FXUS61 KRLX 261853
AFDRLX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
153 PM EST SAT DEC 26 2009
.SYNOPSIS...
LOW PRESSURE AND COLD FRONT ARRIVE LATE SUNDAY. LIGHT SNOW
ACCUMULATION FROM PASSING WAVE LATE SUNDAY THROUGH SUNDAY NIGHT.
ARCTIC AIR AND UPSLOPE SNOW MONDAY THROUGH MONDAY NIGHT.
&&
.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/...
MAIN FEATURE WILL BE A WAVE THAT PASSES WITH A LIGHT SNOW
ACCUMULATION LATE SUNDAY THROUGH SUNDAY NIGHT...BUT OTHER SMALLER
WAVES WILL ALSO HAVE IMPACTS DURING THE REMAINDER OF THE SHORT
TERM PERIOD.
DESPITE LACK OF QPF IN MODELS SUNDAY MORNING...NAM SHOWS VORTICITY
AXIS...AS WELL AS WEAK TROPOPAUSE UNDULATIONS ZIPPING THROUGH A
RAPID SOUTHWEST FLOW. SO I INCLUDED A SLIGHT CHANCE OF SNOW IN THE
OHIO VALLEY FOR THIS REASON. HOWEVER...THESE MINOR FEATURES WILL NOT
BE THE MAIN SHOW.
WOBBLY CENTER OF UPPER LOW FINALLY PICKS A DIRECTION BY MOVING
FROM SOUTHERN LAKE MICHIGAN VICINITY SUNDAY MORNING...THROUGH THE
EASTERN LAKES BY MID MONDAY MORNING. MODELS ARE NOT TOTALLY IN LINE
WITH THE EXACT POSITIONING OF THE UPPER LOW CENTER...BUT REGARDLESS
TO ITS SOUTH...FAIRLY STRONG VORTICITY AXIS WILL BE SENT THROUGH THE
AREA LATE SUNDAY AFTERNOON AND EVENING...COUPLED WITH Q VECTOR
CONVERGENCE AND STRONG COLD AIR ADVECTION. MODEL SOUNDINGS SHOW THAT
AS THIS FEATURE PASSES...SATURATED LAYER WILL INCLUDE A THICK NEARLY
ISOTHERMAL LAYER WITHIN THE DENDRITIC GROWTH ZONE /MINUS 12 TO MINUS
18 CELSIUS/. THUS I AM EXPECTING THAT THE FEATURE WILL BE
ACCOMPANIED BY A BRIEF YET PRODUCTIVE LIGHT SNOW FOR MOST OF THE
AREA SUNDAY EVENING...BUT ESPECIALLY NORTHERN LOWLANDS AND INTO
THE WV MOUNTAINS. LIKELY TO CATEGORICAL POPS SEEMED WARRANTED FOR
THE AFFECTED LOCATIONS. GENERALLY LOOKING AT ROUGHLY AN INCH FOR THE
AFFECTED LOWLANDS...AND TWO OR THREE INCHES IN THE WEST VIRGINIA
MOUNTAINS.
ONE WAVE EXITS MONDAY...BUT MODELS HAVE COME INTO AGREEMENT ON A
SECONDARY WAVE DROPPING OUT OF THE NORTHWEST LATE IN THE DAY. THE
VEERING WINDS BEHIND THAT WAVE LOOK FAVORABLE FOR UPSLOPE SNOW
LASTING THROUGH MONDAY NIGHT. EVEN THOUGH SATURATION ONLY REACHES TO
750MB...THE AIR MASS WILL BE COLD ENOUGH FOR THE DENDRITIC GROWTH
ZONE TO MAKE UP MOST OF THE TEMPERATURE PROFILE OF THAT LAYER. I
WENT AHEAD AND PLACED LIKELY POPS IN THE NORTHERN MOUNTAINS FOR
NOW...WITH LIGHT ACCUMULATION. HOWEVER...IF THIS MODEL TREND
CONTINUES TO HOLD...EXPECT HIGHER POPS AND ACCUMULATIONS...AND
FURTHER SOUTHWARD EXTENSION DOWN THE MOUNTAINS.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
GENERALLY WENT WITH ECMWF/HPC SENERIO...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 WENDESDAY 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 WENDESDAY...THURSDAY AND
FRIDAY. 85H TEMPS ARE COLD ENOUGH FOR SNOW FOR THE MOST PART...BUT
SFC TEMPS WILL BE MARGINAL FOR AN ALL SNOW SENERIO...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 /19Z 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...MDP/ARJ
LONG TERM...JS
AVIATION...TRM
