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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 312340
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
740 PM EDT THU JUL 31 2014

.SYNOPSIS...
AN UPPER TROUGH OF LOW PRESSURE WILL CONTINUE TO RETROGRADE WEST
TO THE MISSISSIPPI RIVER VALLEY...AND THE CENTER OF SURFACE HIGH
PRESSURE WILL SHIFT TO OUR EAST INTO FRIDAY. THIS WILL RESULT IN A
RETURN OF MOISTURE TO THE REGION ALONG WITH INCREASING CHANCES OF
SHOWERS AND THUNDERSTORMS THIS EVENING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF 600 PM EDT THURSDAY...

SHOWERS AND ISOLATED TSRA SPREAD FROM SRN WV INTO THE MTN EMPIRE
EAST TOWARD THE NRV...THEN SPREADING NEWD ACROSS THE NC/VA
FOOTHILLS AND PIEDMONT. MADE SOME ADJUSTMENTS TO POPS AS COVERAGE
IS MORE SCATTERED OR ISOLATED ATTM. MODEST INSTABILITY RESIDES
ACROSS THE PIEDMONTS WITH SFC LI OF -3 TO -5. OVERALL THOUGH
EXPECT THUNDER THREAT TO BE DIMINISHING THIS EVENING WITH SKIES
SOCKED IN WITH CLOUDS...AND DEPARTING UPPER VORT WHICH IS
PROVIDING SOME LIFT. OTHER FORECAST GRIDS ON TARGET...THOUGH MADE
SOME HOURLY ADJUSTMENTS TO SKY COVER TO ACCOUNT FOR LATEST SAT
TRENDS.

PREVIOUS VALID DISCUSSION...
WINDS ALOFT ARE LIGHT...WHICH WILL MAKE FOR SLOW CELL MOVEMENT
AND THE POSSIBILITY OF LOCALLY HEAVY RAIN DURING THE EVENING.
PRECIP WILL NOT GO AWAY ALTOGETHER AS DEEPER MOISTURE ARRIVES
FROM THE CAROLINA COAST TO INTERACT WITH AN APPROACHING UPPER
LEVEL DISTURBANCE. AS THE DISTURBANCE NEARS FROM THE CENTRAL
MISSISSIPPI RIVER VALLEY...EXPECT RAIN COVERAGE TO INCREASE
AGAIN...WITH HIGHEST RAINFALL CHANCES EXPECTED TOWARD DAWN ACROSS
THE MOUNTAINS AS SOUTHEASTERLY FLOW FORCES THE MOIST AIR INTO THE
HIGHER TERRAIN.

RAINFALL WILL BE WIDESPREAD ON FRIDAY...THOUGH WITH OCCASIONAL
BREAKS...AS THE UPPER LEVEL DISTURBANCE PASSES ACROSS OUR AREA.
WITH HIGH PRESSURE STILL HUGGING THE SURFACE TO CREATE A STABLE
LAYER IN THE ATMOSPHERE...BELIEVE THAT THUNDERSTORMS WILL BE
MAINLY ISOLATED...ALTHOUGH A FEW MAY DEVELOP ABOVE THE HIGH
PRESSURE WEDGE. REGARDLESS...LOCALLY HEAVY RAIN WILL STILL BE
POSSIBLE...WITH AN INCH PER HOUR RATES IN A FEW AREAS ALONG THE
BLUE RIDGE. THAT STATED...MUCH OF OUR AREA HAS BEEN DRY
LATELY...AND THE GROUND IS VERY CAPABLE OF ABSORBING PERIODS OF
HEAVY RAIN. AS SUCH...DO NOT BELIEVE THERE IS A MAJOR CONCERN FOR
MORE THAN ISOLATED MINOR FLOODING THROUGH FRIDAY EVENING.

THE HIGH PRESSURE WEDGE AND RAINFALL WILL ALSO KEEP A CAP ON
HEATING...AND DO NOT SEE FRIDAY AFTERNOON TEMPERATURES WARMING
MUCH...ESPECIALLY ACROSS THE NORTH CAROLINA MOUNTAINS WHERE THE
CHANGE IN TEMPERATURES FROM EARLY MORNING LOWS MAY BE ONLY 2 TO 4
DEGREES. AS SUCH...MAY WANT TO KEEP A LIGHT JACKET HANDY AS HIGHS
RANGE FROM THE MID 60S TO THE MID 70S AREAWIDE.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
AS OF 315 PM EDT THURSDAY...

SHORT WAVE DIGS DOWN THE WEST SIDE OF THE UPPER TROF FRIDAY NIGHT
AND SATURDAY OVER THE OHIO VALLEY. MODELS BRING THE BEST VORTICITY
ADVECTION WITH THIS FEATURE INTO THE COUNTY WARNING ON SUNDAY.

THERE SHOULD BE A BRIEF BREAK IN THE INTENSITY AND AREAL COVERAGE OF
THE PRECIPITATION ON FRIDAY NIGHT AND SATURDAY. THEN THE PROBABILITY
OF PRECIPITATION INCREASES AGAIN FOR SATURDAY NIGHT AND SUNDAY.
MODELS SHOWING BEST UPPER DIFFLUENCE AND JET SUPPORT LATE SATURDAY
INTO SUNDAY TOO. LARGEST PRECIPITATION AMOUNTS WILL BE GREATLY
INFLUENCED BY THE AMOUNT...OF LACK OF...UPSLOPE...EFFICIENT RAIN
PROCESSES WITH HIGH PRECIPITABLE WATER VALUES AND THE IMPACT OF THE
COAST FRONT AND PRECIPITATION ALONG THAT BOUNDARY.

BUFKIT AND MIXED LAYER LIFTED INDEX SHOWED A STABLE LAYER NEAR THE
SURFACE ON FRIDAY NIGHT THEN BETTER INSTABILITY ON SATURDAY. IN-SITU
WEDGE IS NOT AS PRONOUNCED BY THEN AND GFS SHOWED SOME INSTABILITY
BY SATURDAY AFTERNOON. ENOUGH TO KEEP THUNDER IN FOR SATURDAY
AFTERNOON AND AGAIN ON SUNDAY.

LITTLE CHANGE IN THE AIR MASS THIS TIME FRAME WITH 850 MB
TEMPERATURES FROM +14 TO +16 AND PRECIPITABLE WATER VALUES AS HIGH
AS 2.0 INCHES IN THE FAR SOUTHEAST COUNTY WARNING AREA ON SUNDAY.
NOTHING EXTREME SO GUIDANCE WILL HAVE A GOOD HANDLE ON HIGHS AND
LOWS.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 330 PM EDT THURSDAY...

MONDAY THROUGH WEDNESDAY THE TROFFING IN THE EAST FLATTENS. A
SURFACE COLD FRONT COMES SOUTH THROUGH NEW ENGLAND MONDAY
TUESDAY...BUT WILL ONLY MOVE SO FAR SOUTH WITH THE BOUNDARY PARALLEL
TO THE UPPER FLOW.

THIS WILL KEEP THE FORECAST AREA ON THE WARM UNSTABLE AIR MASS ON
THE SOUTH SIDE OF THE FRONT THROUGH THURSDAY. DEEPEST MOISTURE AND
BEST LIFT WILL BE FOCUSED ALONG THE COAST FRONT ACROSS THE CAROLINAS
AND GEORGIA. NOT SEEING ANY ORGANIZED FORCING FOR THE COUNTY WARNING
AREA.

TEMPERATURES WILL BE NEAR NORMAL THROUGH THE PERIOD.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 730 PM EDT THURSDAY...

COMPLICATED FORECAST FOR AVIATION GIVEN VARIANCE IN SHOWERS THIS
EVENING. OVERALL...NOT LOOKING GOOD FOR FLYING AS WE HEAD INTO
OVERNIGHT AND FRIDAY AS ALL MODELS IN GOOD AGREEMENT ON
SHOWERS...HEAVY AT TIMES TO MOVE ACROSS...BUT SEEMS THE BULLSEYE
IS OVER THE NC MTNS INTO FAR SW VA. THE PATTERN FAVORS BCB/ROA FOR
HEAVIER PRECIP. STILL WITH MOISTURE IN OVERRUNNING SITUATION...THE
CIGS WILL DROP TO MVFR/IFR BY 12Z FRIDAY AND THEN AFTER...MODELS
DISAGREE ON EXTENT OF LOWER CIGS. THE 18Z NAM IS KEEPING CIGS SUB
1KFT AT MOST TAF SITES WHILE THE GFS SHOWS VFR RETURNING IN THE
AFTERNOON WITH SCATTERED CONVECTION. LEANED INTO
BETWEEN...ESPECIALLY IN THE EAST. HENCE A LOW CONFIDENCE FORECAST
AFTER MID MORNING TOMORROW.

THINK SHORTWAVE PASSES BY ENOUGH LATE IN THE DAY SO THAT SHOWERS
POSSIBLY TAPER OFF AND END IN THE MTNS....BUT WILL NOT FORECAST
THIS YET...BASED ON MODEL DIFFERENCES.

EXTENDED AVIATION DISCUSSION...
THE BROAD UPPER TROUGH OF LOW PRESSURE WILL LINGER ACROSS THE
EASTERN UNITED STATES THROUGH SUNDAY CONTINUING TO RETROGRADE
FROM THE EASTERN/CENTRAL GREAT LAKES TO THE WESTERN GREAT LAKES BY
THE WEEKEND.

FOR SATURDAY AND SUNDAY...THE AIR MASS WILL SLOWLY BECOME WARMER
AND MORE UNSTABLE. SCT SHRA/TSRA EXPECTED AGAIN SATURDAY WITH
ONLY LIMITED INSTABILITY EVIDENT. FOR SUNDAY...BETTER CHANCE OF
TSRA WITH BETTER INSTABILITY ACROSS MUCH OF THE CWA...SW FLOW
ALOFT...AND INCREASING MOISTURE LEVELS. THUS...BRIEF PERIODS OF
MVFR-IFR CIGS/VSBYS EXPECTED IN SHRA/TSRA SATURDAY AND MORE
LIKELY SUNDAY AFTERNOON. SOME DRYING WITH A RETURN TO OVERALL VFR
POSSIBLE MONDAY INTO TUESDAY AS ANOTHER WEAK COOL FRONT SWEEPS IN
FROM THE NW AND TAKES MOST MOISTURE TO THE SE OF THE REGION.
-- End Changed Discussion --

&&

.EQUIPMENT...
THE NOAA WEATHER RADIO AT WYTHEVILLE VA...WZ2500...BROADCASTING
ON A FREQUENCY OF 162.450 MHZ...IS OFF THE AIR. TECHNICIANS ARE
WAITING ON DELIVERY OF PARTS TO MAKE REPAIRS. THE EARLIEST THE
RADIO WILL BE WORKING AGAIN IS FRIDAY.

&&

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

&&

$$
SYNOPSIS...NF
NEAR TERM...NF/WP
SHORT TERM...AMS
LONG TERM...AMS
AVIATION...NF/WP
EQUIPMENT...DS