FXUS61 KRNK 101733
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1233 PM EST THU DEC 10 2009
.SYNOPSIS...
A LARGE HIGH PRESSURE SYSTEM WILL BUILD EAST INTO THE MID ATLANTIC
REGION FROM TODAY INTO FRIDAY BRINGING STRONG WINDS AND MUCH
COLDER AIR. WEAK LOW PRESSURE WILL TRACK SOUTH OF THE REGION OVER
THE WEEKEND AND MAY SPREAD WINTRY PRECIPITATION IN OUR AREA LATE
SATURDAY NIGHT INTO SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
STRONG COLD AIR ADVECTION TODAY WILL PROMOTE STEADY OR FALLING
TEMPERATURES IN THE MOUNTAINS...AND NOT MUCH IF ANY RISE EAST OF
THE MOUNTAINS. PRESSURE GRADIENT ALSO REMAINS STRONG...AND THIS
WILL PERMIT SOME ADVISORY GUSTS VCNTY OF THE MTNS. MORNING RAOBS
INDICATE 40 KT 85H WINDS...SO NOT OUT OF THE QUESTION FOR SOME 40
KT GUSTS ALONG THE RIDGE TOPS THROUGH THE AFTERNOON. ALONG THE
WINDWARD SLOPES OF WV...LIGHT SNOW OR FLURRIES WILL CONTINUE WITH
POTENTIAL FOR LIGHT ACCUMULATIONS (AN INCH OR LESS) THERE.
WITH THE WINDS...WIND CHILLS WILL BE IN THE TEENS TO AROUND 20
DEGREES THIS AFTERNOON. THE WIND CHILLS WILL BECOME MORE OF A
CONCERN TONIGHT...ESP IN THE MTNS WHERE STRONG WINDS WILL CONTINUE
EVEN INTO THE OVERNIGHT. HIGH PRESSURE WILL CONTINUE 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 /18Z THURSDAY THROUGH TUESDAY/...
STRONG WNW FLOW OVER THE MTNS WILL CONTINUE THROUGH TONIGHT
RESULTING IN BREEZY CONDITIONS WITH SFC GUSTS OF 25-30 KTS. HIGH
PRESSURE WILL EVENTUALLY BUILD OVHD FOR FRIDAY AND RESULT IN
DIMINISHING WINDS. ANY CLOUD COVER THROUGH TONIGHT WILL BE MAINLY
CONFINED TO THE WINDWARD SLOPES OF WVA...PRIMARILY WEST AND NORTH
OF LWB. ELSEWHERE EXPECT MAINLY CLEAR SKIES WITH VFR CONDITIONS
PREVAILING.
VFR WEATHER WITH UNRESTRICTED FLIGHT CONDITIONS ARE EXPECTED OVER
ALL TERMINAL FORECAST SITES (KROA...KLYH...KDAN...KBLF...KLWB)
SATURDAY...BUT THEN DETERIORATE SATURDAY NIGHT INTO SUNDAY.
AN AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP OVER THE GULF OF
MEXICO SATURDAY...THEN SLIDE TO ALONG THE SOUTH CAROLINA COAST BY
SUNDAY. THIS WILL BRING AN INCREASE IN CLOUD COVER SATURDAY NIGHT
AND A THREAT FOR A WINTRY MIX OVER THE MID ATLANTIC REGION SUNDAY.
THE SYSTEM SHOULD EXIT THE REGION SUNDAY NIGHT WITH IMPROVED
FLIGHT CONDITIONS MONDAY.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR VAZ007-009>020-
022>024-035.
NC...WIND ADVISORY UNTIL 6 PM EST THIS EVENING FOR NCZ001-002-018.
WV...NONE.
&&
$$
SYNOPSIS...JJ
NEAR TERM...JJ/PM
SHORT TERM...KK
LONG TERM...SK
AVIATION...PM
