Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 042343 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 743 PM EDT FRI SEP 4 2015 .SYNOPSIS... A BACKDOOR COLD FRONT WILL MOVE INTO THE AREA TONIGHT AND STALL OVER THE SOUTHERN PORTION OF THE REGION ON SATURDAY. ANTICIPATE SHOWERS AND STORMS THROUGH AT LEAST THE EARLY PART OF TONIGHT IN ASSOCIATION WITH THE FRONT AND AN UPPER LEVEL DISTURBANCE MOVING INTO THE REGION. COOLER AND SOMEWHAT DRIER WEATHER IS EXPECTED TOWARDS THE END OF THE WEEKEND INTO EARLY NEXT WEEK. A RESURGENCE OF ATLANTIC MOISTURE RETURNS TO THE AREA BY THE MIDDLE PART OF NEXT WEEK. && .NEAR TERM /THROUGH SATURDAY/... AS OF 600 PM EDT FRIDAY... UPDATED FORECAST TO REFLECT DOWNWARD TREND IN POPS OVER THE WESTERN CWA...CONCENTRATING MORE ACROSS THE EASTERN HALF OF THE CWA. MLCAPES AT 21Z IN THE 1500-2000 J/KG RANGE OVER SOUTHSIDE VA INTO THE FOOTHILLS. ATMOSPHERE BEING WORKED OVER WITH OUTFLOW OUTRUNNING THE STORMS AND CUTTING OFF INFLOW IN THE EASTERN CWA...WITH BEST CONCENTRATION SITUATED SOUTH OF PSK-BCB. LOCAL WRF TAKES THIS ACTIVITY SOUTH OF OUR CWA BY 01Z...WITH THE SHOWERS AND STORMS OVER THE PIEDMONT NORTHEAST OF LYH AND NORTH OF LEXINGTON WEAKENING BY 0Z. OTHER ADJUSTMENTS TO THE FORECAST WERE TAKING INTO ACCOUNT RAIN COOLED TEMPS...AND CLOUD COVER. PREVIOUS AFTERNOON DISCUSSION... SHOWERS AND THUNDERSTORMS CONTINUE TO SPREAD SOUTH ACROSS THE REGION IN ASSOCIATION WITH BOTH THE APPROACH OF A BACKDOOR COLD FRONT...SURFACE HEATING...AND THE PASSAGE OF AN UPPER LEVEL DISTURBANCE FROM A SMALL CLOSED LOW OVER THE AREA OF MICHIGAN AND WISCONSIN. COVERAGE HAS BEEN THE LEAST OVER PARTS OF THE NEW RIVER VALLEY AND THE MOUNTAIN EMPIRE REGION OF SOUTHWEST VIRGINIA FOR MUCH OF THE AFTERNOON. THIS WILL CHANGE HAS WE HEAD INTO THE LATE AFTERNOON AND EARLY EVENING AS THE ACTIVITY TO THE NORTH CONTINUES TO HEAD SOUTH. SHOWERS AND THUNDERSTORMS WILL CONTINUE PAST SUNSET THANKS TO BOTH THE INFLUENCE OF THE FRONT AND THE UPPER LEVEL DISTURBANCE...HOWEVER THE ACTIVITY IS EXPECTED TO BECOME MORE FOCUSED OVER THE SOUTHERN AND SOUTHEAST PARTS OF THE AREA AS TIME PROGRESSES. BY MIDNIGHT...ONLY ISOLATED TO SCATTERED SHOWERS ARE EXPECTED TO BE OVER PARTS OF THE AREA. LOW LEVEL FLOW WILL BECOME PROGRESSIVELY MORE NORTHEAST TO EAST THROUGH A DEEPER LAYER OF THE ATMOSPHERE. THIS WILL HELP REGENERATE CLOUD COVER OVERNIGHT AFTER AN INITIAL DECREASE. LOW TEMPERATURES TONIGHT WILL NOT BE MUCH DIFFERENT THAN THOSE REALIZED THIS MORNING. ANTICIPATE LOWER 60S ACROSS THE MOUNTAINS AND MID TO UPPER 60S ACROSS THE PIEDMONT. FOR SATURDAY...HIGH PRESSURE WILL SLOWLY START TO NOSE ITS WAY SOUTH ALONG THE LEE OF THE APPALACHIANS. NOTABLY DRIER AIR WILL STILL BE A COUPLE DAYS AWAY...BUT THE INSTABILITY WILL BE LESS SATURDAY AS COMPARED TO TODAY. HOWEVER...IT WILL NOT BE TOO WEAK AS TO PREVENT THE DEVELOP OF ISOLATED TO SCATTERED SHOWERS...THE THE GREATEST CONCENTRATION OVER THE SOUTHWEST PARTS OF THE REGION. AN ISOLATED THUNDERSTORM CANNOT BE RULED OUT...BUT ANY THAT FORM WILL NOT BE AS POTENT AS THOSE OF TODAY. HIGH TEMPERATURES WILL BE ABOUT TEN DEGREES COOLER THAN THOSE OF TODAY. EXPECT MID TO UPPER 70S ACROSS THE MOUNTAINS AND UPPER 70S TO AROUND 80 ACROSS THE PIEDMONT. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... AS OF 300 PM EDT FRIDAY... WILL START SATURDAY EVENING OFF WITH WEAK HIGH PRESSURE WEDGING SOUTHWARD AGAINST THE EASTERN FACE OF THE APPALACHIANS...RESULTING IN LIGHT NORTHEASTERLY WINDFLOW. THE UPSLOPE WINDS ALONG THE RIDGES MAY SUPPORT A FEW SHOWERS INTO EARLY SUNDAY...BUT EXPECT ANY THUNDERSTORMS LEFT FROM EARLIER IN THE DAY TO WEAKEN BY SUNSET WITH THE LOSS OF DAYTIME HEATING. FOR SUNDAY...WEAK HIGH PRESSURE WILL REMAIN IN PLACE ACROSS THE MID ATLANTIC...WITH WINDS SHIFTING MORE EASTERLY. THE FLOW OFF THE ATLANTIC WILL MAKE FOR CONTINUED COOLER TEMPERATURES...WITH AFTERNOON HIGHS RANGING FROM THE MID 70S MOUNTAINS TO LOW 80S EAST OF THE BLUE RIDGE. THE HIGH PRESSURE WEDGE WILL BE SHALLOW ENOUGH ACROSS THE PIEDMONT OF NORTH CAROLINA THAT A FEW SHOWERS AND ISOLATED STORMS WILL DEVELOP WITH AFTERNOON HEATING. MAY ALSO SEE A FEW SHOWERS DEVELOP ALONG THE MOUNTAIN RIDGES DUE TO THE UPSLOPE WINDS...BUT EXPECT COVERAGE WILL BE SPOTTY AT BEST. RAINFALL WILL AGAIN FIZZLE AROUND SUNSET WITH THE LOSS OF DAYTIME HEATING. FOR LABOR DAY...HIGH PRESSURE WILL GRADUALLY SLIDE EAST...DECREASING ITS INFLUENCE ACROSS THE MID ATLANTIC. THIS WILL ALLOW WINDS TO SHIFT INCREASINGLY SOUTHERLY TO DRAW MORE UNSTABLE AIR FROM THE CAROLINAS INTO OUR AREA. AS SUCH...EXPECT SLIGHTLY BETTER COVERAGE OF SHOWERS DEVELOPING WITH AFTERNOON HEATING. WILL ALSO SEE INCREASED INSTABILITY AS SUBTLE UPPER LEVEL DISTURBANCES PASS ACROSS THE AREA...AND THEREFORE EXPECT SLIGHTLY BETTER COVERAGE OF THUNDERSTORMS. UPPER LEVEL WINDS WILL BE LIGHT...RESULTING IN SLOW CELL MOVEMENT...WHICH WOULD MAKE FOR LOCALLY HEAVY RAIN AS STORMS REMAIN PARKED OVER LOCATIONS FOR EXTENDED PERIODS OF TIME. TEMPERATURES WILL TAKE ON A WARMING TREND...WITH AFTERNOON HIGHS RANGING FROM THE LOW 80S WEST TO THE UPPER 80S EAST. OVERNIGHT TEMPERATURES THROUGH THE PERIOD WILL REMAIN SEASONABLE... GENERALLY RANGING FROM THE LOW TO MID 60S MOST LOCATIONS...WITH A FEW MID/UPPER 50S IN THE DEEPER MOUNTAIN VALLEYS. PATCHY MOUNTAIN VALLEY FOG WILL ALSO BE A COMMON OCCURRENCE EACH NIGHT. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... AS OF 330 PM EDT FRIDAY... A GENERAL SUMMERTIME WEATHER PATTERN WILL RETURN FOR THE MIDDLE OF NEXT WEEK...WITH SPOTTY SHOWERS AND THUNDERSTORMS DEVELOPING EARLY EACH AFTERNOON WITH DAYTIME HEATING...AND DIMINISHING TOWARD SUNSET AS HEATING ENDS. EXPECT ONLY SPOTTY COVERAGE OF RAINFALL ON TUESDAY DUE TO WEAK SUPPORTING DYNAMICS...HOWEVER COVERAGE WILL INCREASE EACH DAY FOR WEDNESDAY AND THURSDAY AS A COLD FRONT APPROACHES FROM THE NORTHWEST. BY NEXT THURSDAY...LONG RANGE WEATHER FORECAST MODELS DIFFER AS TO WHERE THE COLD FRONT WILL BE LOCATED...WITH THE ECMWF MODEL BRINGING THE FRONT ACROSS OUR AREA...WHILE THE GFS MODEL KEEPS THE FRONT WELL TO OUR NORTH. GIVEN WHAT APPEARS TO BE WEAK UPPER LEVEL SUPPORT TO GIVE THE FRONT A SOUTHWARD PUSH...HAVE TRENDED TOWARD THE GFS MODEL AND TRIMMED BACK RAIN CHANCES FOR THAT DAY. EXPECT WARM AND MUGGY CONDITIONS FOR THE PERIOD...WITH HIGHS RANGING FROM THE UPPER 70S/LOW 80S ACROSS THE MOUNTAINS...TO THE UPPER 80S FOR THE PIEDMONT. LOWS WILL HOLD GENERALLY IN THE LOW TO MID 60S...PERHAPS WITH A FEW UPPER 50S ACROSS THE MOUNTAINS. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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AS OF 735 PM EDT FRIDAY... EXPECT A FEW SHRA/TSRA AROUND THROUGH ABOUT MIDNIGHT/04Z...WITH ROA HAVING A LIGHT RAIN SHOWER TIL 02Z. LYH MAY SEE A SHOWER IN THE VICINITY AS SMALL AREA MOVES SOUTHWEST FROM BUCKINGHAM COUNTY. STRONGEST CONVECTION WILL STAY IN A CORRIDOR FROM TRI-HLX AT 00Z THEN DISSIPATE...MOVING SOUTH INTO TNB-UKF BY 02-3Z. ISSUE OVERNIGHT WILL BE BACKDOOR FRONT AND LOWER CIGS PLUS PROSPECTS OF FOG. WILL LEAN TOWARD PREVIOUS FORECAST COMBINED WITH OUR LOCAL WRF WHICH FAVORS SOME IFR/MVFR CIGS/VSBYS LATE TONIGHT AT ALL SITES...WITH THE BLF/LWB/BCB AREA HAVING WORSE CONDITIONS. CONFIDENCE IS HIGH THAT SUB VFR WILL OCCUR...BUT LOW ON HOW FAR DOWN THE CIGS/VSBYS GO. SATURDAY MORNING INTO THE EARLY AFTERNOON...EXPECT A GRADUAL TREND OF CEILINGS AND VISIBILITIES IMPROVING TO VISUAL FLIGHT RULES LEVELS. ISOLATED SHOWERS WILL BE ON THE INCREASE AROUND NOONTIME...BUT CONFIDENCE IN THEIR LOCATION IS NOT GREAT ENOUGH TO INCLUDE ANY IN THE PREVAILING WEATHER OF THE FORECASTS. EXTENDED AVIATION DISCUSSION... HIGH PRESSURE WILL GRADUALLY WORK INTO THE REGION BY THE END OF THE WEEKEND...AND REMAIN OVER THE AREA INTO THE EARLY PART OF NEXT WEEK. LINGERING MOISTURE AND AN EASTERLY FETCH WILL HELP MAINTAIN SOME ISOLATED TO SCATTERED SHOWERS ACROSS MAINLY WESTERN AND SOUTHERN PARTS OF THE AREA...ESPECIALLY ON SATURDAY AND SUNDAY AFTERNOON. MOISTURE STARTS TO INCREASE AGAIN MONDAY INTO TUESDAY WHILE THE INFLUENCE OF THE RIDGE WEAKENS. COVERAGE OF SHOWERS...AND POSSIBLY A FEW STORMS...WILL LIKEWISE START TO INCREASE. PAST SATURDAY...CEILINGS AND VISIBILITIES WILL PRIMARILY BE VISUAL FLIGHT RULES. THE EXCEPTION WILL BE LINGERING PATCHY MVFR RULES ACROSS PARTS OF THE REGION SATURDAY AFTERNOON. ALSO...OVERNIGHT AND EARLY MOUNTAIN AND RIVER VALLEY INSTRUMENT FLIGHT RULES/MARGINAL VISUAL FLIGHT RULES FOG/MIST ARE EXPECTED.
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&& .HYDROLOGY... AS OF 745 PM EDT THURSDAY... THE WEEKLY UNITED STATES DROUGHT MONITOR ISSUED ON SEPTEMBER 3RD SHOWS THE EFFECT OF A DRIER THAN NORMAL AUGUST ACROSS MUCH OF THE AREA. ABNORMALLY DRY CONDITIONS...D0 ON THE DROUGHT SCALE HAVE BEEN EXPANDED INTO A LARGE PORTION OF SOUTHSIDE VIRGINIA COVERING MUCH OF THE DAN AND LOWER ROANOKE RIVER BASINS. PARTS OF THE UPPER YADKIN RIVER BASIN IN NORTH CAROLINA ARE ALREADY IN D1 OR MODERATE DROUGHT. AUGUST RAINFALL WAS AS LOW AS 50 PERCENT OF NORMAL OR LESS IN PARTS OF THE AFOREMENTIONED AREAS. SEVERAL NWS COOPERATIVE CLIMATE STATIONS IN SOUTHERN VIRGINIA RECORDED WELL UNDER 2 INCHES OF RAIN THE ENTIRE MONTH OF AUGUST INCLUDING HUDDLESTON IN BEDFORD COUNTY AT 1.17 INCHES AND ROCKY MOUNT IN FRANKLIN COUNTY AT 1.36 INCHES. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...DS NEAR TERM...DS/WP SHORT TERM...NF LONG TERM...NF AVIATION...DS/WP HYDROLOGY...PC

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