Area Forecast Discussion
Issued by NWS Blacksburg, VA

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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/...
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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.
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&& .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/...
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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.
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&& .HYDROLOGY...
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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.
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&& .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

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