Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 011401 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1001 AM EDT TUE SEP 1 2015 .SYNOPSIS... AN UPPER LEVEL RIDGE OF HIGH PRESSURE WILL STRENGTHEN OVER THE APPALACHIANS AND CENTRAL MID ATLANTIC REGION TODAY...KEEPING US IN A RATHER STAGNANT PATTERN WITH ISOLATED AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS THROUGH LATE IN THE WEEK. A WEAK BACKDOOR COLD FRONT WILL DROP SOUTH THROUGH THE AREA BY THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1000 AM EDT TUESDAY... ONLY MODEST ADJUSTMENTS TO THE EARLY MORNING PACKAGE...BASICALLY TO DECREASE CLOUD COVER ACROSS THE AREA...AS WELL AS TO PROLONG THE PATCHY FOG ALONG THE GREENBRIER RIVER IN SOUTHEAST WEST VIRGINIA THROUGH 11 AM. APPEARS THAT...WITH THE BEGINNING OF SEPTEMBER HERE...WE ARE INTO THE TIME OF YEAR WHERE LOWER SUN ANGLES WILL ALLOW FOG TO LINGER LONGER INTO THE MORNING. OTHERWISE...THE EARLY MORNING FORECAST PACKAGE APPEARS TO BE ON TRACK. AS OF 223 AM EDT TUESDAY... RIDGING BOTH SURFACE/ALOFT TO STRENGTHEN ACROSS THE REGION TODAY IN THE WAKE OF A WEAK PASSING SHORTWAVE EARLY THIS MORNING AND AHEAD OF THE WEAK UPPER DISTURBANCE NOW IN THE WESTERN OHIO VALLEY. THIS SHOULD RESULT IN LIMITED FORCING WITH ANY CONVECTIVE COVERAGE MAINLY TIED TO OROGRAPHICS AND LOW LEVEL CONVERGENCE BETWEEN WEAK ONSHORE FLOW OUT EAST AND WEAK NW TRAJECTORIES OVER THE WEST. MODELS ALSO INDICATED POCKETS OF HIGHER SURFACE-85H THETA-E OVER THE WEST/SW AND IN THE FAR NW LATER ON. HOWEVER MOST SOLUTIONS REMAIN WITH AN OVERALL DISORGANIZED SHOTGUN PATTERN TO SHOWERS DESPITE DECENT INSTABILITY PER STRONG HEATING AND LACK OF MUCH CAP ALOFT. THEREFORE RUNNING WITH OVERALL SLIGHT POPS MAINLY MOUNTAINS WITH RIBBONS OF MORE CHANCE NATURE COVERAGE ALONG THE HIGHER RIDGES IN A FEW SPOTS. WILL BE ON THE HOT SIDE TO START SEPTEMBER GIVEN A BIT MORE SUN THAN THE LAST FEW DAYS AND LIGHT FLOW. THIS COULD PUSH HIGHS ABOVE 90 SE AND WELL INTO THE 80S ELSEWHERE OUTSIDE THE HIGHER ELEVATIONS. WEAK NW FLOW MAY TAKE A FEW SHRA/ISOLATED TSRA JUST EAST OF THE MOUNTAINS INTO EARLY THIS EVENING BEFORE FADING BUT GIVEN LACK OF SUPPORT THINK MOST ABOUT GONE AROUND SUNSET. OTHERWISE OPENING UPPER WAVE SLIPS SOUTHEAST TOWARD THE REGION LATER TONIGHT AND HELPS LOWER 5H HEIGHTS UNDER STRONG SURFACE RIDGING. THIS SYSTEM COULD SPARK A BAND OR TWO OF SHOWERS MAINLY NW LATE BUT GIVEN LACK OF MUCH LIFT AFTER LOSS OF HEATING CUT BACK TO MOSTLY SLIGHT CHANCE POPS OVERNIGHT MAINLY NW. HOWEVER THIS FEATURE MAY BRING ENOUGH CLOUDS TO KEEP LOW TEMPS UP A BIT MORE SO APPEARS MOSTLY UNIFORM MID TO UPPER 60S OVERNIGHT.
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&& .SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/... AS OF 345 AM EDT TUESDAY... VERY DIFFUSE UPPER-LEVEL PATTERN IN PLACE AT THE BEGINNING OF THIS PERIOD...WITH WEAK...SMALL CHANGES THROUGH THE PERIOD THAT WILL DICTATE THE WEATHER. WE BEGIN WITH A BUILDING UPPER RIDGE ENCOMPASSING MUCH OF THE EASTERN 2/3RD OF THE NATION SOUTH OF THE CANADIAN BORDER. UNDERLYING THIS BROAD UPPER RIDGE ARE SEVERAL WEAK SYSTEMS...A WEAK UPPER TROUGH TRAVERSING THE NORTHERN PERIPHERY OF THE UPPER RIDGE THROUGH THE OH VALLEY AND THE REMNANTS OF ERIKA OFF THE NC COAST. THE AFOREMENTIONED UPPER TROUGH WILL SLIDE SOUTHEAST THROUGH THE DAY ALLOWING FOR A BRIEF LOWERING OF UPPER HEIGHTS. THIS FEATURE WILL ALSO TRACK INTO THE REGION DURING PEAK HEATING...WHICH SHOULD BE SUFFICIENT TO SPARK ISOLATED TO SCATTERED AFTERNOON CONVECTION...ESPECIALLY ACROSS THE MOUNTAINS. WARM TEMPS ALOFT WILL INHIBIT ANY SIGNIFICANT COVERAGE WITH THIS FEATURE. CONVECTION WILL BE LARGELY DIURNAL AND SHOULD DISSIPATE QUICKLY AFTER SUNSET. MOST FAVORED AREAS FOR SHOWERS/THUNDERSTORMS WED AFTERNOON/EVENING SHOULD BE NEAR THE I-64 CORRIDOR. HOWEVER...WITH LIMITED DYNAMICS...20-30 POPS SHOULD BE SUFFICIENT. FOR THURSDAY...THE WEAK UPPER TROUGH CONTINUES TO SLIDE SOUTHWARD INTO THE CAROLINAS OR EASTERN TN VALLEY. MEANWHILE...THE UPPER RIDGE BECOMES VERY HIGH AMPLITUDE INTO EASTERN CANADA WITH 588DM HEIGHTS EVEN NORTH OF THE GREAT LAKES...ALL IN RESPONSE TO DEEPENING LOW PRESSURE ALONG THE WEST COAST. WITH THE UPPER TROUGH WEAKENING AND RIDGING ALOFT...CONVECTION WILL BE ISOLATED TO SCATTERED AT BEST AND ALMOST ENTIRELY DRIVEN BY DIURNAL/DIFFERENTIAL HEATING. BEST FOCUS SHOULD BE ACROSS THE WESTERN MOUNTAINS. LITTLE SUPPORT FOR MORE THAN 30 POPS ANYWHERE...MOSTLY 20 POPS. BY FRIDAY...A STRONG 1030MB HIGH BEGINS TO TAKE SHAPE ACROSS SOUTHEAST CANADA AND NEW ENGLAND UNDERNEATH THE STRONG/HIGH AMPLITUDE UPPER RIDGE. 590DM HEIGHTS ARE NOTED EVEN NORTH OF THE CANADIAN BORDER. AS THE RIDGE BUILDS INTO NEW ENGLAND...THE MID- WEEK WEAK UPPER TROUGH SINKS SOUTH INTO THE SOUTHEAST U.S...WHICH COULD BECOME A FOCUS FOR PRECIPITATION IN THE EXTENDED DEPENDING ON ITS NORTHWARD EXTENT. MORE IMPORTANTLY FOR OUR REGION AT THIS POINT IS A HEALTHY BACKDOOR FRONT BEGINNING TO TAKE SHAPE ACROSS THE MID-ATLANTIC THAT WILL ADVECT SOUTHEAST INTO THE CWA BY SATURDAY. A MARKED INCREASE IN INSTABILITY IS NOTED IN ADVANCE OF THIS FEATURE...WHICH WILL REPRESENT SLIGHT COOLING AND MODEST DRYING. WE SHOULD SEE AN INCREASE IN CONVECTION ALONG AND IN ADVANCE OF THE BOUNDARY FROM THE NORTH AND NORTHEAST BY FRIDAY AFTERNOON...AND THIS HAS BEEN REFLECTED IN THE POPS. TEMPERATURES WILL REMAIN ABOVE NORMAL THROUGH THIS PERIOD...GENERALLY ON THE ORDER OF 5 DEGREES FOR DAYTIME MAX TEMPS AND NEARLY 10 DEGREES ABOVE NORMAL FOR MIN TEMPS. MOST MODELS WERE IN GENERAL AGREEMENT ON MAX/MIN TEMPS THROUGH THE PERIOD. && .LONG TERM /SATURDAY THROUGH MONDAY/... AS OF 400 AM EDT TUESDAY... THE BACKDOOR COLD FRONT WILL MOVE SOUTHWARD THROUGH THE REGION SATURDAY...FOLLOWED BY DRIER/SLIGHTLY COOLER AIR...ESPECIALLY SUN-MON AS SFC HIGH PRESSURE SLIDES SOUTHWARD ALONG THE MID- ATLANTIC COAST. THE MID-WEEK WEAK UPPER LOW WILL BECOME CUT OFF IN THE AL/GA/SC REGION. MEANWHILE...A STRONG UPPER RIDGE WILL REMAIN FIRMLY ENTRENCHED ACROSS THE REGION WITH 500MB HEIGHTS IN THE 593DM RANGE THROUGH THE WEEKEND. SHOWERS/THUNDERSTORM CHANCES SATURDAY WILL BE BEST IN THE WEST/SOUTHWEST PART OF THE CWA NEAR THE SOUTHWESTWARD MOVING BACKDOOR FRONT. CONVECTION CHANCES SUN- MON WILL BE CONFINED TO THE FAR SOUTH CENTRAL/SOUTHWEST PARTS OF THE CWA NEAR THE CUTOFF UPPER LOW AND STALLED BACKDOOR FRONT. TEMPERATURES WILL BE SLIGHTLY COOLER THROUGH MUCH OF THE CWA THIS PERIOD THANKS TO THE BACKDOOR FRONT AND INCREASING NORTHEAST-EAST MARITIME FLOW. DEWPOINTS/RH VALUES WILL ALSO BE LESS...ESPECIALLY ACROSS THE NORTHEAST PART OF THE CWA. THE EXCEPTION MAY BE THE SOUTHWEST PART OF THE CWA...WHICH WILL LIKELY REMAIN WARMER AND MORE HUMID GIVEN THE SYNOPTIC PATTERN IN PLACE. THE COOLING WILL BE MOST NOTABLE IN MAX TEMPS...WHICH WILL BE NEAR NORMAL...WHILE MIN TEMPS ARE LIKELY TO REMAIN WELL ABOVE NORMAL. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... AS OF 642 AM EDT TUESDAY... FOG AND LOW CLOUDS REMAIN THE MAIN ISSUES EARLY THIS MORNING WITH MOST OF THIS OF THE PATCHY NATURE WHILE BEING CONFINED TO THE VALLEYS FOR THE MOST PART. THUS WILL NEED TO INIT WITH A RANGE FROM LIFR/IFR AT KLWB TO MVFR AT MOST OTHER LOCATIONS EXCLUDING KROA/KBLF WHERE APPEARS WILL STAY VFR OVER THE NEXT COUPLE OF HOURS. FOG/STRATUS WILL FADE EARLY THIS MORNING SO EXPECTING VFR CONDITIONS TO RETURN BY MID MORNING WITH THE NEXT ROUND OF DIURNAL CONVECTION HOLDING OFF UNTIL THIS AFTERNOON. THUS KEEPING VCSH AT KBLF/KLWB AND INCLUDING AT KBCB WITH BKN VFR CIGS AT 4-6KFT. MAY SEE SOME BROKEN VFR CIGS ELSEWHERE ALONG/EAST OF THE BLUE RIDGE ALL WELL BUT KEEPING ALL OTHER LOCATIONS WITHOUT ANY CONVECTION FOR NOW. EXTENDED AVIATION DISCUSSION... THE FORECAST AREA WILL REMAIN IN A WEAKLY FORCED SYNOPTIC ENVIRONMENT THROUGH MIDWEEK...WITH CHANCES FOR DIURNAL CONVECTION MAINLY FROM THE BLUE RIDGE WEST...AND SOME MVFR/IFR FOG/STRATUS DEVELOPMENT AT NIGHT...ESPECIALLY AT KBCB AND KLWB. FOR FRIDAY INTO SATURDAY WILL SEE HIGH PRESSURE IN CONTROL THOUGH THE POSITION OF THE HIGH OVER THE MID ATLANTIC MAY SLIDE MORE MVFR CIGS OFF THE ATLANTIC INTO OUR EASTERN TAF LOCATIONS. && .EQUIPMENT... AS OF 400 AM EDT MONDAY... THE DEW POINT READING AT KJFZ...RICHLANDS VA AWOS...IS INCORRECT. AT THIS TIME WE DO NOT KNOW WHEN THIS SENSOR WILL BE REPAIRED. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/MBS NEAR TERM...JH/NF SHORT TERM...RAB LONG TERM...AMS/RAB AVIATION...JH/MBS/NF/WP EQUIPMENT...

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