Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 140518 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 118 AM EDT SUN SEP 14 2014 .SYNOPSIS... HIGH PRESSURE WILL PASS FROM THE GREAT LAKES TO NEW ENGLAND TONIGHT...AND THEN BUILD SWEETHEART ACROSS THE MID ATLANTIC FOR SUNDAY. WARMER WEATHER RETURNS FOR MONDAY AS HIGH PRESSURE MOVES OFFSHORE...ALLOWING WINDS TO SHIFT SOUTHWESTERLY. THE NEXT COLD FRONT MOVES THROUGH EARLY TUESDAY MORNING BRINGING COOLER THAN NORMAL TEMPERATURES FOR THE REMAINDER OF THE WEEK. && .NEAR TERM /THROUGH TODAY/...
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AS OF 115 AM EDT SUNDAY... UPDATED TO ADD SLIGHT CHC POPS FOR SHOWERS ACROSS FAR SW AND INCREASING WEDGE AND CLOUDINESS WITH NE LOW LEVELFLOW ACROSS MUCH OF THE EASTERN PORTION OF THE AREA. ADDED SOME PATCHY FOG IN OVERNIGHT AS WELL TO PARTS OF THE WEST GIVEN CLEARING SKIES EARLIER AND OBS AT BLF AND JFZ. PREV DISCUSSION AS OF 930 PM EDT SATURDAY... UPDATE PRIMARILY FOR TEMPERATURES AND DEW POINTS. SOME MOUNTAIN TEMPERATURES ALREADY AT FORECASTED LOWS FOR THE NIGHT...THEREFORE LOWERED ANOTHER CATEGORY. DEW POINTS ALSO DROPPING OFF QUICKLY AS DRY AIR RUSHED IN. GOOD NIGHT TO SHUT OFF THE AIR CONDITIONER AND OPEN WINDOWS. AS OF 700 PM EDT SATURDAY... A COLD FRONT HAS PUSHED SOUTH OF THE AREA AND INTO THE CAROLINAS THIS EVENING. A STRONGER THAN EXPECTED NORTHWEST FLOW IS HELPING TO SCOUR CLOUDS WHILE DEW POINTS ARE DROPPING INTO THE 50S. AT HSP...THE DEW POINT WAS AT 39F AT 700 PM. EXPECTING WINDS TO STAY UP FOR A FEW MORE HOURS AND CONTINUE TO MIX THIS DRIER AIR TO THE LOWER LEVELS. DRY HIGH PRESSURE WILL CONTINUE TO EDGE SOUTHWARD...TURNING SURFACE WINDS TO THE NORTHEAST OVERNIGHT AND INTO SUNDAY MORNING. MOISTURE TRAPPED IN THE BOUNDARY LAYER MAY CREATE A VEIL OF CLOUDS OVER THE AREA THROUGH THE MORNING. MODELS...ESPECIALLY THE NAM...BRINGING LIGHT RAIN AND DRIZZLE INTO THE AREA EARLY SUNDAY MORNING...THEN PASSING SHOWERS THROUGH THE AFTERNOON. WITH THE SURGE OF THE FRONT INTO THE CAROLINAS LATE THIS AFTERNOON...DO NOT THINK MODELS ARE HANDLING THE SITUATION VERY WELL WITH MORE DRY AIR ENTERING THE FORECAST AREA. THEREFORE...BACKED OFF ON PCPN CHANCES OVERNIGHT. AS OF 345 PM EDT SATURDAY... FORECAST AREA REMAINS IN THE ZONAL FLOW SOUTH OF THE ACTIVE NORTHERN JET STREAM. NO ORGANIZED SYNOPTIC SYSTEMS TONIGHT OR SUNDAY WITH ONLY A SLIGHT COOLING TREND. 850 MB TEMPERATURES DROP INTO THE +10 TO +12 RANGE ON SUNDAY. DRIER AIR SEEN ON WATER VAPOR LOOP MOVES INTO THE NORTHERN COUNTY WARNING AREA TONIGHT. ZONAL FLOW KEEPS MOISTURE...ESPECIALLY BELOW 700 MB...OVER EXTREME SOUTHERN VIRGINIA AND NORTHERN NORTH CAROLINA. WONT SEE MUCH DRYING AT LOW LEVEL EITHER. MODELS KEEP MOISTURE OVER THE MOUNTAINS THROUGH SUNDAY...BUT DO SHOW SOME POSSIBLE DRYING IN THE EAST BY SUNDAY AFTERNOON. AFTER A BRIEF PERIOD OF SURFACE AND LOW LEVEL WEST WINDS TONIGHT...HIGH PRESSURE WILL BUILDING BACK SOUTH DOWN THE EAST COAST SUNDAY. BUFKIT FROM THE NAM/SREF SUGGEST A SHALLOW LAYER OF LOW LEVEL UPSLOPE WINDS...MAINLY BELOW 850 MB...WILL DEVELOP SHORTLY AFTER MIDNIGHT AND CONTINUE THROUGH MIND MORNING. FOR SUNDAY AFTERNOON MODELS VEER SHOWING MOISTURE MOVING BACK NORTH AND A RETURN OF INSTABILITY INTO THE FAR SOUTHWEST COUNTY WARNING AREA. WILL KEEP PROBABILITY OF PRECIPITATION IN THE SOUTHWEST AND REMOVE IN THE SOUTHEAST AND NORTHWEST. LOCAL WRF BRINGS LOWER TO MID 50S SURFACE DEW POINTS INTO THE SOUTHERN COUNTY WARNING AREA BY SUNDAY AFTERNOON. BUT IT HAS GONE DOWN THAT PATH BEFORE. MORE BELIEVABLE WOULD BE DRIER DEW POINTS IN THE NORTH AND A MUCH SMALLER DROP IN THE SOUTH.
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... AS OF 345 PM EDT SATURDAY... WITH WEAK HIGH PRESSURE BUILDING INTO THE AREA SUNDAY NIGHT...ANY LINGERING EVENING PRECIPITATION SHOULD WANE. SKIES WILL REMAIN MOSTLY CLOUDY...WHICH SHOULD KEEP LOW TEMPS WARMER THAN GUIDANCE VALUES. ON MONDAY...OUR FOCUS TURNS TO AN APPROACHING UPPER LEVEL SHORTWAVE THAT WILL MOVE INTO THE GREAT LAKES BY 00Z (8 PM EDT) TUESDAY. IN ADVANCE OF THIS FEATURE...PWAT VALUES VALUES SURGE AND INSTABILITY INCREASES. IN ADDITION...NAM/ECMWF/GFS ALL SHOW A WEAK UPPER LEVEL WAVE PASSING OVER OUR AREA IN ADVANCE OF THE GREAT LAKES WAVE. ALL OF THIS SPELLS SCATTERED SHOWERS AND EVEN A FEW THUNDERSTORMS....ESPECIALLY ACROSS THE SOUTHERN BLUE RIDGE WHERE LOW LEVEL CONVERGENCE WILL BE THE GREATEST. DESPITE A PARTLY SUNNY SKY...PUSHED HIGHS UP A COUPLE OF DEGREES WITH GOOD WAA IN ADVANCE OF THE APPROACHING SYSTEM. HIGHEST POPS DURING THE SHORT TERM PERIOD WILL BE MONDAY NIGHT...ASSOCIATED WITH THE COLD FRONT THAT MOVES THROUGH OUR AREA. PRECIP WILL ALSO BE AIDED BY UPPER LEVEL SUPPORT IN THE FORM OF RR QUAD OF DEPARTING UPPER LEVEL JET. THE NAM WAS CONSIDERABLY SLOWER COMPARED TO THE SREF/GFS/ECMWF AND WAS NOT USED. NORTHWEST WINDS BEHIND THE FRONT WILL GENERATE A FEW UPSLOPE SHOWERS IN SE WV EARLY...BUT A LARGE MAJORITY OF THE FORECAST AREA WILL BE DRY ON TUESDAY. COLD AIR WILL BE LACKING BEHIND THIS FRONT...AND WITH DOWNSLOPING WINDS FOR THE EASTERN PORTION OF OUR FORECAST AREA...PUSHED HIGHS UP A COUPLE OF DEGREES EAST OF THE BLUE RIDGE.&& && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 345 PM EDT FRIDAY... MEDIUM RANGE MODELS...AS WELL AS THE GFS/ECMWF MODEL ENSEMBLE MEANS AGREE THAT A BROAD UPPER TROF WILL COVER THE EASTERN U.S. THROUGH THE LONG TERM PERIOD. THERE ARE DIFFERENCES IN THE MODELS...HOWEVER...ON THE AMPLITUDE OF THE TROF. THIS LOOKS TO KEEP A WEDGE OF HIGH PRESSURE IN PLACE THROUGH MUCH OF THE LONG TERM PERIOD...WITH A LOW LEVEL EASTERLY FLOW. AS HIGH PRESSURE BUILDS ON WEDNESDAY...A LOW LEVEL EASTERLY FLOW DEVELOPS...ADVECTING HIGHER THETA-E AIR INTO REGION. LOW LEVEL CONVERGENCE IN THE MOUNTAINS...MAY SPARK SCATTERED SHOWERS. ON THE WEST SIDE OF THE EAST FLOW...ISOLATED THUNDER ALSO BE POSSIBLE. THIS PATTERN CONTINUES ON THURSDAY. TEMPS FOR WEDNESDAY AND THURSDAY WILL BE HIGHLY DEPENDENT ON CLOUD COVER. WITH THE POTENTIAL FOR LOW CLOUDS IN EASTERLY FLOW...TRENDED TOWARD THE COOLER ECMWF GUIDANCE FOR TEMPS DURING THIS PERIOD. ECMWF AND GFS BOTH STRENGTHEN THE WEDGE ON FRIDAY...WHICH WILL BRING COOLER TEMPS TO THE AREA...AND PUSHES MOISTURE SOUTH AND WEST. CONTINUED TO LEAN TOWARD COOLER ECMWF VALUES FOR HIGHS. MODELS HINTS AT ANOTHER UPPER LEVEL SYSTEM MOVING INTO THE REGION EARLY NEXT WEEKEND...THAT WOULD REINFORCE THE UPPER LEVEL TROF OVER OUR AREA. && .AVIATION /05Z SUNDAY THROUGH THURSDAY/... AS OF 700 PM EDT SATURDAY... A COLD FRONT HAS PUSHED SOUTH OF THE AREA AND INTO THE CAROLINAS THIS EVENING. A STRONGER THAN EXPECTED NORTHWEST FLOW IS HELPING TO SCOUR CLOUDS WHILE DEW POINTS ARE DROPPING INTO THE 50S. AT HSP...THE DEW POINT WAS AT 39F AT 700 PM. EXPECTING WINDS TO STAY UP FOR A FEW MORE HOURS AND CONTINUE TO MIX THIS DRIER AIR TO THE LOWER LEVELS. DRY HIGH PRESSURE WILL CONTINUE TO EDGE SOUTHWARD...TURNING SURFACE WINDS TO THE NORTHEAST OVERNIGHT AND INTO SUNDAY MORNING. MOISTURE TRAPPED IN THE BOUNDARY LAYER MAY CREATE A VEIL OF MVFR CLOUDS OVER THE AREA THROUGH THE MORNING...THEN SCOUR TOWARDS THE AFTERNOON. MODELS...ESPECIALLY THE NAM...BRINGING LIGHT RAIN AND DRIZZLE INTO THE AREA EARLY SUNDAY MORNING...THEN PASSING SHOWERS THROUGH THE AFTERNOON. WITH THE SURGE OF THE FRONT INTO THE CAROLINAS LATE THIS AFTERNOON...DO NOT THINK MODELS ARE HANDLING THE SITUATION VERY WELL WITH MORE DRY AIR ENTERING THE FORECAST AREA. THEREFORE...BACKED OFF ON PCPN CHANCES FOR ALL SITES. LOW CONFIDENCE ON CEILINGS HEIGHTS WITH DRY AIR ADVECTING IN...BUT DID RAISE A CATEGORY. LWB WILL LIKELY SEE CLEARING THROUGH THE NIGHT AND THEREFORE WILL HAVE A GOOD CHANCE FOR FOG TO FORM BEFORE SUNRISE. HIGH PRESSURE SKIRTS EASTWARD SUNDAY...BUT WILL CONTINUE TO INFLUENCE THE WEATHER ALONG AND EAST OF THE BLUE RIDGE. WITH LESS INFLUENCE ACROSS THE WEST...A FEW SHOWERS MAY PASS NEAR BLF/LWB DURING THE AFTERNOON. CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE IN THE TAFS. EXTENDED AVIATION DISCUSSION... BEYOND SUNDAY...BROAD UPPER TROUGH DEVELOPING ACROSS THE NORTHERN STATES...WITH THE RNK CWA ON THE SOUTHERN EDGE OF THIS BROAD UPPER TROUGH...LEADING TO PRIMARILY CONTINUED ZONAL FLOW. LATEST MODEL TRENDS BEGINNING TO FAVOR POTENTIAL CHANGE TO A MORE NW FLOW ALOFT AS THE WEEK PROGRESSES...WHICH SHOULD ATTEMPT TO PUSH THE PESKY DEEP MOISTURE FURTHER SOUTH AWAY FROM THE REGION. OVERALL...EXPECT MVFR CONDITIONS TO PERSIST INTO MONDAY AS AFOREMENTIONED UPPER TROUGH BRINGS MORE CLOUDS AND SHOWERS TO THE REGION. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PH NEAR TERM...AMS/RCS/SK SHORT TERM...PH LONG TERM...PH AVIATION...RCS

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