Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 160812 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 412 AM EDT TUE SEP 16 2014 .SYNOPSIS...
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A WEAK COLD FRONT WILL PASS ACROSS THE REGION FROM THE NORTHWEST THIS MORNING BEFORE STALLING OVER THE CAROLINAS LATER TODAY AND TONIGHT. WEAK LOW PRESSURE ALONG THE FRONT MAY BRING A FEW SHOWERS INTO TONIGHT BEFORE A COOL WEDGE OF HIGH PRESSURE SETTLES IN FROM THE NORTH EARLY WEDNESDAY. THE HIGH WILL STRENGTHEN TO THE NORTH OF THE REGION THROUGH THE REST OF THE WEEK KEEPING RATHER COOL BUT OVERALL DRY WEATHER IN PLACE.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 250 AM EDT TUESDAY... WEAK COLD FRONT TO THE NW WILL SLIDE INTO THE MOUNTAINS THIS MORNING BEFORE CROSSING THE PIEDMONT BY AFTERNOON. MOISTURE REMAINS LIMITED WITH THE BOUNDARY GIVEN MOST SUPPORT HEADING OFF TO THE NE BUT STILL EXPECT A FEW SHRA BANDS ACROSS THE WESTERN SLOPES EARLY ON PER DECENT WEST/NW TRAJECTORY AND SEEN VIA THE LATEST HRRR. THUS KEEPING A LOW END POP FAR FAR WEST THIS MORNING AND MAINLY CLOUDS ELSW WITH SOME PATCHY FOG AROUND EARLY. MODELS THEN SHOW A WEAK WAVE DEVELOPING ALONG THE FRONT OVER THE CAROLINAS THIS AFTERNOON IN RESPONSE TO PASSING SHORTWAVE ENERGY ALOFT. SOME SOLUTIONS A BIT MORE ROBUST IN DEVELOPING SHOWERS MAINLY NW NC RIDGES EARLY THIS AFTERNOON...AND THEN SPREADING EAST ACROSS SRN VA AND THE REST OF NW NC LATER. THIS PROVIDED ENOUGH HEATING TO DEVELOP SOME INSTABILITY WHILE KEEPING MOISTURE DEEP ENOUGH UNDER DEEP WESTERLY FLOW ALOFT. SINCE APPEARS SHRA RATHER WIDELY SCATTERED IN THIS REGIME...LOWERED POPS SOME THIS AFTERNOON BUT KEPT IN LOW CHANCES MAINLY NW NC AND ISOLATED FARTHER NORTH ALONG THE BLUE RIDGE WHERE GUIDANCE SHOWS SOME WEAK CONVERGENCE ALONG 85H THETA-E RIDGING LATE. KEPT IN A TSRA MENTION AS WELL UNDER THE PASSING WAVE ALOFT OVER THE SW AND WHERE THE BEST FORECAST CAPES OF AROUND 1K J/KG COULD OCCUR. OTRW BECOMING PARTLY SUNNY EXCEPT IN THE WESTERN UPSLOPE AREAS WHERE CLOUDS LIKELY TO HANG IN FOR MOST OF THE DAY. THIS WILL LIKELY MAKE FOR A RANGE IN HIGHS FROM 65-70 SE WEST VA...TO THE MID/UPPER 70S BLUE RIDGE...TO LOW 80S SE GIVEN DOWNSLOPE AND MORE SUN. WEAK HIGH PRESSURE TO SLIDE EAST FROM THE OHIO VALLEY TO THE MID ATLANTIC COAST OVERNIGHT ALLOWING THE LOW LEVEL FLOW TO BECOME MORE EASTERLY FROM NE TO SW AFTER MIDNIGHT. THIS WILL TEND TO LOCK IN ANY RESIDUAL MOISTURE AND GRADUALLY INCREASE LOW LEVEL MOISTURE WITHIN THE DEVELOPING WEDGE ALONG THE BLUE RIDGE IN VIRGINIA. LATEST NAM LOOKS OVERDONE WITH SHOWERS LINGERING BEHIND THE EXITING WAVE ALOFT WITH MORE OF A TRANSITION FROM ISOLATED -SHRA TO MORE DRIZZLE LIKELY LATE. THEREFORE LEFT IN LOW POPS SOUTH/EAST DURING THE EVENING AND THEN INCLUDED POCKETS OF MOSTLY -RA BLUE RIDGE LATE WITH DRIZZLE/FOG INCLUDED. OTRW MORE CLOUDS OVERNIGHT WITH LOWS RATHER CHILLY UNDER THE DEVELOPING ONSHORE FLOW PUTTING MOST IN THE 50S EXCEPT CLOSER TO 60 SE.
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&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
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AS OF 400 AM EDT TUESDAY A SERIES OF WEAK DISTURBANCES WILL TRAVERSE THE REGION IN A PREVAILING NORTHWEST FLOW ALOFT. THE FIRST WILL HAVE PASSED THROUGH THE REGION BY EARLY WED...WITH ANOTHER SLATED FOR THE THU-FRI TIME FRAME. TOWARD THE END OF THE PERIOD INTO THE BEGINNING OF THE LONG TERM PERIOD...AN UPPER RIDGE IS FORECAST TO BUILD NORTHWARD FROM THE GULF COAST STATES. THE AIR MASS WILL BE QUITE STABLE THROUGH THE PERIOD...ESPECIALLY IN LIGHT OF AN OVERWHELMING DOMINANCE MOST OF THE PERIOD OF A MARITIME EASTERLY FLOW WILL YIELD EXTENSIVE PERIODS OF LOW CLOUDS...ESPECIALLY IN UPSLOPE AREAS ALONG THE BLUE RIDGE AND THE ALLEGHANYS. AT TIMES...PRIMARILY DURING THE LATE NIGHT/EARLY MORNING HOURS...THE LOWER ATMOSPHERE SHOULD BECOME SATURATED ENOUGH TO SUPPORT -DZ IN THESE SAME AREAS...ROUGHLY FROM TNB-HLX-ROA AND VICINITY. MOISTURE IS SHALLOW AND AS NOTED ABOVE INSTABILITY IS NEAR ZERO THROUGHOUT THE PERIOD...SO HAVE ONLY MENTIONED -DZ AT THIS POINT AND NO MENTION OF -RW AND ESPECIALLY NO MENTION OF ANY -TSRA. HAVE KEPT POPS AT OR BELOW 15 PERCENT THROUGHOUT THE SHORT TERM. MODELS DEPICT VERY LITTLE VARIATION IN MOISTURE FIELDS AND RESULTANT TEMPERATURES FROM DAY-TO-DAY THROUGH THE PERIOD...BUT THERE ARE SUBTLE DIFFERENCES IN THE LOW-LEVEL WIND FIELD THAT WILL DICTATE THE CLOUD COVER AND RESULTANT TEMPERATURES. AT THIS POINT...WED AND FRI APPEAR TO BE THE COOLEST...BUT THE WEDGE IS WEAKEST WED AFTERNOON BETWEEN SHORT WAVES AND A SMALL POTENTIAL FOR A BRIEF PERIOD OF LIGHT NW FLOW WED AFTERNOON. BY FRI...A STRONG WEDGE WILL BE DEVELOPING ACROSS THE REGION AS A LARGE 1032MB SFC HIGH SETS UP ACROSS NEW ENGLAND AND THE NORTHERN MID-ATLANTIC COAST. HAVE GENERALLY USED A BLEND OF MODEL TEMPS FOR MAX/MINS THROUGH THE PERIOD...BUT DID LEAN TOWARD THE COOLER MET MOS FOR WED BASED ON RECENT SIMILAR EVENTS OVER THE PAST WEEK OR SO. TEMPERATURES WILL BE SLIGHTLY BELOW TO WELL BELOW NORMAL THROUGH THE PERIOD...ESPECIALLY MAX TEMPS.
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&& .LONG TERM /SATURDAY THROUGH MONDAY/...
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AS OF 400 AM EDT TUESDAY... A STRONG WEDGE WILL BE IN PLACE FOR SATURDAY AND IT APPEARS IT COULD BE STRONG ENOUGH TO ALLOW SOME DRIER AIR TO FILTER INTO THE REGION FROM THE NORTHEAST AND PUSH THE LOW CLOUDS TOWARD THE MRX/RNK CWA BORDER...NAMELY TOWARD SMYTH/TAZEWELL COUNTIES AND THE NW NC MOUNTAIN COUNTIES. BY SUN...A STRONG SHORT WAVE IS APPROACHING FROM NORTHWEST WITH A CONTINUED DEEPENING OF THE UPPER TROUGH BEYOND THIS. THE 00Z ECMWF HAS COME INTO BETTER AGREEMENT WITH THE EARLIER RUNS OF THE GFS. SHOWERS APPEAR TO BE A GOOD BED FOR SUN INTO SUN NIGHT..BUT CONFIDENCE IN TSRA AT THIS POINT IS LOW...ESPECIALLY EAST OF THE BLUE RIDGE. WITH THE EVENT BEING A PREDOMINATE NW FLOW EVENT...THE BEST CHANCE SHOULD BE WEST OF THE ALLEGHANY FRONT. A PROGRESSIVE TREND TOWARD COOLER WEATHER SHOULD FOLLOW THEREAFTER INTO EARLY NEXT WEEK WITH AN OVERALL WINTERLIKE PATTERN IN PLACE...NAMELY A DEEPENING UPPER LOW CENTERED OF HUDSON BAY AND A SERIES OF NW FLOW SHORT WAVES KEEPING A COLD CYCLONIC FLOW IN PLACE ACROSS THE REGION. THE EARLIER RUN OF THE GFS FLIRTED WITH SUB ZERO 850MB TEMPS EARLY NEXT WEEK...BUT HAS NOW COME INTO BETTER AGREEMENT WITH THE 00Z GFS HOLDING THEM MORE IN THE +4C TO +6C RANGE.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/... AS OF 100 AM EDT TUESDAY... BAND OF MOSTLY MID DECK AHEAD OF THE COLD FRONT NEAR THE OHIO RIVER WILL CONTINUE TO SLIDE EAST OVERNIGHT WITH SPOTTY MAINLY MOUNTAIN SPRINKLES OR -SHRA POSSIBLE. HOWEVER ANY PRECIP APPEARS TOO ISOLATED TO MENTION IN THE TAFS SO KEEPING THINGS DRY FOR NOW. HOWEVER LOW LEVEL UPSLOPE FLOW WILL KEEP IFR/LIFR CIGS AT KBLF WITH MVFR CIGS DEVELOPING AROUND KLWB AND PERHAPS KBCB. ELSW THINKING THAT CIGS SHOULD REMAIN VFR OVERNIGHT WITH PATCHY FOG LIKELY DEVELOPING AROUND KDAN AND POSSIBLY AT KLYH. HOWEVER GIVEN CLOUDS...SOME LINGERING SPREAD IN TEMPS/DEWPOINTS AND A LIGHT BREEZE AHEAD OF THE FRONT...APPEARS FOG FORMATION MAY BE SLOWER IN SPOTS SO DELAYED UNTIL ALMOST DAYBREAK IN SPOTS. ANY FOG/STRATUS FADES TUESDAY BY 14Z/10AM...WITH BKN VFR CIGS TAKING SHAPE. A FEW SHOWERS MAY SKIRT BY KBLF/KBCB DURING THE MORNING AS THE ACTUAL SURFACE COLD FRONT CROSSES OTRW EXPECTING LIMITED PRECIP AT THIS POINT. WEDGE WILL START TO REDEVELOP BEHIND THE FRONT TUESDAY NIGHT WITH LOW LEVEL MOISTURE LIKELY LEADING TO WIDESPREAD LOWER CIGS INCLUDING STRATUS BY EARLY WEDNESDAY MORNING. ALSO ADDED SHOWERS POSSIBLE ESPCLY DURING THE EVENING ACROSS SOUTHERN SECTIONS AS A WAVE PASSES TO THE SOUTH. OTRW SHOULD INIT AS VFR TUESDAY NIGHT DURING THE END OF THE CURRENT VALID TAF PERIOD. EXTENDED AVIATION DISCUSSION... BROAD UPPER TROUGH REMAINS IN PLACE ACROSS THE EASTERN STATES FOR THE REMAINDER OF THE WEEK ALLOWING A LARGE AREA OF HIGH PRESSURE TO BUILD SOUTH FROM THE GREAT LAKES FOR MID WEEK BEFORE WEDGING IN FROM OFF THE MID ATLANTIC COAST BY THE WEEKEND. THIS SHOULD PUSH THE PESKY DEEP MOISTURE FURTHER SOUTH AWAY FROM THE REGION. HOWEVER BIGGER CONCERN WILL BE WITH TRAPPED RESIDUAL LOW LEVEL MOISTURE THAT MAY KEEP SOUTHERN/WESTERN LOCATIONS STUCK IN PERIODS OF MVFR CIGS ESPCLY WEDNESDAY INTO FRIDAY AS THE LOW LEVEL EAST/SE FLOW TAKES SHAPE. HIGH PRESSURE MAY BE STRONG ENOUGH TO PUSH THE LOW LEVEL MOISTURE TO THE SOUTHWEST SATURDAY AND WITH HEATING/MIXING COULD SEE THINGS RETURN TO OVERALL VFR FOR EARLY IN THE WEEKEND...BUT NOT UNTIL SATURDAY AFTERNOON AT THIS POINT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RAB LONG TERM...AMS/RAB AVIATION...JH/PC/WP

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