AS LOW LEVEL MOISTURE CONVERGENCE HAS
DIMINISHED IN RESPONSE TO LOW LEVEL JET BACKING.  BELIEVE THAT OUR
AREA WILL STAY DRY THROUGH MOST OF THE NIGHT WITH THE EXCEPTION OF
THE FAR NORTHWESTERN PART OF THE AREA LATE TONIGHT.  BY LATE TONIGHT
WEAK SHORTWAVE TROUGH NOW MOVING ACROSS CENTRAL HIGH PLAINS WILL
MOVE EAST SUPPLYING ASCENT THAT WILL EVENTUALLY MOVE INTO NORTHERN
MISSOURI AFTER MIDNIGHT.  THIS ASCENT IN ADDITION TO THE LEVEL JET
WHICH WILL VEER AGAIN AND WILL PROVIDE ADDITIONAL LOW LEVEL
CONVERGENCE UNDERNEATH THE ASCENT THAT WILL BE ENOUGH FOR
THUNDERSTORM DEVELOPMENT LATER THIS EVENING AND OVERNIGHT OVER IOWA
AND NORTHERN MISSOURI. SO WILL MAINTAIN A SLIGHT CHANCE OF
THUNDERSTORMS LATE TONIGHT OVER NORTHEAST MISSOURI.

A COMPROMISE OF MOS GUIDANCE LOOKS REASONABLE GIVEN THAT THEY ARE
CLOSE TO CURRENT DEWPOINTS WITH CLOUD COVER ALREADY MOVING OVER THE
AREA.

BRITT

.LONG TERM:  (FRIDAY THROUGH NEXT THURSDAY)
ISSUED AT 253 PM CDT THU AUG 27 2015

SHOWERS AND STORMS WILL LIKELY MOVE THROUGH PARTS OF NORTHEAST AND
CENTRAL MO AND WEST CENTRAL IL...NORTH AND WEST OF STL ON FRIDAY AS
A SOUTHWESTERLY LOW LEVEL JET BRINGS INCREASING LOW LEVEL MOISTURE
INTO THIS AREA AHEAD OF AN APPROACHING UPPER LEVEL TROUGH OVER
THE NORTHERN PLAINS AND ITS ASSOCIATED SURFACE LOW MOVING EASTWARD
THROUGH WESTERN IA ALONG WITH ITS TRAILING COLD FRONT. THE THREAT
FOR CONVECTION MAY SHIFT AS FAR SOUTHEASTWARD AS THE STL AREA BY
12Z SATURDAY AS THE SURFACE LOW MOVES EASTWARD THROUGH EASTERN IA
AND DRAGS THE COLD FRONT INTO THE NORTHWESTERN PORTION OF OUR
FORECAST AREA. THE CONVERGENCE ALONG THE COLD FRONT WILL WEAKEN AS
IT MOVES SLOWLY SOUTHEASTWARD THROUGH OUR FORECAST AREA SATURDAY
AND SATURDAY NIGHT AS THE UPPER LEVEL TROUGH MOVES EASTWARD
THROUGH THE GREAT LAKES REGION. THE NAM MODEL SEEMS A LITTLE TOO
SLOW WITH THE PROGRESSION OF THE UPPER TROUGH AND ASSOCIATED COLD
FRONT AND MAY BE A LITTLE TOO STRONG. ITS POPS AND QPF MAY ALSO
BE TOO HIGH FOR FRIDAY NIGHT THROUGH SATURDAY NIGHT. PREFER THE
MODEL SOLUTIONS OF THE ECMWF AND GFS WHICH HAVE LIGHTER AND MORE
SCATTERED QPF FOR SATURDAY AND SATURDAY NIGHT. WILL REDUCE THE
POPS INTO THE SLIGHT CHANCE CATAGORY ACROSS SOUTHEAST MO AND
SOUTHWEST IL BY LATE SATURDAY NIGHT AND SUNDAY ALONG AND AHEAD OF
THE WEAK COLD FRONT AND A WEAK UPPER LEVEL TROUGH...SHEAR AXIS.
ANY NOTICEABLE COOLING BEHIND THIS FRONT WILL BE MAINLY ACROSS
NORTHEAST MO SATURDAY AND SATURDAY NIGHT. THE MODELS TRY TO BUILD
AN UPPER LEVEL RIDGE NORTHEASTWARD INTO NORTHERN MO FOR THE NEXT
WORK WEEK WITH WEAK UPPER LEVEL TROUGHING OR A SHEAR AXIS
REMAINING NEAR SOUTHEAST MO AND SOUTHWEST IL. SURFACE AND LOW
LEVEL WINDS WILL BE MAINLY SOUTHEASTERLY/SOUTHERLY WITH SURFACE
AND 850 MB RIDGING EAST OR SOUTHEAST OF THE AREA. TEMPERATURES
SHOULD BE SLIGHTLY ABOVE NORMAL. WILL KEEP THE FORECAST DRY FROM
SUNDAY NIGHT THROUGH THE REMAINDER OF THE EXTENDED FORECAST...
ALTHOUGH COULD NOT RULE OUT A FEW SHOWERS/STORMS MAINLY ACROSS
SOUTHEAST MO/SOUTHWEST IL NEAR WEAK UPPER LEVEL LOWS/TROUGHING
...SHEAR AXIS.

GKS

&&

.AVIATION:  (FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 629 PM CDT THU AUG 27 2015

EXPECT VFR FLIGHT CONDITIONS AND SLOWLY INCREASING SOUTH-
SOUTHEASTERLY FLOW THROUGH FRIDAY EVENING. SOME FOG IS POSSIBLE
AGAIN TONIGHT IN RIVER VALLEYS, THOUGH IT MAY NOT BE AS DENSE OR
LONG LASTING AS THIS MORNING. MORE HIGH CLOUD COVER AND INCREASING
BOUNDARY LAYER WINDS WILL HINDER FOG DEVELOPMENT...SO I BACKED OFF
PREVAILING 2 MILES AT KSUS AND KCPS TO TEMPO. WILL SEE HOW THE
NIGHT SHAPES UP...MAY NEED TO BACK OFF FURTHER.

SPECIFICS FOR KSTL:

VFR FLIGHT CONDITIONS WILL PREVAIL AT LAMBERT THROUGH FRIDAY
EVENING. EXPECT THE WIND TO GRADUALLY CONTINUE VEERING TO THE
SOUTHEAST AND WILL INCREASE TO 8-12KTS BY LATE FRIDAY MORNING.

CARNEY

&&

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

$$

WFO LSX


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