FXUS61 KRNK 072109
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
409 PM EST MON DEC 7 2009

.SYNOPSIS...
HIGH PRESSURE WILL HEAD EAST OFF THE ATLANTIC COAST AS A WEAK
DISTURBANCE MOVES THROUGH THE OHIO VALLEY TONIGHT INTO TUESDAY. A
STRONG AREA OF LOW PRESSURE WILL MOVE THROUGH THE GREAT LAKES
REGION TUESDAY NIGHT INTO WEDNESDAY...BRINGING A COMPLEX SERIES OF
FRONTS THROUGH OUR REGION.

&&

.NEAR TERM /THROUGH TUESDAY/...
GOING WITH A BLEND OF THE GFS/NAM FOR TONIGHT...WITH MOISTURE 
CONTINUING TO STREAM ACROSS IN THE MID/HIGH LVLS. LOW LVL MOISTURE 
WILL STAY BANKED UP ACROSS THE MTNS OF WV/FAR SW VA THROUGH THE 
NIGHT...WITH DRYING TAKING PLACE JUST ABOVE THIS LAYER OVERNIGHT. 
MODELS SPIT OUT LIGHT QPF OVER FAR NW CWA IN THE GREENBRIER AREA 
THIS EVENING BUT NOT EXPECTING MUCH. MAIN CONCERN THIS EVENING IS 
MODEL SOUNDINGS SHOWING DRIZZLE POTENTIAL. HAVE INSERTED SOME 
FREEZING DRIZZLE FOR THE EVENING IN PORTIONS OF THE GREENBRIER 
VALLEY AND HIGHLANDS. WILL ISSUE AN SPS TO COVER ANY LIGHT GLAZE ON 
SIDEWALKS. THE MOISTURE LAYER DISSIPATES AFTER MIDNIGHT SO ONLY 
LOOKING AT A 3 TO 6 HOUR PERIOD AT BEST OF FZDZ.

TEMPS TONIGHT WILL BE BASED ON THE MAV/MET BLEND AND WITH CLOUD 
COVER AROUND ESPECIALLY IN THE WEST LOWS SHOULD BE IN THE MID 20S TO 
LOWER 30S. TEMPS TODAY ONLY MANAGED TO GET INTO THE MID TO UPPER 30S 
IN THE MTNS WHILE MORE SUN IN THE PIEDMONT BOOSTED THEIRS UP TOWARD 
50. GIVEN A LAG IN CLOUD COVER IN THE EAST THIS EVENING...THE TEMPS 
THERE COULD DROP OFF QUICKER THIS EVENING...THEN STEADY OUT 
OVERNIGHT ONCE THE HIGH LVL CLOUDINESS ARRIVES.

TUESDAY...ALL EYES TURN ON THE STORM SYSTEM PUSHING OUT OF THE 
ROCKIES INTO THE PLAINS. GFS/ECMWF ARE QUICKER IN BRINGING PRECIP 
BACK INTO THE CWA BY TUESDAY MORNING...AND HAVE LEANED IN THIS 
DIRECTION AS SOUTHEAST FLOW ABOVE THE SFC INCREASES...LEADING TO 
SOME LIFT ALONG THE SOUTHERN BLUE RIDGE. WITH TEMPS AT OR BELOW 
FREEZING IN THE MORNING COULD SEE PATCHY FREEZING RAIN IN THE NC 
MTNS/FAR SW VA B4 WARMER AIR ARRIVES BY 15Z. NOT EXPECTING MUCH ICE 
ACCUMULATION.

AS THE MOISTURE STREAMS NE THE SFC WEDGE WILL TIGHTEN AND DEEPEN 
ALTHOUGH MODEL SOUNDING SUGGEST A SHALLOW LAYER OF COLD AIR. WITH 
LEFTOVER SNOW COVER AND MOIST GROUND...THIS LAYER MAY START OFF A 
LITTLE COLDER THAN THE MODELS SUGGEST. BY AFTERNOON WILL BE SEEING 
SUB FREEZING TEMPS CONFINED TO THE MTN VALLEYS ALONG AND NORTH OF 
I-64 FROM SUMMERS COUNTY WV TO AMHERST COUNTY WITH PATCHY AREAS 
SOUTH ALONG THE BLUE RIDGE AND HIGHLANDS. STILL NOT EXPECTING 
ANYTHING MORE THAN A LIGHT COATING. 

TEMPS WILL BE TRICKY ESPECIALLY IN THE FAR ERN CWA AS PRECIP WILL 
NOT REACH THERE UNTIL AFTERNOON. STILL NOT CONFIDENT ON THE WARMER 
MOS SO AM KEEPING THING AT OR BELOW THE COOLEST MOS GIVEN EVAP 
COOLING INTO WEDGE...CLOUD COVER AND EVENTUALLY RAINFALL. NOSE OF 
WARM AIR WILL CHANGE ANY FREEZING PRECIP OVER THE SW VA MTNS BY 
MIDDAY.

THE OTHER CONCERN IN THE LATE AFTERNOON THROUGH TUESDAY NIGHT PERIOD 
IN THE FAR SW WILL BE THE LOW LVL JET WITH MODELS SUGGESTING 50-65 
KNOTS AT TIMES. CROSS SECTIONS SHOW POTENTIAL FOR GUSTS ABOVE 60 
KNOTS ON THE RIDGES TUESDAY EVENING...BUT WITH LIMITED COVERAGE WILL 
KEEP ANY HIGH WIND WATCH OUT OF THE FORECAST FOR NOW AND MENTION IN 
THE HWO. STILL LOOKS LIKE WIND ADVISORY A SURE BET TUESDAY NIGHT 
INTO WEDNESDAY FOR THE MTNS OF SW VA/FAR SRN WV/NW NC.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
A STRONG LOW PRESSURE SYSTEM WILL PUSH NORTHEASTWARD TO THE GREAT 
LAKES TUESDAY NIGHT. NAM IS STILL SLOWER WITH THIS SYSTEM AND HAVE 
LEANED TOWARD THE GFS DURING THIS TIME PERIOD. MAINLY A FREEZING 
RAIN EVENT WITH SOME SLEET MIXED IN AS BUFKIT SOUNDINGS SUPPORT NEAR 
TO BELOW FREEZING TEMPERATURES AT THE SURFACE WITH STRONG WARM 
ADVECTION AROUND 850MB. THIS EVENT WILL BE IMPACT PORTIONS OF THE 
THE ALLEGHANY HIGHLANDS...ROANOKE AND SHENANDOAH AREAS ALONG WITH 
PORTIONS OF GREENBRIER IN SOUTHEAST WEST VIRGINIA. BELIEVE THE SLEET 
WILL BE BRIEF AS THE LAYER OF COLD AIR UNDER THE WARM NOSE WILL NOT 
BE THICK ENOUGH. WITH A WEDGE IN PLACE SURFACE TEMPERATURES WILL BE 
BELOW FREEZING IN THE ALLEGHANY HIGHLANDS AND THE GREENBRIER 
VALLEY. WITH SNOW ALREADY ON THE GROUND...GROUND TEMPERATURES 
WILL REMAIN COLD WHICH WILL ALSO ALLOW A HIGHER PROBABILITY FOR 
FREEZING RAIN. ICE ACCUMULATION WILL BE UP TO A TENTH OF AN 
INCH...SO ONLY HAVE MENTION IN THE HWO AT THIS TIME. 

THE MOISTURE WILL WRAP AROUND AS THE LOW PRESSURE PULLS OUT OF THE 
AREA THURSDAY MORNING. WITH A WESTERLY FLOW ANTICIPATE LINGERING 
PRECIP IN THE WESTERN UPSLOPE AREAS OF SOUTHEAST WEST VIRGINIA 
THROUGH THE DAY THURSDAY. THIS WILL TAPER OFF THURSDAY NIGHT AS HIGH 
PRESSURE PUSHES BACK INTO THE AREA FROM THE SOUTHWEST. A PUSH OF 
COLD AIR FROM THE NORTHWEST WILL FILTER INTO THE FORECAST AREA WHICH 
WILL ALLOW LOW TEMPERATURES TO FALL INTO THE UPPER TEENS IN THE 
MOUNTAINS TO MID 20S IN THE PIEDMONT AREA OF VIRGINIA AND NORTH 
CAROLINA.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
THERE IS REASONABLE AGREEMENT BETWEEN THE GEFS/GFS/ECMWF REGARDING 
PRECIPITATION THIS WEEKEND. HOWEVER...THERE IS MUCH DISAGREEMENT 
WITH HOW COLD THE ATMOSPHERE MAY BE LEADING UP TO THIS EVENT. VERY 
DRY AIR...IN THE FORM OF 8F-15F DEWPOINTS WITH CONTINENTAL HIGH 
PRESSURE OVERHEAD WILL PRECEDE THE EVENT FRIDAY INTO FRIDAY NIGHT. 
THE 12Z OP GFS IS MUCH COLDER THAN THE 12Z ECMWF AND THE 12Z 
GEFS FOR THE ENTIRE EVENT SAT AND SAT NIGHT...SO PRECIP TYPE IS
DIFFICULT THIS FAR OUT. RIGHT NOW THE OP GFS LOOKS TOO
COLD...HOWEVER...DESPITE THE QUICK WAA AT H85...BOUNDARY LAYER IS
GOING TO BE SUBFREEZING CONSIDERING MANY SPOTS WILL DECOUPLE FRIDAY
NIGHT...AND THEN CLOUDS WILL MOVE IN QUICKLY SATURDAY. THIS SHOULD
PREVENT MUCH INSOLATION...AND MAY EVENTUALY GIVE A SLEET/SNOW MIX IN
THE BLUE RIDGE...WITH POSSIBLY MORE SNOW INTO SE WEST VA.
CONSIDERING UNCERTAINTY WILL KEEP WX TYPE JUST RAIN OR SNOW FOR
NOW. ALONG THE PIEDMONT AND SOUTHSIDE...ONSET OF PRECIP MAY FIRST
BE SNOW BUT THEN QUICKLY CHANGE OVER TO RAIN AS WARM AIR OVERCOMES
ANY WEDGE THAT MAY BE IN PLACE ALONG THE SE CWA. AS WINDS BECOME
MORE S AND SW SATURDAY NIGHT...PRECIP MAY CHANGE TO ALL RAIN SAVE
SE WEST VA. CONJECTURE AT THIS POINT BUT THIS IS DEFINITELY A
SYSTEM TO WATCH FOR WINTRY PRECIPITATION. THE AREA OF LOW PRESSURE
ALONG THE COAST EXITS INTO SUNDAY...WITH UPSLOPE PRECIP ACROSS SE
WEST VA...ALTHOUGH A MOSTLY WEST WIND ISN'T VERY FAVORABLE. ALBEIT
DRY INTO THE END OF THE LONG TERM...H85 TEMPS REMAIN AROUND 0C SO
NO BIG WARMUPS ARE EXPECTED.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
GETTING SOME MVFR CIGS WONDERING INTO THE WV MTNS ATTM...AND WILL
SEE CIGS LOWER AT BLF/LWB AS THE AFTN WEARS ON AND INTO THE
EVENING. THE 12Z GFS MOISTURE PROFILES SEEM TO BE HANDLING THE LOW
CLOUDINESS BETTER THAN THE NAM. GIVEN THIS...THINK WE WILL SEE IFR
CONDITIONS ROLL IN ACROSS BLF AROUND 00Z THIS EVENING. POTENTIAL
EXISTS FOR -DZ OR -FZDZ THIS EVENING IN THE WV MTNS...BUT LEFT OUT
OF THE TAF SITES FOR NOW AS MOISTURE DEPTH IS NO GREATER THAN
AROUND 1KFT. CIGS SCOUR OUT OVERNIGHT...BUT THEY MAY LINGER LONGER
AS MODELS TEND TO SPEED UP LOW CLOUDS DISSPATING DURING THE NIGHT.
STILL FORESEE VFR CIGS BEFORE 12Z. WITH SNOW PACK AND/OR WET
GROUND...WE COULD SEE FOG DEVELOP AND FOR NOW GOING TO ADD IT TO
LWB...BUT COULD SEE ROANOKE AND BLF GETTING INTO THE MIX AS WELL
OVERNIGHT INTO TUE MORNING. HIGH CLOUDS WILL REMAIN THROUGH THE
PERIOD AND WILL SEE AC/AS INCREASE TUESDAY MORNING IN THE
EAST...WITH LOWER CLOUDS ARRIVING AHEAD OF THE NEXT SYSTEM B4 THE
END OF THIS TAF PERIOD ACROSS BLF/LWB WITH MVFR CIGS EXPECTED AT
LIGHT RAIN/FREEZING RAIN OR SLEET POSSIBLE AT BLF/LWB.

THIS SYSTEM WILL IMPACT ALL TAF SITES FROM TUESDAY EVENING THROUGH
WEDNESDA NIGHT WITH WINTRY MIX EXPECTED FROM ROA-BLF CORRIDOR
NORTHWARD TUE NIGHT. ANOTHER IMPACT WILL BE STRONG SOUTHEAST TO
SOUTHERLY LOW LVL WINDS TUESDAY EVENING THROUGH WED MORNING...WITH
GREATEST IMPACT ACROSS THE BLF-TNB AREA WITH GUSTS OF 40-50 KNOTS
POSSIBLE OUTSIDE OF A COLD AIR WEDGE.

THE SYSTEM AND ASSOCIATED RAIN WILL MOVE OUT OF THE AREA BY
WEDNESDAY AFTERNOON. TIGHTENING PRESSURE GRADIENT AND WESTERLY
WINDS WILL INCREASE ACROSS THE REGION. WINDY AND GUSTY CONDITIONS
POSSIBLE INTO THURSDAY NIGHT.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.

&&

$$
SYNOPSIS...RCS/WP
NEAR TERM...WP
SHORT TERM...REB
LONG TERM...KM
AVIATION...RCS/WP