Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 301125
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
725 AM EDT WED JUL 30 2014

.SYNOPSIS...
AN UPPER LEVEL TROUGH OF LOW PRESSURE ALONG WITH A COOL AREA OF
SURFACE HIGH PRESSURE WILL REMAIN ACROSS THE REGION TODAY AND
TONIGHT. FROM THURSDAY INTO THE WEEKEND...THE UPPER TROUGH WILL
RETROGRADE WEST TOWARD THE MISSISSIPPI RIVER VALLEY. THIS WILL
ALLOW FOR ATLANTIC MOISTURE TO MAKE ITS WAY BACK INTO THE AREA AND
BRING AN INCREASING THREAT FOR SHOWERS AND STORMS.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 AM EDT WEDNESDAY...

WEAK WESTERLY FLOW UNDER THE 5H TROUGH ALOFT WILL PERSIST OVER THE
NEXT 24 HOURS ALLOWING ADDED WEAK SHORTWAVE ENERGY TO CROSS THE
REGION THROUGH EARLY TONIGHT. INITIAL WAVE CAUSING SHRA OVER THE
FAR SE SHOULD FINALLY EXIT EARLY THIS MORNING LEAVING BEHIND AREAS
OF MID/LOW CLOUDS FROM THE BLUE RIDGE EAST UNDER A RESIDUAL WEAK
SURFACE TROUGH AXIS. EXPECT THIS CLOUD COVER TO FADE TO AN
INCREASING CU FIELD WITH HEATING THIS AFTERNOON WITH FORECAST
RAOBS SHOWING A LAYER OF MOISTURE ALOFT BETWEEN 7H-85H. HOWEVER
APPEARS ENOUGH WEAK SURFACE RIDGING TO KEEP ANY SHRA TO MINIMUM
THROUGH EARLY AFTERNOON BEFORE A MID LEVEL WAVE UNDER THE COLD
POCKET TO THE NW APPROACHES. THIS MAY COMBINE WITH JUST ENOUGH
MOISTURE TO PRODUCE A FEW SHRA NORTH-NW BY MID TO LATE AFTERNOON
ALTHOUGH MODELS REMAIN MEAGER WITH ANY PRECIP AS BASICALLY ONLY
THE NAM SHOWS MUCH DEVELOPMENT. HOWEVER LAPSES WILL BE QUITE STEEP
AND GIVEN THE WEAK FLOW UNDER HEATING APPEARS ENOUGH TO INCLUDE A
20-30 POP GREENBRIER/HIGHLANDS DOWN THE BLUE RIDGE WITH AN
ISOLATED TSRA MENTION MAINLY NORTH. OTRW WILL CALL IT MAINLY PC
FOR INTERVALS OF CLOUDS ESPCLY EARLY...AND AGAIN THIS AFTERNOON
WITH HIGHS MOSTLY 70S MOUNTAINS AND LOW 80S SE PENDING CLOUDS.

ANOTHER IMPUSLE ALOFT SWINGING UNDER THE BASE OF THE 5H COLD POOL
WILL JET EAST CROSSING THE FAR SOUTHERN AREAS THIS EVENING.
MOISTURE AGAIN LIMITED WITH THIS FEATURE ALTHOUGH MAY BE JUST
ENOUGH WEAKNESS AND EARLY EVENING CONVERGENCE PER LOW LEVEL SW
FLOW TO DEVELOP SHRA SE SIMILAR TO TONIGHT. THUS EXTENDED SLIGHT
POPS FARTHER EAST INTO THE PIEDMONT MAINLY BEFORE MIDNIGHT. OTRW
PASSING OF THIS SHORTWAVE SHOULD ALLOW MORE CLEARING MOUNTAINS
WHILE MID DECK MAY AGAIN LINGER PIEDMONT OVERNIGHT AS SEEN VIA
MOST MODEL RH SOLUTIONS ATTM. WILL AGAIN BE QUITE A COOL NIGHT
ESPCLY IF CLEARING DEVELOPS SOONER AND DEWPOINTS DONT RISE TOO
MUCH. HOWEVER BUT MAY HARD PRESSED TO REACH RECORDS AS EXPECT A
BIT MORE VALLEY FOG LATE WITH SLIGHTLY HIGHER MOISTURE LEVELS TO
KEEP READINGS ABOVE RECORDS FOR NOW.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
AS OF 345 AM EDT WEDNESDAY...

THE LARGE UPPER LEVEL TROUGH AFFECTING THE EASTERN HALF OF THE
NATION WITH COOLER THAN AVERAGE TEMPERATURES DURING THE EARLY HALF
OF THE WEEK WILL BEGIN TO AMPLIFY WEST OF THE MISSISSIPPI RIVER ON
THURSDAY. THIS WILL CAUSE WINDS ALOFT TO SHIFT FROM WESTERLY TO
SOUTHWESTERLY...WHICH WILL BEGIN THE PROCESS OF RETURNING TROPICAL
MOISTURE BACK INTO OUR AREA. REGARDLESS...THAT PROCESS WILL TAKE AT
LEAST A DAY...AND EXPECT THURSDAY TO BE MOSTLY DRY...BUT WITH
INCREASING CLOUDS. WITH THE 500MB HEIGHT RISES AS THE TROUGH
RETROGRADES...EXPECT WARMER AFTERNOON TEMPERATURES...WITH HIGHS
RANGING FROM THE MID 80S ACROSS THE SOUTHSIDE...TO THE MID/UPPER 70S
ACROSS THE MOUNTAINS.

AS HIGH PRESSURE IN THE LOW LEVELS CONTINUES TO PUSH OFFSHORE
THURSDAY EVENING...RAIN WILL GRADUALLY WORK ITS WAY NORTH THROUGH
THE CAROLINAS THURSDAY NIGHT...AND EXPECT TO START THE DAY FRIDAY
WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS OUR AREA.
BELIEVE THAT THE MOUNTAINS...ESPECIALLY THE BLUE RIDGE...WILL HAVE
THE HIGHEST RAINFALL CHANCES DUE TO THE SOUTHEASTERLY FLOW AT THE
SURFACE FORCING THE MOISTURE INTO THE HIGHER TERRAIN. AND WITH
PRECIPITABLE WATER VALUES QUICKLY RAMPING UP TO BETTER THAN 1.5
INCHES...BELIEVE THAT THE SHOWERS AND THUNDERSTORMS DURING THE
MORNING AND AFTERNOON WILL BE EFFICIENT RAINFALL PRODUCERS. RAINFALL
WILL DIMINISH FRIDAY NIGHT WITH THE LOSS OF DAYTIME HEATING...BUT DO
NOT EXPECT SHOWERS TO GO AWAY COMPLETELY.

MORE SHOWERS AND THUNDERSTORMS CAN BE EXPECTED ON SATURDAY AREAWIDE
AS THE MID ATLANTIC REMAINS SITUATED IN A PATTERN OF DEEP SOUTHWEST
FLOW ALOFT...CARRYING UPPER LEVEL DISTURBANCES ACROSS THE AREA TO
INTERACT WITH TROPICAL MOISTURE RIDING NORTH ALONG THE APPALACHIAN
CHAIN. RAINFALL AND WIDESPREAD CLOUD COVER WILL KEEP AFTERNOON HIGH
IN THE MID 70S TO LOW 80S...WHILE OVERNIGHT LOWS WILL BE MILD...
FALLING INTO THE UPPER 50S TO THE MID 60S.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 325 PM EDT TUESDAY...

UPPER LOW OVER THE NORTHEAST FLATTENS BY SUNDAY WITH A SHORT WAVE
PASSING NORTH OF THE FORECAST AREA ON SUNDAY. ECMWF SUGGESTS
ANOTHER COLD FRONT WILL APPROACH THE AREA FROM THE NORTH ON TUESDAY
AND POSSIBLY MOVE ALL THE WAY THROUGH THE MID ATLANTIC REGION ON
WEDNESDAY. NOT ALL THE EXTENDED GUIDANCE SUPPORTS A TROF AS
AMPLIFIED AS THE ECMWF SO STILL QUESTIONABLE HOW FAR SOUTH FRONT
WILL ADVANCE.

AHEAD OF THAT FRONT FORECAST AREA STAYS IN TYPICAL AIR MASS FOR
SUMMER WITH NEAR NORMAL TEMPERATURES AND ENOUGH MOISTURE AND
INSTABILITY FOR A DAILY THREAT OF AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 700 AM EDT WEDNESDAY...

PATCHY FOG ACROSS THE DEEPER VALLEY LOCATIONS WILL KEEP BRIEF IFR
TO LIFR CONDITIONS GOING UNTIL AROUND 13Z/9AM AT KLWB/KBCB BEFORE
THE FOG QUICKLY ERODES AND VFR RETURNS. OTRW EXPECTING ANY
LINGERING CLOUDS ELSW TO STAY AT VFR LEVELS EARLY THIS MORNING.

UPPER TROUGH UNDERCUT BY WEAK SURFACE HIGH PRESSURE WILL REMAIN IN
PLACE INTO THIS AFTERNOON WITH SCATTERED CU EARLY DEVELOPING INTO BKN
4-6K FT CLOUD BASES MOST SPOTS WITH HEATING BY MID/LATE AFTERNOON.
AN ISOLATED SHRA WILL BE POSSIBLE MAINLY NORTHWEST THIRD GIVEN THE
APPROACH OF ANOTHER WAVE FROM THE NW BUT TOO IFFY TO INCLUDE ANY
MENTION. ALSO MAY SEE SPOTTY SHOWERS LINGER ALONG AND EAST OF THE
BLUE RIDGE THROUGH LATE EVENING AS ANOTHER IMPULSE PASSES SOUTH. OTRW
KEEPING IT VFR FROM MID MORNING ON WITH GOOD FLYING CONDITIONS
LINGERING INTO TONIGHT WITH ANY CIGS LIKELY TO FADE WITH LOSS OF
HEATING BUT PERHAPS NOT UNTIL AFTER MIDNIGHT IN SPOTS.

SHOULD SEE MORE MVFR TO IFR IN FOG ACROSS THE VALLEYS OVERNIGHT
WITH PERHAPS BOTH KLYH/KDAN SEEING BETTER COVERAGE LATE. APPEARS
KLWB COULD AGAIN DROP TO LIFR AFTER MIDNIGHT IF SKIES CLEAR FAST
ENOUGH.

EXTENDED AVIATION DISCUSSION...

A BROAD TROUGH OF LOW PRESSURE WILL BE ACROSS THE EASTERN UNITED
STATES THROUGH SUNDAY. HOWEVER...IT WILL START CENTERED OVER THE
REGION...AND THEN RETROGRADE WEST TO NEAR THE MISSISSIPPI RIVER BY
SUNDAY. THIS TRANSITION WILL ALLOW FOR BETTER CHANCES OF
SHOWERS...AND PERHAPS A FEW THUNDERSTORMS...TO OCCUR ACROSS THE
REGION AS ATLANTIC MOISTURE WILL BE ABLE TO WORK ITS WAY INTO THE
AREA. APPEARS COVERAGE WILL BE MORE ISOLATED ON THURSDAY WITH
LINGERING OVERALL VFR...THEN INCREASING FROM FRIDAY INTO THE
WEEKEND AS A DEEPER SOUTHERLY TRAJECTORY STARTS TO DEVELOP. ALONG
WITH THIS MOISTURE WILL COME BETTER CHANCES FOR SUB- VFR
CONDITIONS...ESPECIALLY UNDER ANY HEAVIER SHOWER OR STORM THAT
FORMS...BUT ALSO DURING THE OVERNIGHT HOURS AS BOUNDARY LAYER
MOISTURE GETS TRAPPED UNDER THE NOCTURNAL INVERSION.

&&

.CLIMATE...
JULY 30TH RECORD LOWS:

ROANOKE......54...1997
BLUEFIELD....50...1981
DANVILLE.....60...1972/81/83/2013
LEWISBURG....46...2013
LYNCHBURG....52...1997
BLACKSBURG...50...1973/81


JULY 31ST RECORD LOWS:

ROANOKE......49...1914
BLUEFIELD....49...1997
DANVILLE.....55...1966
LEWISBURG....48...1997
LYNCHBURG....49...1997
BLACKSBURG...44...1997

&&

.EQUIPMENT...
THE NOAA WEATHER RADIO AT WYTHEVILLE VA...WZ2500...BROADCASTING
ON A FREQUENCY OF 162.450 MHZ...IS OFF THE AIR...DUE TO PHONE LINE
ISSUES. PHONE COMPANY IS WORKING ON IT. THE RADIO IS NOT EXPECTED
TO BE BACK IN SERVICE ANY SOONER THAN WEDNESDAY MORNING.

&&

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

&&

$$
SYNOPSIS...DS/JH
NEAR TERM...JH
SHORT TERM...NF
LONG TERM...AMS
AVIATION...DS/JH/RAB
CLIMATE...PH
EQUIPMENT...DS


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