000
FXUS63 KLSX 200505
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1105 PM CST WED NOV 19 2008
.UPDATE...
/914 PM CST WED NOV 19 2008/
COLD AIR SC MAKING SLOW BUT STDY SWD PROGRESS INTO N MO AND W
CNTRL IL ATTM...AND SEE NO REASON FOR THIS MVMT TO CHG MUCH DURG
THE OVRNGT HRS. EXTRAP PLACES LEADING EDGE OF THE CLDS NR A KJEF-
KTAZ LN BY RUFLY 06Z...AND ENTERING OUR FAR S COUNTY ARND 09Z.
TEMPS N OF THE FNT ARE COLD BUT MIXING AND CLDS ARE KEEPING
READINGS UP A BIT...AND AT 03Z LWR 30S ARE STILL BEING REPORTED IN
THE COLD AIR AS FAR N AS N IA. EXTRAP OF POST FNTL TEMPS AND
PROGGED PSTN OF CDFNT NR THE AR/LA BDR AT 12Z SUGGESTS THAT GOING
MINS MAY BE JUST A WEE BIT TOO COLD. HV ALTERED HRLY TEMP GRIDS
UP A BIT TO REFLECT THIS THINKING, BUT ALSO TO REFLECT A COND FALL IN THE
12-14Z TIME FRAME AS CAA WL BE QUITE ROBUST ATTM. RESULTANT MIN
GRID IS ABT 1-2 DEGREES WRMR THAN ERYR FCST.
TRUETT
&&
.DISCUSSION...
ANOTHER IN A SERIES OF SHORT WAVE FEATURES...DRIVING A PRE-FRONTAL
TROUGH THROUGH THE FORECAST AREA THIS AFTERNOON...WITH ONLY MARKED
EFFECT IS CHANGE IN WIND DIRECTION. TRUE SURFACE COLD FRONT LAGS
ABOUT 100 MILES BEHIND TROUGH...AND IS WELL DELINEATED BY LOW
STRATUS DECK THAT CURRENTLY IS PUSHING SOUTHEAST ACROSS IOWA AND
NEBRASKA.
AFTER PLEASANT FALL CONDITIONS TODAY...CLOUDS AND LOW LEVEL COLD
ADVECTION WILL MAKE FOR A GREY AND BLUSTERY DAY ACROSS THE LSX CWA
ON THURSDAY...WITH MAXIMUM TEMPERATURES NEARLY 20 DEGREES LOWER
THAN THOSE EXPERIENCED TODAY. AXIS OF POLAR JET SINKS SOUTHWARD
INTO THE LOWER MISSISSIPPI VALLEY ON THURSDAY...PLACING NORTHERN AND
EASTERN PORTIONS OF CWA ON THE CYCLONIC SHEAR SIDE OF JET...THUS
DECIDED TO INTRODUCE A CHANCE OF FLURRIES DURING THE DAY AND EARLY
EVENING. CLEARING SKIES ON FRIDAY NIGHT WILL MAKE FOR A VERY COLD
NIGHT FRIDAY MORNING...THUS TRENDED TOWARD LOW SIDE OF GUIDANCE.
TEMPERATURES GRADUALLY WILL MODIFY THROUGH THE WEEKEND...BEFORE
ANOTHER CLIPPER BRINGS ANOTHER SURGE OF COLD AIR INTO THE REGION FOR
THE EARLY PART OF NEXT WEEK.
DURING THE EXTENDED RANGE...USED A BLEND OF THE ECMWF AND NEFS AS
BASIS FOR THE FORECAST...GIVEN THE INCONSITENCIES IN THE OPERATION
MEDIUM RANGE MODELS OF LATE. HOWEVER...IT APPEARS THE LARGE SCALE
FLOW BEGINS TO TRANSITION BY THE MIDDLE OF NEXT WEEK...WITH ZONAL
FLOW DOMINATING THE CENTRAL PLAINS. VESTIGES OF THE LAST IN THE
SERIES OF CLIPPERS MAY GENERATE LIGHT PRECIPITATION SUNDAY NIGHT
INTO MONDAY...WITH A RAIN/SNOW MIX POSSIBLE BY MONDAY MORNING.
MOISTURE WILL BE LIMITED...THUS KEPT POPS ON THE LOW SIDE. BASED ON
LARGE SCALE TRENDS...AFTER A COOL START...TEMPERATURES SHOULD
MODERATE CLOSER TO SEASONAL VALUES BY THE MIDDLE OF THE WEEK.
SF/EAX
&&
.AVIATION...
/1052 PM CST WED NOV 19 2008/
FOR THE 06Z TAFS...CDFNT/PREFRONTAL TROF HAS PUSHED SE OF STL/SUS
ATTM. N-NWLY SFC WND WILL INCRS IN SPEED AND BCM GUSTY IN STL AND
SUS AS IT RECENTLY HAS IN UIN AND COU...AS STG SFC RDG BLDS SEWD
INTO THE CWA AND AS COLD AIR FILTERS S-SEWD INTO THE AREA AS WELL.
THESE N-NWLY SFC WNDS WILL BE RELATIVELY STG AND GUSTY ON THU.
ALTHOUGH THE MOS CLOUD GUIDANCE CONTS TO IGNORE IT...THE LOW LVL
STRATUS CLOUDS ARND 1500-2500 FT WILL CONT TO DROP SWD FM NRN MO
INTO CNTRL MO LT TGT. THESE LOW LVL CLOUDS WILL MOVE INTO
COU...STL AND SUS ARND 06Z THU. THESE LOW LVL CLOUDS SHOULD LINGER
THRU THE DAY ON THU...POSSIBLY BREAKING UP AND RISING SLIGHTLY IN
HGT BY LT THU AFTN INTO THE EVNG.
GKS
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&
$$
WFO LSX
