FXUS61 KRNK 100818
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
318 AM EST THU DEC 10 2009

.SYNOPSIS...
A LARGE HIGH PRESSURE SYSTEM WILL BUILD EAST INTO THE MID ATLANTIC
REGION OVERNIGHT INTO FRIDAY BRINGING STRONG WINDS AND MUCH
COLDER WEATHER.

&&

.NEAR TERM /THROUGH TONIGHT/...
500 MB TROUGH AXIS FINALLY PUSHES EAST OF THE FORECAST AREA
TODAY...AND WE WILL HAVE STRONG COLD ADVECTION INTO THE AREA-
ESPECIALLY THE MTNS. THE PRESSURE GRADIENT IS STILL STRONG...AND
THE NAM IS SHOWING 50 KNOT 850 MB WINDS THRU 18Z...WHILE THE GFS
IS A LITTLE WEAKER. WITH THE ADDED SUBSIDENCE AS THE 500 MB TROUGH
PASSES...AND THE STRONG COLD ADVECTION...HAVE DECIDED TO KEEP THE
WIND ADVISORY GOING FOR THE HIGH ELEVATIONS OF THE SW VA AND NW NC
MTNS. HAVE ALSO KEPT THE HIGH WIND WARNING FOR GRAYSON...ASHE AND
WATAUGA COUNTIES WHERE THE HIGHEST ELEVATIONS ARE. THINK THAT
WINDS WILL BE DIMINISHING SOME THIS AFTERNOON...BUT WITH GOOD
MIXING WE COULD STILL TAP SOME STRONGER WINDS FOR A FEW GUSTS EVEN
IN THE AFTERNOON...SO HAVE EXTENDED THE ADVISORIES/WARNINGS TO 600
PM. TEMPS WILL STRUGGLE TO RISE IN THE MTNS TODAY. HAVE KEPT HIGHS
BELOW FREEZING FOR MUCH OF THE MTNS. WILL BE A COLD DAY IN THE
MTNS WITH THE WINDS- WIND CHILLS WILL BE IN THE TEENS TO AROUND 20
DEGREES. HIGH PRESSURE CONTINUES TO BUILD EAST TOWARD THE AREA
TONIGHT...BUT IT LOOKS LIKE THERE WILL BE ENOUGH OF A GRADIENT FOR
WINDS TO CONTINUE MOST PLACES. FOR THAT REASON...HAVE KEPT LOW
TEMPS HIGHER THAN THE VERY LOW DEWPOINTS IN THE SINGLE DIGITS. IF
ANY VALLEY AREAS DECOUPLE...WE COULD SEE TEMPS SEVERAL DEGREES
COLDER THAN THE FCST WHICH IS IN THE TEENS IN THE MTNS...AND
AROUND 20 IN THE PIEDMONT. 

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
CANADIAN HIGH PRESSURE WILL CONTROL OUR WEATHER FRIDAY AND FRIDAY
NIGHT. WILL CONTINUE TO FAVOR HIGHS AND LOW DURING THE PERIOD BELOW 
THE COLDEST GUIDANCE. THIS WEEKEND...A SHORTWAVE TROUGH MOVING 
THROUGH THE OHIO VALLEY WILL TEAM UP WITH MOISTURE AND OVERRUNNING 
IN ASSOCIATION WITH A SYSTEM PASSING TO OUR SOUTH. THE TREND OF THE 
MODELS HAS BEEN TO SLOW THE ARRIVAL OF PRECIPITATION. WILL KEPT THE 
SLOWER ONSET OF PRECIPITATION ON SATURDAY NIGHT. A SATURATED WARM 
NOSE CENTERED AT 800 MB IS CURRENTLY PROGGED VIA THE GFS TO 
ACCOMPANY THIS PRECIPITATION ALONG WITH MUCH OF THE AREA SEEING 
SUB-FREEZING TEMPERATURES AT THE ONSET OF THE PRECIPITATION. THIS 
SUGGESTS A RAIN...FREEZING RAIN OR SLEET FORECAST LATE SATURDAY 
NIGHT. MODEL SOUNDINGS CONTINUE TO SUPPORT A SMALL WINDOW FOR WINTRY 
WEATHER LATE SATURDAY NIGHT INTO SUNDAY MORNING. ECMWF IS STILL 
HOLDING ON TO THE SLOWER ARRIVAL WITH MOST OF MOISTURE TO OUR SOUTH. 
 GIVEN THE POTENTIAL FOR SIGNIFICANT MODEL RUN TO RUN VARIABILITY  
OF THE FORECAST...AND DUE TO OFFICE POLICY...WILL HAVE A FORECAST 
SATURDAY NIGHT WITH EITHER RAIN...SNOW OR RAIN AND SNOW MIX AS THE 
PRECIPITATION TYPES.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
MODELS CONTINUE TO TREND TOWARD SLOWER SOLUTION FOR THE WKND
WEATHER SYSTEM...WHICH IS ESSENTIALLY AN UPPER WAVE IN GENERAL SW
FLOW OVERRUNNING A WEAK WEDGE. THE ECMWF AND MOST OF GFS ENSEMBLE
MEMBERS TRACK BULK OF PRECIP TO OUR SOUTH WITH A STRONGER HIGH
PRESSURE OVR MID ATLANTIC...WHILE 12Z OPERATIONAL GFS SPREADS
OVERRUNNING PRECIP INTO OUR WRN CWA BY EARLY SUNDAY COMING OUT OF
TN/KY. GIVEN ONGOING UNCERTAINTY...WILL CONTINUE TO GO WITH A
COMPROMISE BTWN LATEST ECMWF AND GFS...BUT IN LINE WITH THE SLOWER
TRENDS. SO STILL NOTHING HIGHER THAN CHC POPS FOR NOW...WITH NEAR
LIKELY ACROSS THE SOUTH FOR SUNDAY. AS FOR P-TYPE ISSUES...WEDGE
EXPECTED TO BE IN PLACE GIVEN SFC HIGH POSITION AND CERTAINLY A
CHANCE FOR MORNING MIX OF FREEZING RAIN OR SLEET FOR CENTRAL TO
NORTHERN PORTION OF CWA...THEN LIKELY TO CHANGE TO RAIN EVERYWHERE
BY AFTERNOON AS THE HIGH SHIFTS OFF THE COAST TO UNFAVORABLE
POSITION TO SUPPORT ONGOING WEDGE. GIVEN THIS IS STILL DAY 4 TIME
FRAME AND UNCERTAINLY EXISTS AS TO PRECIP EVEN REACHING MUCH INTO
THE CWA...WILL HESITATE TO SPECIFICALLY MENTION THESE MIXED
PTYPES...AND INSTEAD WILL CONTINUE WITH SIMPLE CHC SNOW OR RAIN TO
INDICATE SOMETHING WINTRY POSSIBLE. IF CONFIDENCE IS HIGHER BY
TOMORROW WE WOULD THEN BEGIN TO ADD SPECIFIC MENTION OF THE OTHER
LIKELY PTYPES. LIKELIHOOD OF ANY SIGNIFICANT IMPACTS FROM THIS
APPEAR VERY MINIMAL AT THE MOMENT HOWEVER.

GENERAL SW FLOW TO CONTINUE INTO EARLY NEXT WEEK WITH NO SIGNIFICANT 
COLD AIR ADVECTION BEHIND WKND SYSTEM YET LINGERING MOISTURE AND 
POSSIBLE WEAK WAVES OF ENERGY IN THE FLOW COULD KEEP SOME SPOTTY 
SHWRS IN THE WRN UPSLOPE AREAS. NEXT POTENTIAL SYSTEM TO IMPACT 
REGION FOR LATE MONDAY NIGHT OR TUESDAY IS A SLIGHTLY DEEPER WAVE IN 
SPLIT FLOW...AND RECENT MODEL TRENDS ARE NOW TO WARM UP AIR MASS 
AHEAD OF THIS ENOUGH SUCH THAT WINTRY PRECIP NOT AS LIKELY AS IT 
ONCE APPEARED...OTHER THAN PERHAPS HIGHEST ELEVATIONS IF PRECIP 
COMES IN OVERNIGHT. ECMWF ACTUALLY TRACKS THIS WELL SOUTH OF AREA 
BUT WEAK SFC FRONTAL PASSAGE WOULD STILL BRING SOME LIGHT UPSLOPE 
SHWRS BACK TO THE WESTERN MTNS. NOTHING HIGHER THAN CHC POPS WITH 
THIS SYSTEM FOR NOW...AND GIVEN SPLIT FLOW REGIME THERE IS LIKELY 
TO REMAIN QUITE A BIT OF UNCERTAINTY WITH THIS AS WELL UNTIL WE GET 
WITHIN A COUPLE OF DAYS. LIKELY A STRONGER COLD FRONTAL PASSAGE WITH 
THIS SYSTEM COMPARED TO WKND ONE...SO AT LEAST A BRIEF RETURN OF 
COLDER AIR BEHIND IT BY MID WEEK...BUT LARGE SCALE PATTERN 
SUGGESTING LOWER AMPLITUDE FLOW COMPARED TO CURRENT REGIME...SO 
TEMPS NOT TOO FAR BELOW NORMAL DESPITE IMPRESSIVE TROUGH OVER THE 
GREAT LAKES.

&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
SATELLITE IMAGE INDICATED A LARGE AREA OF 3K-5K SC TO OUR WEST
ASSOCIATED WITH COLD POOL BEHIND THE COLD FRONT. EXPECT THIS DECK
OF CLOUDS TO ARRIVE BLF/LWB CORRIDOR EARLY THIS MORNING...AND BREAK 
INTO THIS AFTERNOON. TYPICALLY GUIDANCE IS A LITTLE TOO OPTIMISTIC
WITH THE RETREAT OF UPSLOPE CLOUDINESS SO AT LEAST KEPT A BKN
LAYER INTO THIS AFTERNOON. DECENT WINDS REMAIN JUST OFF THE
SURFACE INTO THIS AFTERNOON...SO CONTINUED SOME 25-30KT WIND GUSTS
LWB/BLF/ROA THROUGH THURSDAY AFTERNOON.

MAINLY VFR WEATHER WITH UNRESTRICTED FLIGHT CONDITIONS ARE EXPECTED
OVER ALL TERMINAL FORECAST SITES (KROA...KLYH...KDAN...KBLF...KLWB)
TODAY INTO SATURDAY AS LARGE SURFACE RIDGE OF HIGH PRESSURE BUILDS
EAST INTO MID ATLANTIC REGION. ANOTHER WEAK STORM SYSTEM MAY LIFT
NORTHEAST INTO THE MID ATLANTIC REGION LATER SATURDAY INTO
SUNDAY...BRINGING AN INCREASED THREAT OF MIXED PRECIPITATION AND A
LOWERING OF FLIGHT CATEGORIES BACK INTO MVFR...AND POSSIBLY IFR
RANGE.

&&

.HYDROLOGY...
RAINFALL BETWEEN 1 AND 2 INCHES OVER THE PAST 24 HOURS HAS
COMBINED WITH LEFTOVER SNOW MELT IN SPOTS TO PRODUCE MINOR
FLOODING ALONG AREA RIVERS. MINOR FLOODING IS NOW EXPECTED ALONG
THE DAN RIVER AT SOUTH BOSTON AS WELL AS ON THE LOWER ROANOKE
RIVER AT RANDOLPH...AND AT BREMO BLUFF ON THE JAMES. SOME MINOR
FLOODING IS ALSO EXPECTED ALONG THE GREENBRIER RIVER AT ALDERSON
THROUGH THURSDAY MORNING.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR VAZ007-009>014-
     016>020-022>024-035.
     HIGH WIND WARNING UNTIL 6 PM EST THIS EVENING FOR VAZ015.
NC...WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR NCZ002.
     HIGH WIND WARNING UNTIL 6 PM EST THIS EVENING FOR NCZ001-018.
WV...NONE.

&&

$$
SYNOPSIS...JJ
NEAR TERM...JJ
SHORT TERM...KK
LONG TERM...SK
AVIATION...KK/KM
HYDROLOGY...