FXUS61 KRNK 251417
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
917 AM EST WED NOV 25 2009
.SYNOPSIS...
AN UPPER LEVEL DISTURBANCE WILL BRING SOUTHWESTERLY FLOW AND DRIER
AIR TO THE REGION BY LATE TODAY. LATE THURSDAY...A STRONG
COLD FRONT WILL BRING MUCH COLDER AIR ALONG WITH MOUNTAIN SNOW
SHOWERS INTO FRIDAY NIGHT. HIGH PRESSURE WILL BUILD EAST ACROSS THE
SOUTHEAST STATES DURING THE WEEKEND ALLOWING FOR A GRADUAL
MODERATION IN TEMPERATURES THROUGH SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
RNK 00Z SOUNDING SHOWED LOW LEVEL MOISTURE UP TO 6 KFT
WITH A LIGHT SOUTHWEST FLOW. THE WEDGE OF HIGH PRESSURE WILL
SLOWLY ERODE TODAY UNDER INCREASING SOUTHWEST FLOW AND DRIER AIR AT
MID LEVELS. TRIMMED POPS ASSOCIATED WITH SHORTWAVE LIFTING ACROSS
THE OHIO VALLEY...BECAUSE THE SOUTHERN END OF PCPN IS DRIER UP.
THE 12Z NAM SHOWED PCPN LIFTING NORTH QUICKLY THIS MORNING ACROSS
NORTHERN WEST VIRGINIA WITH WEAK MOISTURE STARVED FRONT.
WITH FLOW BECOME SOUTHWEST...CLOUDS WILL MIX OUT TODAY AND BY MID TO
LATE AFTERNOON THERE WILL BE A SIGNIFICANT BREAK IN CLOUD COVER FOR
MOST AREAS. TEMPERATURES WILL HIGHLY BE DEPENDENT ON CLOUD COVER
FOR THIS AFTERNOON...SIMILAR TO YESTERDAY. WILL MAKE SOME MINOR
ADJUSTMENTS IN CLOUD COVER...TEMPERATURES AND POPS.
.PREVIOUS DISCUSSION...
MINOR UPDATE TO REMOVE MENTION OF DRIZZLE EARLY THIS MORNING AS
MOST HAS DISSIPATED PER OBS AND RADAR...BUT STILL SOME PATCHY
LIGHT FOG TO PERSIST THROUGH MID MORNING. KEEPING SLIGHT CHC LIGHT
RAIN IN FAR WEST FOR A FEW MORE HOURS UNTIL BAND OF SHWRS WITH
ISENTROPIC LIFT OVER CENTRAL WV SLIDES PAST. THIS SHOULD BE BY 15Z
IF NOT EARLIER. PREVIOUS DISCUSSION BELOW...
SHALLOW MOISTURE AND WEDGE OF HIGH PRESSURE WILL SLOWLY ERODE
UNDER INCREASING SOUTHWEST FLOW AND DRIER AIR AT MID LEVELS TODAY.
SHORT WAVE LIFTS ACROSS THE OHIO VALLEY AND WILL BRING BRIEF
PERIOD OF ISENTOPIC LIFT MAINLY ACROSS THE WEST THIS MORNING. SOME
AREAS OF DRIZZLE AND LIGHT FOG INITIALLY THIS MORNING IN THE NEW
RIVER VALLEY...ALONG THE BLUE RIDGE AND IN THE PIEDMONT MAINLY
NORTH OF THE ROANOKE RIVER WHERE THE WEDGE IS THE STRONGEST.
EXPECT THAT THIS WILL MIX OUT THROUGHOUT THE DAY AND BY MID TO
LATE AFTERNOON THERE WILL BE A SIGNIFICANT BREAK IN CLOUD COVER
FOR MOST AREAS...LAST AREA TO BREAK OUT WILL BE FAR NORTHEAST.
TEMPERATURES THEN TRICKY DEPENDING ON AREAS OF SUN...AND LEANED
TOWARD WARMER MET GUIDANCE SINCE A FEW SPOTS THAT BROKE OUT
YESTERDAY WARMED UP ABOVE GUIDANCE. LYH AND AREAS NORTHEAST MAY BE
THE EXCEPTION.
CONTINUED CLEARING FOR TONIGHT...BUT WITH SOUTHWEST FLOW ALOFT NOT
SURE TO WHAT DEGREE DECOUPLING WILL TAKE PLACE...WHICH MAKES MIN
TEMP FORECAST ALSO TRICKY. LEANING TOWARD SOME DECOUPLING EAST OF
BLUE RIDGE AND IN SOME MTN VALLEYS...BUT WINDS STAYING UP ON
RIDGES...WHICH WILL MEAN SOME RIDGES MAY HAVE WARMER MINS THAN
ANYWHERE ELSE. OVERALL...WARMED IT UP A FEW DEG IN THE PIEDMONT IN
CASE SOME WINDS CONTINUE...BUT STILL GOING COOLER THAN MET LOWS.
LOW LEVEL CLOUDS BEGIN TO EASE BACK INTO THE WESTERN UPSLOPE AREAS
TOWARD MORNING AS NEXT STRONG WAVE APPROACHES WHICH COULD ALSO HELP
TO KEEP TEMPS A LITTLE WARMER. COLD ADVECTION DOES NOT BEGIN IN
EARNEST UNTIL LATER THURSDAY.
&&
.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
STRONG 500MB LOW OVER THE GREAT LAKES WILL SWING AN INITIAL SURFACE
COLD FRONT ACROSS THE APPALACHIANS WHILE...AN 850MB FRONT PUSHES
THROUGH OVERNIGHT INTO FRIDAY MORNING. STRONG COLD AIR ADVECTION
WILL FOLLOW AND FILTER IN BEHIND THE FRONT WITH 850MB TEMPERATURES
RANGING BETWEEN -2 TO -6 DEGREE C FROM WEST TO EAST. ALTHOUGH...ONE
KEY FACTOR IS LIMITED MOISTURE WITH THIS SYSTEM. LOW LEVEL MOISTURE
INCREASES FROM WEST TO EAST WITH THE MOST BEING PLACED IN THE
UPSLOPE AREAS OF SOUTHEAST WEST VIRGINIA.
AS WINDS TURN MORE NORTHWEST IN THE WAKE OF THE COLD FRONT...UPSLOPE
FLOW INCREASES. EXPECT SNOW TO MIX WITH THE RAIN SHOWERS BEFORE
TURNING TO ALL SNOW WEST OF THE BLUE RIDGE MOUNTAINS IN THE HIGHER
ELEVATIONS FRIDAY. THIS IS SUPPORTED BY BUFKIT SOUNDINGS WHICH
INDICATES BLUEFIELDS SURFACE TEMPERATURE AND ALOFT NOT RISING ABOVE
FREEZING ALL DAY ON FRIDAY WHILE LEWISBURG HOVERS A COUPLE DEGREES
+/- OF FREEZING. MAINTAINED LIKELY/CAT POPS FOR SOUTHEAST WEST
VIRGINIA WITH THE UPSLOPE COMPONENT BEGINNING THURSDAY NIGHT.
DOWNSLOPE FLOW WILL AID IN DRYING OUT THE PIEDMONT AREAS OF VIRGINIA
AND NORTH CAROLINA THUS HAVE KEPT A DRY FORECAST THROUGH THE
SATURDAY NIGHT.
FRIDAY...THE UPPER LEVEL LOW PUSHES EAST OVER THE ATLANTIC AND
CONTINUES TO DEEPEN. WHILE AT THE SURFACE...THE GRADIENT TIGHTENS AS
A RIDGE OF HIGH PRESSURE AT THE SURFACE TRIES TO NOSE INTO THE AREA
FROM THE SOUTHWEST. THEREFORE...WEST TO NORTHWEST WINDS WILL
INCREASE SIGNIFICANTLY. MODELS HAVE 850MB WINDS PROGGED CLOSE TO 50
KNOTS EARLY FRIDAY AND LASTING THROUGH THE SATURDAY. WINDS MAY GUST
AS HIGH AS 45 MPH ALONG THE RIDGES...MAY NEED TO THINK ABOUT A
POSSIBLE WIND ADVISORY AS IT GETS CLOSER. FOR NOW...WILL LEAVE
MENTION IN THE HWO.
THE COLD AIR ADVECTION PULLS OUT OF THE FORECAST AREA FRIDAY NIGHT
AND THE WEST NORTHWESTERLY FLOW WEAKENS. HOWEVER...THE WESTERN
UPSLOPE AREAS OF WEST VIRGINIA MAY STILL SEE A FEW LIGHT SNOW
SHOWERS CONTINUING INTO THE EARLY MORNING HOURS SATURDAY BEFORE
TAPERING OFF AS SHORT WAVE RIDGING BUILDS IN.
MAX TEMPERATURES WILL BE IN THE LOW 40S WEST TO NEAR 60 EAST BEFORE
DROPPING INTO THE UPPER 30S IN THE MOUNTAINS TO LOWER 50S IN THE
PIEDMONT.
LOW TEMPERATURES WILL BE DROPPING BELOW NORMAL FIRDAY NIGHT AS MIN
TEMPS WILL FALL INTO THE MID TO UPPER 20S WEST OF THE BLUE RIDGE TO
NEAR FREEZING IN THE EAST.
&&
.LONG TERM /SUNDAY THROUGH TUESDAY/...
THE TREND FOR DRY AND MILDER WEATHER WILL CONTINUE THROUGH SUNDAY AS
THE RIDGE BUILDS OVER OUR REGION. HOWEVER...THE DRY WEATHER WILL BE
SHORT LIVED. OUR EYES TURN WEST AN APPROACHING TROUGH IN THE CENTRAL
U.S. THERE IS VAST DIFFERENCES IN THE MODEL GUIDANCE OF THE TIMING
AND SUBSEQUENT WEATHER AND TEMPERATURES FOR OUR AREA MONDAY THROUGH
TUESDAY. THE 12Z GFS IS VERY FAST WITH THE SYSTEM WITH A COLD
FRONTAL PASSAGE MONDAY NIGHT. THE 00Z ECMWF SOLUTION HAS THE TROUGH
DEEPENING MORE AND BREAKING OFF TO FORM A CLOSED LOW IN THE CENTRAL
U.S. WITH ASSOCIATED WARM FRONTAL PRECIPITATION STARTING TO APPROACH
WESTERN PORTIONS OF OUR AREA MONDAY NIGHT...WITH A MUCH WARMER
SOLUTION ON TUESDAY STILL IN THE WARM SECTOR AS COMPARED TO THE GFS
COLDER POST COLD FRONT SOLUTION. THE HPC SOLUTION IS A SLIGHTLY
FASTER SOLUTION TO THE SLOWER ECMWF GUIDANCE. HAVE FOLLOWED CLOSELY
WITH HPC GUIDANCE FOR THIS PERIOD.
&&
.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
IFR TO LIFR CEILINGS REMAIN AT ROA AND LYH UNDER THE DEEPEST
PORTION OF THE WEDGE..WITH DAN AND BLF IN MVFR CONDITIONS BUT ON
THE EDGE AND EXPECT LIFTING CEILINGS AT THESE LOCATIONS BY AROUND
14Z. WILL TAKE TO MIDDAY AT ROA AND LYH...BUT EVEN HERE AS
SOUTHWEST FLOW INCREASES AND DRIER AIR MOVES IN ALOFT...IT WON'T
TAKE TOO LONG TO MIX SHALLOW WEDGE DOWN FROM THE TOP. LWB SHOULD
REMAIN VFR TODAY...AND ALL LOCATIONS WILL BE VFR BY MID AFTERNOON
WITH PARTIALLY CLEARING SKIES.
WITH CONTINUED CLEARING OVERNIGHT...AND POTENTIAL FOR DECOUPLING
IN THE PIEDMONT AND MTN VALLEYS...SOME LIGHT FOG IS POSSIBLE BUT
FOR NOW ONLY INCLUDED AT LYH. MAY BE ABLE TO FORM AT LWB AS WELL
DEPENDING ON TIMING OF STRATUS LAYER IN FROM THE WEST TOWARD
MORNING AS WEAK COLD ADVECTION BEGINS. LOOKS NOW LIKE THIS WILL RESULT
IN MVFR CEILINGS TO BLF AND LWB BEFORE 12Z...BUT WILL HELP PREVENT
ANY FOG FROM FORMING. NEEDS CLOSE WATCHING THOUGH.
ARRIVAL OF ANOTHER...STRONGER COLD FRONT LATE THURSDAY WILL
LIKELY BRING A RETURN TO MVFR TO IFR CONDITIONS IN UPSLOPE AREAS
WEST OF THE BLUE RIDGE ALONG WITH COLDER AIR AND MOUNTAIN RAIN TO SNOW
SHOWERS. DOWNSLOPE WINDS EAST OF THE BLUE RIDGE WILL KEEP THOSE
AREAS MAINLY VFR RANGE INTO SUNDAY.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.
&&
$$
SYNOPSIS...JH/SK
NEAR TERM...KK/SK
SHORT TERM...REB
LONG TERM...DS
AVIATION...AMS/SK
