FXUS61 KRNK 080431
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1131 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 OVERNIGHT 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/...
CLOUDS REMAIN STUCK ACROSS THE UPSLOPE ZONES TONIGHT IN
STRONG/UNIFORM WESTERLY FLOW PER 00Z RAOBS. SOME OF THIS MOISTURE
ALSO BLEEDING OVER INTO THE NEW RIVER/ROANOKE VALLEYS AIDED BY A
30+ KNOT LOW LEVEL JET. FORECAST RAOBS SUGGEST THAT CLOUDS WILL
HOLD OVER THE WEST FOR AT LEAST A FEW MORE HOURS BEFORE THE LOW
LEVEL FLOW STARTS TO BACK MORE SW BY MORNING. SINCE STILL SEEING A
FEW LIGHT RADAR RETURNS TO THE NW WILL LEAVE IN THE ONGOING
-DZ/-FZDZ MENTION A WHILE LONGER ALTHO MOST SPOTS STILL ABOVE
FREEZING ACROSS THE NW. ELSW EXPECT MAINLY CLEAR SKIES TO PREVAIL
WITH ONLY SOME AC/CI ARRIVING LATE. RAISED LOW TEMPS A FEW DEGREES
IN THE WEST PER CLOUD COVER WHILE LOWERING A LITTLE OVER THE EAST
WHERE BETTER RAD COOLING SHOULD PREVAIL OVERNIGHT. FOR
TUESDAY...TOYED WITH PUTTING UP A HIGH WIND WATCH FOR THE FAR
WESTERN COUNTIES BASED ON THE 50-55 KT 85H JET OFF GUIDANCE AND
BUFKIT RAOBS SHOWING THE STRONG WINDS NEAR THE SURFACE AT BLF
TUESDAY NIGHT. HOWEVER LATEST RUNS INCLUDING THE NEW 00Z NAM A BIT
WEAKER...AND TURNING MORE SOUTHERLY SOONER...WITH THE STRONGER
SPEEDS MORE IN THE OVERNIGHT 3RD PERIOD SO WONT ISSUE A WATCH FOR
NOW. PREVIOUS DISCUSSION BELOW...

ALL EYES TURN ON THE STORM SYSTEM PUSHING OUT OF THE ROCKIES INTO
THE PLAINS ON TUESDAY. 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 /04Z TUESDAY THROUGH SATURDAY/...
MVFR CEILINGS REMAIN BANKED UP AGAINST THE WESTERN SLOPES TONIGHT 
IN DEEP WESTERLY FLOW ALOFT. HOWEVER AS THE LOW LEVEL TRAJECTORY
BACKS MORE SW LATE SHOULD SEE SOME DECREASE IN LOW CLOUDS DURING
THE PREDAWN HOURS ESPCLY AT BLF. LWB MAY CLEAR FOR A BRIEF PERIOD
BUT SINCE IFFY WILL KEEP IN A MVFR CIG UNTIL ABOUT 09Z BEFORE
SCATTERING OUT WITH SOME FOG AROUND BY MORNING. WITH WET
GROUND...SOME FOG ALSO POSSIBLE UNDER CLEAR SKIES OVER THE EAST
SO INCLUDING A SLIGHT VSBY REDUCTION AT DAN. HIGH AND MID CLOUDS
WILL INCREASE TUESDAY MORNING...WITH LOWER CLOUDS ARRIVING AHEAD
OF THE NEXT SYSTEM BY EVENING AT MOST SITES AND CONTINUING INTO
THE OVERNIGHT. WITH 18Z/00Z GUIDANCE NOW A BIT SLOWER WITH THE
ONSET OF THE PRECIP LATER TUE...KEPT IT A BIT SLOWER AT BLF/LWB
WITH PTYPE MOSTLY RAIN DURING THE DAYLIGHT PERIOD. THINK A MIX TO
-FZRA WILL OCCUR AT LWB AFTER 00Z. ELSW EXPECTING MVFR CIGS AND
PRECIP TO ARRIVE LATE IN THE AFTERNOON WITH AGAIN MOSTLY JUST RAIN
AT THIS POINT. IFR CONDITIONS LIKELY IN LOW CIGS AND PRECIP/FOG
TUESDAY EVENING.

ANOTHER IMPACT WILL BE STRONG SOUTHEAST TO SOUTHERLY LOW LEVEL
WINDS TUESDAY EVENING THROUGH WED MORNING...WITH GREATEST IMPACT
ACROSS THE BLF AREA WHERE STRONGER WINDS LIKELY OUTSIDE OF THE
COLD AIR WEDGE. FOR NOW INCLUDING GUSTS TO AROUND 30 KTS AT BLF
TUESDAY EVENING AS RAINFALL MAY TEND TO DAMPEN MIXING SOMEWHAT.
ALSO LOW LEVEL WIND SHEAR A GOOD POSSIBILITY ELSW AS THE STRONG
JET WILL REMAIN JUST ABOVE THE SURFACE COOL POOL DURING THE
EVENING AND OVERNIGHT.

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. HIGH PRESSURE BUILDS IN ON FRIDAY
BRINGING A RETURN TO VFR ACROSS THE REGION ALONG WITH LIGHTER
WINDS. ANOTHER WEAK STORM SYSTEM LOOKS TO BRING A POSSIBLE MIXED
BAG OF PRECIP BACK TO THE AREA WITH MVFR/IFR CONDITIONS ON
SATURDAY.

&&

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

&&

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