Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 260144
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
844 PM EST THU DEC 25 2014

.SYNOPSIS...
HIGH PRESSURE WILL BRING QUIET WEATHER TO THE REGION TONIGHT INTO
SATURDAY. THEN AS THE HIGH PUSHES TO OUR EAST...A COLD FRONT
APPROACHING FROM THE WEST WILL RESULT IN A CHANCE OF RAIN FOR
SATURDAY NIGHT AND SUNDAY. OUR WEATHER WILL THEN REMAIN UNSETTLED
INTO EARLY NEXT WEEK AS HIGH PRESSURE TRIES TO BUILD INTO THE
REGION FROM THE WEST...WHILE THE RESIDUAL FRONT STALLS TO THE SE.
&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
AS OF 815 PM EST THURSDAY...

OTHER THAN FOR SOME LINGERING LOW CLOUDS ACROSS THE FAR NW
MOUNTAINS IN SE WEST VA...MAINLY A TEMP FORECAST OVERNIGHT AS HIGH
PRESSURE BUILDS ABOUT OVERHEAD BY DAYBREAK. GIVEN THE DEGREE OF
DRY AIR ALOFT AND GREAT RADIATIONAL COOLING CONDITIONS UNDER
MAINLY CLEAR SKIES...LOWERED TEMPS A CAT OR SO ESPCLY VALLEYS
WHERE ALREADY IN THE 20S IN SPOTS...AND COULD DROP INTO THE UPPER
TEENS TOWARD DAWN. ELSW APPEARS OVERALL LOWS MAINLY MID 20S TO
THE LOW 30S...AS EXPECT SOME SLOW DROP IN DEWPOINTS UNDER THE
SURFACE RIDGING DESPITE MOIST GROUND CONDITIONS. OTRW FEW CHANGES
OVERNIGHT.

PREVIOUS VALID DISCUSSION AS OF 300 PM EST THURSDAY...

WE WILL HAVE QUIET WEATHER THROUGH THE END OF THE WEEK WITH RIDGING
ALOFT AND HIGH PRESSURE BUILDING AT THE SURFACE THROUGH TOMORROW
AFTERNOON. EXPECT CLEAR SKIES EAST OF THE BLUE RIDGE...BUT NORTHWEST
WINDS CONTINUE TO GENERATE UPSLOPE CLOUDS WEST OF THE RIDGE...AND
VISIBLE SATELLITE PICS SHOW THE CLOUDS ERODING FROM THE SOUTH A BIT
SLOWER THAN ANTICIPATED. MODEL GUIDANCE IS INDICATING THAT MOISTURE
TRAPPED UNDER THE SUBSIDENCE INVERSION WILL KEEP THE CLOUDS
LINGERING INTO TONIGHT. THE LOWER CLOUDS SHOULD BE GONE AS WE HEAD
TOWARD DAYBREAK...BUT MID/HIGH CLOUDS WILL THEN OVERSPREAD THE
REGION INTO FRIDAY NIGHT AS THE UPPER RIDGE AXIS PUSHES TO OUR EAST
AND A WEAK SHORT WAVE MOVES THROUGH. BLUSTERY NORTHWEST WINDS WILL
BE CALMING DOWN AS WE HEAD TOWARD EVENING...THEN EXPECT WINDS TO
REMAIN LIGHT THROUGH FRIDAY NIGHT. NIGHT TIME TEMPERATURES WILL BE
RUNNING A BELOW NORMAL WITH READINGS GENERALLY IN THE UPPER 20S TO
LOWER 30S TONIGHT...BUT FRIDAY SHOULD WARM TO SEASONABLE LEVELS
WITH MOST LOCATIONS IN THE 50S TO NEAR 60 DEGREES.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 300 PM EST THURSDAY...

FORECAST AREA WILL BE UNDER THE INFLUENCE OF A HIGH PRESSURE RIDGE
OFF THE SOUTHEASTERN U.S. COAST EARLY SATURDAY. THIS WILL MAKE FOR A
VERY MILD DAY WITH HIGHS RUNNING WELL ABOVE NORMAL FOR LATE
DECEMBER...GENERALLY IN THE 50S TO LOW 60S FAR SE. THE DAY STARTS
OUT MOSTLY SUNNY BUT CLOUDS WILL INCREASE THROUGH THE DAY AS A SLOW-
MOVING FRONTAL BOUNDARY ASSOCIATED WITH A TROUGH AND SHORT-WAVE OVER
THE CENTRAL U.S. IMPINGES ON THE RIDGE BY EVENING. CLOUDS AND POPS
WILL INCREASE OVERNIGHT SATURDAY WHICH WILL HELP TO HOLD OVERNIGHT
TEMPS UP AT UNSEASONABLY MILD LEVELS...UP TO 15F OR MORE ABOVE
NORMAL IN THE MOUNTAINS. HENCE DO NOT EXPECT ANY P-TYPE ISSUES AT
THE ONSET OF THIS EVENT AS HIGH CHANCE AND THEN LIKELY POPS DEVELOP
FROM EARLY TO MIDDAY SUNDAY. FRONT WILL BE SLOW TO MOVE EAST AS IT
ENCOUNTERS THE DEEP-LAYERED SOUTHWEST FLOW AROUND THE SOUTH ATLANTIC
RIDGE AND EXPECT CLOUDS AND RAIN CHANCES TO CONTINUE MUCH OF SUNDAY
AND ON INTO EARLY MONDAY. WITH NO SIGNIFICANT SOURCE OF COLD AIR
THERMAL PROFILES CONTINUE TO INDICATE ALL RAIN FOR THIS EVENT
ALTHOUGH 12Z GFS WAS COLDER THAN PREVIOUS RUNS WITH FAR NW
GREENBRIER SLIPPING BELOW 0C AT H85 BY 12Z MONDAY..ALBEIT WITH
LITTLE OR NO QPF AT THAT TIME. GEM AND ECMWF ARE WARMER AND WETTER
WITH QPF BY 12Z MONDAY SHOWING UP TO 0.75 INCHES IN THE SOUTHWEST
CWA BUT USED A BLEND OF MODELS AND HPC FOR SUBSTANTIALLY LESS IN THE
GRIDS BY THAT TIME...GENERALLY AROUND 0.25 TO 0.50 IN THE SOUTHWEST
AND LESSER AMOUNTS NORTH. HIGHS SUNDAY WILL BE MILD AGAIN BUT A
LITTLE LESS SO THAN SATURDAY DUE TO FULL OVERCAST...UPPER 40S NW TO
MID-50S SHOULD DO IT.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 300 PM EST THURSDAY...

EARLY PART OF NEXT WEEK LOOKS TO BE UNSETTLED WITH LARGE SCALE
TROUGH OVER THE WESTERN TWO THIRDS OF THE COUNTRY EJECTING AT LEAST
ONE FINAL S/WV PIECE OF ENERGY TOWARD SRN APPALACHIANS ON
MONDAY...WITH POTENTIALLY SOME VERY LIMITED LINGERING MOISTURE ON
WESTERN SLOPES INTO TUESDAY.  STILL SOME MODEL DIFFERENCES IN 12Z
CYCLES...WITH ECMWF AND CANADIAN REMAINING MOST AGGRESSIVE WITH S/WV
AND AMOUNT OF MOISTURE OVERRUNNING THE RNK FCST AREA AS SFC LOW
TRACKS TO THE SOUTH. ECMWF IS FASTER THAN WET CANADIAN AND HAS ANY
PRECIP EXITING BY MIDDAY MONDAY.  GFS AND AT LEAST SOME OF ITS
ENSEMBLES ARE WEAKER AND MORE PROGRESSIVE WITH THIS S/WV...KEEPING
MOST LIGHT PRECIP TO OUR SOUTH.  IN ALL CASES...LOW LEVEL THERMAL
PROFILES TOO WARM FOR ANY WINTRY PRECIP. BEST FOR NOW TO GO WITH
COMPROMISE OF ALL THESE IDEAS...WHICH ENDS UP BEING CLOSE TO ECMWF
BUT LEANING A LITTLE TOWARD GFS.  NOT GOING AS WET SLOW AS CANADIAN.
BUT WITH UNCERTAINTY THROUGH LATE MONDAY DO NOT FEEL IT PRUDENT TO
GO WITH HIGHER THAN 50 POP ANYWHERE...BUT HAVE HIGHEST POPS IN EAST
MONDAY WITH EXITING SYSTEM...AS WELL AS LINGERING UPSLOPE CHANCE
POPS FAR WEST...AND KEEPING SOME VERY LOW CHANCE POPS INTO MON NIGHT
PERIOD.

AFTER THAT MODELS NOW IN BETTER AGREEMENT THAT BY MID WEEK A FLAT
UPPER TROUGH SETTLES MORE INTO THE EASTERN THIRD OF THE COUNTRY WITH
SPLIT FLOW OVER THE ROCKIES...AS SIGNIFICANT ENERGY CUTS OFF FROM
THE FLOW OVER SRN CALIFORNIA. GOOD TO SEE ALL THE MODELS AGREEING ON
THIS IDEA...YET HAVE TO BE A LITTLE LEERY OF MODEL SKILL IN
DEVELOPING THIS CUTOFF...SO STILL CANNOT RULE OUT SOME WEAK WAVES
HEADING IN OUR DIRECTION THROUGH MID WEEK...BUT CHANCES LOOK BETTER
FOR BROAD DRY BUT COOL SURFACE HIGH TO DOMINATE WITH WESTERLY
FLOW...AND PERHAPS STILL JUST ENOUGH MOISTURE TO SNEAK OUT SOME
SPRINKLES OR FLURRIES IN THE FAR WEST AT TIMES.  HAVE LOWERED POPS
TUESDAY TO ONLY SLIGHT CHANCE IN FAR WEST...AND DECIDED TO TAKE OUT
COMPLETELY FOR WED GIVEN MODEL AGREEMENT OF DRY HIGH PRESSURE REALLY
PUSHING IN FROM WEST...ALTHOUGH STILL SOME WEAKLY CYCLONIC FLOW AT
MID LEVELS AND LIKELY SOME LOW LEVEL CLOUDS IN WEST IN ADDITION TO
POSSIBILITY OF HIGH LEVEL CLOUDS EVERYWHERE.

MOST LIKELY DRY INTO THURSDAY AS WELL...BUT ECMWF ADVERTISING SOME
BETTER ENERGY ONCE AGAIN TRYING TO PUSH INTO THE SFC RIDGE LATE IN
THE WEEK...LATEST 12Z RUN SLOWED THIS DOWN A BIT...SO HAVE LEFT POPS
OUT FOR NOW UNTIL PERHAPS OVERNIGHT...AND THEN WILL HAVE TO SEE WHAT
FUTURE RUNS DO WITH THIS BY NEXT FRIDAY.

GRADUAL COOLING TREND THROUGH THIS PERIOD DUE TO BROAD BUT RATHER
FLAT UPPER TROUGH AND ASSOCIATED LARGE SFC HIGH FROM CENTRAL U.S.
SHIFTING TOWARD APPALACHIANS...AND TEMPS WILL END UP PRETTY CLOSE TO
SEASONAL NORMS BY MID WEEK. BOTTOM LINE IS NO MAJOR WINTRY WEATHER
TO DEAL WITH THROUGH NEW YEARS DAY.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
AS OF 555 PM EST THURSDAY...

LOW LEVEL MOISTURE UNDER THE COLD POOL HAS RETREATED NORTH OF THE
AREA THIS EVENING AND NOT EXPECTING MUCH IN THE WAY OF ADDED CLOUD
COVER OVERNIGHT GIVEN DRY ADVECTION IN PLACE. THIS COMBINED WITH
HIGH PRESSURE BUILDING OVERHEAD SHOULD PROVIDE FOR WIDESPREAD VFR
TONIGHT UNDER LIGHT WINDS. CANT COMPLETELY RULE OUT SOME SPOTTY
FOG LATE...MAINLY IN THE RIVER BOTTOMS NEAR THE AIRPORTS AND
ESPCLY OVER THE EAST GIVEN THE WET GROUND FROM RAINFALL ON
WEDNESDAY. LATEST MODELS SHOW A GRADUAL LOWERING OF DEWPOINTS AS
WELL OVERNIGHT...BUT GIVEN FAVORABLE FORECAST FOG STABILITY VALUES
WILL KEEP SOME REDUCED BUT BRIEF VFR/MVFR VSBYS IN SPOTS AT TIMES
TOWARD DAYBREAK.

HIGH SLIDES TO THE EAST FRIDAY ALLOWING A WEAK RETURN SW FLOW TO
DEVELOP BY AFTERNOON. HOWEVER OTHER THAN FOR SOME SHEARED WARM
ADVECTION MID/HIGH CLOUDS THE COLUMN REMAINS QUITE DRY SO
CONTINUED GOOD FLYING CONDITIONS FOR FRIDAY INTO FRIDAY NIGHT.

EXTENDED DISCUSSION...

ANOTHER COLD FRONT WILL APPROACH THE REGION SATURDAY AND BE OVER
OR JUST WEST OF THE AREA SUNDAY. THIS MAY ALLOW MULTIPLE WEAK
WAVES OF LOW PRESSURE TO RIDE UP THE BOUNDARY AND ACROSS THE
REGION LATER SATURDAY NIGHT/SUNDAY RESULTING IN PERIODS OF SUB-
VFR IN LOWER CIGS/RAIN. BOUNDARY MAY LINGER OVER OR JUST SOUTH OF
THE AREA EARLY NEXT WEEK PENDING FUTURE PROGRESS OF THIS SLOW
MOVING SYSTEM BY THEN. THIS COULD LEAVE SOME DEGREE OF MOISTURE
INCLUDING MVFR CIGS OVER THE TAF SITES INTO AT LEAST MONDAY OR
MONDAY NIGHT BEFORE PERHAPS SEEING SOME IMPROVEMENT TO VFR ON
TUESDAY.

&&

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

&&

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



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