FXUS61 KRLX 261012
AFDRLX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON WV
509 AM EST SAT DEC 26 2009

.SYNOPSIS...
SOME SUNSHINE TODAY. TURNING GRADUALLY COLDER OVER WEEKEND. LIGHT 
SNOW ACCUMULATION FROM PASSING WAVE LATE SUNDAY THROUGH SUNDAY 
NIGHT. ARCTIC AIR AND UPSLOPE SNOW MONDAY THROUGH MONDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
MODELS SHOW A DRY SLOT ROTATING OVER THE REGION TODAY...PROVIDING 
DRY WEATHER AND SOME SUNSHINE. AS THE UPPER LOW SLOWLY SLIDES 
EASTWARD TONIGHT...COLDER AIR BEGINS FILTERING INTO THE AREA. THIS 
WILL ALLOW FOR CLOUDS TO PUSH IN FROM THE WEST AND A CHANCE OF 
SOME LIGHT SNOW IN THE WEST BY LATE SATURDAY NIGHT AS 850 MB 
TEMPERATURES GET COLD ENOUGH TO OVER TURN THE LOWER LEVELS.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY 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 /TUESDAY THROUGH FRIDAY/...
HIGH PRESSURE TO BRING DRY WEATHER TUE.

UPPER FLOW BACKS TO THE SW WED AND THEN A NUMBER OF SOUTHERN STREAM 
S/W/S MOVE THROUGH THAT FLOW TO BRING ABOUT A LOT OF HIGH AND MID 
CLOUD.  SCHC TO CHC POPS ARE ALSO MAINTAINED AS DECK LOWERS ENOUGH 
TO SUPPORT PRECIP REACHING THE SFC AT TIMES.

THERE REMAINS SOME QUESTION AS TO WHETHER THIS WEATHER PATTERN COMES 
TO A CRESCENDO NEAR OR JUST BEYOND THE END OF THE PD.  PATTERN 
FEATURES HIGH LATITUDE BLOCKS OVER BOTH ALASKA AND GREENLAND...THE 
LATTER REINFORCED BY CURRENT SYSTEM.  ECMWF IS NOW THE BULLISH MODEL 
WITH A MAJOR IF NOT EPIC E COAST SNOWSTORM WHILE GFS KEEPS WAVE 
FLATTER...FARTHER S AND MUCH FASTER AFTER IT WAS SHOWING MAJOR EVENT 
JUST TWO DAYS AGO.  USED HPC CHC POPS THU NT-FRI AND THEN START TO 
DRY FROM THE W FRI NT.

USED MOSTLY A BLEND OF ADJMEXBC AND MOSGUIDEBC FOR TEMPERATURES...A 
BIT HIGHER THAN PREV FCST.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
CLEARING WILL CONTINUE TO GRADUALLY MOVE NORTHWARD OVER THE REGION 
THIS MORNING. THIS WILL LEAVE VFR CONDITIONS FOR LATER TODAY. A 
STRATUS DECK WILL THEN MOVE IN FROM THE WEST AS A UPPER LEVEL LOW 
PRESSURE SYSTEM SLOWLY SLIDES TOWARD THE AREA TONIGHT. 

AFTER 12Z SUNDAY...
IFR POSSIBLE IN LIGHT SNOW SUNDAY NIGHT INTO MONDAY.

&&

.RLX WATCHES/WARNINGS/ADVISORIES...
WV...NONE.
OH...NONE.
KY...NONE.
VA...NONE.

&&

$$
SYNOPSIS...TRM/MDP/RPY
NEAR TERM...RPY
SHORT TERM...MDP
LONG TERM...TRM
AVIATION...RPY