FXUS61 KRNK 040450
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1150 PM EST THU DEC 3 2009

.SYNOPSIS...
HIGH PRESSURE WILL BUILD OVER THE AREA FRIDAY. AN AREA OF LOW
PRESSURE IS EXPECTED TO DEVELOP OVER THE EASTERN GULF OF MEXICO
FRIDAY NIGHT AND MOVE UP THE ATLANTIC COAST SATURDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
STILL SEEING SOME LIGHT RETURNS ON UPSTREAM RADARS AT JKL AND RLX.
RNK SOUNDING SHOWS THIS MOISTURE TRAPPED BELOW A SUBSIDENCE
INVERSION AT 5500 FT. MOISTURE IS A LITTLE DEEPER ON THE ILN
SOUNDING UPSTREAM...BUT IT STILL DOES NOT LOOK LIKE THE DEPTH OF
THE MOISTURE WILL BE ENOUGH FOR ICE CRYSTAL GROWTH...SO I EXPECT
DRIZZLE OR FREEZING DRIZZLE MAINLY ON WESTERN SLOPES. CURRENT FCST
IS IN GOOD SHAPE...WILL MAKE ADJUSTMENTS FOR CURRENT TEMPS AND
CONTINUE TO CARRY THE DRIZZLE AND FREEZING DRIZZLE IN THE WEATHER
GRIDS. 

PREVIOUS DISCUSSION... HIGHEST ELEVATIONS IN THE NC
MTNS...BEECH MTN...IN THE CLOUDS AND GETTING SOME ICING ON
ELEVATED SURFACES FROM FREEZING DRIZZLE. HAVE LOOKED AT OTHER
WEBCAMS AND CHECKED WHAT TEMPS ARE AVAILABLE...AND IT LOOKS LIKE
ONLY ELEVATIONS ABOVE 4000 FT PROBABLY BELOW FREEZING.
HOWEVER...THE FREEZING LEVEL WILL BE DROPPING OVERNIGHT...SO I
HAVE ADJUSTED THE WEATHER GRIDS TO ADD IN MORE FREEZING DRIZZLE
OVERNIGHT. IN ADDITION...THE RLX RADAR SHOWS AN INCREASE IN
COVERAGE IN LIGHT RETURNS THE PAST COUPLE HOURS...SO I HAVE ADDED
IN A SLIGHT CHC POP FOR WESTERN GREENBRIER. THINK THAT MOISTURE IS
STILL TOO SHALLOW FOR DENDRITIC GROWTH...SO WOULD BE LIGHT RAIN OR
FREEZING RAIN. FOR THE MOST PART...THINK WE ARE LOOKING AT DRIZZLE
OR FREEZING DRIZZLE. SFC TEMPS ARE STARTING OUT QUITE A BIT ABOVE
FREEZING...SO ROADS SHOULD NOT BE A PROBLEM- MAIN CONCERN WOULD BE
BRIDGES AND OVERPASSES...AND THAT WOULD BE LATE TONIGHT AS THE
TEMPS DROP INTO THE UPPER 20S IN THE HIGH ELEVATIONS. WILL PLAN ON
ISSUING A SPECIAL WEATHER STATEMENT FOR THE CHC OF THAT HAPPENING.

PREVIOUS DISCUSSION... 
FORECAST AREA WILL REMAIN UNDER INFLUENCE OF DEEP SW FLOW ALOFT
AHEAD OF A FULL LATITUDE MID CONUS LONG WAVE TROF. WEAK LOW LEVEL
WESTERLY TRAJECTORY PERSISTS AROUND EXITING NEW ENGLAND STORM
SYSTEM. PERSISTENT LOW LEVEL CLOUD COVER REMAINS ON THE WINDWARD
SLOPES OF THE APPALACHIAN MTNS WITH SOME VERY LIGHT (MAINLY TRACE)
PRECIPITATION OCCURRING ACROSS WVA AND INTO THE HIGHLANDS OF VA.
THIS MOISTURE IS EXPECTED TO REMAIN BANKED UP AGAINST THE WEST
SIDE OF THE MOUNTAINS THROUGH EARLY FRIDAY...AND WITH TEMPS
FALLING AOB FREEZING...POTENTIAL EXISTS FOR SOME FLURRIES OR LIGHT
FREEZING DRIZZLE. FLURRIES ARE CERTAINLY NO BIG DEAL BUT IT MAY BE
WORTH EMPHASIZING POTENTIAL GLAZING HAZARD WITH THE FREEZING
DRIZZLE...SOMETHING FOLKS WON'T PAY ATTENTION TOO UNTIL THEY STEP
OUT THE DOOR IN THE MORNING AND THEIR FEET FLY OUT FROM UNDER THEM
DUE TO A LIGHT GLAZE ON AN ELEVATED SET OF STAIRS. CLOUDS SHOULD
BE LIMITED EAST OF THE BLUE RIDGE WITH PC TO CLEAR SKIES OUT EAST
OVERNIGHT WITH SOME INCREASE IN HIGH CLOUDS BY MORNING. LOW TEMPS
29-33 WEST UNDER OOZING 85H COLD ADVECTION WHILE MOSTLY 30S EAST
WHERE BETTER RAD CONDITIONS MAY ALLOW VALUES TO FALL BELOW MOS IN
SPOTS.

ON FRIDAY INTO FRIDAY EVENING...SURFACE HIGH PRESSURE WILL BE 
OVER THE REGION. THE DAY AS A WHOLE SHOULD BE DRY...HOWEVER...WITH
THE SOUTHWEST FLOW ALOFT...LOOK FOR INCREASING CIRRUS IN ADVANCE OF
DEVELOPING SYSTEM TO OUR SOUTH. TEMPS WILL BE SEASONALLY
COOL...MAYBE A FEW DEGREES SHY OF THE NORM...WHICH WILL SET THE STAGE
FOR POTENTIAL WINTER EVENT OVER THE WEEKEND.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
ALL EYES ARE SET ON LOW PRESSURE DEVELOPING ALONG THE SOUTHEAST 
COAST FRIDAY NIGHT WITH UPPER JET ROUNDING THE BASE OF THE TROUGH 
AND STREAMING NORTH ACROSS THE MID ATLANTIC. HOW WILL THIS IMPACT 
THE AREA IN TERMS OF SNOWFALL AND ACCUMULATION.

LEANING TOWARD A BLEND OF THE ECMWF/12Z GFS AND 09Z SREF. THE 12 NAM 
THIS MORNING SEEMED OVER DONE AND TOO FAR WEST WITH QPF WITH THIS 
EVENT...AND DID NOT INITIALIZE AS WELL AT 8H UPSTREAM ACROSS THE 
PLAINS AS THE GFS.

FRIDAY NIGHT...WILL SEE CLOUDS INCREASING WITH LIGHT PRECIP...RAIN 
IN THE EAST SNOW IN THE WEST ARRIVING AFTER 06Z...BUT MORESO AFTER 
12Z SAT. FORECAST SOUNDINGS SUGGEST THAT THE RAIN/SNOW LINE WILL HUG 
THE BLUE RIDGE EARLY...WITH A MIX OF RAIN/SNOW INTO THE FOOTHILLS 
AND NRN PIEDMONT OF OUR CWA SAT MORNING. BY AFTERNOON...THE 
RAIN/SNOW LINE SHIFTS FURTHER WEST WITHA COLD RAIN EXPECTED OVER THE 
PIEDMONT.

AS THE UPPER VORT PASSES ACROSS THE CAROLINAS LATE SAT 
AFTERNOON...THE PROFILE COOLS ONCE AGAIN...AND THE RAIN WILL CHANGE 
BACK TO SNOW BEFORE IN THE PIEDMONT. 

THIS EVENT LOOKS LIKE IT WILL LAST NO MORE THAN 12 HOURS. 
ANTECEDENT/LIMITING FACTORS ARE A WETTER...WARMER GROUND...AND A 
LACK OF COLD AIR BEFOR ONSET AND SPEED OF SYSTEM WITH DEEP 
MOISTURE/CONVECTION OFF THE COAST. FACTORS FOR ACCUMULATING SNOWS 
WILL BE THE STRONG JET/LIFT/DIVERGENCE THAT SHOULD ALLOW FOR THE 
PRECIP TO FALL HEAVIER. THE MAIN QUESTION WILL BE WHERE THE BEST 
UPPER FORCING SETS UP...AND ATTM IT SEEMS THAT THE BLUE RIDGE AND 
EAST ARE IN LINE FOR THAT.

GOING WITH THE ABOVE...AND LOOKING AT MODEL QPF/HPC 
GUIDANCE...LEANING TOWARD A CONSERVATIVE TOTAL ON SNOW WITH 1-3 
INCHES ALONG/WEST OF THE BLUE RIDGE WITH LOCALLY HIGHER AMOUNTS 
ALONG THE PEAKS OF THE BLUE RIDGE FROM BUFFALO MTN TO NRN AMHERST 
COUNTY...AND SOME AROUND MT ROGERS. VALLEY AREAS SUCH AS ROANOKE ARE 
NOT EXPECTED TO SEE AS MUCH.

AGAIN...THIS MAY CHANGE...BUT TRENDS SUGGEST A LOW IMPACT 
EVENT...POTENTIAL ADVISORY AT BEST. FOR NOW WILL KEEP THIS 
HIGHLIGHTED IN THE HWO.

BEYOND THIS EVENT...THE TROUGH KICKS EAST SAT NIGHT WITH PRECIP 
ENDING BY MIDNIGHT IN THE EAST. HIGH PRESSURE OVERHEAD AND CLEARING 
SKIES WILL BRING VERY COLD TEMPS ESPECIALLY TO THE WESTERN CWA GIVEN 
THAT THERE COULD BE SOME LIGHT SNOW COVER.

SUNDAY...SUNSHINE RETURNS MELTING OFF ANY SNOW AS SW RIDGE ALOFT 
PUSHES ACROSS.  MAY SEE SOME CIRRUS RETURN BY THE AFTERNOON SO KEPT 
SKY COVER IN THE MOSTLY SUNNY RANGE OF 30 PERCENT.

SUNDAY NIGHT...WEAK SHORTWAVE PUSHES ACROSS AND ONLY EXPECTING SOME 
MID/HIGH CLOUDS. KEPT TEMPS COOL...ALTHOUGH WITH FASTER RETURN FLOW 
BLF/AND THE HIGHER MTNS IN THE SW COULD BE WARMER AS WELL AS ROANOKE.

&&

.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 /06Z FRIDAY THROUGH TUESDAY/...
WESTERLY LOW LEVEL FLOW AND ABUNDANT LOW LEVEL MOISTURE IN THE
OHIO AND TN VALLEYS WILL KEEP IFR TO MVFR UPSLOPE LOW CLOUDS IN
THE MTNS...AFFECTING BLF AND LWB. IN ADDITION...SOME DRIZZLE IS
LIKELY...AND TEMPS WILL DROP TO NEAR FREEZING AT BOTH LOCATIONS
TOWARD DAYBREAK. SO I HAVE INCLUDED A TEMP GROUP WITH FREEZING
DRIZZLE AT BOTH BLF AND LWB. LOW CLOUDS WILL BE SLOW TO LIFT
DURING THE DAY FRIDAY AT BLF AND LWB. BLF WILL LIKELY REMAIN MVFR. 

A STORM SYSTEM WILL BRING LOWER CIGS/LIKELY MFR OR IFR...AND
WINTRY PRECIP FOR ALL TAF SITES SATURDAY FOLLOWED BY VFR UNDER
HIGH PRESSURE FOR SUNDAY INTO MONDAY.

&&

.HYDROLOGY...
RUNOFF FROM WIDESPREAD WETTING RAINS WEDNESDAY...1-2 INCHES...
RESULTED IN RISES ON AREA RIVERS. NO FLOODING IS FORECAST ATTM...
ALTHOUGH THE DAN RIVER AT SOUTH BOSTON MAY GET CLOSE TO ITS
FLOOD STAGE OF 19.0 FEET ON FRIDAY. IF YOU ARE MONITORING THE
SOUTH BOSTON GAGE FROM THE INTERNET...THE READING IS
BOGUS...INDICATING A NEAR STEADY 9.8 FEET. THE GAGE IS STUCK!
PLEASE RELY ON THE LATEST RIVER FORECAST FOR THE MORE RELIABLE
INFORMATION.

&&

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

&&

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