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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 250558
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
158 AM EDT FRI JUL 25 2014

.SYNOPSIS...
A COLD FRONT WILL DROP SOUTHEAST OF THE AREA OVERNIGHT WITH HIGH
PRESSURE BUILDING IN ON FRIDAY. A DEVELOPING TROUGH OVER THE
MIDWEST WILL ALLOW SEVERAL UPPER DISTURBANCES TO POSSIBLY AFFECT
THE AREA OVER THE WEEKEND FOLLOWED BY A STRONG COLD FRONT LATER
MONDAY.

&&

.NEAR TERM /THROUGH TODAY/...
-- Changed Discussion --
AS OF 130 AM EDT FRIDAY...

UPDATE AS SHOWERS...SOME HEAVY ARE POPPING UP IN/AROUND ROANOKE.
MESOANALYSIS SUGGEST DEEP MOISTURE CONVERGENCE WITH POOLING OF
SOME HIGHER THETA-E IN THIS AREA. HIGH-RES MODELS SHOWING ISOLATED
SHOWERS AROUND THROUGH MUCH OF THE NIGHT NEAR/EAST OF THE BLUE
RIDGE SO UPPED POPS TO 20ISH TO COVER THIS. PATCHY DRIZZLE ALSO
EXPECTED ALONG AND EITHER SIDE OF THE BLUE RIDGE GIVEN LOW LVL
MOISTURE DEPTH AND SFC FLOW TURNING MORE NE-E.

DRIER AIR IS LAGGING SO HAVE ALSO UPPED DEWPOINTS PER LATEST
TRENDS..

PREVIOUS VALID DISCUSSION...
INCREASING CONCERN THAT LOW CLOUDS WILL LIKELY PERSIST ALL
NIGHT...ESPECIALLY EAST OF THE BLUE RIDGE AND AREAS WHERE LOW
CLOUDS DO NOT PERSIST WILL LIKELY SEE FOG DEVELOPMENT AS DRIER AIR
WILL LIKELY NOT ADVECT SIGNIFICANTLY INTO THE CWA UNTIL AFTER
DAYBREAK FRI. HAVE ADDED SOME PATCHY DENSE FG TO AREAS ALONG THE
BLUE RIDGE.

FRIDAY LOOKS LIKE A DRY DAY WITH LOWER HUMIDITY AS DEWPOINTS DROP
BACK INTO THE UPPER 50S NW AND L/M 60S FAR SE. HIGH TEMPS WILL BE
FAIRLY CLOSE TO MID-JULY NORMALS..RANGING FROM UPPER 70S NW TO M/U
80S SE.
-- End Changed Discussion --

&&

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

MAINLY DRY AND SEASONAL WEATHER EXPECTED FRIDAY NIGHT INTO AT LEAST
SATURDAY MORNING AS WEAK SURFACE HIGH PRESSURE LINGERS OVER
AREA...THEN DRIFTS EAST AND OFFSHORE BY SATURDAY AFTERNOON.

WEAK DISTURBANCE AND ASSOCIATED WARM MOIST ADVECTION IN NORTHERN
STREAM FORECAST TO MOVE EAST THROUGH THE UPPER GREAT LAKES INTO NEW
ENGLAND SATURDAY AFTERNOON INTO SATURDAY EVENING MAY BE CLOSE ENOUGH
TO BLACKSBURG FORECAST AREA TO SUPPORT DEVELOPMENT OF WIDELY
SCATTERED SHOWERS/THUNDERSTORMS MAINLY NORTH OF I64. HOWEVER...
BETTER THREAT FOR EXPANDING AREA OF PRECIPITATION WILL LIKELY BEGIN
TOWARD DAYBREAK SUNDAY CONTINUING INTO SUNDAY NIGHT AS MUCH MORE
FORMIDABLE SHORT WAVE TROF IN ITS WAKE HELPS TO AMPLIFY WHAT WILL
BECOME AN UNUSUALLY STRONG LONG WAVE TROF OVER THE UPPER GREAT LAKES
BY/DURING THE LONG TERM PERIOD.

STRONG WARM MOIST ADVECTION AND INCREASINGLY FAVORABLE JET DYNAMICS
ASSOCIATED WITH THIS SECOND SHORT WAVE SHOULD SUPPORT THE
DEVELOPMENT OF A MORE ORGANIZED CONVECTIVE EVENT...ESPECIALLY DURING
THE TIME OF PEAK HEATING ON SUNDAY AFTERNOON INTO SUNDAY NIGHT.

SOUTHWEST TO WESTERLY WINDS WOULD IMPLY MOST FAVORABLE AREA FOR
SHOWERS/STORMS WOULD BE ACROSS THE WESTERN FLANKS OF THE
APPALACHIANS...WITH A LOWER THREAT EAST OF THE BLUE
RIDGE...MINIMIZED ACROSS SOUTHSIDE VA INTO NORTH CENTRAL NC DUE TO
NEGATIVE INFLUENCE OF DOWNSLOPING...DISPLACEMENT FROM BETTER
DYNAMICS...AND PREFRONTAL STORMS THAT MAY ARRIVE WELL AFTER TIME OF
BEST HEATING ON SUNDAY.

REGARDLESS...SOUTHWESTERLY WINDS IN ADVANCE OF THIS SYSTEM SHOULD
HELP TO ADVECT SOME VERY WARM AIR BACK INTO THE REGION...WITH HIGHS
OVER THE WEEKEND RANGING FROM THE 70S ACROSS THE HIGHEST
ELEVATIONS...TO 90F OR A BIT ABOVE ACROSS MUCH OF THE PIEDMONT.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 330 PM EDT THURSDAY...

LONG TERM PERIOD WILL BE CHARACTERIZED BY UNUSUALLY DEEP LONG WAVE
TROF THAT WILL REMAIN CENTERED OVER THE UPPER GREAT LAKES THROUGHOUT
MUCH OF NEXT WEEK AS SERIES OF SHORT WAVE TROFS HELP TO AMPLIFY THIS
FEATURE.

COLD FRONT EXPECTED TO MOVE INTO AND THROUGH THE MOUNTAINS MONDAY
MORNING...LIKELY PRECEDED AND ACCOMPANIED BY SCATTERED
SHOWERS/THUNDERSTORMS...POSSIBLY LINGERING INTO THE EVENING AS
COOLER AIR ALOFT AND UPSLOPE INCREASES ACROSS THE WESTERN FLANKS OF
THE APPALACHIANS. WITH EARLIER ARRIVAL OF FRONT...AND ASSOCIATED
CLOUDS/THREAT OF PRECIPITATION...DAYTIME HIGHS MAY BE HARD PRESSED
TO REACH THE 70S ACROSS SOME OF THE HIGHER ELEVATIONS...ESPECIALLY
IN WESTERN GREENBRIER COUNTY WV.

EAST OF THE BLUE RIDGE...FRONT NOT LIKELY TO CLEAR THE PIEDMONT
COUNTIES UNTIL MID TO LATE AFTERNOON ON MONDAY. INCREASING SOUTHWEST
TO WESTERLY WINDS AND ASSOCIATED COMPRESSIONAL HEATING...AND BETTER
PREFRONTAL INSOLATION MAY HELP DRIVE TEMPERATURES WELL UP INTO THE
80S BEFORE LEVELING OFF WITH ARRIVAL OF SCATTERED FRONTAL
CLOUDS/SHOWERS.

MUCH OF THE REST OF THE LONG TERM FORECAST APPEARS TO WARRANT
MOSTLY DRY AND COOL CONDITIONS AS SURFACE RIDGE OF HIGH PRESSURE
NOSES INTO AND THEN OVER BLACKSBURG FORECAST AREA. MOST AREAS WILL
REMAIN 5-10F BELOW NORMAL THROUGH THE PERIOD. MANY MOUNTAIN
VALLEYS...ALONG WITH THE HIGHEST RIDGES WILL LIKELY EXPERIENCE AT
LEAST A COUPLE OF NIGHTS WHERE TEMPERATURES FALL INTO THE 40S.

APPROACH OF ANOTHER SHORT WAVE TROF RIDING AROUND THE BASE OF THE
UPPER TROF MAY HELP BACK LOW LEVEL FLOW SUFFICIENTLY ON THURSDAY TO
WARRANT A LOW CHANCE THREAT FOR SOME SHOWERS ACROSS THE SOUTHWESTERN
MOUNTAIN ON THURSDAY...BUT PRECIPITATION AMOUNTS FROM THIS
DISTURBANCE...IF ANY...APPEAR TO BE SCANT AT BEST.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 140 AM EDT FRIDAY...

AVIATION FORECAST PROVING DIFFICULT THIS MORNING WITH SHRA POPPING
UP IN ROANOKE. CIGS AROUND THE AREA VARY FROM VFR AT
LWB/LYH/BLF...TO IFR AT ROA/DAN. THINK THE OVERALL REGIME THIS
MORNING WILL BE OF MVFR/IFR CIGS AND OCCASIONAL IFR/LIFR FOG.
DRIER AIR SIFTING SE TOWARD SE WV...AND IF THE LEVELS ABOVE THE
BOUNDARY LAYER DRY OUT...FOG AND LOW CLOUDS WILL BE REALIZED AT
BLF/LWB...AS WE ARE ALREADY SEEING THIS JUST WEST TOWARD FAR SW VA
INTO ERN KY. HIGHER DEWPOINTS OUT EAST PLUS HEAVIER RAIN FROM
THURSDAY WILL KEEP/BRING CIGS UNDER 1KFT THIS MORNING. SAME FOR
ROANOKE. BCB IS IFFY BUT WE HAD SHOWERS...SO VARIABLY IFR TO MVFR
HERE. CONFIDENCE HIGH ON SUB VFR CONDITIONS THIS MORNING BUT LOW
ON VSBYS/CIGS.

SFC HIGH OVER THE MID ATLANTIC/OHIO VALLEY SHIFTS SE OVERHEAD. MAY
BE A CASE WHERE CLOUDS STAY STUCK UNDER INVERSION LONGER WITH LACK
OF MIXING. DRIER AIR WILL TRY TO WORK IN LATE MORNING/AFTERNOON
WITH VFR EXPECTED THOUGH SOME LOW LVL MOISTURE REMAINS STUCK
ACROSS DAN-TNB CORRIDOR...SO COULD SEE SOME BKN HIGH END MVFR CIGS
HERE...LOWER IN THE MTNS...AND PERHAPS AS FAR NORTH AS BCB.
CONFIDENCE IS NOT HIGH THOUGH SO KEPT VFR FOR NOW. MODELS ALSO
SHOWING SOME SHRA DEVELOPMENT ACROSS THE SRN BLUE RIDGE AND
POTENTIALLY UP TO BCB/BLF. AGAIN THINK DRY AIR ALOFT WILL KEEP
THIS SITUATED SOUTH OF BLF/BCB/DAN.



EXTENDED AVIATION DISCUSSION...

EXPECT MAINLY VFR THROUGH SUNDAY EXCEPT FOR OVERNIGHT FOG IN THE
VLYS OF LWB/BCB. ANOTHER FRONT IS GOING TO ARRIVE BY MONDAY.
BEFORE THIS SEVERAL DISTURBANCES IN NW FLOW ALOFT MAY BRING
SHRA/TSRA TO THE BLF/LWB CORRIDOR. SATURDAY IS LESS LIKELY AS
MODELS FAVOR A NWD TREND IN CONVECTION TOWARD PA/NRN VA. SUNDAY
COULD BE MORE FAVORABLE...BUT STILL LOOKS LIKE A NWD TRACK. WILL
HAVE TO WATCH HOW THIS DEVELOPS...BUT POTENTIAL FOR SUB VFR
SHRA/TSRA IN THE MTNS IS POSSIBLE LATE THIS WEEKEND. BETTER THREAT
WILL BE WITH THE FRONT MONDAY WITH UPPER TROUGH MOVING ACROSS BY
TUESDAY DRYING THINGS OUT.
-- End Changed Discussion --

&&

.HYDROLOGY...
-- Changed Discussion --
AS OF 330 PM EDT THURSDAY...

U.S. DROUGHT MONITOR ISSUED THIS MORNING AND VALID THROUGH 12Z
TUESDAY JULY 22 SHOWED EXPANSION OF THE EXISTING ABNORMALLY DRY
CONDITIONS INTO MOST OF OUR SE WV COUNTIES AND FAR WESTERN
VA...MAINLY THE UPPER JAMES RIVER BASIN. 30-DAY RAINFALL DEFICITS
IN MUCH OF THIS AREA ARE RUNNING 2 TO 3 INCHES OR ONLY 25 TO 50
PERCENT OF NORMAL AND 60-DAY RAINFALL NUMBERS NOT MUCH BETTER.
JULY IS CLIMATOLOGICALLY THE WETTEST MONTH IN OUR CWA WITH AN
AVERAGE RANGING FROM 4 TO 5 INCHES.
-- End Changed Discussion --

&&

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

&&

$$
SYNOPSIS...PC
NEAR TERM...PC/RAB/WP
SHORT TERM...WERT
LONG TERM...WERT
AVIATION...PC/WP
HYDROLOGY...PC