Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 262316
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
616 PM EST FRI DEC 26 2014

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER THE AREA THROUGH TONIGHT. A WEAK
COLD FRONT WILL APPROACH FROM THE WEST SATURDAY...WHILE A WAVE OF LOW
PRESSURE MOVES TOWARD THE SOUTHERN APPALACHIANS FROM THE GULF
COAST AREA BY SUNDAY. ANOTHER WEAK WAVE WILL APPROACH ALONG THIS
FRONT SUNDAY NIGHT. THESE LOW PRESSURE WAVES WILL SPREAD AN AREA
OF LIGHT TO MODERATE RAINFALL ACROSS THE REGION FROM EARLY SUNDAY
THROUGH MONDAY.
&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
AS OF 325 PM EST FRIDAY...

HIGH PRESSURE WILL REMAIN IN CONTROL TONIGHT WITH LIGHT
WINDS...RESULTING QUICKLY FALLING TEMPS BY THIS EVENING. PATCHY
HIGH CLOUDS ARE EXPECTING TO MOVE INTO WESTERN PORTIONS OF THE
FCST AREA THIS EVENING...AND AN UPPER WAVE MAY EVEN BRING SOME
SCATTERED TO BROKEN CLOUDS MID LAYER CLOUDS IN FROM THE WEST
OVERNIGHT AS THEY TRY TO CROSS INTO THE PIEDMONT. THIS IS THE
FACTOR THAT WILL MAKE OVERNIGHT TEMPS A LITTLE TRICKY...AND WOULD
OTHERWISE GO EVEN COLDER THAN THE CHILLIER MAV GUIDANCE IF THESE
WERE TO REMAIN SCATTERED AND THIN. GIVEN THE POSSIBILITY OF A
PERIOD OF THICKER CLOUDS...WILL COMPROMISE BETWEEN THE COLDER MAV
AND MILDER MET...AT LEAST THATS THE CASE IN THE WEST. STILL MOST
TEMPS WILL GET WELL BELOW FREEZING...BUT SOME HIGHER ELEVATION
LOCATIONS MAY NOT...SUCH AS BLUEFIELD OR EVEN BOONE. FEEL MORE
CONFIDENT THAT THE MID AND HIGH CLOUDS WILL AT LEAST PREVENT RIVER
VALLEY FOG FROM FORMING TONIGHT...AND THUS SHOULD BE NO WORRIES OF
FREEZING FOG AS THERE WAS LAST NIGHT. MAY STILL NEED TO KEEP AN
EYE ON GREENBRIER RIVER VALLEY IF THEY GET SEVERAL HOURS OF CLEAR
SKIES TOWARD MORNING.

SATURDAY WILL SEE THE SFC HIGH SLOWLY GIVE WAY TO WEAK SW
FLOW...AND WEAK WARM ADVECTION...SO ANOTHER MILD DAY ON
TAP...LIKELY 3-5 DEG WARMER THAN TODAY. EXPECTING SOME LOW 60S IN
EAST OF THE BLUE RIDGE AND EVEN A FEW SPOTS IN THE MTN VALLEYS
REACHING 60. WOULD HAVE TO GET INTO MID TO UPPER 60S FOR RECORDS.
MORE HIGH CLOUDS MAY BEGIN TO MOVE IN FROM THE WEST AND SOUTHWEST
AHEAD OF APPROACHING FRONTAL BOUNDARY AND DEVELOPING WAVE DOWN
ALONG GULF COAST...BUT MOST OF THE DAY SHOULD BE SUNNY.

MODELS SPREAD LIGHT PRECIP ACROSS THE REGION FROM THE SOUTHWEST
OVERNIGHT...WITH SOME DIFFERENCES STILL IN TIMING. GENERAL TREND
HAS BEEN A MINOR SLOW DOWN OF ARRIVAL...AND WITH INITIALLY DRY AIR
IN PLACE THIS CERTAINLY SEEMS REASONABLE. INITIALLY VIRGA MAY
MANAGE TO GET SOME SPRINKLES DOWN TO SOME HIGHER ELEVATIONS OVER
NW NC AND SE WV BY AROUND MIDNIGHT...BUT BEST CHANCES OF LIGHT
MEASURABLE RAINFALL LOOK TO MOVE IN WELL AFTER THAT. FROM ROANOKE
NORTHEASTWARD...PROBABLY WILL NOT SEE ANY LIGHT RAIN UNTIL
DAYBREAK. NO ISSUES WITH ANY LOW LEVEL OR SFC TEMPS AT OR BELOW
FREEZING AS PRECIP MOVES IN...SO WE ARE CONFIDENTLY LOOKING AT
RAIN ONLY WITH THIS EVENT. IN FACT...MOST PLACES WILL REMAIN IN
THE 40S FOR OVERNIGHT LOWS GIVEN WARM ADVECTION AND CLOUD COVER.
THROUGH SATURDAY NIGHT ALL THE COLD AIR WILL REMAIN LOCKED OVER
THE MIDWEST U.S.
&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AS OF 300 PM EST FRIDAY...

MOST OF THIS FORECAST PERIOD WILL BE DEALING WITH UPCOMING RAINFALL EVENT
WHICH SHOULD BE GETTING UNDERWAY EARLY SUNDAY FROM SOUTHWEST TO
NORTHEAST AS DEEP LAYER SOUTHWESTERLY FLOW AROUND SOUTH ATLANTIC
RIDGE WILL PROVIDE A MOIST GULF OF MEXICO INFLOW WITH PWATS
STEADILY INCREASING TO SLIGHTLY IN EXCESS OF 1.0 INCH AT KRNK ON BOTH
NAM AND GFS BUFKIT PROFILES BY MIDDAY SUNDAY...WHICH IS ROUGHLY 2 STD.
DEVIATIONS ABOVE LATE DECEMBER CLIMO...SO PLENTY OF MOISTURE
AVAILABLE. SEVERAL WEAK WAVE WILL TRACK ALONG THE FRONTAL BOUNDARY
SUNDAY INTO EARLY MONDAY BUT WITH MODEST UPPER LEVEL SUPPORT. WILL
CONTINUE WITH LIKELY TO CATEGORICAL POPS MUCH OF SUNDAY WITH TEMPS
AGAIN FAIRLY MILD...FROM UPPER 40S NW TO UPPER 50S SE. SURFACE
TEMPS REMAIN WELL ABOVE FREEZING SUNDAY NIGHT EXCEPT POSSIBLY AT
HIGHEST NORTHWEST ELEVATIONS AND THICKNESS PARAMETERS CONTINUE TO
INDICATE A PURE LIQUID EVENT ALTHOUGH A FEW HOURS OF MIXED R-S
CANNOT BE RULED OUT IN FARTHEST NW GREENBRIER. LIKELY OR HIGH
CHANCE POPS WILL DIMINISH SLOWLY AS THE FINAL WEAK SURFACE WAVE
TRACKS OFF TO THE NORTHEAST BY EARLY TO MIDDAY MONDAY. SEE
HYDROLOGY SECTION FOR QPF/HYDRO IMPACTS. COLD AIR ADVECTION MONDAY
NOT VERY IMPRESSIVE AS H85 TEMPS FALL TO AROUND 0C IN THE CENTRAL
CWA BY LATE MONDAY NOT TO 0C IN THE SOUTHEAST UNTIL EARLY TUESDAY
MORNING AND THAT IS ON THE COLDER ECMWF SOLUTION...NAM/GFS ARE
SOMEWHAT WARMER. STILL A FEW SNOW SHOWERS POSSIBLE IN THE NW
MOUNTAINS AS TEMPS CLIMB ONLY INTO LOW 40S FAR NW BUT STILL REACH
LOW 50S IN THE SOUTHEAST UNDER DIMINISHING CLOUD COVER.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 330 PM EST FRIDAY...

LONG RANGE MODELS...AT LEAST AT THE LARGER SCALE...ARE IN AGREEMENT
WITH FAIR CONTINUITY AS WE TRANSITION INTO THE NEW YEAR.  BROAD
UPPER LEVEL TROUGH IS PROGGED TO EXTEND FROM EASTERN CANADA...
SOUTHWEST THROUGH THE CENTRAL CONUS INTO A CUTOFF AREA OF LOW
PRESSURE OVER SOUTHERN CALIFORNIA.  A HIGH AMPLITUDE RIDGE WILL BE
POSITIONED OFF THE PAC NW COAST. THIS PATTERN WILL FOCUS VERY COLD
AIR INTO THE ROCKIES AND WESTERN PLAINS...TEMPERATURES 15 TO 25
DEGREES BELOW NORMAL FROM WYOMING TO WEST TEXAS.  HERE IN THE EAST
IT WILL TREND COLDER...BUT ONLY TO THE TUNE OF 5 DEGREES OR SO BELOW
NORMAL...NOTHING EXTREME. THE MILDER AIR WILL GET SUPPRESSED INTO
THE FAR SOUTHEAST CONUS...I.E. FLORIDA.

ITS GOOD TO SEE ALL THE MODELS AGREEING FOR A CHANGE...YET HAVE TO
BE A LITTLE LEERY OF MODEL SKILL AS THEY GENERALLY DO NOT HANDLE
ENERGY THAT MAY GET EJECTED FROM CUTOFF LOWS OVER THE SOUTHWESTERN
CONUS.  ATTM...MODELS KEEP OUR FORECAST AREA DRY FROM TUESDAY
THROUGH THURSDAY...ANY UPPER LEVEL ENERGY THAT TRIES TO EJECT OUT OF
THE UPPER LEVEL TROUGH BECOMING SHEARED IN THE FAST WESTERLY FLOW
ALOFT.  CERTAINLY CAN`T RULE OUT SOME VERY LIGHT PRECIP FROM ONE OF
THE WAVES DURING THE WEEK...BUT CHANCES FOR MEASURABLE LOOKS PRETTY
MINISCULE...AND WILL LEAVE POPS OUT OF THE FORECAST ATTM IN FAVOR OF
A MAINLY DRY FORECAST.

BY THE END OF THE WEEK...AND PROBABLY MORE SO FOR NEXT WEEKEND...
THERE SHOULD BE ENOUGH OF A CHANGE IN THE UPPER LEVEL FLOW TO ALLOW
FOR DEEPER MOISTURE TO RETURN TO THE FORECAST AREA.  THE UPPER LOW
WHICH IS FORECAST TO BE NEARLY STATIONARY OVER THE SOUTHWESTERN
CONUS FOR MUCH OF NEXT WEEK IS PROGGED TO BE KICKED EAST BY THE
ARRIVAL OF A STRONG PAC NW SHORTWAVE.  TIMING OF THE EJECTING UPPER
LOW WILL BE CRUCIAL IN DETERMINING TIMING AND EXTENT OF DEEPER
MOISTURE THAT RETURNS TO OUR FORECAST AREA.  THIS MAY BE AS EARLY AS
FRIDAY AND AS LATE AS SATURDAY.  TIMING AND TRACK OF THE SYSTEM WILL
ALSO DETERMINE P-TYPE.  TEMPERATURES LOOK TO BE BORDERLINE
CRITICAL...SUGGESTING AT LEAST SOME WINTRY MIX.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
AS OF 550 PM EST FRIDAY...

HIGH PRESSURE WILL COVER THE REGION TONIGHT THROUGH SATURDAY WITH
VFR CONDITIONS AND LIGHT WINDS. PERIODS OF BROKEN MID/HIGH CLOUDS
WILL CROSS THE AREA TONIGHT AND SHOULD LIMIT TOO MUCH IN THE WAY
OF FOG IN THE RIVER VALLEYS SUCH AS AT KLWB. HOWEVER AGAIN GIVEN
FAVORABLE FOG STABILITY VALUES AND POTENTIAL FOR THE VALLEYS TO
RADIATE FASTER LATE PENDING DEGREE OF CLOUDS...INCLUDED A BRIEF
TEMPO GROUP FOR MVFR TYPE FOG/STRATUS AT KLWB TOWARD DAWN. IF
SKIES SHOULD HAPPEN TO CLEAR EVEN MORE BEFORE DAYBREAK THEN MORE FOG
COULD FORM NEAR THE RIVER AGAIN...RESULTING IN VERY LOCALIZED IFR
CONDITIONS OR WORSE LATE. CANT TOTALLY RULE OUT SOME ISOLATED
PATCHES OF FOG AS WELL AT KBCB/KLYH BUT WONT INCLUDE FOR NOW.

ANOTHER COLD FRONT WILL APPROACH THE REGION LATE SATURDAY WITH
VFR CLOUDS FILLING IN ACROSS THE REGION AND CEILINGS STEADILY
LOWERING OVERNIGHT.

EXTENDED DISCUSSION...

SATURDAY NIGHT THROUGH MONDAY...THE FRONT WILL STALL NEAR THE
WEST SIDE OF THE APPALACHIANS AS MULTIPLE WEAK WAVES OF LOW
PRESSURE ARE EXPECTED TO RIDE UP THIS BOUNDARY... RESULTING IN A
PROLONGED PERIOD OF RAIN AND IFR TO MVFR CONDITIONS. IFR
CONDITIONS ARE NOT LIKELY TO DEVELOP UNTIL EARLY MORNING SUNDAY
IN THE WEST...AND PERHAPS NOT UNTIL SATURDAY EVENING IN THE EAST.

THE FRONT MAY LINGER JUST TO THE SOUTH OF THE AREA EARLY NEXT
WEEK...BUT AT THIS TIME CONFIDENCE IS FAIRLY HIGH THAT AIRPORTS
WILL REMAIN DRY WITH VFR CONDITIONS PREVAILING AS STRONG HIGH
PRESSURE SLOWLY BUILDS IN FROM THE WEST. SOME MVFR CEILINGS COULD
LINGER AT KDAN MONDAY NIGHT INTO TUESDAY BEFORE ALL LOCATIONS
RETURN TO VFR ON WEDNESDAY.
&&

.HYDROLOGY...
AS OF 300 PM EST FRIDAY...

DETERMINISTIC MODELS AND VARIOUS ASSOCIATED ENSEMBLE PACKAGES CONTINUE TO
DIFFER SOMEWHAT ON EXACT TIMING OF THE RAINFALL AND TOTAL QPF BUT GENERAL
CONSENSUS IS ANOTHER MODERATE RAINFALL EVENT IS ON TAP WITH FINAL QPF RANGING
FROM 0.75 TO 1.00 INCH BY THE TIME IT WRAPS UP DURING THE DAY MONDAY.
NAEFS AND SREF ENSEMBLES SEEM TO BE CLUSTERING WELL IN THE 0.75 INCH BASIN
AVERAGE RANGE FOR MOST OF OUR RIVERS BASIN. THESE AMOUNTS ARE FAIRLY SIMILAR
TO THE RECENT DEC. 23-24 EVENT. ENSEMBLE RIVER FORECASTS USING THE ABOVE RANGE OF
QPFS ABOVE DO NOT INDICATE ANY FLOOD THREAT BUT DO ALLOW FOR MINOR RISES OF
SEVERAL FEET ON SOME RIVERS. RATES OF RAINFALL WILL BE MODEST AND
NOT EXPECTED TO POSE MUCH OF AN ISSUE WITH FASTER RUNOFF...DESPITE
FAIRLY WET SOILS. 6-HOUR FLASH FLOOD GUIDANCE VALUES RANGE FROM
ABOUT 1.7 TO OVER 3 INCHES SO SHOULD NOT APPROACH EVEN BANKFULL ON
THE SMALLER STREAMS.

&&

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

&&

$$
SYNOPSIS...AMS/SK
NEAR TERM...SK
SHORT TERM...PC
LONG TERM...PM
AVIATION...AMS/JH/SK
HYDROLOGY...PC


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