FXUS61 KRNK 041748
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1248 PM EST FRI DEC 4 2009

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND INTO THE AREA FROM THE WEST TODAY BEFORE
WEAKENING OVERNIGHT. AN AREA OF LOW PRESSURE IS EXPECTED TO
DEVELOP ALONG THE SOUTHEAST COAST LATER TONIGHT AND MOVE
NORTHEAST OFF THE MID ATLANTIC COAST ON SATURDAY. COLD HIGH
PRESSURE WILL BUILD IN BEHIND THE SYSTEM FOR SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
THERE IS LINGERING LOW LEVEL MOISTURE IN THE MTNS...BUT ONLY A
WEAK WESTERLY FLOW...SO AREA RADARS NO LONGER SHOW ANY LIGHT
PRECIP RETURNS. LOOKING AT THE 12Z RNK SOUNDING...LOOKS LIKE THE
LOW CLOUDS MAY REMAIN TRAPPED UNDER A STRONG INVERSION IN THE
MTNS. THIS WILL KEEP HIGH TEMPS A LITTLE COOLER THAN FCST ACROSS
THE FAR WEST. IN CONTRAST...ONLY THIN CIRRUS IS INDICATED THRU
MUCH OF THE DAY IN THE PIEDMONT...SO TEMPS MAY BE A DEGREE OR TWO
WARMER THERE. WILL MAKE MINOR ADJUSTMENTS TO TEMPS AND SKY COVER
TODAY. NO OTHER CHANGES NEEDED. 

PREVIOUS FORECAST...
LOW LEVEL MOISTURE IS BELOW 5500 FT AND WARM NOSE BETWEEN 6-9 KFT
TO KEEP DENDRITIC GROWTH FROM HAPPENING THIS MORNING. WITH LIGHT
RADAR RETURNS CONTINUING ACROSS SOUTHEASTERN WEST VIRGINIA...WILL
HAVE POPS LOW WITH A CHANCE OF DRIZZLE...POCKETS OF FREEZING
DRIZZLE ACROSS WESTERN SLOPES UNTIL 14Z FRIDAY. SURFACE HIGH
PRESSURE BUILDS INTO THE REGION LATER TODAY WITH BREAKS IN THE
CLOUDS EXPECTED. CLOUDS WILL RETURN OVERNIGHT AS A SURFACE LOW
PRESSURE SYSTEMS DEVELOPS OFF THE SOUTHEAST COAST. THIS SYSTEM
WILL BRING PRECIPITATION BACK INTO THE REGION AFTER MIDNIGHT
TONIGHT.

P-TYPE WILL BE A LITTLE TRICKY AT THE ONSET FOR AREAS EAST OF THE 
BLUE RIDGE. IN THE PIEDMONT...85H TEMPERATURES NEAR FREEZING WITH 
WET BULB SURFACE TEMPERATURES NEAR 40F. WARM SURFACE BOUNDARY LAYER 
WILL BE SHALLOW AND AROUND 1500 FT THICK TO HAVE ONSET OF 
PRECIPITATION IN THE PIEDMONT AS RAIN WITH A FEW SNOW FLAKES MIXED 
IN. IN THE FOOTHILLS AND ROANOKE/SOUTHERN SHENANDOAH VALLEY...WET 
BULB TEMPERATURES IN THE MID 30S WITH SURFACE BOUNDARY LAYER 
THICKNESS BETWEEN 800-1200 FT. THE BOUNDARY LAYER MAY BE LOW 
ENOUGH TO HAVE EARLY MORNING PRECIPITATION IN THIS AREAS AS SNOW WITH 
A FEW COLD RAIN DROPS MIXED IN. ALONG AND WEST OF THE BLUE
RIDGE...ALL SNOW IS EXPECTED.

ACCUMULATIONS WILL BE LITTLE...IF ANY...PRIOR TO SUNRISE SATURDAY. 
GROUND TEMPERATURES ACROSS THE AREA WILL BE IN THE 40S WITH THE 
EXCEPTION OF HIGHER ELEVATIONS IN THE MID TO UPPER 30S. MOST OF THE 
SNOW FALLING DURING THE EARLY MORNING HOURS WILL MELT ON CONTACT. IF 
ANY SNOW ACCUMULATES BELOW 3000 FEET...IT WILL LIKELY BE ON ELEVATED 
AND GRASSY SURFACES. HIGHER ELEVATIONS ABOVE 3000 FEET COULD 
POSSIBLY SEE LIGHT SNOW ACCUMULATIONS ON ALL SURFACES.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
MAIN CONCERN CONTINUES TO BE WITH PRECIP ON SAT AS A STRONG UPPER 
VORT SWINGS THRU THE BASE OF THE 5H TROF AND ENHANCES LOW
PRESSURE OFF THE NC COAST. MODELS HAVE SPED UP TIMING OF THE ONSET
OF THE BEST LIFT EARLIER IN THE MORNING AND SUBSEQUENT DEPARTURE
OF WHAT THERE IS OF DEEP RH DURING THE LATE AFTERNOON. SINCE WILL
BE DEALING WITH MAINLY MID/UPPER LEVEL FEATURES TO PRODUCE SIG
PRECIP STILL QUESTIONS WITH THE DEGREE OF MOISTURE TO WORK WITH
GIVEN MOST RH NEAR THE COAST/OFFSHORE WITH THE SURFACE FEATURE.
APPEARS BEST DEFORMATION ZONE AXIS ALOFT WILL SETUP ACROSS FAR
WESTERN VA WHILE DEEPER Q-VECTOR AND WEAK FGEN FORCING SNEAK OUT
ACROSS THE SOUTHERN BLUE RIDGE AND POINTS EAST BY AFTERNOON.
HOWEVER THE UPPER JET WILL BE JUST ABOUT OVERHEAD WESTERN VA
SUPPORTING A LITTLE MORE LIFT ACROSS THE NW AND IN THE RIGHT REAR
OF THE JET OVER THE SE ZONES WHERE MOISTURE WILL BE BETTER. THIS
SCENARIO COULD ACTUALLY LIMIT QPF AMOUNTS IN BETWEEN WHERE THE
UPPER DYNAMICS MAY ACTUALLY BE BEST. THIS CURRENTLY SUPPORTED BY
LOWERING MODEL QPF AND ESPCLY THE SREF/GFS WHICH SHOW ONLY A
COUPLE TENTHS IN THE WEST AND A QUARTER TO ONE HALF INCH SE WHERE
MORE RAIN LIKELY.

RAOB PROFILES SUGGEST PTYPE MOSTLY SNOW IN THE WEST AND NORTH OF 
HIWAY 460 AFTER SOME BRIEF RAIN THERE EARLY ON. THICKNESSES COOL
IN THE AFTERNOON AS THE LOW DEVELOPS WITH PRECIP CHANGING TO SNOW
IN THE PIEDMONT AFTER 18Z BEFORE TAPERING OFF EARLY IN THE EVENING
IF NOT SOONER. SOME BANDING STILL APPEARS POSSIBLE MAINLY SOUTHERN
BLUE RIDGE OTRW SNOWFALL ACCUMULATIONS TRICKY GIVEN WARM/WET
GROUND AND SNOWFALL DURING THE DAYLIGHT HOURS IN EARLY DECEMBER.
USING A BLEND OF THE ABOVE MENTIONED LIGHTER QPF AND THE SLIGHTLY
WETTER 00Z ECMWF HAVE SNOWFALL TOTALS OF MAINLY 1-2 INCHES
NORTH/WEST WITH 3 INCHES OR SO AT HIGHER ELEVATIONS MAINLY NW
UNDER THE DEFORMATION AXIS. LOOKS TOO WARM FOR MUCH ACCUMULATION
SOUTH/EAST OF ROA/LYH UNLESS SNOWFALL IS HEAVIER AND CHANGES OVER
SOONER. THUS RUNNING WITH A 6-10 HOUR WINDOW OF CAT POPS MOST
AREAS INTO SAT AFTERNOON WITH A CONTINUED MENTION IN THE HWO FOR
NOW. ALSO LOWERED TEMPS SINCE QUICKER TIMING SHOULD MEAN LITTLE
RISES AND FALLING VALUES SE BY AFTERNOON.

SYSTEM TAKES MOISTURE OUT OF THE AREA SAT NIGHT WITH COLD HIGH 
PRESSURE BUILDING OVERHEAD BY SUNDAY MORNING. UNDER CLEAR SKIES 
EXPECT SOME AREAS THAT DO HAVE SOME SNOW ON THE GROUND TO SEE LOWS 
DROP INTO THE UPPER TEENS OTRW 20S MOST SPOTS. HIGH GETS BOOTED 
OFFSHORE SUNDAY ALLOWING FOR WEAK RETURN FLOW TO DEVELOP SUNDAY 
AFTERNOON AND CONTINUE SUNDAY NIGHT. CONTINUED STRONG SW FLOW ALOFT 
LIKELY TO BRING SOME HIGH CLOUDS BACK IN LATER SUNDAY FOLLOWED BY 
MORE WARM ADVECTION MID DECK SUNDAY NIGHT. THIS IN COMBO WITH CHILLY 
85H TEMPS SHOULD KEEP HIGHS A LITTLE BELOW MOS SUNDAY BUT NOT AS 
COLD SUNDAY NIGHT.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
LEANED MEDIUM RANGE TOWARDS HPCGUIDE WHICH WAS A BLEND OF ECMWF AND 
GFS ENSEMBLES. QUASI ZONAL FLOW EXPECTED WITH SOME AMPLIFICATION OF 
THE PATTERN ON TUESDAY INTO WEDNESDAY. ON MONDAY...THE UPPER LEVEL 
TROUGH WILL PUSH EAST INTO THE ATLANTIC OCEAN AS HIGH PRESSURE/RIDGE 
ALOFT SLIDES EAST ACROSS OUR AREA. MOISTURE SLOWLY INCREASES AS A 
FRONTAL BOUNDARY APPROACHES FROM THE WEST MONDAY NIGHT INTO TUESDAY. 
AS THE LOW PRESSURE CENTER AND FRONT SPREAD EAST THE CHANCES OF PCPN 
INCREASE TUESDAY NIGHT AND WEDNESDAY. AS LOW PRESSURE LIFTS 
NORTHEAST AND COLD FRONT PUSHES INTO THE ATLANTIC OCEAN. KEEP SOME 
CHCY POPS IN THE WESTERN MOUNTAINS WEDNESDAY NIGHT INTO THURSDAY. 
HIGH PRESSURE WILL BUILD EAST INTO THE AREA FROM THE TENNESSEE 
VALLEY ON THURSDAY INTO FRIDAY.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
LOW LEVEL MOISTURE TRAPPED UNDER AN INVERSION WILL KEEP MVFR CIGS
MOST OF THE DAY AT BLF AND LWB...THOUGH THEY ARE EXPECTED TO LIFT
OT VFR BEFORE 00Z. HOWEVER...DETERIORATING FLIGHT CONDITIONS ARE
EXPECTED OVERNIGHT INTO SATURDAY AS A COASTAL LOW PRESSURE
DEVELOPS. PRECIPITATION WILL SPREAD INTO THE AREA BY AROUND
DAYBREAK...AND CIGS/VSBYS WILL RAPIDLY LOWER TO IFR AT ALL TAF
SITES BY 15Z- PROBABLY SOONER. THE PRECIPITATION WILL BE MAINLY
ALL SNOW AT BLF AND LWB...SNOW WITH SOME RAIN MIX AT ROA AND
LYH...AND MAINLY RAIN AT DAN. THE SNOW WILL LIKELY BE HEAVY
ENOUGH TO ACCUMULATE ON THE GROUND...THOUGH SHOULD BE SLUSHY AND
WET. WITH THE HEAVIER SNOW...FLIGHT CONDITIONS WILL LIKELY DROP TO
VLIFR. 

THE PRECIP WILL MOVE OUT OF THE AREA QUICKLY LATER SATURDAY
AFTERNOON...AND THERE WILL BE IMPROVING FLIGHT CONDITIONS. ALL
SITES SHOULD BECOME VFR BY 00 TO 03Z. HIGH PRESSURE WILL BRING VFR
CONDITIONS FOR SUNDAY INTO MONDAY. ANOTHER WEAK COLD FRONT MAY
BRING BRIEF MVFR CONDITIONS IN CLOUDS AND LIGHT PRECIP BY MONDAY
NIGHT INTO TUESDAY.

&&

.HYDROLOGY...
THE DAN RIVER AT SOUTH BOSTON IS EXPECTED TO CREST JUST BELOW
FLOOD STAGE THIS MORNING. PLEASE SEE THE LATEST WBCRVSRNK PRODUCT
FOR ADDITIONAL DETAILS.

&&

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

&&

$$
SYNOPSIS...JH/PM
NEAR TERM...JJ/RCS
SHORT TERM...JH
LONG TERM...KK
AVIATION...JH/JJ
HYDROLOGY...