FXUS61 KRLX 262109
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
252 PM EST SAT DEC 26 2009
.SYNOPSIS...
UPPER LOW PRESSURE AND SURFACE TROUGH ARRIVE LATE SUNDAY WITH LIGHT
SNOW ACCUMULATIONS. DESCENT UPSLOPE SNOW EVENT ANTICIPATED AS ARCTIC
AIR ARRIVES UNDER IDEAL NORTHWEST FLOW SUNDAY NIGHT AND MONDAY.
&&
.NEAR TERM /THROUGH SUNDAY/...
AREA WILL BE IN THE DRY SLOT OF A LARGE...OLD LOW PRESSURE CENTER
STACKED SURFACE AND ALOFT OVER THE MIDWEST THIS PERIOD. NE WV
SHOULD CLEAR OUT LATE TODAY AND THIS EVENING AS OCCLUSION PULLS AWAY
FROM THAT AREA.
AS PER LATEST GUIDANCE AND TYPICAL BEHAVIOR WITH THESE LARGE...OLD
SYSTEMS...HAVE SLOWED ARRIVAL OF CLOUDS AND PRECIPITATION FROM THE W
SUNDAY. AFTER APPROACHING THE AREA FROM THE W LATE TONIGHT VIA
INITIAL SPOKE IN THE CYCLONIC FLOW...THIS INITIAL PUSH OF CLOUD
BREAKS UP TO ALLOW SUNSHINE FOR A GOOD PORTION OF SUNDAY. MAIN AREA
OF CLOUDINESS AND PRECIPITATION FINALLY PUSHES INTO THE AREA IN
ERNEST LATE SUN AFTERNOON WITH THE AID OF A PUSH OF COLD ADVECTION.
PRECIPITATION IS LIKELY TO START AS MELTED SNOW / RAIN / IN WARM
NEARLY S FLOW AHEAD OF WHAT BY THEN EVOLVES INTO A NEW COLD FRONT.
USED ADJUSTED BIAS CORRECTED MAV FOR LOWS TONIGHT AND ADJUSTED BIAS
CORRECTED MET FOR HIGHS SUN...HIGHER ALL AROUND TO REFLECT SLOWER
ARRIVAL OF COLDER AIR...AS WELL AS MORE SUNSHINE THAN PREVIOUSLY
FORECAST FOR SUN WITH NEARLY S...SOMEWHAT DOWNSLOPE FLOW.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AN UPPER LEVEL SHORT WAVE APPROACHES THE AREA FROM THE NORTHWEST ON
MONDAY NIGHT. ALTHOUGH LATEST ECMWF/SREF/GEM/UKMET LOOK FASTER IN
THEIR QPF FIELDS...THE GFS/NAM SHOW AT LEAST SOME FORCING...ABOUT
3-4 UNITS OMEGA...AND MOISTURE IN THE FORM OF RN GREATER THAN 85
PERCENT WITHIN THE DENDRITE GROWTH ZONE. NAM BRINGS GOOD QVECTOR
CONVERGENCE ALOFT BUT NOT COUPLED ANY FORCING IN THE MID OR LOWER
LEVELS.
HOWEVER...A BIGGER/STRONGER UPPER WAVE...EVIDENT IN PRESSURES
WITHIN THE 1.5 PVU ISENTROPIC SURFACE MOVES IN...ALONG WITH
PVA...MID LEVEL 2-D FRONTOGENESIS IN THE PRESENCE OF A SATURATED
DENDRITE GROWTH ZONE BY MON 12Z. MODELS ARE IN FAIR AGREEMENT WITH
H850 TEMPS DROPPING INTO THE MINUS 11-13C SUGGESTING ANY PCPN IN THE
FORM OF SNOW.
THEREFORE...HAVE LIKELY POPS ENTERING THE CWA FROM THE NORTHWEST...
SPREADING EAST ACROSS THE NORTHERN TWO THIRDS OF THE CWA THRU 12Z.
SNOW ACCUMULATIONS SHOULD BE LIGHT...ABOUT 1.5 INCHES OR LESS ACROSS
THE NORTH SECTIONS...AND EVEN LOWER AMOUNTS CENTRAL AND SOUTHERN
LOWLANDS OF WV...OH AND KY.
THE COLUMN SATURATES QUICKLY OVER THE NORTHEAST MOUNTAINS PROVIDING
LIGHT SNOW ACCUMULATIONS OVERNIGHT. THE AFOREMENTIONED MOISTURE AND
FORCING PROVIDED BY THE UPPER WAVE WILL IMPACT THE NORTHEAST
MOUNTAINS ON MONDAY ENHANCING UPSLOPE SNOW. ALLOWED CATEGORICAL POPS
ACROSS THE NORTHEAST SECTIONS AND SNOW ACCUMULATIONS UP TO 6 INCHES
OVER THE HIGHEST PEAKS OF POCAHONTAS AND RANDOLPH COUNTIES BY 00Z
TUESDAY.
ON TUESDAY...MOISTURE WITHIN THE DENDRITE GROWTH ZONE REMAINS
FAVORABLE FOR ICE CRYSTAL FORMATION...WHILE STRONG NORTHWEST FLOW
AND COLD AIR ADVECTION LOOK IDEAL FOR PURE UPSLOPE SNOW ACROSS THE
EASTERN MOUNTAINS. HOWEVER...MOISTURE RUNS OUT QUICKLY BY EARLY TUE
AFTERNOON ALLOWING UP TO AN ADDITIONAL INCH OVER THE HIGHER
PEAKS...AND LESSER AMOUNTS ACROSS THE REST HIGHER ELEVATIONS DOWN
SOUTH THRU RALEIGH COUNTY.
FOR TEMPERATURES...DECREASED LOWS OVER THE NORTHEAST MOUNTAINS PER
MODEL CONSENSUS OF H850 TEMPS IN THE MINUS 12-14C SUNDAY NIGHT.
INCREASED HIGHS A DEGREE OR TWO ACROSS PORTIONS OF CENTRAL AND
WESTERN SLOPES OF WV PER POSSIBLE CLOUD BREAKS EXPECTED PER GEM-R
AND GMOS GUIDANCE. USED BIAS CORRECTED SREF FOR LOWS MON NIGHT PER
SREF/GFS/UKMET KEEPING H850 TEMPS WITHIN MINUS 12 TO 14C. WENT
SIMILAR TO HPC GUIDE. BACK TO COOLER THE BIAS CORRECTED SREF FOR
LOWS TUESDAY NIGHT PER CLEARING AND ASSOCIATED RADIATIONAL COOLING
EXPECTED.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
GENERALLY WENT WITH ECMWF/HPC SCENARIO...AS GFS APPEARS TO BE A TAD
FAST. HIGH PRESSURE OVER THE REGION WILL CONTINUE TO SLIDE
EASTWARD DURING THE DAY ON WEDNESDAY. DEVELOPING LOW PRESSURE OVER
THE GULF OF MEXICO WILL MOVE NORTHEASTWARD WEDNESDAY NIGHT AND
THURSDAY. THE LOW WILL BE OVER THE CAROLINAS BY FRIDAY MORNING AND
CONTINUE UP THE COAST FRIDAY AND FRIDAY NIGHT.
EVEN WITH THE TRACK BEING UNCERTAIN ATTM...WENT AHEAD AND
INCREASED CLOUDS AND POPS FOR LATE WEDNESDAY...THURSDAY AND
FRIDAY. 85H TEMPS ARE COLD ENOUGH FOR SNOW FOR THE MOST PART...BUT
SFC TEMPS WILL BE MARGINAL FOR AN ALL SNOW SCENARIO...SO WENT WITH
A SNOW/RAIN MIX DURING THE DAYTIME HOURS AND MOSTLY ALL SNOW
DURING NIGHT TIME HOURS THROUGH FRIDAY.
COLD AIR AND NORTHWEST FLOW BEHIND THIS SYSTEM WILL KEEP THE
CHANCE FOR SNOW SHOWERS INTO THE WEEKEND.
&&
.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
AREA FOR THE MOST PART WILL BE IN A DRY SLOT BETWEEN TWO AREAS OF
CLOUDINESS THIS PERIOD. THE FIRST AREA OF CLOUD WITH MVFR TO IFR
CONDITIONS NE PORTION OF WV ARE ASSOCIATED WITH A SLOW MOVING
OCCLUSION IN THAT AREA. SPOTTY DRIZZLE IS NOT EVEN OUT OF THE
QUESTION. CONDITIONS SHOULD IMPROVE THIS EVENING AS THE OCCLUSION
PULLS AWAY FROM THE AREA...ALLOWING THE DRY SLOT TO TAKE CONTROL.
THE LEADING EDGE OF THE SECOND AREA OF CLOUDINESS WAS IN WESTERN
OH...BUT THESE CLOUDS COVER MUCH OF THE MIDWEST...IN ASSOCIATION
WITH A LARGE...OLD LOW PRESSURE SYSTEM STACKED UP SURFACE AND
ALOFT. THESE CLOUDS WILL SLOWLY ENCROACH UPON THE AREA FROM THE W
SUN...PROBABLY TAKING UNTIL JUST BEYOND THE END OF THE 24-HOUR TAF
PERIOD TO GET THE THE AIRPORTS ALONG THE OHIO RIVER. PATCHY 5KFT
CLOUD WILL APPROACH TONIGHT BUT THEN BREAK UP AS IT MOVES ACROSS THE
AREA SUN MORNING.
FLOW WILL BE SW...GUSTY ALONG THE OHIO RIVER THIS AFTERNOON...AND
THEN LIGHT SW TONIGHT AND SUN MORNING BEFORE BECOMING A BIT GUSTY
FOR MUCH OF THE AREA BY SUN AFTERNOON. FLOW ALOFT WILL BE MODERATE
FROM THE SW.
AFTER 18Z SUNDAY...
IFR POSSIBLE IN LIGHT SNOW SUNDAY NIGHT INTO MONDAY.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...NONE.
OH...NONE.
KY...NONE.
VA...NONE.
&&
$$
SYNOPSIS...TRM/ARJ/JS
NEAR TERM...TRM
SHORT TERM...ARJ
LONG TERM...JS
AVIATION...TRM
