FXUS61 KRNK 262333
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
633 PM EST SAT DEC 26 2009
.SYNOPSIS...
A STRONG LOW IN THE MIDWEST WAS CENTERED OVER EASTERN IOWA. A
WEAKER COASTAL LOW WILL MOVE NORTH TOWARD NEW ENGLAND TONIGHT WHILE
THE MID WEST LOW TRACKS TOWARD UPPER MICHIGAN. WEAK...BUT COLDER
HIGH PRESSURE WILL BUILD INTO THE MID ATLANTIC REGION TONIGHT AND
SUNDAY.
&&
.NEAR TERM /THROUGH SUNDAY/...
THICK JET ENHANCED CIRRUS ACROSS THE SERN HALF OF THE CWA WILL
SLOWLY SHIFT TO OUR EAST TONIGHT. ONCE THE CWA CLEARS OUT...WEAK
HIGH PRESSURE WILL BE OVER THE AREA AND THERE SHOULD BE GOOD
RADIATION CONDITIONS. EXCEPTION WILL BE HIGHER ELEVATIONS...WHERE
STRONGER SW FLOW AROUND THE MASSIVE UPPER LOW NOW OVER WISC WILL
KEEP RIDGES MIXED. I HAVE GONE A LITTLE COOLER THAN GUIDANCE FOR
LOW TEMPS MOST LOCATIONS.
SUNDAY...THE UPPER LOW DRIFTS EASTWARD...AND COLDER AIR CONTINUES
TO FILTER INTO THE AREA. OVERALL..HIGHS SHOULD BE A FEW DEGREES
COOLER THAN TODAY.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AN UPPER LEVEL LOW WILL SWING THROUGH THE GREAT LAKES REGION
SUNDAY NIGHT...WITH A STRONG SHORT WAVE MOVG THRU THE CENTRAL
APPLNS...AS THE FORECAST AREA CATCHES THE SOUTHERN PERIPHERY.
SOUTHWEST WINDS AHEAD OF THE SURFACE WAVE INCREASES MOISTURE AND AS
WINDS TURN TOWARD A WEST NORTHWEST FLOW...THIS WILL ENHANCE THE
UPSLOPE COMPONENT AND BRING SNOW SHOWERS SUNDAY NIGHT/MONDAY.
THE LATEST MODEL RUNS HAVE THE PRECIP HANGING IN THROUGH TUESDAY
MORNING IN THE FAVORABLE WESTERN UPSLOPE REGIONS. MAINTAINED THE
LIKELY POPS IN THE UPSLOPE AREAS OF SE WV...AND CATEGORICAL WESTERN
GREENBRIER THROUGH EARLY MONDAY AFTERNOON. THEN HAVE POPS TAPERING
OFF FROM EAST TO WEST BY MONDAY NIGHT. HIGHEST POPS WILL REMAIN IN
THE NORTHERN TIP OF GREENBRIER WHICH MAY LAST THROUGH THE DAY
MONDAY. PRECIP WILL BE LIGHT THOUGH...ACCUMULATIONS SHOULD BE JUST A
FEW INCHES AT BEST.
MODELS PROG 850H WINDS INCREASING TO 50 KNOTS FROM MONDAY AFTERNOON
INTO MONDAY NIGHT. WINDS ON RIDGE TOPS COULD GUST TO 20 TO 30 MPH
LATE MONDAY AND LASTING THROUGH TUESDAY MORNING.
HIGH PRESSURE WILL SLIDE EAST ACROSS THE REGION ON TUESDAY WHICH
WILL ALLOW THE WINDS TO SUBSIDE FAIRLY QUICKLY.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
SURFACE HIGH PRESSURE EXPECTED TO BE IN CONTROL ACROSS THE EASTERN
SEABOARD AT THE OUTSET OF THE EXTENDED PERIOD BUT CHANGES WILL BE IN
OFFING AFTER ABOUT WED. OPERATIONAL GFS AND GFS ENSEMBLES STILL
CARRYING ONLY A WEAK FLAT WAVE OUT OF THE WESTERN GOMEX MID- TO LATE
WEEK WITH THE BULK OF THE PRECIPITATION ALONG AND THEN EAST OF THE
CAROLINA COAST AND VERY LITTLE REACHING BACK THIS FAR WEST.
ECMWF HOWEVER...IS CONSIDERABLY SLOWER AND MORE DEVELOPED WITH A
CLOSED SURFACE LOW OVER THE NE GULF BY LATER ON THURSDAY WHICH IT
MOVES RAPIDLY NORTHEAST THE VA CAPES BY 12Z FRIDAY. WITH NO REAL
BLOCKING SURFACE HIGH OVER NEW ENGLAND THAT SEEMS REASONABLE...BUT
WOULD MEAN A BETTER CHANCE FOR PRECIPITATION HERE...POTENTIALLY WINTRY
THU INTO FRI. AGAIN THE LACK OF A SURFACE HIGH AND STRONG WEDGE OF
COLD AIR WOULD MITIGATE AGAINST A PURELY SNOW OR FROZEN EVENT. ECMWF
H85 TEMPS FLIRTING WITH 0C AT THE ONSET OF PRECIP BUT RISE TO THE +1
TO +5C RANGE ACROSS THE CWA...SO IT COULD WIND UP MAINLY A RAIN
EVENT. AT THIS POINT HAVE INCREASED GRID POPS TO HIGHER CHANCE ON
THURSDAY WITH MAINLY SNOW IN THE WEST...A MIX IN BETWEEN AND RAIN IN
THE SOUTHEAST. BEYOND 12Z FRIDAY EC MODEL SHOWS DEEPENING AND
PHASING OF A COASTAL CYCLONE WHICH WOULD POTENTIALLY BRING A MAJOR
STORM TO NEW ENGLAND AND OR PENNSYLVANIA BUT LEAVE THIS AREA MAINLY
IN THE BACKLASH WITH STRONG COLD AIR ADVECTION...THE USUAL MOUNTAIN
SNOW SHOWERS AND MUCH COLDER AIR DROPPING THROUGH THE OHIO VALLEY
INTO THE CWA DURING THE DAY SATURDAY. H85 TEMPS FALL TO -14 TO -16C
ON BOTH GFS AND EC MODELS SO CONFIDENCE IN A SHIFT TO MUCH COLDER
REGIME IS HIGHER THAN IN THE EVENTUAL OUTCOME OF A STORM.
&&
.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
MAINLY VFR WEATHER IS EXPECTED AT BLACKSBURG TERMINAL FORECAST
POINTS (KROA...KLYH...KDAN...KBLF...KLWB) THROUGH SUNDAY. SOUTHWEST
TO WESTERLY SURFACE WINDS HAVE TRANSPORTED SIGNIFICANTLY DRIER AIR
INTO MOST OF THE BLACKSBURG FORECAST AREA...WITH DEW POINTS NOW IN
THE TEENS TO LOWER 20S WEST OF THE BLUE RIDGE...TO THE 20S ACROSS
THE PIEDMONT.
EXCEPTION IS ACROSS SOUTHEASTERN CORNER OF THE FORECAST AREA...INCLUDING
AREA AROUND DANVILLE...WHERE DEW POINTS HAVE ONLY FALLEN BACK INTO
THE 30S. SINCE ATMOSPHERE HAS DECOUPLED IN THIS AREA...IT IS
POSSIBLE THAT KDAN MAY EXPERIENCE MVFR TO POSSIBLY IFR CONDITIONS
LATE TONIGHT UNTIL SHORTLY AFTER DAYBREAK ON SUNDAY...WHEN RISING
TEMPERATURES AND INCREASING SURFACE WINDS SHOULD QUICKLY MIX OUT
SHALLOW MOISTURE LAYER. WILL THEREFORE CONTINUE TO MENTION RESTRICTION
TO FLIGHT CONDITIONS LATER TONIGHT AT KDAN...BUT HAVE REMOVED THREAT
AT KLYH CONSIDERING AMOUNT OF DRY AIR THAT HAS FINALLY ENTRAINED
INTO THAT AREA.
AN UPPER TROF WILL BRING COLDER AIR BACK INTO THE REGION SUNDAY
NIGHT THROUGH MONDAY NIGHT...WITH UPSLOPE LOW LEVEL WINDS IN THE
MOUNTAINS. SNOW SHOWERS ARE EXPECTED IN KBLF AND KLWB WHICH WILL
RESULT IN MVFR TO OCCASIONALLY IFR CEILINGS AND VISIBILITIES.
DOWNSLOPING WINDS EAST OF THE BLUE RIDGE...SHOULD ASSURE THAT
MAINLY VFR WEATHER PREVAILS AT KROA...KLYH...AND KDAN THROUGH
WEDNESDAY.
LOOKING FURTHER AHEAD...A LARGE STORM SYSTEM MAY IMPACT PORTIONS OF
THE MID APPALACHIAN AND MID ATLANTIC REGION AS EARLY AS THURSDAY...
ONCE AGAIN BRINGING AN INCREASED THREAT OF WIDESPREAD MVFR OR IFR
CONDITIONS.
&&
.HYDROLOGY...
FLOOD WARNINGS REMAIN IN EFFECT FOR DANVILLE...PACES AND SOUTH
BOSTON ON THE DAN RIVER...AND FOR RANDOLPH ON THE ROANOKE RIVER.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.
&&
$$
SYNOPSIS...JJ
NEAR TERM...JJ
SHORT TERM...REB
LONG TERM...PC
AVIATION...AMS/JJ/WERT
HYDROLOGY...PC
