000
FXUS63 KLSX 272038
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
238 PM CST MON DEC 27 2010
.DISCUSSION...
/238 PM CST MON DEC 27 2010/
SEVERAL CONCERNS WITH THIS FORECAST STARTING WITH THE POTENTIAL FOR
REDEVELOPMENT OF FOG TONIGHT. LIKE YESTERDAY...THERE HAS BEEN
CLEARING OVER MUCH OF THE CWA WHICH WILL LAST MOST OF THE NIGHT.
THE SHORTWAVE TROUGH MOVING EWD ACROSS THE CNTRL PLAINS CURRENTLY
DOESN'T HAVE MUCH MID-HIGH LEVEL CLOUDS ASSOCIATED WITH IT. SHOULD
BE DECENT RADIATIONAL COOLING THIS EVENING BEFORE SWLY WINDS PICK UP
LATER THIS EVENING/OVERNIGHT WHICH WILL SHOULD CAUSE DEWPOINT
DEPRESSION TO DROP ENOUGH FOR AT LEAST AREAS OF FOG...ESPECIALLY
ALONG AND NORTH OF INTERSTATE 70 TONIGHT. HAVE GONE ON THE COOL
SIDE ON TEMP GUIDANCE TONIGHT AND AGAIN TOMORROW AS MELTING SNOW
COVER WILL HINDER WARM-UP.
MODELS ARE IN GOOD AGREEMENT THAT THE TROUGH CURRENTLY MOVING
ONSHORE IN THE SWRN CONUS WILL BRING PRECIPITATION TO AREA SOUTH
OF INTERSTATE 70 ON WEDNESDAY. FORECAST SOUNDINGS STILL SUGGEST
THAT THERE MAY BE SOME LIGHT FREEZING RAIN DURING THE
PRECIPITATION'S ONSET BEFORE STRONG WARM AIR ADVECTION CAUSES A
TURNOVER TO ALL LIQUID DURING THE MORNING HOURS. THE CHANCE OF
RAIN WILL THEN DIMINISH INTO WEDNESDAY NIGHT AS WEAK SUBSIDENCE
DEVELOPS BEHIND THE EXITING SYSTEM. HAVE RAIN CHANCES INCREASING
AGAIN ON THURSDAY AS MODELS DO DEPICT SOME WEAK LARGE SCALE ASCENT
AHEAD OF WRN CONUS TROUGH WITH INCREASING LOW LEVEL MOISTURE
CONVERGENCE/TRANSPORT. ADVECTION FOG IS ALSO LIKELY TO DEVELOP
WEDNESDAY NIGHT INTO THURSDAY AS DEWPOINTS CLIMB FROM THE MID 30S
INTO THE MID 40S OVER RESIDUAL SNOW COVER OR EXPOSED SUBFREEZING
GROUND TEMPERATURES.
FORECAST CONFIDENCE IS BETTER TODAY AS WE GO THROUGH THE WEEKEND
THAN THE PAST FEW DAYS. WHILE THERE IS STILL SOME SPREAD AMONGST
THE GFS/ECMWF ENSEMBLE MEMBERS...THERE IS DECENT AGREEMENT BETWEEN
THE GLOBAL MODELS REGARDING THE TIMING OF PRECIPITATION AND THE
FRONT PASSAGE THROUGH THE WEEKEND. 00Z AND 12Z RUNS OF THE
GFS/ECMWF/CANADIAN GEM ALL SHOW THE CLOSED LOW AT THE BASE OF THE
WRN CONUS LONGWAVE EJECTING NEWD ACROSS THE UPPER MIDWEST EARLY IN
THE WEEKEND...WITH THE ASSOCIATED FRONTAL PASSAGE MOVING ACROSS
THE CWA AROUND 00Z FRIDAY NIGHT. RAIN STILL LOOKS LIKELY ALONG
WITH A SLIGHT CHANCE OF THUNDERSTORMS AHEAD OF THE FRONT THURSDAY
NIGHT INTO FRIDAY GIVEN THE INCREASING ASCENT AND LOW LEVEL
MOISTURE CONVERGENCE/TRANSPORT. WITH THE CLOSED LOW PASSING SO FAR
OFF TO THE NORTHWEST...ANY DEFORMATION SNOW WILL STAY IN THE UPPER
MIDWEST WITH OUR AREA LIKELY EXPERIENCING THE DRY SLOT TO THE
SOUTH OF THE LOW. THINK ANY TRANSITION TO SNOW/SLEET BEHIND THE
FRONT WILL BE QUICK AND DOESN'T LOOK SIGNIFICANT AT THIS POINT. AS
THE MID SHIFT FORECASTER MENTIONED...THE ECMWF NO LONGER SHOWS A
STRONGLY PHASED TROUGH THAT LINGERS BEHIND THE GFS/GEM SOLUTIONS
LIKE IT DID YESTERDAY...SO HAVE GONE DRY FROM SATURDAY ONWARD.
UPPER FLOW TURNS ZONAL OVER THE WEEKEND WITH NO STRONG INTRUSION
OF COLD AIR...SO HIGHS IN THE 30S AND LOWER 40S BEHIND THE FRONT
SEEM REASONABLE.
BRITT
&&
.AVIATION...
/1138 AM CST MON DEC 27 2010/
DENSE FOG HAS DISSIPATED OVER KCOU AND KUIN...THOUGH STILL HAVE SOME
LIGHT FOG WITH MVFR/IFR VSBYS FOR ANOTHER HOUR OR SO. OTHERWISE...
DEALING WITH MVFR/IFR CIGS WHICH WILL SCATTER OUT BETWEEN NOW AND
21Z. ONCE CLOUDS SCATTER OUT...WILL ONLY BE DEALING WITH SOME HIGH
CLOUDS DUE TO A SHORTWAVE THAT WILL SLIDE THROUGH REGION THIS
EVENING. AS FOR WINDS...EXPECT SOUTH TO SOUTHWEST WINDS THROUGH THE
FORECAST PERIOD.
SPECIFICS FOR KSTL...MVFR CIGS SLOWLY ERODING OVER KSTL LATE THIS
MORNING...WITH SATELLITE SHOWING SOME BREAKS IN THE CLOUD COVER OVER
METRO AREA AS OF 1715Z. SO HAVE CIGS SCATTERING OUT BY 19Z. ONCE
CLOUDS SCATTER OUT...WILL ONLY BE DEALING WITH SOME HIGH CLOUDS DUE
TO A SHORTWAVE THAT WILL SLIDE THROUGH REGION THIS EVENING. AS FOR
WINDS...EXPECT 5 TO 10 KT SOUTH TO SOUTHWEST WINDS THROUGH THE
FORECAST PERIOD.
BYRD
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&
$$
WFO LSX
