-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 061134
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
634 AM EST FRI DEC 6 2013

.SYNOPSIS...
A COLD FRONT MOVES ACROSS SOUTHEASTERN WEST VIRGINIA TODAY THEN
CRAWLS ACROSS VIRGINIA TONIGHT. ARCTIC HIGH PRESSURE WELL BEHIND
THE FRONT WILL WEDGE SOUTH ALONG THE MOUNTAINS SATURDAY...BEFORE
INTERACTING WITH PRECIPITATION RETURNING NORTH BY SUNDAY.
SOUTHWESTERLY FLOW RETURNS MONDAY BEFORE A STRONGER COLD FRONT
ARRIVES TUESDAY MORNING. COLD AND DRY HIGH PRESSURE RETURNS BY
TUESDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 400 AM EST FRIDAY...

ALTHOUGH THE MAIN BODY OF RAINFALL WILL BE SLOW TO MOVE EAST
TODAY...FROM TIME TO TIME RENEGADE SHOWERS WELL EAST OF THE FRONT
WILL DEVELOP IN THE VERY MOIST WARM SECTOR WITH DECENT ISENTROPIC
LIFT. ATTM...A QUICK MOVING SLUG OF RAIN IS ENTERING NW NC AND
WILL REACH THE NEW RIVER VALLEY IN A FEW HOURS IF IT HOLDS
TOGETHER. SHALLOW NATURE OF THE FRONT EDGE OF THE ARCTIC AIR IS
ALREADY ARRIVING ACROSS SE WEST VA...WITH TEMPS AT LWB/BLF HEADED
DOWN. HOWEVER...REALLY TRICKY TEMP FORECAST THERE AS THE BOUNDARY
GETS PUSHED BACK WEST A TAD WITH AREA OF LOW PRESSURE DEVELOPING
ALONG THE FRONT AND PASSING OVER THE NEW RIVER VALLEY LATER
TODAY. WOULD THINK LWB/BLF HAVE REACHED THEIR HIGHS FOR TODAY IN
THE MORNING BUT LAV GUIDANCE SAYS NO. HARD TO SEE MUCH TEMP RISE
SO WILL KEEP TEMPS STEADY THERE TODAY. NICE SHOT OF WINDS THANKS
TO THE ARRIVAL OF A LOW LEVEL JET STREAK AS LOW PRESSURE MOVES SW
TO NE RIGHT ALONG THE BLUE RIDGE LATE AFTERNOON. NOT OUT OF THE
QUESTION THAT ONE OF THE STRONGER RENEGADE SHOWERS IS ABLE TO TAP
INTO THESE GUSTY WINDS ALOFT PRODUCING A 40 MPH GUST AS THE
SHOWERS RACE TO THE NE. ALSO CAN`T RULE OUT A RUMBLE OF THUNDER OR
TWO...AS A FEW STRIKES WERE EVEN OBSERVED A FEW HOURS AGO JUST
EAST OF LYH. MAIN BODY OF RAINFALL THEN IS FORCED EAST FINALLY
THIS EVENING AS RIPPLES OF LOW PRESSURE DART INTO PA/NY/NJ. AS
WINDS VEER SHARPLY THIS EVENING...DOWNSLOPING MAY CREATE THE
TYPICAL RAIN SHADOW WITH MUCH LESS PRECIP THROUGH THE ROANOKE AND
NEW RIVER VALLEYS AS RAIN REDEVELOPS THROUGH THE PIEDMONT AND
SOUTHSIDE LATE TONIGHT. AGAIN LLVL NATURE OF THE ARCTIC AIRMASS
MAKES P TYPE QUITE TRICKY ACROSS THE HIGHEST PARTS OF SE WEST VA
LATE TONIGHT. THE SAVING GRACE IS THAT MOST OF THE PRECIP WILL BE
GONE. WITH MOISTURE/QPF DWINDLING QUICKLY BEHIND THE
FRONT...WOULDN`T EXPECT MUCH...ALTHOUGH THERE COULD BE A LIGHT MIX
OF FIRST FREEZING RAIN...THEN SLEET AND POSSIBLY SNOW JUST AFTER
SUNRISE SATURDAY ABOVE 3000 FEET ACROSS SE WEST VA. GENERALLY HAVE
MINOR AMOUNTS OF ICE/SLEET/SNOW BUT IT IS IMPORTANT TO POINT OUT
THAT THIS WILL NOT BE THE TYPICAL SMOOTH TRANSITION FROM RAIN TO
SNOW AS THE PRECIP CUTS OFF IN SE WEST VA.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
-- Changed Discussion --
AS OF 530 AM EST FRIDAY...

WINTER STORM WATCH IN EFFECT FROM 4AM SUNDAY THROUGH 4AM MONDAY.

MODELS REMAIN UNCHANGED AND VERY CONSISTENT FROM RUN TO RUN. THE
ONLY NOTABLE TREND IS THAT THEY ARE TRENDING COLDER IN TERMS OF
TEMPERATURE PROFILES FOR SUNDAY. THAT BEING SAID AND MAKING ONLY
SUBTLE CHANGES TO THE GRIDS...REMAIN CONFIDENT THERE WILL BE
SIGNIFICANT WINTRY PRECIPITATION ACROSS OUR REGION SUNDAY. DETAILS
CONTAINED WITHIN PREVIOUS FORECAST DISCUSSIONS REMAIN VALID SO THE
REMAINDER OF THIS DISCUSSION WILL LOOK VERY SIMILAR IF YOU HAVE
BEEN FOLLOWING ALONG THE PAST SEVERAL DAYS.

STARTING WITH SATURDAY...SURFACE FRONT WILL BE SOUTH OF THE REGION
WITH COLD HIGH PRESSURE BUILDING INTO THE AREA FROM THE NORTHWEST.
THE SURFACE HIGH IS OF ARCTIC ORIGIN AND IS THE ONE THAT HAS
JACKFROST WORKING OVERTIME ACROSS THE NORTHERN PLAINS AND THE
INTERMOUNTAIN WEST. BY SUNDAY MORNING A PIECE OF THIS ANTICYCLONE
IS EXPECTED TO BE CENTERED OVER NEW YORK AND PENNSYLVANIA TO THE
TUNE OF 1036 MB. THIS IS A CLASSIC POSITION FOR COLD AIR TO
CHANNEL DOWN THE EAST SIDE OF THE APPALACHIANS SETTING UP A DAM OF
COLD AIR THAT WILL BE HARD TO DISPLACE. BY SUNDAY MORNING
TEMPERATURES WILL HAVE FALLEN CLOSE TO FREEZING ACROSS OUR
FORECAST AREA...BUT MORE IMPORTANTLY IS THE DEWPOINT WHICH WILL
HAVE DIPPED INTO THE LOWER 20S. THIS WILL PROMOTE WET BULB
TEMPERATURES WELL BELOW FREEZING.

LOOKING ALOFT...CONDITIONS ARE A BIT DIFFERENT...STRONG UPPER
LEVEL TROUGH REMAINS OVER THE CENTRAL AND WESTERN CONUS...THE
BAROCLINIC ZONE ALONG ITS EASTERN PERIPHERY AND RIGHT OVER OUR
PART OF THE WORLD. THIS WILL SET STAGE FOR ANOTHER WAVE OF LOW
PRESSURE TO DEVELOP ALONG THE BAROCLINIC ZONE AND MOVE NORTHEAST
WITHIN THE EASTERN PART OF THE UPPER TROUGH. WARM MOIST AIR WILL
GET DRAWN NORTHWARD...FLOWING OVERTOP OF THE STALLED FRONT TO OUR
SOUTH...BUT MORE IMPORTANTLY OVERRUNNING THE COLDER DOME OF HIGH
PRESSURE WHICH BE IN PLACE ACROSS OUR REGION. ISENTROPIC LIFT WILL
RESULT IN THE DEVELOPMENT OF WIDESPREAD PRECIPITIATION.

SATURDAY AS A WHOLE LOOKS DRY...ASIDE FOR SOME LINGER MORNING
RAIN FROM DANVILLE SOUTH AND EAST. GUIDANCE REMAINS UNCHANGED WITH
DEEPER MOISTURE GETTING PUSHED SOUTH OF OUR REGION...THE LARGE
ARCTIC HIGH BUILDING IN FROM THE NORTH. COULD EVEN HAVE SOME
CLEARING TAKE PLACE ACROSS OUR NORTHERN CWA PENDING STRENGTH OF
THE DRY ADVECTION. AS SUCH...ADVERTISING A PARTLY SUNNY SATURDAY
AFTERNOON FOR AREAS NORTH OF ROUTE 460...BLF-ROA-LYH. TEMPERATURES
WILL BE CHILLY WITH LOW LEVEL NORTH/NW FLOW PROMOTING READINGS IN
THE 30S WEST TO 40S/NEAR 50 FAR SOUTH.

MAIN CONCERN FOR WINTRY WEATHER WILL COME INTO PLAY LATE SAT
NIGHT INTO SUNDAY AND PERHAPS LINGERING INTO SUNDAY NIGHT.
MODEL GUIDANCE SUGGESTS ONSET OF WINTRY PRECIPITATION WILL BEGIN
IN THE NORTH CAROLINA HIGH COUNTRY AFTER MIDNIGHT SATURDAY NIGHT
AND THEN SPREAD NORTHWARD INTO VIRGINIA AND WEST VIRGINIA BY
DAYBREAK SUNDAY. FORECAST SOUNDINGS SUGGEST THE PRECIPITATION MAY
BEGIN AS A PERIOD OF SLEET IN NORHT CAROLINA AND SOUTHSIDE
VIRGINIA...AND BEGINNING AS A PERIOD OF SNOW THEN SLEET IN THE
MOUNTAINS OF VIRGINIA AND WEST VIRGINIA. AS WE TRANSITION THROUGH
THE DAY SUNDAY ALL OF THE PRECIPITATION CHANGES OVER TO FREEZING
RAIN...WHICH WILL THEN BE THE PRIMARY HIGH IMPACT METEOR TO
CONTEND WITH FOR THE REMAINDER OF THE EVENT.

WITH MODELS INDICATING LESS OF A WARM NOSE ALOFT NORTH OF THE
ROANOKE VALLEY...POTENTIAL IS THERE FOR SEVERAL INCHES OF
SNOW/SLEET (1 TO 3?) BEFORE THE CHANGE TAKES PLACE TO FREEZING
RAIN SUNDAY AFTERNOON. FARTHER SOUTH AND EAST...ONLY TRACE AMOUNTS
OF FROZEN PRECIPITATION IS EXPECTED WITH THE PRIMARY CONCERN BEING
THE FREEZING RAIN. QPF FROM 12Z/7AM SUNDAY THROUGH 12Z/7AM MONDAY
IS EXPECTED TO RANGE FROM 0.50 TO 1.00. BLENDING THIS WITH THE
EXPECTED SURFACE TEMPERATURES AND P-TYPE FOR THE AREA THIS
TRANSLATES INTO ABOUT A QUARTER OF AN INCH OF ICE ACCRETION ACROSS
NORTH CAROLINA AND SOUTHSIDE VA TO AS MUCH AS A HALF INCH OF ICE
ACROSS PORTIONS OF THE GREENBRIER VALLEY...WV/VA HIGHLANDS AND
INTO THE SHENANDOAH VALLEY OF VA. IN ADDITION TO THE ICE...1-3
INCHES OF SNOW/SLEET SEEM PLAUSIBLE FOR THE VA/WV HIGHLANDS NORTH
OF THE ROANOKE VALLEY. GROUND ZERO FOR ICING APPEARS THAT IT WILL
BE ALONG THE BLUE RIDGE FROM BLACKSBURG AND ROANOKE NORTH AND
EAST INTO THE SHENANDOAH VALLEY.

PRECIPITATION THAT FALLS SUNDAY WILL PUT A BOAT ANCHOR ON THE
THERMOMETER. HIGH TEMPERATURES SUNDAY WILL LIKELY OCCUR JUST PRIOR
TO THE ONSET OF PRECIPITATION...THEN EVAPORATIONAL COOLING WILL
DRAG READINGS LOWER...AND REMAINING THERE FOR THE REST OF THE DAY.
MOST AREAS WILL REMAIN AOB 32 FOR MUCH OF THE DAY. AREAS WEST OF
THE APPALACHIAN DIVIDE...TAZEWELL AND SMYTH WILL HAVE THE BEST
CHANCE FOR RECOVERING ABOVE 32 AS WARMER AIR MOVES NORTH THROUGH
THE TENNESSEE VALLEY. BY SUNDAY NIGHT...WARMER AIR WILL CONTINUE
TO INFILTRATE THE AREA FROM THE SOUTH TO THE NORTH. THIS WILL
RESULT IN AN EVENTUAL RISE TO ABOVE FREEZING VALUES...PARTICULARLY
ACROSS THE SOUTHERN CWA AND IN THE FAR WEST. PROLONGED FREEZING
RAIN WILL LIKELY CONTINUE FOR THE VA COUNTIES NORTH OF
460...AWAITING MIXING ON MONDAY TO FINALLY BREAK THE WEDGE.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 350 PM EST THURSDAY...

COMPLICATED FORECAST CONTINUES THROUGH THE EXTENDED PERIODS AS
SOUTHWEST FLOW ALOFT CONTINUES ACROSS THE REGION AT THE SAME TIME
ARCTIC AIR CONTINUES TO STREAM SOUTHEASTWARD FROM WESTERN/CENTRAL
CANADA INTO THE CENTRAL AND EASTERN U.S. OUR REGION REMAINS ON OR
NEAR THE BOUNDARY BETWEEN THE ARCTIC AIR AND THE WARMER AIR TO THE
SOUTHEAST...HOWEVER...THROUGH THE LONGER TERM PERIODS IT APPEARS
THAT THE ARCTIC AIR WILL WIN OUT ACROSS OUR REGION AND THE FRONTAL
WILL FINALLY BE PUSHED INTO THE SE STATES AS THE UPPER FLOW
FINALLY BECOMES NW.

MON MORNING WE ARE STILL DEALING WITH THE END OF THE POTENTIAL
SIGNIFICANT ICING EVENT ADDRESSED IN THE SHORT TERM PERIODS AS THE
WEDGE BOUNDARY FINALLY LIFTS INTO NORTHERN VA. MODELS HAVE
CONTINUED TO TREND COLDER...WHICH REQUIRES HOLDING ONTO THE -FZRA
A FEW MORE HOURS INTO MID-MORNING MONDAY THAN EARLIER INDICATED.
WILL CHANGE ALL PRECIPITATION TO -RA BY 15Z MON AS THE FORECAST
AREA BRIEFLY MOVES INTO A WARM SECTOR SANDWICHED BETWEEN THE
RETREATING COLD AIR WEDGE AND THE NEXT SURGE OF ARCTIC AIR TO THE
WEST. THROUGH THE DAYLIGHT HOURS...WE SHOULD SEE ONLY LIQUID PCPN
ACROSS THE REGION.

BY 06Z TUE...THE NEXT SURGE OF ARCTIC AIR SHOULD MOVE INTO OUR WV
COUNTIES AND OUR FAR SW VA CONTINUES. GIVEN THE STRENGTH OF THIS
SECOND SURGE OF COLD AIR...WOULD EXPECT -RA TO QUICKLY CHANGE TO
-SN FROM WEST TO EAST DURING THE EVENING. AT THE SAME TIME...THE
DEEPER MOISTURE IS SHIFTING EAST INTO THE PIEDMONT WHERE AT THIS
POINT IT SHOULD STILL BE WARM ENOUGH FOR MOSTLY -RA. THUS...SNOW
ACCUMULATIONS OUTSIDE MOUNTAIN UPSLOPE -SHSN EASTERN WV...SHOULD
BE MINIMAL...BUT COULD NOT RULE OUT AN INCH OR SO IN SOME SPOTS
WEST OF I-81/I-77. THERE IS CONSIDERABLE DISCREPANCY BETWEEN THE
GFS/ECMWF IN THIS TIME FRAME...WITH THE ECMWF PUSHING THE MOISTURE
WELL EAST OF THE CWA BEFORE ANY APPRECIABLE COLD AIR MOVES INTO
THE REGION FROM THE WEST...WHILE THE GFS TRIES TO MOVE YET A THIRD
WAVE ALONG THE FRONTAL BOUNDARY ACROSS THE REGION FROM THE SW.
GIVEN THE OVERALL CONFLUENT FLOW IN THIS TIME FRAME...NOT
EXPECTING ANY SIGNIFICANT PCPN OR MORE IMPORTANTLY WINTER WX
ISSUES. AGAIN...HOWEVER...THERE WILL BE MOUNTAIN UPSLOPE
-SHSN...WITH MINOR SNOW ACCUMULATIONS EASTERN WV COUNTIES INTO FAR
SW VA AND THE NW NC MOUNTAINS.

FOR THE REMAINDER OF THE EXTENDED...AT THIS POINT IT APPEARS DRY.
THE CENTER OF THE ARCTIC AIR MASS DRIFTS OVER THE REGION BY THU
WITH A VERY DRY/COLD AIR MASS. AGAIN...THERE ARE CONSIDERABLE
DIFFERENCES BETWEEN THE ECMWF AND GFS WITH RESPECT TO TEMPERATURES
IN THIS TIME FRAME. GIVEN THE STRENGTH OF THIS ARCTIC AIR
MASS...HAVE LEANED HEAVILY TOWARD THE COLDER GFS. THE COLDEST DAY
SHOULD BE THU WHEN THE ARCTIC HIGH IS CENTERED RIGHT OVER THE CWA.
WOULD NOT BE THE LEAST SURPRISED TO SEE MIN TEMPERATURES IN THE
SINGLE DIGITS IN LOCATIONS SUCH AS LWB. HOWEVER...THE PREVAILING
WEST AS OPPOSED TO A STRONG NW-N FLOW ALOFT SHOULD RESULT IN THE
COLDER AIR REMAINING NORTH AND WEST OF THE CWA..SO WE SHOULD STAY
AOA 20 DEGREES FOR MINS ACROSS THE PIEDMONT. ANY PRECIPITATION
WED-FRI SHOULD BE CONFINED TO UPSLOPE MOUNTAIN -SHSN WITH DRIER
DOWNSLOPE WEST FLOW EAST OF THE ALLEGHANYS. EVEN ACROSS EASTERN
WV...SNOW ACCUMULATIONS SHOULD BE FAIRLY LIMITED WITH OVERALL
SNOW ACCUMULATIONS THERE EVEN AN INCH OR LESS.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AS OF 1145 PM EST THURSDAY...

STRONG COLD FRONT WILL BE APPROACHING FROM THE OHIO VALLEY...STALLING
WEST OF THE APPALACHIAN MOUNTAINS TONIGHT. A BROAD BAND OF RAIN
FROM CENTRAL PENNSYLVANIA TO CENTRAL TENNESSEE WILL BRING RAIN
WITH MVFR VISIBILITIES TO KLWB AND KBLF TONIGHT. STRATUS AND FOG
WITH SCATTERED SHOWERS IS EXPECTED FOR THE REST OF THE AREA.
CEILINGS WERE ALREADY MVFR AT 00Z/7PM. HIGH CONFIDENCE THAT
KROA...KBCB...KLYH AND KDAN WILL LOWER TO IFR OR LIFR OVERNIGHT WITH
MVFR FOG. LITTLE IMPROVEMENT IS EXPECTED ON FRIDAY. CEILINGS WILL
REMAIN IN THE IFR TO MVFR RANGE WITH RAIN BECOMING MORE
WIDESPREAD...ESPECIALLY IN THE LATE AFTERNOON AND EVENING.

EXTENDED AVIATION...A COLD FRONT WILL MAKE SLOW PROGRESS ACROSS
THE AREA LATE FRIDAY...RESULTING IN MVFR AND IFR CONDITIONS IN
ADDITION TO WIDESPREAD RAIN SHOWERS...BEFORE THE FRONT PASSES EAST
FRIDAY NIGHT INTO SATURDAY MORNING. MAY SEE A BRIEF IMPROVEMENT TO
VFR ON SATURDAY AS HIGH PRESSURE BUILDS IN FROM THE
NORTH...HOWEVER IFR WILL RETURN SATURDAY NIGHT AS ANOTHER SYSTEM
APPROACHES FROM THE SOUTHWEST...BRINGING FREEZING RAIN...SNOW AND
SLEET TO THE AREA SUNDAY. AN ARCTIC COLD FRONT WILL MOVE THROUGH
ON MONDAY...BRINGING A SLOW IMPROVEMENT TO VFR FOR TUESDAY.

HIGH PRESSURE IS EXPECTED TO PROVIDE FAIR WEATHER WITH VFR
CONDITIONS FROM TUESDAY THROUGH THURSDAY.

&&

.CLIMATE...
-- Changed Discussion --
WARM TEMPERATURES WILL APPROACH RECORDS AT SOME CLIMATE SITES.
BELOW ARE THE CURRENT RECORDS.

DECEMBER 6 CURRENT RECORD HIGH MINIMUM TEMPERATURES (YEAR)

ROA52(2011)
LYH52(2011)
DAN60(2011)
BCB51(2011)
BLF56(2011)
LWB 52  (1998)
-- End Changed Discussion --

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
VA...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH LATE
     SUNDAY NIGHT FOR VAZ010>020-022>024-032>035-043>047-058-
     059.
NC...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH LATE
     SUNDAY NIGHT FOR NCZ001>006-018>020.
WV...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH LATE
     SUNDAY NIGHT FOR WVZ042>045.
-- End Changed Discussion --

&&

$$
SYNOPSIS...JH/KM
NEAR TERM...KM
SHORT TERM...PM
LONG TERM...RAB
AVIATION...AMS/KK
CLIMATE...CF