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[Printable]
780
FXUS61 KRNK 301703
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
103 PM 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 1250 PM EDT WEDNESDAY...

VIA LAPS DATA...WEAK INSTABILITY IS STARTING TO DEVELOP ON THE
SOUTHEAST EDGE OF THE FORECAST AREA...SOUTH INTO CENTRAL NORTH
CAROLINA...WITHIN THE REGION WHERE HIGHER DEW POINT AIR...UPPER
50S TO AROUND 60...WAS STARTING TO WORK ITS WAY BACK INTO THE
REGION ON LIGHT EASTERLY WINDS. ANOTHER AREA OF INSTABILITY WAS
JUST WEST OF THE NORTHWEST PART OF THE FORECAST AREA IN CENTRAL
WEST VIRGINIA. BOTH THE LATEST OUTPUT FROM THE HRRR AND RNK WRF-
ARW MODELS SHOW THESE REGIONS OF THE FORECAST AREA GAINING
INCREASED INSTABILITY THROUGH THE AFTERNOON WITH ISOLATED SHOWERS
DEVELOPING. ENOUGH INSTABILITY MAY YIELD A THUNDERSTORM OR TWO
ACROSS THE FAR SOUTHEAST PARTS OF THE REGION. THERE
ALSO...ALTHOUGH NOT AS ROBUST ALONG THE FAR NW AND SE PARTS OF THE
REGION...SOME WEAK INDICATION THAT SOME ISOLATED SHOWERS MAY BE
POSSIBLE ALONG AND NEAR THE CREST OF THE BLUE RIDGE THIS
AFTERNOON.

HAVE MADE ADJUSTMENTS DOWNWARDS TWO OR THREE DEGREES THE FORECAST
HIGH TEMPERATURE FOR MUCH OF THE AREA. OUR ONGOING FORECAST HAD
BEEN RUNNING A BIT WARM COMPARED TO REALITY. HAVE ALSO INCREASED
DEW POINTS A BIT ACROSS THE SOUTHEAST PART OF THE AREA BASED UPON
THE LATEST OBSERVATIONS AND EXPECTED TRENDS THROUGH THE AFTERNOON.

AS OF 955 AM EDT WEDNESDAY...

VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS WERE STILL
INDICATING POCKETS OF LIGHT FOG THIS MORNING OVER PARTS OF THE
REGION. THE GREATEST CONCENTRATION WAS IN THE GREENBRIER VALLEY.
THE TREND HAS BEEN FOR A QUICK DISSIPATION...AND THIS IS EXPECTED
TO CONTINUE SO THAT LITTLE IF ANY FOG IS EXPECTED TO REMAIN BY
1100 AM. NO MAJOR ADJUSTMENTS TO THE FORECAST AT THIS TIME. STILL
ANTICIPATE THE DEVELOPMENT OF ISOLATED SHOWERS THIS
AFTERNOON...ESPECIALLY ACROSS THE NORTHERN QUARTER OF THE FORECAST
AREA...AND POTENTIALLY SOUTH ALONG THE SPINE OF THE BLUE RIDGE. A
MORE ROBUST AREA OF CONVECTION MAY APPROACH THE REGION FROM THE
NORTH TOWARD THE EARLY EVENING. HAVE TWEAKED HOURLY TEMPERATURE...DEW
POINT...WIND AND SKY COVER GRIDS TO REFLECT THE LATEST
OBSERVATIONS AND ANTICIPATED TRENDS INTO THE EARLY AFTERNOON.

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 IMPULSE 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 /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 100 PM EDT WEDNESDAY...

HIGH CONFIDENCE IN LIGHT WINDS THROUGH THE TAF PERIOD.
MED/HIGH CONFIDENCE VFR EAST OF THE BLUE RIDGE.
MEDIUM CONFIDENCE VFR YIELDING TO MVFR/IFR IN FOG/STRATUS TONIGHT
WEST OF THE BLUE RIDGE.

WEATHER THIS TAF PERIOD SHOULD BE QUITE SIMILAR TO WHAT WE HAD
YESTERDAY AS ENERGY ROTATES AROUND THE UPPER TROF AND COMBINES
WITH INSTABILITY IN THE COLD POOL OF AIR TO PRODUCE A GOOD CU FIELD
AND SOME ISOLATED SHOWERS...ESPECIALLY FROM THE BLUE RIDGE WESTWARD.
BELIEVE THE CU WILL BE A VFR SCT V BKN TYPE SITUATION. WILL LEAN
OPTIMISTIC AND KEEP SCT EXCEPT FOR KBLF/KLWB WHERE BKN WILL BE
MORE LIKELY DUE TO PROXIMITY TO SHORT WAVE ENERGY. WILL ALSO KEEP
TAFS DRY SINCE EXTENT OF ANY SHOWERS WILL BE QUITE LIMITED.

EXPECTING ANOTHER ROUND OF MVFR/IFR FOG AND STRATUS OVERNIGHT FOR
KLWB/KBLF/KBCB BUT IF CU/SC CLOUD DECK LINGERS IT MAY DELAY ONSET
AND ULTIMATELY LIMIT EXTENT OF FOG/STRATUS. WILL CHOOSE TO GO WITH
QUICKER CU/SC DISSIPATION THIS EVE/TONIGHT AND MORE AGGRESSIVE
FOG/STRATUS OVERNIGHT. MOISTURE WILL BE ON THE INCREASE FROM THE SOUTH
TOMORROW AS MORE SHORT WAVE ENERGY ROUNDS THE BASE OF THE UPPER TROF
BUT ANY SIGNIFICANT AFFECTS LOOK TO BE BEYOND THIS TAF ISSUANCE.

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 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. TECHNICIANS ARE WORKING ON THE PROBLEM.

&&

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

&&

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




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