FXUS61 KRNK 100025 AAA
AFDRNK
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BLACKSBURG VA
725 PM EST WED DEC 9 2009
.SYNOPSIS...
A LARGE HIGH PRESSURE SYSTEM WILL BUILD EAST INTO THE MID ATLANTIC
REGION TONIGHT INTO FRIDAY BRINGING STRONG WINDS AND MUCH COLDER
WEATHER.
&&
.NEAR TERM /THROUGH THURSDAY/...
UPDATED TO EXTEND THE HIGH WIND WARNING OVER A COUPLE CTYS IN THE
NW NC MTNS AS WELL AS GRAYSON CTY IN SW VA. ALTHO WINDS THERE HAVE
BEEN MUCH LIGHTER THAN ELSW EXPECT AS THE COLDER AIR ARRIVES WILL
SEE THE INVERSION LOWER ALLOWING A TRAPPED/CHANNELING TYPE
SCENARIO WITH THE W/NW WINDS OVERNIGHT. LATEST BUFKIT RAOBS ALSO
DEPICT 50-60 KTS JUST OFF THE SURFACE AFTER MIDNIGHT SO KEEPING
THE WARNING GOING. ELSW...GRADIENT LOOKS A BIT WEAKER BUT ENOUGH
WITH THE 85H JET AND COLD AIR TO KEEP AN ADVISORY OVER THE REST
OF THE MOUNTAINS THRU 4 AM. MUCH OF THE EAST HAS BEEN STUCK IN THE
LINGERING WEDGE COOL POOL THRU THE AFTERNOON AND APPEARS EVEN THO
IT WILL FINALLY BREAK IN THE NEXT FEW HOURS NOT EXPECTING SPEEDS
STRONG ENOUGH TO WARRANT EXTENDING THE NPW. OTRW SLIGHT DOWNWARD
ADJUSTS TO POPS ACROSS THE NW PER LITTLE IN THE WAY OF ECHOES AND
STARTED WITH MORE CLEARING EARLY ON WITH THE COLD POOL LOW CLOUDS
STILL TO THE NW. PREVIOUS DISCUSSION BELOW...
LATEST SATELLITE PICTURES AND SURFACE OBSERVATIONS SHOWING TENACIOUS
COOL MOIST WEDGE OVER THE FOOTHILLS OF VA AND NC FINALLY BEGINNING
TO ERODE. INCREASING PRESSURE GRADIENT AND MOMENTUM TRANSFER OF
WARMER AND DRIER AIR ALOFT SUPPORTING RAPID CLEARING AND TEMPERATURE
SPIKE WELL INTO THE 50S/LOWER 60S. SOUTHWESTERLY WINDS OF 50-60 KNOTS
AT 850 MILLIBARS...WITH 100 KNOT WINDS AS LOW AS 680 MILLIBARS...MORE
THAN SUFFICIENT TO JUSTIFY EXISTING HIGH WIND WARNINGS AND ADVISORIES
THROUGH 700 PM. HAVE ALREADY RECEIVED MANY SURFACE-BASED WIND
GUSTS TO NEAR/AROUND 60 MPH WITH NUMEROUS TREES DOWN DUE TO NEARLY
SATURATED GROUND AND WIND LOADING ACROSS THE HIGHER TERRAIN FROM
THE NEW RIVER VALLEY WEST AND SOUTH.
STRONGEST PRESSURE GRADIENT AND PRESSURE RISES PASS OFF TO NORTH
AND EAST OF AREA EARLY TONIGHT...AND WITH ONSET OF NIGHTFALL...SHOULD
EXPERIENCE SUFFICIENT DECOUPLING OF LOWER ATMOSPHERE TO ALLOW FOR
DISCONTINUATION OF HIGH WIND WARNINGS ACROSS THE WEST (ALTHOUGH
MAY HAVE TO BE REPLACED FOR AWHILE WITH A WIND ADVISORY ALONG AND
WEST OF THE BLUE RIDGE)...WITH WIND ADVISORIES EXPIRING EAST OF
THE BLUE RIDGE.
STRONG COLD ADVECTION LATER TONIGHT SHOULD SUPPORT SOME SCATTERED UPSLOPE
SNOW SHOWERS ACROSS THE EXTREME WEST AS TEMPERATURES FALL THROUGH THE
20S. HOWEVER...TRAJECTORIES REMAIN MAINLY FROM THE WEST AS OPPOSED
TO THE NORTHWEST...SO UPSLOPE PRECIPITATION NOT EXPECTED TO BE
SIGNIFICANT. EAST OF THE BLUE RIDGE...INFLUENCE OF DOWNSLOPING
WINDS SHOULD MAINTAIN MOSTLY CLEAR SKIES...BUT ARRIVAL OF COLDER
BOUNDARY LAYER AIR WILL BE DELAYED UNTIL LATE TONIGHT...SO TEMPERATURES
PROBABLY WILL NOT FALL MUCH BELOW FREEZING ACROSS MUCH OF THE
PIEDMONT.
COLD ADVECTION CONTINUES OVER THE ENTIRE AREA ON THURSDAY...WITH
ANY UPSLOPE CLOUDS AND SPOTTY SNOW SHOWERS/FLURRIES EXPECTED TO
END BY/SHORTLY AFTER NOON AS SURFACE RIDGE NUDGES CLOSER TO AREA.
GOOD INSOLATION THROUGHOUT THE DAY IN MOST LOCATIONS SHOULD ALLOW
FOR TRANSFER OF MODERATELY STRONG WESTERLY WINDS ALOFT TO IMPACT
THE SURFACE...SO GUSTY WINDS ARE LIKELY...BUT NOT LIKELY TO REACH
ADVISORY LEVELS.
MAVMOS TEMPERATURES (COLDER WEST AND WARMER EAST) PREFERRED OVER
METMOS GUIDANCE THROUGH THE PERIOD. BOUNDARY LAYER TEMPERATURES
EXPECTED TO COOL SUFFICIENTLY TO JUSTIFY COLDER READINGS ACROSS
THE WEST TONIGHT...WITH UPSLOPING CLOUDS ALSO EXPECTED TO
SUFFICIENTLY INHIBIT EXTENT OF DAYTIME HEATING ON THURSDAY.
INFLUENCE OF STRONG DOWNSLOPING AND LATER ARRIVAL OF COLDER
BOUNDARY LAYER AIR EAST OF THE BLUE RIDGE SHOULD HELP TO KEEP
FOOTHILLS AND PIEDMONT WARMER THAN THOSE DEPICTED BY METMOS
PROJECTIONS.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
THE BIGGEST CHANGE TO THE FORECAST FOR THE THURSDAY NIGHT THROUGH
SUNDAY TIME PERIOD IS THE TIMING OFF THE ARRIVAL TIME OF
PRECIPITATION THIS WEEKEND.
CONDITIONS STILL LOOK TO BE DRY AND COLD THURSDAY NIGHT THROUGH
FRIDAY NIGHT WITH A VAST AREA OF CANADIAN ORIGIN HIGH PRESSURE
BUILDING OVER THE REGION. WILL CONTINUE TO FAVOR HIGHS AND LOW
DURING THE PERIOD BELOW THE COLDEST GUIDANCE.
WE HAVE BEEN FORECASTING THE ARRIVAL PRECIPITATION FOR THIS WEEKEND
IN ASSOCIATION WITH BOTH A SHORTWAVE TROUGH MOVING THROUGH THE
OHIO VALLEY...TEAMING UP WITH MOISTURE AND OVERRUNNING IN
ASSOCIATION WITH A SYSTEM PASSING TO OUR SOUTH. WHILE THIS SCENARIO
STILL LOOKS PROMISING...WHAT HAS CHANGED IS THE TIMING THESE TWO
EVENTS OCCURRING. WE ARE NOW LOOKING AT THE ONSET OF PRECIPITATION
ABOUT 12 HOURS LATER THAN CONSIDERED EARLIER. WILL NOW HAVE A
COMPLETELY DRY SATURDAY FORECAST WITH SATURDAY EVENING DRY AS WELL.
WILL WORK SLIGHT TO CHANCE POPS OF PRECIPITATION INTO THE REGION
FROM THE SOUTH AFTER ABOUT MIDNIGHT 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. GIVEN THE POTENTIAL FOR SIGNIFICANT MODEL RUN TO RUN
VARIABILITY PAST DAY 3 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...AND THE TYPES WILL
BE SURFACE TEMPERATURE BASED...32 AND BELOW...SNOW...32 TO 33...RAIN
SNOW MIX...ABOVE 33 RAIN.
&&
.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 /00Z THURSDAY THROUGH MONDAY/...
DID INCLUDE A FEW HRS OF A WIND SHEAR GROUP THIS EVENING...BUT
SHOULD SUBSIDE BY LATE EVENING. COLD AIR/PRESSURE RISES WILL
ESCAPE INTO THE SOUTHSIDE AND PIEDMONT LATER TONIGHT...SO ALTHOUGH
WINDS ARE MEEK ATTM IN THOSE LOCATIONS...THERE COULD BE SOME 25KT GUSTS
THERE IN THE NEXT SEVERAL HRS. ALSO..LOWERING INVERSION WITH
CONTINUED CAA WILL ALLOW GOOD MOMENTUM TRANSFER LWB/BLF/ROA SO DID
KEEP SOME 25-30KT GUST THERE THROUGH TONIGHT. CURRENT SAT PIC AND
CANADIAN SKY COVER GUIDANCE INDICATE A 3K-5K DECK TO ARRIVE
BLF/LWB CORRIDOR AFTER MIDNIGHT...AND BREAK UP INTO THURSDAY.
TYPICALLY GUIDANCE IS A LITTLE TOO OPTIMISTIC WITH THE RETREAT OF
UPSLOPE CLOUDINESS SO AT LEAST KEPT A BKN LAYER INTO THE PM
THURSDAY THERE. DECENT WINDS REMAIN JUST OFF THE SURFACE INTO
TOMORROW...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)
THURSDAY 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.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WIND ADVISORY UNTIL 4 AM EST THURSDAY FOR VAZ007-009>014-
016>020-022>024-035.
HIGH WIND WARNING UNTIL 4 AM EST THURSDAY FOR VAZ015.
NC...WIND ADVISORY UNTIL 4 AM EST THURSDAY FOR NCZ002.
HIGH WIND WARNING UNTIL 4 AM EST THURSDAY FOR NCZ001-018.
WV...WIND ADVISORY UNTIL 4 AM EST THURSDAY FOR WVZ042>045.
&&
$$
SYNOPSIS...WERT
NEAR TERM...JH/WERT
SHORT TERM...DS
LONG TERM...SK
AVIATION...KM/WERT
