Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 300809
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
409 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 /08Z WEDNESDAY THROUGH SUNDAY/...
AS OF 100 AM EDT WEDNESDAY...

PATCHY SHOWERS JUST SOUTH/SE OF KDAN SHOULD FINALLY EXIT IN THE
NEXT HOUR OR TWO LEAVING MAINLY VFR CIGS EAST OF THE BLUE RIDGE
AND SCATTERED CLOUDS OVER THE WEST. COULD SEE KDAN DROP DOWN TO
HIGH END MVFR FOR A FEW HOURS BEFORE SUNRISE OTRW KEEPING CIGS
MAINLY IN THE 4-7K FT RANGE FROM KROA EAST OVERNIGHT. WEAK WAVE
ALOFT RESPONSIBLE FOR THE SHOWERS AND CLOUDS SHOULD FINALLY KICK
OUT BY EARLY WEDNESDAY ALLOWING MORE CLEARING ESPCLY WEST BY DAWN.
THIS MAY LEAD TO PATCHY VALLEY FOG GIVEN GOOD RADIATIONAL
CONDITIONS WITH MVFR POSSIBLE AT KLWB/KBCB AND AN OUTSIDE CHANCE
OF SEEING IFR AT KLWB. HOWEVER LOWER CIGS AT KBLF AND KLWB LOOK
LESS LIKELY NOW WITH ANY LOW CIGS LIKELY DUE TO FOG/STRATUS
FORMATION LATE.

UPPER TROUGH UNDERCUT BY WEAK SURFACE HIGH PRESSURE WILL REMAIN IN
PLACE WEDNESDAY WITH SCATTERED CU/AC EARLY INCREASING TO BKN 4-6K
FT CLOUD BASES MOST SPOTS WITH HEATING. AN ISOLATED SHRA WILL BE
POSSIBLE MAINLY WESTERN THIRD GIVEN THE APPROACH OF ANOTHER WAVE
FROM THE NW BUT TOO IFFY TO INCLUDE ANY MENTION. OTRW KEEPING IT
VFR FROM MID MORNING ON WITH GOOD FLYING CONDITIONS LINGERING INTO
WEDNESDAY NIGHT WITH ANY CIGS LIKELY TO FADE WITH LOSS OF HEATING.

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...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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