FXUS63 KLSX 111151
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
452 AM CST FRI DEC 11 2009

.DISCUSSION...
/258 AM CST FRI DEC 11 2009/

FOCUS OF THIS FORECAST IS THE CHANCES OF/TYPE OF LIGHT PRECIPITATION 
THIS WEEKEND.  MODELS SHOWING THE SAME BASIC UPPER PATTERN THEN NEXT 
48-72 HOURS WITH ELONGATED E-W ORIENTED TROUGH OVER CANADA AND 
QUASI-ZONAL FLOW OVER THE CONUS. 

EXPECT TO STAY DRY THROUGH MIDDAY SATURDAY AS ATMOSPHERE REMAINS DRY 
UNDER NEUTRAL OR SUBSIDENT VERTICAL MOTION AS HEIGHTS RISE ACROSS
THE AREA. GFS/NAM ARE SHOWING SIMILAR TIMING AND STRENGTH WITH LOW
AMPLITUDE SHORTWAVE TROUGH THAT WILL RACE ACROSS MO/IL TOMORROW
NIGHT. SURFACE HIGH OVER THE MID-SOUTH WILL MOVE EAST TODAY AND LOW
LEVEL LOW WILL TURN OUT OF THE SOUTH BY EARLY SATURDAY WHICH WILL
ADVECT MOISTURE INTO THE REGION. INSENTROPIC ANALYSIS SUGGESTS
AN INCREASING CHANCE OF LIGHT RAIN OR DRIZZLE BY LATE SATURDAY
WITH A BETTER CHANCE FOR MEASUREABLE OF RAIN ON SATURDAY NIGHT AS
WEAK ASCENT INCREASES IN ADVANCE OF UPPER TROUGH. LOW LEVEL
MOISTURE WILL REMAIN OVER THE REGION ON SUNDAY MORNING IN THE WAKE
OF THE TROUGH KEEPING DRIZZLE A POSSIBILITY BEFORE DRYING OCCURS
ON SUNDAY AFTERNOON. DECIDING ON PRECIPITATION TYPE WILL BE A
CLOSE CALL AS LOW LEVEL THERMAL PROFILES WILL BE CLOSE TO FREEZING.
FOR NOW...COMBINATION OF GFS/NAM MOS/2M LOCAL WRF AND 2M SREF MEAN
TEMPS SUGGEST THAT PERSISTENT SLY FLOW AND CLOUDS SHOULD BE ENOUGH
TO KEEP MOST OF THE PRECIP LIQUID EXCEPT FOR A BRIEF PERIOD OVER
PARTS OF NERN MO LATE SATURDAY NIGHT/SUNDAY MORNING.

DEEPER TROUGH AND ASSOCIATED COLD FRONT WILL MOVE ACROSS THE MIDWEST 
MONDAY/MONDAY NIGHT BUT HAVE KEPT ONLY SLIGHT CHANCES GOING AS
GULF MOISTURE GETS CUTOFF AS LOW LEVEL MOISTURE TURNS W-SWLY
BEHIND WEEKEND SYSTEM AND BEST DYNAMICS STAY OVER THE GREAT LAKES.

BRITT
&&

.AVIATION...
/452 AM CST FRI DEC 11 2009/

FOR THE 12Z TAFS...AS SURFACE RIDGE MOVES OFF TO THE EAST...WINDS 
WILL SWITCH TO THE SOUTH FOR THE REST OF THE FORECAST VALID TIME. AS 
FOR SKY COVER...CIRRUS ALONG AND SOUTH OF I-70 SHOULD MOVE OUT BY 
MIDDAY...WITH ANOTHER BATCH MOVING INTO THE AREA THIS EVENING.

BYRD
&&

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

$$

WFO LSX