FXUS61 KRNK 042340
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
640 PM EST FRI DEC 4 2009
.SYNOPSIS...
LOW PRESSURE WILL DEVELOP AND MOVE RAPIDLY ALONG THE SOUTHEAST
COAST LATE TONIGHT AND SATURDAY...REACHING THE OUTER BANKS OF NORTH
CAROLINA BY SATURDAY AFTERNOON...AND EXITING THE MID ATLANTIC COAST
AREA BY SATURDAY EVENING. COLD HIGH PRESSURE WILL BUILD IN BEHIND
THE SYSTEM FOR OVERNIGHT SATURDAY INTO SUNDAY.
&&
.NEAR TERM /THROUGH SATURDAY/...
CURRENT WATER VAPOR SHOWS A HIGHLY AMPLIFIED PATTERN...WITH A
STRONG JET MOVG ACROSS NRN MEXICO AND UPPER LEVEL MOISTURE
STREAMING NORTHWARD TOWARD THE REGION. THE TPW LOOP SHOWS DEEP
MOISTURE LURKING OVER THE GULFMEX AND OFF THE SOUTHEAST COAST...
WITH PWATS OF 1.0 TO 1.5 INCHES. MODELS ARE IN GOOD AGREEMENT NOW
IN LIFTING THE STRONG WAVE OVER SRN TX NEWD INTO THE SRN APPLNS BY
SAT AFTERNOON. THIS IS A LITTLE MORE WESTWARD AND SLOWER THAN
PREVIOUS MODELS...AND KEEPS AN ASSOCIATED SFC LOW CLOSER TO THE
SOUTHEAST COAST. IN ADDITION...MODELS HAVE THE 850 MB LOW INLAND
AS FAR WEST AS THE NW NC PIEDMONT....AND THE GFS IN PARTICULAR IS
GENERATING A LOT OF QPF INTO THE BLUE RIDGE IN RESPONSE TO
FRONTOGENETICAL FORCING IN THE 850 TO 700 MB LAYER. NOT READY TO
JUMP ON HEAVY PRECIP...BUT WITH THE LOW MOVING CLOSER TO THE
COAST...I HAVE UPPED THE PRECIP AMOUNTS TO .3 TO .4 IN THE
MTNS...AND CLOSER TO A HALF INCH ROA TO LYH AND EASTWARD.
P-TYPE WILL STILL BE A LITTLE TRICKY AT THE ONSET...EVEN IN THE
MTNS...WITH A WARM BOUNDARY LAYER. WILL HAVE TO COOL THE COLUMN
FROM THE TOP DOWN...SO HIGHER ELEVATIONS WILL START OFF SNOW...BUT
VALLEYS AND EAST OF THE BLUE RIDGE IN VA WILL LIKELY START OFF
RAIN AND THEN GRADUALLY CHANGEOVER TO ALL SNOW- AT LEAST NORTH OF
THE RT 460 CORRIDOR. SO SNOW ACCUMULATION WILL BE HIGHLY ELEVATION
DEPENDENT. WITH THE CURRENT QPF FCST...HAVE RAISED SNOW TOTALS
MORE INTO THE 2 TO 4 INCH RANGE FOR THE MTNS...AND 1 TO 2 OR
PERHAPS 3 INCHES FOR ROA TO LYH EASTWARD INTO BUCKINGHAM COUNTY.
SINCE THE GROUND IS SO WARM...IT WILL TAKE DECENT SNOWFALL RATES
TO ACCUMULATE...AND IT WILL LIKELY MELT A LOT ON THE ROADS. EVEN
WITH A LITTLE HIGHER QPF...IT WILL BE HARD TO REACH WARNING
CRITERIA...5 INCHES MTNS AND 4 INCHES EAST OF MTNS...SO WILL BE
ISSUING ADVISORIES THAT COVER ALL OF THE MTNS...AND THEN ROA-LYH-
APPOMATTOX-BUCKINGHAM AREAS NORTHWARD. HAVE KEPT LOW TEMPS NEAR
FREEZING WHERE WE HAVE THE ADVISORIES...WITH LITTLE RISE DURING
THE DAY SATURDAY.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
THE COASTAL LOW WILL BE PULLING NORTHEAST AS HIGH PRESSURE BUILDS
INTO THE FORECAST AREA FROM THE WEST SATURDAY NIGHT. WINDS WILL BE
TURNING OUT OF THE NORTH EARLY SUNDAY MORNING THEREFORE...CUTTING
OFF ANY MOISTURE THAT REMAINS. THERE WILL BE SOME LINGERING SNOW
SHOWERS ACROSS THE COUNTY WARNING AREA BEFORE TAPERING OFF FROM WEST
TO EAST LATE SATURDAY NIGHT.
SATURDAY WILL BE THE COLDEST NIGHT THUS FAR. SKIES WILL BE CLEARING
OUT OVERNIGHT AND WITH SNOW ON THE GROUND...TEMPERATURES WILL EASILY
FALL INTO THE UPPER TEENS WEST OF THE BLUE RIDGE WITH MID 20S IN THE
PIEDMONT AREAS OF VIRGINIA AND NORTH CAROLINA.
SUNDAY WILL HAVE MOSTLY CLEAR SKIES AND LIGHT WINDS WITH THE HIGH
OVERHEAD. TEMPERATURES WILL RISE INTO THE LOWER 40S WITH ONLY UPPER
30S IN THE HIGHER ELEVATIONS. THE PIEDMONT AREAS WILL LIKELY SEE MID
40S.
THE HIGH WILL BE SLIDING EAST SUNDAY NIGHT WITH CLEAR SKIES AND
LIGHT WINDS. WINDS WILL BE OUT OF THE SOUTHWEST WHICH WILL ALLOW
WARMER AIR INTO THE AREA AND IS SUPPORTED BY THE GFS 850MB
TEMPERATURES. THEY ARE PROGGED TO RISE IN THE RANGE OF +1 TO
+4C...HIGHEST SOUTH. HAVE WENT WITH MID 20S FOR MINS ACROSS THE
BOARD FOR SUNDAY NIGHT.
CLOUDS WILL BE INCREASING AHEAD OF A WEAK BOUNDARY MONDAY.
HOWEVER...MOISTURE WILL REMAIN SHALLOW WITH PLENTY OF MID LEVEL DRY
AIR IN PLACE WHICH IS ALSO SUPPORTED BY THE BUFKIT SOUNDINGS. HAVE
SLIGHT CHANCE POPS MAINLY IN THE WESTERN ZONES BEGINNING MONDAY
AFTERNOON GOING THROUGH MONDAY NIGHT AS A RESULT OF UPSLOPE FLOW.
STAYED CLOSE TO MOS GUIDANCE FOR TEMPERATURES MONDAY AND MONDAY
NIGHT.
&&
.LONG TERM /TUESDAY THROUGH FRIDAY/...
LEANED MEDIUM RANGE GRIDS TOWARDS A BLEND OF HPCGUIDE AND ECMWF 00Z.
QUASI ZONAL FLOW EXPECTED WITH SOME AMPLIFICATION OF THE PATTERN ON
TUESDAY INTO WEDNESDAY. HIGH PRESSURE WILL SLIDE EASTWARD ON
TUESDAY. DECIDED TO DECREASE POPS FOR TUESDAY AND PLAY BEST CHANCES
IN THE WEST. MOISTURE SLOWLY INCREASES AS A FRONTAL BOUNDARY
APPROACHES FROM THE WEST TUESDAY AFTERNOON. AS THE LOW PRESSURE
CENTER AND FRONT SPREAD EAST THE CHANCES OF PCPN INCREASE TUESDAY
NIGHT AND WEDNESDAY. ELECTED TO GO WITH LIKELY POPS FOR WEDNESDAY
WITH THE CONSISTENCY OF THE MODELS. 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. PLAYED
HIGHEST POPS IN THE NORTHWEST. HIGH PRESSURE WILL BUILD EAST INTO
THE AREA FROM THE TENNESSEE VALLEY ON THURSDAY INTO THURSDAY NIGHT.
KEPT SOME CHCY POPS IN THE WEST WITH THE PASSAGE OF A WARM FRONT
ON FRIDAY.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
LOW CLOUDS AND WINTRY WEATHER(SNOW/RAIN) WILL HINDER AVIATION
OPERATIONS LATE TONIGHT AND SATURDAY. PILOTS SHOULD CHECK AIRMETS
AND SIGMETS FOR TURBULENCE...ICING AND IFR/MOUNTAIN OBSCURATIONS.
DETERIORATING FLIGHT CONDITIONS ARE EXPECTED TONIGHT INTO SATURDAY
AS A COASTAL LOW PRESSURE DEVELOPS. MOISTURE IS SLOWLY LIFTING
NORTH ACROSS THE CAROLINAS THIS EVENING. PRECIPITATION WILL SPREAD
INTO OUR AREA BY AROUND DAYBREAK...AND CIGS/VSBYS WILL RAPIDLY
LOWER TO IFR AT ALL TAF SITES BY 15Z- PROBABLY SOONER. THE
PRECIPITATION WILL BE MAINLY ALL SNOW AT BLF AND LWB...SNOW WITH
SOME RAIN MIX AT ROA AND LYH...AND MAINLY RAIN AT DAN. THE SNOW
WILL LIKELY BE HEAVY ENOUGH TO ACCUMULATE ON THE GROUND...THOUGH
SHOULD BE SLUSHY AND WET. WITH THE HEAVIER SNOW...FLIGHT
CONDITIONS WILL LIKELY DROP TO VLIFR.
THE PRECIP WILL MOVE OUT OF THE AREA QUICKLY LATER SATURDAY
AFTERNOON...AND THERE WILL BE IMPROVING FLIGHT CONDITIONS. ALL
SITES SHOULD BECOME VFR BY 00 TO 03Z. HIGH PRESSURE WILL BRING VFR
CONDITIONS FOR SUNDAY INTO MONDAY. ANOTHER WEAK COLD FRONT MAY
BRING BRIEF MVFR CONDITIONS IN CLOUDS AND LIGHT PRECIP BY MONDAY
NIGHT INTO TUESDAY. IFR CONDITIONS MAY BE POSSIBLE TUESDAY NIGHT
AND WEDNESDAY.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WINTER WEATHER ADVISORY FROM 4 AM TO 7 PM EST SATURDAY FOR
VAZ007-009>020.
WINTER WEATHER ADVISORY FROM 10 AM TO 11 PM EST SATURDAY FOR
VAZ022>024-034-035-045>047.
NC...WINTER WEATHER ADVISORY FROM 4 AM TO 7 PM EST SATURDAY FOR
NCZ001-002-018.
WV...WINTER WEATHER ADVISORY FROM 4 AM TO 7 PM EST SATURDAY FOR
WVZ042>045.
&&
$$
SYNOPSIS...JJ
NEAR TERM...JJ
SHORT TERM...REB
LONG TERM...KK
AVIATION...JJ/KK
