Area Forecast Discussion

000
FXUS63 KLSX 222108
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
308 PM CST WED FEB 22 2012

.SHORT TERM...
ISSUED AT 227 PM CST WED FEB 22 2012
(THIS EVENING AND TONIGHT)

TEMPERATURES ACROSS MUCH OF THE AREA REACHED NEARLY 20 DEGREES
ABOVE NORMAL TODAY...DESPITE CLOUD COVER THROUGH MUCH OF THE EARLY
AFTERNOON. GUSTY SOUTHWEST WINDS WILL BEGIN TO TAPER OFF THIS
EVENING...THOUGH CONTINUED SOUTHERLY WINDS OVERNIGHT AHEAD OF THE
APPROACHING SYSTEM WILL KEEP LOW TEMPERATURES FROM DROPPING OFF
TOO MUCH. CURRENTLY HAVE OVERNIGHT LOWS IN THE LOWER 40S ACROSS
THE CWA...WHICH IS IN LINE WITH SREF...LOCAL WRF...AND GFS OUTPUT.

THE MAIN QUESTION DURING THIS TIME FRAME IS THE SOUTHWARD EXTENT OF
PRECIPITATION ASSOCIATED WITH A CLIPPER LIKE SYSTEM DROPPING OUT
OF THE NORTHERN PLAINS OVERNIGHT. THE ECMWF SEEMS A BIT
OVERZEALOUS IN BRINGING MEASURABLE PRECIPITATION AS FAR SOUTH AS THE
STL METRO AREA BY 12Z....SO HAVE SIDED WITH THE MORE CONSERVATIVE
GFS...NAM...AND SREF...INCLUDING LOW CHANCE POPS ACROSS
NORTHEASTERN MISSOURI AND WEST CENTRAL ILLINOIS. THOUGH THERE
APPEARS TO ONLY BE A SMALL WINDOW OF ENHANCED ISENTROPIC LIFT THAT
COULD HELP FACILITATE PRECIPITATION ACROSS THE NORTHERN TIER OF
THE CWA BEFORE THE AREA POTENTIALLY BECOMES DRY SLOTTED...THERE
IS STILL SOME UNCERTAINTY DUE TO THE LACK OF OVERALL MODEL
AGREEMENT REGARDING THE POSITION AND EASTWARD PROGRESSION OF THE
SYSTEM. ANY DEVIATION COULD GREATLY IMPACT THE EXTENT OF
PRECIPITATION RECEIVED IN THE CWA DURING THE EARLY MORNING HOURS.

JP

&&

.LONG TERM...
ISSUED AT 247 AM CST WED FEB 22 2012
(THURSDAY THROUGH TUESDAY)

THURSDAY CONTINUES TO PRESENT A GREAT DEAL OF UNCERTAINTY. THE SFC
LOW MENTIONED ABOVE CONTINUES TO DEEPEN SLIGHTLY WITH A WEAK CDFNT
PUSHING SWD. HOWEVER...THIS FNT LACKS POST-FRONTAL COLD AIR...BUT
DOES ADVECT IN MUCH DRIER AIR. THE PROGD 500MB MASS FIELDS WUD
SUGGEST AT LEAST A CHANCE OF PRECIP ON THURS. WITH MOST MDLS
PUSHING THE CDFNT SWD AHEAD OF THE MAIN TROF...BELIEVE IT WILL BE
DIFFICULT TO GET MUCH MORE THAN SPRINKLES. HOWEVER...THE ECMWF/GEM
SUGGEST A SFC LOW TRACK FURTHER S THAN THE OTHER MDLS. THIS SOLN
COUPLED WITH THE PROGD 500MB FIELD...WILL THEREFORE KEEP LOW
CHANCE POPS GOING FOR NOW.

AS FOR TEMPS ON THURSDAY...HAVE CONTINUED TREND AOA GUIDANCE AND
HOLD TEMPS STEADY OR SLOWLY DROP AFTER FROPA. FOR FRI...HAVE GONE
WITH A BLEND OF GUIDANCE AS AREA REMAINS UNDER CAA AND CLOUDS AS
THE SFC RIDGE BUILDS INTO THE REGION.

FOR THE EXTD...NOT MUCH TO DISCUSS THO PATTERN DOES BECOME MORE
ACTIVE...THO THE SYSTEMS SEEM TO HAVE LITTLE IMPACT ON THE CWA.
MDLS COMING INTO AGREEMENT WITH SYSTEM SUN NIGHT INTO MON. THE
ECMWF IS STILL NOT AS AMPLIFIED AS THE GFS/DGEX...THO STRONGER
THAN CYCLE YESTERDAY. HAVE KEPT POPS CAPPED AT LOW CHANCE DUE TO
CONTINUED UNCERTAINTY WITH THIS SYSTEM. GFS/DGEX ALSO SUGGEST A
LACK OF MOISTURE RETURN WHICH ALSO LIMITS PRECIP.

MDLS ALSO AGREE WITH A MUCH COLDER AIRMASS BEHIND THE SYSTEM INTO
TUES. HAVE CONTINUED A BLEND OF GUIDANCE THRU THE EXTD AS MDLS ARE
IN RELATIVE GOOD AGREEMENT.

TILLY

&&

.AVIATION...
ISSUED AT 1121 AM CST WED FEB 22 2012

WINDS AROUND 10-15KT HAVE SETTLED IN ACROSS THE AREA TODAY...THOUGH
GUSTS SEEM TO BE A BIT PATCHY. HOWEVER...WINDS HAVE BEEN
INCREASING THROUGH THE MORNING HOURS...SO STILL CONFIDENT THAT
GUSTS UP TO 20-25 KT WILL BE WIDESPREAD ACROSS THE AREA THROUGH
THE AFTERNOON HOURS. CURRENTLY EXPECTING GUSTS TO TAPER OFF DURING
THE EARLY EVENING HOURS...WITH THE WSW WINDS BACKING OVERNIGHT AND
BECOMING SOUTHERLY BY EARLY THURSDAY MORNING AHEAD OF THE NEXT
FRONT THAT WILL MOVE THROUGH KUIN LATE THURSDAY MORNING...AND KCOU
AND METRO AREA TAF SITES BY EARLY AFTERNOON. EXPECT CIGS TO REMAIN
SCT-BKN VFR THROUGH THE VALID TAF PERIOD...THOUGH THERE IS A
CHANCE FOR RAIN SHOWERS...PRIMARILY AFFECTING KUIN...DURING THE LATE
OVERNIGHT TO EARLY MORNING HOURS. CONFIDENCE IS STILL A BIT LOW AT
THIS TIME...SO HAVE ELECTED TO DEFER MENTION TO LATER TAF
ISSUANCES.

SPECIFICS FOR KSTL...

METRO AREA TAF SITES CAN EXPECT BKN-SCT VFR CIGS TO PERSIST
THROUGH THE VALID TAF PERIOD. SW WINDS WILL BECOME GUSTY AROUND
20-25KT THIS AFTERNOON...BEFORE TAPERING OFF EARLY THIS EVENING.
OVERNIGHT...WINDS WILL GRADUALLY BACK TO A MORE SOUTHERLY
DIRECTION AHEAD OF A FRONT THAT WILL MOVE THROUGH AROUND 18-19Z
THURSDAY AFTERNOON. EXPECT WESTERLY WINDS FOR KSTL THROUGH THE
END OF THE PERIOD POST-FROPA...THOUGH NOT EXPECTING GUSTS LIKE
THERE HAVE BEEN THE PAST FEW DAYS.

JP

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion