FXUS61 KRNK 111717
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1217 PM EST FRI DEC 11 2009

.SYNOPSIS...
A LARGE HIGH PRESSURE SYSTEM WILL MOVE EAST ACROSS THE AREA TODAY 
AND TONIGHT...THEN OFF THE COAST SATURDAY. LOW PRESSURE WILL TRACK 
SOUTH OF THE REGION OVER THE WEEKEND AND WILL LIKELY SPREAD WINTRY 
PRECIPITATION INTO OUR AREA LATE SATURDAY NIGHT INTO SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...

COLD AIR CONTINUES TO FILTER INTO THE AREA THIS AFTERNOON. SOME
HIGH CLOUDS RESTRICTING FULL SOLAR HEATING AND COLD AIR MIXING HAS
KEPT TEMPERATURES ON THE COOL SIDE. WITH SLOW WARM UP FROM
BITTERLY COLD MORNING LOWS...WILL LOWER AFTERNOON HIGHS A FEW
DEGREES.

ALL RIVERS HAVE CRESTED THIS MORNING AND WILL BE FALLING THROUGH
THE DAY. ONLY RIVER WITH MINOR FLOODING IS THE ROANOKE RIVER AT
RANDOLPH.

PREVIOUS FORECAST...WATER VAPOR LOOP SHOWS A BROAD TROUGH ACROSS
MUCH OF THE EASTERN U.S...BUT WITH SHORT WAVE ENERGY LIFTING
NORTHEAST AND LEAVING STRONG ZONAL FLOW OVER THE MID ATL REGION.
IN THIS ZONAL FLOW...HIGH PRESSURE OVER THE TN VALLEY THIS MORNING
SHOULD FINALLY MOVE OVER THE AREA TONIGHT. WINDS WILL CONTINUE TO
BREEZY TODAY...AND WITH AN ARCTIC AIRMASS IN PLACE OVER THE
AREA...IT WILL BE A COLD DAY. LOOKS LIKE HIGHER ELEVATIONS OF
GREENBRIER AND BATH COUNTIES WILL CONTINUE TO SEE WIND CHILLS
BELOW MINUS 5 DEGREES THROUGH DAYBREAK...SO WILL KEEP THE WIND
CHILL ADVISORY GOING THRU 1000 AM. HOT SPRINGS AIRPORT...ELEVATION
NEARLY 3800 FEET...HAS HAD WIND CHILLS AROUND MINUS 10 DEGREES ALL
NIGHT. THERE IS A THREAT FOR SOME THICKER CIRRUS ON THE SOUTH SIDE
OF THE UPPER JET...SO HAVE PARTLY CLOUDY SKIES ACROSS NW NC.
OTHERWISE...SHOULD BE A SUNNY DAY.

SFC WINDS WILL DECOUPLE TONIGHT FOR ALL BUT THE RIDGES...AND OTHER 
THAN SOME THINNER CIRRUS POSSIBLE...LOOKS LIKE THERE WILL BE GOOD 
RADIATIONAL COOLING CONDS. DEWPOINTS WILL STILL BE IN THE SINGLE 
DIGITS. WITHOUT SNOW COVER...I DONT THINK WELL SEE ANY LOWS DROP
INTO THE SINGLE DIGITS...BUT EASILY THE TEENS. HAVE GONE CLOSER TO
THE COLDER MET GUIDANCE FOR LOWS.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
SFC HIGH PRESSURE CENTERED OVERHEAD EARLY SATURDAY WILL GIVE WAY TO
APPROACHING WEAK LOW PRESSURE CENTER MOVING NORTHEASTWARD OUT OF
THE GULF COAST REGION BY THE EVENING. PLENTY OF SUN DURING THE DAY
AND LOW DEW PTS SHOULD LEAD TO MILDER TEMPS BUT STILL A BIT BELOW
NORMAL. WITH EAST FLOW GIVEN SFC HIGH POSITION OVER ERN VA...KEPT
TEMPS AT OR BELOW COOLER MET GUIDANCE.

FAIRLY GOOD AGREEMENT IN MODEL TIMING OF ONSET OF OVERRUNNING
PRECIP FROM SOUTHWEST...WITH WIDESPREAD LIGHT PRECIP REACHING THE
NW MTNS BY AROUND 06Z..THEN ACROSS ENTIRE CWA BY 12Z. MEASURABLE
MAY BE A LITTLE SLOWER TO OCCUR THAN MODELS SUGGESTING GIVEN VERY
DRY SFC DEW PTS...BUT NOT CONFIDENT ENOUGH AT THIS POINT TO
INDICATE MUCH OF A DIFFERENCE FROM WHAT BOTH NAM AND GFS ARE
SHOWING. DID INCREASE POPS TO CATEGORICAL OVER THE SW HALF OF CWA
BY 12Z AND THEN EVERYWHERE FOR FIST PART OF SUNDAY. SECOND S/WV
IN WRLY FLOW HELPS TO KICK PRECIP EAST FAIRLY QUICKLY NOW BY SUN
AFTERNOON...WITH ONLY LINGERING UPSLOPE SHWRS IN FAR WEST BY END
OF THE DAY.

WITH SFC HIGH OVER MID-ATLANTIC COAST AS PRECIP BEGINS AND VERY
LOW SFC DEW PTS...STILL LOOKING AT SOME WINTRY P-TYPES AS PRECIP
MOVES IN AFTER MIDNIGHT AND AT LEAST THROUGH THE MORNING HOURS
SUNDAY. VERY WARM ALOFT HOWEVER...AND FCST SOUNDINGS SUGGEST ONLY
BRIEF PERIOD OF SLEET AT THE START...MAYBE SOME SNOW MIXED IN
ACROSS THE NORTH...BEFORE CHANGING TO FREEZING RAIN OR PLAIN RAIN.
DETAILS AND TIMING OF WEDGE BREAKING ARE HARD TO DEPICT EXACTLY AT
THIS POINT...BUT TRIED TO INDICATE SUB-FREEZING TEMPS HOLDING ON
THROUGH MID MORNING NEW RIVER VALLEY TO ABOUT NOON ACROSS FOOTHILL
REGION NORTH OF ROANOKE RIVER...SUCH AS LYH AREA. LIQUID EQUIV
VALUES A QUARTER OF AN INCH OR LESS AND GIVEN SO WARM ALOFT...NOT
EXPECTING VERY EFFICIENT ICE ACCRETION. SOME UPSLOPE COOLING ALONG
BLUE RDG BUT THIS IS FAIRLY SHORT-LIVED SO ONLY SUBTLE ENHANCEMENT
OF ANY LIGHT ICING EXPECTED THERE. OVERALL...ICE ACCUM AMOUNTS
EXPECTED TO REMAIN BELOW WARNING CRITERIA...BUT WILL HAVE TO
CONSIDER ISSUANCE OF ADVISORY. WITH TEMPS WARMING BY END OF SUNDAY
INTO LOW 40S MOST PLACES...ANY ICE SHOULD QUICKLY MELT. NOT
EXPECTED MUCH WIND BEHIND THIS SYSTEM EITHER THIS TIME...MAYBE
10-15 MPH. WARM ADV ACTUALLY BEGINS BEHIND THIS BY SUNDAY NIGHT
WELL IN ADVANCE OF NEXT SYSTEM...AND AS A RESULT INCREASED THE
LOWS FOR SUN NIGHT A FEW DEG. ANY LINGERING UPSLOPE SHWRS IN FAR
WEST QUICKLY FADE AS FLOW TURNS WEST OR WSW OVERNIGHT AND ANTICYCLONIC
FLOW ALOFT RETURNS. MOST OF THESE WILL BE RAIN SHWRS GIVEN WARMING
850 TEMPS.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AREA OF LOW PRESSURE MOVING OUT OF THE GULF OF MEXICO...AND
PROGGED TO AFFECT THE CWA ON TUESDAY TAKING A MORE SOUTHWARD JOG
ON THE ECMWF/GFS/GEFS. HOWEVER...WITH A WEAK 50/50 LOW IN PLACE AND
UPPER RIDGING OVER THE NORTH ATLANTIC...THIS LOW HAS A BETTER
CHANCE OF TAKING MORE OF SW-NE TRACK INTO THE MIDDLE ATLANTIC THAN
THIS WEEKENDS SYSTEM. HOWEVER...DOES NOT APPEAR TO BE MUCH COLD
AIR IN PLACE...UNTIL AFTER THIS SYSTEM EXITS TO THE EAST. IN
FACT...THE BIGGEST CHANGE TO THE LONG TERM WAS TO WARM TEMPS
MONDAY AND TUESDAY...AS H85 ADJUSTMENTS ARE SEVERAL DEGREES WARMER
THAN CURRENT MEX NUMBERS AND GOING FORECAST. COLDER AIR WILL NOT
BE ABLE TO PENETRATE THE MIDDLE ATLANTIC AND SOUTHEAST....UNTIL
ONE OF THE SHRTWVS FROM THE SW CONUS IS ABLE TO PHASE/MERGE WITH
THE POLAR VORTEX MOVING INTO HUDSON BAY. ATTM...APPEARS THAT THE 
PREDOMINATE PRECIP TYPE WOULD BE RAIN FOR TUESDAY'S SYSTEM...WITH 
SNOW IN SE WEST VA WITH UPSLOPE FLOW INTO WED MORNING. BOTH ECMWF/GFS
ALLOW SUB -10C H85 AIR TO ARRIVE WEDNESDAY ACROSS SE WEST 
VA...ALTHOUGH THE BITE WILL BE TAKEN OFF OF THIS CHILL THANKS TO 
DOWNSLOPING FURTHER EAST. ONCE THE TROUGH AXIS MOVES INTO OUR 
CWA...THE DOWNSLOPE COMPONENT WILL WEAKEN...ALLOWING PERHAPS SOME 
LOWER 40S MAX TEMPS TO REACH INTO THE PIEDMONT AND SOUTHSIDE 
THURSDAY. CONSIDERING THE HIGH LATITUDE BLOCKING IN PLACE...THE 
EASTERN TROUGHINESS COULD BE THE BEGINNING OF A PATTERN 
CHANGE...WITH THE COLDER H85 VALUES OFF THE OP GFS FAVORED OPPOSED 
TO THE WARMER ECMWF PAST THURSDAY.

&&

.AVIATION /17Z FRIDAY THROUGH TUESDAY/...
VFR CONDITIONS WILL CONTINUE AT ALL AIRPORTS THROUGH FRIDAY NIGHT
UNDER DRY HIGH PRESSURE MOVING IN FROM THE SOUTHWEST. CENTER OF
HIGH REMAINS TO THE SOUTHWEST HOWEVER...AND STRONG WESTERLY
GRADIENT STILL EXISTS ALOFT TODAY. WESTERLY SFC WINDS WILL PICK
UP TO 10 TO 15 KNOTS BY 15Z...WITH GUSTS 20 TO 25 KNOTS. BY THIS
EVENING...SFC HIGH SETTLES IN MORE OVERHEAD AND MORE COMPLETE
DECOUPLING IS EXPECTED AT ALL SITES SO WINDS WILL DROP OFF TO
LIGHT WESTERLY ALL SITES. SOME VERY THIN CIRRUS POSSIBLE BY
MORNING...BUT NOT WORTHY OF MENTION IN TAFS.

VFR WEATHER WITH UNRESTRICTED FLIGHT CONDITIONS ARE EXPECTED OVER
ALL TERMINAL FORECAST SITES (KROA...KLYH...KDAN...KBLF...KLWB)
AGAIN SATURDAY...BUT THEN IS EXPECTED TO 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 LOWERING CIGS SATURDAY
NIGHT AND EVENTUALLY A WINTRY MIX OF PRECIPITATION BEFORE
DAYBREAK. THIS WILL BRING A RETURN OF IFR CONDITIONS FOR MUCH OF
SUNDAY. THE SYSTEM SHOULD EXIT THE REGION SUNDAY NIGHT WITH
IMPROVED FLIGHT CONDITIONS MONDAY. ANOTHER FRONT WILL AFFECT THE
REGION TUESDAY...AND MAY BRING RAIN...WITH A RETURN TO MVFR OR IFR
CONDITIONS.

&&

.HYDROLOGY...
MINOR FLOODING IS EXPECTED TO END THIS AFTERNOON ALONG THE
ROANOKE RIVER AT RANDOLPH. THE FLOOD STATEMENT (FLSRNK) WILL BE
UPDATED THIS EVENING UNLESS RANDOLPH FALLS BELOW FLOOD STAGE EARLIER.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.

&&

$$
SYNOPSIS...PM/SK
NEAR TERM...JJ/RCS
SHORT TERM...SK
LONG TERM...KM
AVIATION...JJ/SK
HYDROLOGY...RCS