Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 251418 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1018 AM EDT FRI JUL 25 2014 .SYNOPSIS... WEAK HIGH PRESSURE BUILDS SOUTH ACROSS THE AREA TODAY INTO TONIGHT...THEN OFF THE SOUTHEAST COAST SATURDAY. A STRONG COLD FRONT AND UPPER LEVEL TROUGH IMPACTS US BY MONDAY. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1000 AM EDT FRIDAY... ONLY MINOR CHANGES MADE TO GRIDS...MAINLY TO RAISE DEWPOINTS SLIGHTLY AS DRIER AIR FIGHTS TO MOVE SOUTHEAST. PREVIOUS VALID FORECAST... AS OF 330 AM EDT FRIDAY... THE FORECAST DILEMMA TODAY WILL BE THE STRATOCU CURRENTLY OUT THERE AND HOW MUCH LINGERS INTO THIS AFTERNOON AS SFC HIGH BUILDING SOUTH MAY LOCK IT IN ALONG THE BLUE RIDGE WITH SFC FLOW WORKING AROUND TO THE SOUTHEAST AND MODELS FAVORING THETA-E RIDGE IN THE LOW LVLS ACROSS THE SRN BLUE RIDGE. WITH HEATING FROM THE LATE JULY SUN THINK SKIES WILL BECOME MOSTLY SUNNY THIS AFTERNOON...EXCEPT ALONG THE BLUE RIDGE WHERE WILL BE VARYING FROM PARTLY SUNNY TO MOSTLY CLOUDY. THE 00Z NAM IS ACTUALLY SHOWING SOME LIGHT SHRA/TSRA FORMATION IN THE NC MTNS. WILL TAKE THIS SOLUTION BUT NOT AS AGGRESSIVE WITH POPS AND HAVE A TOKEN ISOLATED SHRA/TSRA NEAR BOONE/WEST JEFFERSON THIS AFTERNOON. TONIGHT...CONVECTION IF ANY DISSIPATED WITH WEAK SFC HIGH OVERHEAD. THE ISSUE AGAIN TONIGHT WILL BE IF ANY CLOUDS STAY IN THE MTNS UNDER INVERSION. TAKING THE NAM SOLUTION WILL BE KEEPING THE BLUE RIDGE IN MORE CLOUDS WHILE THE REST OF THE CWA STAYS CLEAR TO PARTLY CLOUDY. SOME HIGH CLOUD WILL BE INCREASING FROM THE NW LATE. DO NOT FORESEE ANY DRIZZLE LATE TONIGHT AS SOUNDING FORECASTS ONLY SHOWING LAYER OF OF MOISTURE 2KFT AROUND BOONE-ROANOKE. ADDED PATCHY FOG IN THE FORECAST GIVEN FLOW TURNING MORE SOUTH...BUT REMAIN LIGHT. AS FOR HIGHS WENT CLOSER TO THE MAV THINKING MORE SUN...AND DRIER AIR ALOFT MAY ALLOW TEMPS TO HEAT UP MORE...BUT STILL A LESS HUMID DAY. HIGHS WILL BE RANGING FROM THE MID TO UPPER 70S MTNS...TO MID 80S PIEDMONT. TONIGHT...TIGHTER GRADIENT BETWEEN HIGHER DEWPOINTS SOUTH AND DRIER AIR NORTH. THINK THE VALLEYS SHOULD DROP TO THE MID TO UPPER 50S WHILE THE SOUTHSIDE VA INTO NC PIEDMONT ONLY FALLS TO THE UPPER 60S.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... AS OF 345 AM EDT FRIDAY... WEAK HIGH PRESSURE WILL PUSH OFF TO THE EAST EARLY SATURDAY...MAKING FOR SUSTAINED SOUTHWESTERLY WIND FLOW IN THE LOW LEVELS THAT WILL CARRY TROPICAL AIR NORTHWARD ALONG THE APPALACHIAN CHAIN. WINDS HIGHER ALOFT WILL BE OUT OF THE WEST NORTHWEST HOWEVER...WHICH WILL RESULT IN A DECENT CAPPING INVERSION ACROSS MOST OF THE AREA. THE INVERSION APPEARS WEAKEST ACROSS THE PIEDMONT...WHERE ISOLATED SHOWERS AND THUNDERSTORMS MAY DEVELOP DURING LATE AFTERNOON/EARLY EVENING AS MAXIMUM DAYTIME HEATING COMBINES WITH A DEVELOPING LEE SIDE TROUGH TO HELP DESTABILIZE THE ATMOSPHERE IN THAT AREA. OUTSIDE OF THAT HOWEVER...EXPECT ABUNDANT SUNSHINE WHICH WILL HELP AFTERNOON TEMPERATURES WARM INTO THE MID TO UPPER 80S ACROSS THE MOUNTAINS... AND INTO THE LOW 90S EAST OF THE BLUE RIDGE. LOOKING INTO EARLY SUNDAY...MODELS ARE PICKING UP ON THE REMNANTS OF A THUNDERSTORM COMPLEX ASSOCIATED WITH AN UPPER LEVEL DISTURBANCE AFFECTING THE INTERSTATE 64 CORRIDOR...WITH SOME RAIN REACHING POSSIBLY AS FAR SOUTH AS HIGHWAY 460. TIMING WILL BE CRITICAL...AS THE LATER IN THE NIGHT THE SYSTEM ARRIVES...THE GREATER THE LOSS OF INSTABILITY AND THEREFORE THE WEAKER THE STORMS. GIVEN THAT THIS ACTIVITY IS EXPECTED TO ARRIVE SHORTLY BEFORE DAWN...BELIEVE THAT THE SEVERE THREAT WILL BE REDUCED...BUT CANNOT RULE OUT SOME GUSTY WINDS. ON SUNDAY EVENING HOWEVER...ANOTHER STRONGER UPPER LEVEL DISTURBANCE IS EXPECTED TO FOLLOW A MORE SOUTHERLY TRACK...APPROACHING FROM THE WESTERN GREAT LAKES THROUGH THE DAY...AND TRIGGER ANOTHER LINE OF THUNDERSTORMS THAT WILL AFFECT OUR AREA DURING THE EVENING. MODELS ARE IN DECENT AGREEMENT THAT WE WILL HAVE 45KTS TO 50KTS OF LOW LEVEL WINDS ENTERING THE CENTRAL APPALACHIANS WITH THE DISTURBANCE...MAKING FOR A DECENT THREAT OF STRONG WINDS AS THE LINE OF THUNDERSTORMS ENTERS THE WESTERN HALF OF OUR AREA. CONFIDENCE IS INCREASING ON THIS SCENARIO. STORMS WILL MOVE ACROSS OUR AREA DURING LATE EVENING...GRADUALLY WEAKENING AS THEY PROCEED EAST IN THE DOWNSLOPE FLOW. A STRONG COLD FRONT WILL ENTER OUR AREA MONDAY MORNING...SHIFTING WINDS NORTHWESTERLY WHICH WILL USHER IN DRIER MORE STABLE AIR. WILL BE CONCERNED MAINLY WITH A FEW UPSLOPE SHOWERS ACROSS THE MOUNTAINS DURING THE DAY...BUT IT IS POSSIBLE A FEW STORMS MAY DEVELOP ACROSS THE PIEDMONT EARLY MONDAY AFTERNOON JUST AHEAD OF THE FRONT. THE COLD FRONT WILL THEN PUSH ANY CONVECTION EAST OF OUR AREA BY LATE AFTERNOON...WITH UNSEASONABLY COOLER AIR BUILDING IN FROM THE NORTHWEST. && .LONG TERM /TUESDAY 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. 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 /14Z FRIDAY THROUGH TUESDAY/... AS OF 730 AM EDT FRIDAY... FOG/LOW CLOUDS DID NOT MATERIALIZE IN TERMINALS WE THOUGHT IT WOULD BUT DID AT TIMES IN DANVILLE. THIS MORNING...SATELLITE/OBS DEPICT IFR CIGS FROM BCB-BLF...WITH VFR/MVFR ELSEWHERE. DEPTH OF MOISTURE APPEARS SHALLOW...AND EXPECT THIS TO LIFT AND THIN OUT THROUGH THE MORNING WHERE ALL SITES WILL BE VFR BY 16-17Z. NOT REALLY SEEING ANY AVIATION ISSUES THIS AFTERNOON AT THE TERMINALS. COULD SEE BKN VFR CIGS NEAR ROA/BCB AND SOUTH INTO THE NC MTNS. ISOLATED SHRA MAY DEVELOP IN THE NC MTNS. TONIGHT...MODELS STILL SHOWING POTENTIAL FOR LOW CLOUDS FORMING NEAR THE BLUE RIDGE. NOT REALLY CONFIDENT THAT TERMINALS WILL GET ANY CIGS SUB VFR. HOWEVER...PATCHY FOG WILL FORM...AS SKIES SHOULD BE MOSTLY CLEAR. WILL TREND LWB DOWN TO TEMPO 1SM WITH ALL BUT ROA/BLF GETTING MVFR/IFR VSBYS. 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. && .HYDROLOGY...
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AS OF 330 PM EDT THURSDAY... RAINFALL YESTERDAY FELL MAINLY EAST OF THE INCREASINGLY DRY AREAS OF THE NEW RIVER VALLEY INTO THE UPPER JAMES BASINS. U.S. DROUGHT MONITOR ISSUED YESTERDAY AND VALID AS OF 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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&& .CLIMATE...
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RAINFALL YESTERDAY (7/24) AT LYNCHBURG AIRPORT OF 3.88 INCHES WAS 2ND HIGHEST ON RECORD AFTER JULY 24 1916 WHEN 4.03 INCHES FELL. IT WAS ALSO THE 2ND HIGHEST FOR ANY JULY DAY. WILL ISSUE PNS (WBCPNSRNK) WITH A FEW MORE DETAILS ON THIS UNUSUAL EVENT.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...WP NEAR TERM...WP SHORT TERM...NF LONG TERM...WERT AVIATION...WP HYDROLOGY...PC CLIMATE...PC

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