FXUS61 KRNK 120226
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
926 PM EST FRI DEC 11 2009

.SYNOPSIS...
A LARGE HIGH PRESSURE SYSTEM WILL MOVE EAST INTO THE MID ATLANTIC
STATES TONIGHT...THEN OFF THE COAST ON SATURDAY. LOW PRESSURE WILL
TRACK SOUTH OF THE REGION OVER THE WEEKEND...BRINGING A WINTRY MIX
OF PRECIPITATION TO PORTIONS OF THE AREA LATE SATURDAY NIGHT INTO
EARLY SUNDAY.

&&

.NEAR TERM /THROUGH SATURDAY/...
PREVIOUS SET OF GRIDS STILL LOOKS GOOD. APPROACH OF SURFACE RIDGE
HAS ALLOWED DECOUPLING OF LOWER ATMOSPHERE IN ALMOST ALL LOCATIONS
WITH EXCEPTION OF HIGHER ELEVATIONS ACROSS THE NORTH...WITH HOT
SPRINGS STILL GUSTING TO 23 KNOTS. EXPECT TO SEE WINDS IN THIS
AREA DIMINISH TO BELOW 10 KNOTS AFTER MIDNIGHT WITH ARRIVAL OF 850
RIDGE. CIRRUS SHIELD JUST TO THE SOUTH OF THE FORECAST AREA SHOULD
REMAIN THERE FOR MUCH OF THE REMAINDER OF THE NIGHT...SO WITH
LIGHT WINDS...DRY AIR...AND CLEAR/NEARLY CLEAR SKIES...PREVIOUSLY
FORECASTED OVERNIGHT LOWS STILL LOOK RIGHT ON TARGET. MADE A FEW
TWEAKS TO ACCOUNT FOR CURRENT HOURLY TEMPERATURE AND DEW POINT 
TRENDS...BUT OTHERWISE LEFT GRID PACKAGE UNCHANGED.

PREVIOUS DISCUSSION...

A STRONG SURFACE HIGH WILL BE OVERHEAD TONIGHT WITH ZONAL FLOW
ALOFT. 85H RIDGE WILL ALSO BE OVER THE AREA WHICH WILL LEAD TO
DIMINISHING WINDS AND GOOD RADIATIONAL COOLING. WITH DEW POINTS
BEING VERY DRY...TEMPERATURES WILL BOTTOM OUT IN THE 10-15F RANGE
ACROSS THE WEST AND IN THE 15-20F RANGE IN THE EAST. MAV/GFS WAS
THE COLDEST GUIDANCE WITH MET/NAM 5-10F WARMER. LIKING THE MAV/GFS
NUMBERS FOR OVERNIGHT LOWS BUT NOT CONFIDENT TO RULE OUT MET/NAM.
THEREFORE...TOOK A BLEND OF THE TWO WITH A SLIGHT WEIGHT TO
MAV/GFS.

THE SURFACE HIGH WILL CONTINUE TO ADVANCE TO THE EAST AND OFF THE 
VA/NC COAST SATURDAY AFTERNOON. LIGHT SOUTHERLY FLOW WILL BE 
ESTABLISHED ACROSS THE WEST WHILE THE EAST REMAINS SOMEWHAT COOL. 
CLOUDS SHOULD HOLD OFF UNTIL THE LATE AFTERNOON AND WILL LIKELY SEE 
UNIFORM TEMPERATURES IN THE 40S...SOME 30S IN HIGHER ELEVATIONS AND 
SHELTERED VALLEYS. I WENT WITH THE COOLER NAM FOR HIGH TEMPERATURES.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
LOOKING AT A WINTRY EVENT SAT NIGHT INTO EARLY SUNDAY. MODELS ARE
PUSHING PRECIP INTO THE AREA AROUND THE 00Z-03Z TIME
FRAME...ALTHOUGH FAVORING SLIGHTLY SLOWER THAN THE GFS/NAM.
LEANING TOWARD THE 12Z NAM ON TEMP PROFILE WITH SOME ADJUSTMENTS
COLDER. THINKING THAT THE COLUMN AND SFC TEMPS ARE GOING TO BE
COLDER GIVEN THE PAST TWO DAYS OF TEMPS IN THE TEENS IN THE MTNS. 

THIS WILL SET THE STAGE FOR ACCUMULATING WINTRY PRECIP...ALBEIT ON
THE LIGHT SIDE AS OPPOSED TO THE PREVIOUS SYSTEM. STILL EXPECT
SLEET/SNOW MIX AT THE ONSET SAT EVENING OVER THE NC MTNS/SW VA
MTNS TO MOVE NORTH ACROSS THE AREA THROUGH MIDNIGHT. WARM NOSE
WILL CHANGE PRECIP OVER TO RAIN...AND THINK WITH SUB-FREEZING SFC
TEMPS LOOKING AT LIGHT ICE ACCRETION ACROSS THE ENTIRE BLUE RIDGE
AND EITHER SIDE...WITH ANOTHER POCKET FURTHER WEST OVER THE
ALLEGHANY MTNS INTO THE GREENBRIER VALLEY. EVEN AREAS ALONG AND
NORTH OF THE ROANOKE RIVER IN THE PIEDMONT WILL SEE SOME POTENTIAL
FOR LIGHT ICE ACCUMULATIONS. AT THIS POINT...WILL CONTINUE TO
HIGHLIGHT THE ICE POTENTIAL IN THE HWO...AS IT IS 3RD PERIOD...AND
A TRACK THAT IS SLOWER COULD DELAY THE ONSET UNTIL LATER SAT NIGHT
INTO SUNDAY...THEREBY CHANGING P-TYPE POTENTIAL.

WITH THE SFC HIGH OVER THE WRN ATLANTIC AND AN IN-SITU WEDGE...
LINGERING POCKETS OF FREEZING RAIN UNTIL ABOUT NOON OVER THE
VALLEYS NORTH OF ROANOKE...B4 WARM NOSE AND WEDGE START TO SHRINK
AND WARM THE SFC TEMPS ABOVE FREEZING. RAINFALL WILL MOVE EAST OF
THE AREA BY LATE SUNDAY AFTERNOON...AS THE LOW PRESSURE SHIFTS OFF
THE COAST. LINGERING MOISTURE ON THE BACK SIDE WITH COLDER AIR
WILL BRING A FEW RAIN/SNOW SHOWERS TO THE MTNS OF WV.

TEMPERATURES ARE GOING TO COOL DOWN SAT EVENING...THEN STEADY OUT
OR RISE TOWARD 12Z SUNDAY. SUNDAY TEMPS SHOULD HOLD STEADY IN THE
WEDGE ACROSS THE FOOTHILLS/SRN SHENANDOAH VALLEY INTO MIDDAY
SUNDAY WITH WARMING TEMPS ELSEWHERE. TRICKY FORECAST ON
HIGHS...BUT THINK COOLER THAN MOS THE WAY TO GO.

SUNDAY NIGHT...NOT EXPECTED MUCH WIND BEHIND THIS SYSTEM EITHER
THIS TIME...MAYBE 10-15 MPH. WARM ADV ACTUALLY BEGINS BEHIND THIS
BY SUNDAY NIGHT WELL IN ADVANCE OF NEXT SYSTEM...AND AS A RESULT
INCREASED THE LOWS FOR SUN NIGHT A FEW DEG. ANY LINGERING UPSLOPE
SHWRS IN FAR WEST QUICKLY FADE AS FLOW TURNS WEST OR WSW OVERNIGHT
AND ANTICYCLONIC FLOW ALOFT RETURNS. MOST OF THESE WILL BE RAIN
SHWRS GIVEN WARMING 850 TEMPS.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
RIDGING AT THE SURFACE AND ALOFT WILL INFLUENCE THE WEATHER FOR 
MONDAY AS SLIGHTLY DRIER AIR AND SUBSIDENCE ENTER THE AREA. A 
SURFACE LOW PRESSURE SYSTEM MOVES INTO THE GREAT LAKES WITH A COLD 
FRONT STRETCHING SOUTHWEST INTO ARKANSAS. THIS WILL PUSH EASTWARD 
MONDAY NIGHT INTO TUESDAY INCREASING MOISTURE OUT AHEAD OF THIS 
SYSTEM WITH THE SOUTHWESTERLY FLOW. MAINTAINED SLIGHT CHANCE POPS 
INCREASING TO CHANCE BY 12Z TUESDAY ACROSS THE FORECAST AREA. THE 
LATEST RUN OF THE ECMWF LOOKS TO BE A LITTLE SLOWER THAN THE GFS ON 
TIMING OF THE PRECIP. HAVE LEANED MORE TOWARD THE FASTER SOLUTION. 

WITH LOWS BELOW FREEZING...SNOW SHOWERS WILL SPREAD FROM NORTHWEST 
TO SOUTHEAST...MAINLY ALONG AND WEST OF THE BLUE RIDGE MOUNTAINS. 

GFS PROGS THE COLD AIR ADVECTION FILTERING IN TUESDAY AFTERNOON AS 
850 MB TEMPS FALL INTO THE RANGE OF +6 TO -6 FROM SOUTHEAST TO 
NORTHWEST. THE COLD AIR BANKS UP AGAINST THE APPALACHIAN MOUNTAINS 
OVERNIGHT WITH -12 IN SOUTHEAST WEST VIRGINIA. EXPECT ANOTHER NIGHT 
WITH LOWS IN THE UPPER TEENS TO LOWER 20S ONCE AGAIN WEDNESDAY 
NIGHT.  

SURFACE HIGH PRESSURE PUSHES INTO THE AREA IN THE WAKE OF THE COLD 
FRONT TUESDAY NIGHT INTO WEDNESDAY AND LASTING THROUGH THE END OF 
THE WEEK. COLD AIR WILL REMAIN IN PLACE THROUGH THURSDAY NIGHT WITH 
TEMPERATURES STAYING BELOW NORMAL.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
VFR WEATHER WITH UNRESTRICTED FLIGHT CONDITIONS WILL CONTINUE OVER ALL
TERMINAL FORECAST SITES (KROA...KLYH...KDAN...KBLF...KLWB) THROUGH 
SATURDAY...BUT WILL GRADUALLY DETERIORATE SATURDAY NIGHT INTO SUNDAY
AS AN AREA OF LOW PRESSURE DEVELOPS OVER THE GULF OF MEXICO AND
THEN LIFTS NORTHEAST ALONG THE SOUTH CAROLINA COAST.

HIGH AND MID LEVEL CLOUDS WILL BEGIN TO ADVECT NORTHEAST INTO THE
MID ATLANTIC REGION ON SATURDAY...BUT LOWER ATMOSPHERE IS NOT
EXPECTED TO BECOME SUFFICIENTLY SATURATED TO BRING CEILINGS DOWN
INTO MVFR RANGE UNTIL AFTER 06Z ON SUNDAY...BY WHICH TIME A WINTRY
MIX OF PRECIPITATION SHOULD BEGIN TO OVERSPREAD THE AREA FROM THE
SOUTHWEST. BY DAYBREAK SUNDAY...MOST TERMINAL FORECAST POINTS
SHOULD SEE CEILINGS AND VISIBILITIES IN THE IFR RANGE...WHICH MAY
VERY WELL PERSIST THROUGH MUCH OF THE DAY.

THE SYSTEM SHOULD EXIT THE REGION SUNDAY NIGHT WITH IMPROVED FLIGHT
CONDITIONS EXPECTED BY MONDAY. ANOTHER WEATHER SYSTEM WILL MOVE
THROUGH THE REGION LATER MONDAY NIGHT INTO TUESDAY...BRINGING AN
INCREASED THREAT OF PRECIPITATION ALONG WITH ANOTHER PERIOD OF
MVFR TO IFR CONDITIONS. STRONG COLD ADVECTION BEHIND THIS SYSTEM
WILL MAINTAIN A THREAT OF UPSLOPE CLOUDS AND MVFR WEATHER ACROSS
THE SOUTHEASTERN WEST VIRGINIA TERMINAL FORECAST POINTS INTO
WEDNESDAY...BUT POST FRONTAL DOWNSLOPING OF WINDS SHOULD ALLOW FOR
RETURN TO VFR WEATHER WITH UNRESTRICTED CONDITIONS TUESDAY NIGHT
INTO WEDNESDAY EAST OF THE BLUE RIDGE.

&&

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

&&

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