Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 131954 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 354 PM EDT SAT SEP 13 2014 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH SUNDAY/...
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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 /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
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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.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/... AS OF 100 PM EDT SATURDAY... WEAK SFC FRONT CONTINUES TO PUSH THROUGH THE AREA AS HIGH PRESSURE BUILDING INTO THE OHIO VALLEY FLOPS OVER THE TOP OF US THROUGH TOMORROW. THIS WILL GIVE US A BIT OF NW FLOW WEATHER EARLY...WITH WINDS ONCE AGAIN BECOMING E/NELY AND SOME MOISTURE RETURN ALONG THE BLUE RIDGE. EAST OF THE BLUE RIDGE FOR KLYH AND KDAN...EXPECT CIGS TO RISE AOA VFR LEVELS DURING THE FIRST PART OF THE TAF PERIOD WITH KDAN TAKING THE LONGEST. OVERNIGHT NELY FLOW RETURNS BUT INDICATIONS ARE THAT LOWER CIGS WILL SKIRT THE AREA. WILL GO OPTIMISTIC AND INDICATE ONLY VFR BUT KDAN STANDS THE BETTER CHANCE OF SEEING SOME MVFR CIGS OVERNIGHT. ALONG THE BLUE RIDGE FOR KBCB AND KROA...EXPECTING SOME IMPROVEMENT TO VFR THIS AFTERNOON. BUT AS LIGHT WIND BECOMES E/NELY MOISTURE RUNNING UP THE SLOPES WILL LIKELY GENERATE A RETURN TO LOWER CIGS. KBCB MAY ALSO SEE SOME DRIZZLE AND -SHRA AS THE MOISTURE LOOKS TO BE GREATER HERE AND WILL COMBINE WITH SOME WAA ALOFT TO SQUEEZE OUT SOME PCPN. WEST OF THE BLUE RIDGE...EXPECT KBLF TO STAY LOCKED INTO LOW CIGS WITH A SLIGHT LIFT FROM IFR TO MVFR THIS EVENING BEFORE GOING BACK TO IFR AS DEEPER MOISTURE AND PREVIOUSLY MENTIONED WAA ARRIVE. KLWB MAY SCATTER OUT THIS EVENING...LEADING TO THE QUESTION OF HOW MUCH RADIATION CAN TAKE PLACE TO GENERATE FOG/STRATUS. IT SEEMS LIGHT NE FLOW WILL ENTER KLWB DURING PRIME FOG TIME SO THIS MAY KEEP THINGS FROM BOTTOMING OUT. WILL INDICATE THIS BUT THE SITUATION COULD GO EITHER WAY. EXTENDED AVIATION DISCUSSION... BUT OVERALL CONDITIONS SHOULD BE MOSTLY MVFR...WITH LESS IFR OR WORSE CIGS/VSBYS. 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 SHORT TERM...PH LONG TERM...PH AVIATION...MBS

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