Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 031747 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 147 PM EDT THU SEP 3 2015 .SYNOPSIS... HIGH PRESSURE ACROSS THE AREA WILL KEEP A HOT AND HUMID AIRMASS IN PLACE THROUGH THE END OF THE WEEK. A BACKDOOR COLD FRONT WILL CROSS THE REGION LATE FRIDAY NIGHT INTO SATURDAY...BRINGING BETTER CHANCES OF SHOWERS AND STORMS IN ADVANCE OF IT LATE FRIDAY INTO FRIDAY NIGHT. DRIER AND COOLER AIR WILL WORK ITS WAY INTO THE AREA FOR THE LATTER HALF OF THE WEEKEND INTO THE START OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1240 PM EDT THURSDAY... LOCAL RADAR IS CONTINUING TO TRACK A SMALL CLUSTER OF SHOWERS INTO THE NORTHWEST PORTION OF THE FORECAST AREA AND AN ISOLATED THUNDERSTORM NORTH OF BLUEFIELD WEST VIRGINIA. THIS ACTIVITY WAS HEADING SOUTH INTO THE REGION. ISOLATED CONVECTION IS ALSO OCCURRING NORTH OF LYNCHBURG VIRGINIA AND OVER PARTS OF THE MOUNTAIN EMPIRE AND NEW RIVER VALLEY REGIONS OF SOUTHWEST VIRGINIA. OUR FORECAST IS STILL GENERALLY ON TRACK FOR ADDITIONAL ISOLATED TO SCATTERED SHOWERS TO EITHER MOVE INTO THE REGION...OVER DEVELOP OVER PARTS OF THE AREA HEADING INTO THE AFTERNOON. THE BEST COVERAGE WILL BE WEST OF THE CREST OF THE BLUE RIDGE...BUT ACROSS THE PIEDMONT WILL BE MORE LIKELY IN THE LATE AFTERNOON HEADING INTO THE EARLY EVENING. MADE NO CHANGES TO FORECAST HIGH TEMPERATURES. CURRENT TRENDS SHOULD ALLOW TEMPERATURES TO REACH OUR FORECAST NUMBERS...OR BE A DEGREE OR TWO SHY BY THE LATE AFTERNOON. AS OF 950 AM EDT THURSDAY... NO MAJOR CHANGES ARE NEEDED FOR THE FORECAST AT THIS TIME. THE ONLY NOTABLE ADJUSTMENT HAS BEEN A SLIGHTLY QUICKER ARRIVAL TIME OF SCATTERED SHOWERS AND ISOLATED STORMS ACROSS THE NORTHWEST PORTION OF THE REGION LATE THIS MORNING. AS OF 240 AM EDT THURSDAY... OVERALL PERSISTENCE FORECAST CONTINUES OVER THE NEXT 24 HOURS WITH YET ANOTHER HOT/HUMID AFTERNOON IN STORE TODAY UNDER SURFACE HIGH PRESSURE AND WARM 85H TEMPS. HOWEVER ENOUGH OF A WEAKNESS ALOFT IN THE WAKE OF THE UPPER WAVE FROM WEDNESDAY TO ELIMINATE ANY CAPPING THIS AFTERNOON ESPCLY GIVEN LOWER 5H HEIGHTS AND SLIGHTLY COOLER MID LEVEL TEMPS. THIS AGAIN SUPPORTS THE POTENTIAL FOR AT LEAST SCATTERED CONVECTIVE DEVELOPMENT ESPECIALLY BLUE RIDGE VICINITY AND POINTS WEST INTO EARLY THIS EVENING. LATEST MODEL SOLUTIONS MOSTLY IN LINE WITH THIS SCENARIO BUT DIFFER ON THE DEGREE OF COVERAGE AND WHERE ANY MORE ORGANIZED CLUSTERS MAY TAKE SHAPE. SPC WRF AGAIN SHOWING MORE WIDESPREAD MOUNTAIN TSRA WITH FOCUS ON RESIDUAL WEAK TROFFINESS SLIDING SE FROM THE OHIO VALLEY INTO WEAK LOW LEVEL CONVERGENCE AIDED BY OROGRAPHICS AND HIGH INSTABILITY. OTHER SOLUTIONS HAVE LESS WITH MORE SHOTGUN FLAVOR FARTHER WEST AND A BIT SLOWER TO INIT UNTIL MID OR LATE AFTERNOON. SINCE THE NCAR CAM PROGS SIMILAR TO THE SPC WRF WHICH WAS BEST YESTERDAY WENT WITH A BIT HIGHER POP COVERAGE OUT TO THE FOOTHILLS WITH PERHAPS A SWATH OF BEST COVERAGE NORTHERN BLUE RIDGE BACK TOWARD THE NEW RIVER...JUST SOUTH OF WHERE CONVECTION WAS ON WEDNESDAY. SEVERE THREAT AGAIN LIMITED BY LITTLE SHEAR BUT SLOW MOVEMENT AND UNIFORM BUT WEAK NORTHERLY FLOW ALOFT COULD SUPPORT A FEW STRONGER BANDS OR PULSE CLUSTERS LATE. HIGH TEMPS AGAIN LOOK TO TOP 90 IN THE EAST AND ESPECIALLY WHERE THE GROUND IS DRIER OVER THE SE. OTRW STAYED A BIT ON THE WARM SIDE OF MOS GIVEN HIGHS ABOVE GUIDANCE OF LATE. ANY CONVECTION SHOULD AGAIN FADE THIS EVENING BUT MAY TEND TO LINGER IN SPOTS OVER THE NORTH/EAST GIVEN APPROACH OF WEAK SHORTWAVE ENERGY FROM THE NW LATE. HOWEVER DID GO MOSTLY DRY AFTER MIDNIGHT WITH MORE FOG AROUND ALTHOUGH COVERAGE QUITE DEPENDENT UPON EARLIER RAINFALL. MUGGY LOWS AGAIN MOSTLY 60S TO AROUND 70. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... AS OF 430 AM EDT THURSDAY... A COMPLEX ARRAY OF WEATHER SYSTEMS ALOFT WILL DICTATE THE WEATHER ACROSS THE REGION THROUGH THE WEEKEND.. HIGH PRESSURE ALOFT WILL BE THE MAIN THEME ACROSS MUCH OF THE EASTERN U.S....WITH AN ANOMALOUS 590DM HIGH ANCHORED ACROSS THE GREAT LAKES. MEANWHILE...A BROAD AREA OF LOW PRESSURE ALOFT...INITIALLY OVER THE REGION TODAY...WILL DRIFT SLOWLY SOUTH THROUGH THE WEEKEND INTO THE SOUTHEAST STATES...WHERE IT IS DESTINED TO LINGER INTO EARLY NEXT WEEK. AS THE UPPER HIGH BUILDS ACROSS THE NORTHEAST U.S...SURFACE HIGH PRESSURE WILL BUILD SOUTHWEST FROM NEW ENGLAND INTO THE MID-ATLANTIC. THIS WILL PUSH A BACKDOOR COLD FRONT THROUGH OUR REGION FRIDAY AFTERNOON/EVENING...THEN INTO SOUTHWEST VA FOR THE WEEKEND...WHERE IT WILL STALL. THE BOUNDARY WILL SERVE AS A FOCUSING MECHANISM FOR CONVECTION FRIDAY AFTERNOON ACROSS MUCH OF THE CWA...BEGINNING IN THE NORTHEAST AT MIDDAY...ADVECTING SOUTHWEST WITH TIME. CONVECTION CHANCES WILL DECREASE ACROSS THE MORE STABLE AREAS BEHIND THE BACKDOOR FRONT SATURDAY...BUT LINGER ACROSS THE SOUTHWEST PART OF THE FRONT SATURDAY AND SUNDAY. THERE WILL BE A DIURNAL SWING TO CONVECTION ON ALL OF THESE DAYS. ALTHOUGH UPPER DYNAMICS ARE VERY WEAK UNDER THE LARGE SCALE UPPER RIDGE...THERMODYNAMICS FRIDAY AFTERNOON ARE QUITE NOTABLE. IN ADDITION...THE TIMING OF THE BACKDOOR FRONT INTO THE REGION DURING PEAK HEATING SHOULD YIELD SOME FAIRLY ROBUST PULSE CONVECTION. CAPES ARE WELL IN EXCESS OF 1000 J/KG ACROSS MUCH OF THE CWA FRI AFTERNOON AND LIS DROP TO AS LOW AS -6 TO -8 IN SOME AREAS...MOST NOTABLY ON THE GFS. PWATS WILL BE CREEPING BACK UP INTO THE 1.5 TO 1.75 RANGE...SO THERE WILL BE LOCALLY HEAVY RAINFALL AS WELL. FORTUNATELY...FROM THAT STANDPOINT...IT HAS BEEN QUITE DRY RECENTLY...SO RAINFALL...OTHER THAN VERY LOCALIZED ISSUES...SHOULD NOT BE A PROBLEM. GREATER CONCERN WOULD BE FOR LOCALIZED DOWNBURSTS AS AFTERNOON TEMPERATURES WILL BE WELL ABOVE NORMAL ONCE AGAIN...WITH 90S COMMON ACROSS THE PIEDMONT AND 80S WEST...EXCEPT MID TO UPPER 70S MOUNTAINS. CONVECTION WILL TEND TO BEGIN IN THE NORTHEAST PART OF THE CWA/I-64 CORRIDOR EARLY IN THE AFTERNOON...WORKING SOUTHWEST TOWARD NW NC AND SW VA BY LATE AFTERNOON. WITH RESPECT TO TEMPERATURES...FRIDAY WILL AGAIN BE A HOT...WELL ABOVE NORMAL DAY AS NOTED ABOVE. MOS GUIDANCE...AS HAS BEEN THE CASE THE PAST SEVERAL DAYS...WAS TOO COOL AGAIN TODAY...AND THUS READINGS WERE RAISED ON AVERAGE 3-4 DEGREES AT MANY LOCATIONS. MIN TEMPS WILL ALSO BE WELL ABOVE NORMAL AGAIN FRIDAY. COOLER/DRIER CONDITIONS WILL FILTER INTO THE AREA FROM THE EAST FOR THE WEEKEND...WITH THE MOST NOTABLE COOLING EAST OF THE BLUE RIDGE...AND TO A LESSER EXTENT IN THE SOUTHWEST PART OF THE CWA NEAR THE STALLED FRONTAL BOUNDARY. OVERALL...GUIDANCE SEEMED TO HAVE A REASONABLE HANDLE ON THE COOLING TREND ACROSS THE EAST. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... AS OF 445 AM EDT THURSDAY... NO SIGNIFICANT CHANCES IN THE SYNOPTIC PATTERN EARLY IN THE WEEK WITH A BROAD UPPER LOW/SHEAR/WEAKNESS ZONE LINGERING ACROSS THE SOUTHEAST STATES AND ALONG THE SC/NC COASTLINE. AN UPPER RIDGE PERSISTS FROM THE SOUTH CENTRAL PLAINS INTO THE NORTHEAST U.S...BUT IS BEING DAMPENED BY A STRONG SHORT WAVE MOVING FROM THE PACIFIC NORTHWEST TOWARD THE GREAT LAKES/NORTHEAST EARLY IN THE WEEK. THE ASSOCIATED FRONTAL BOUNDARY WILL BE APPROACHING THE REGION FROM THE NORTHWEST BY THE MID PART OF NEXT WEEK. CONSIDERABLE QUESTION REMAINS AS TO WHETHER OR NOT THE FRONT WILL ACTUALLY MOVE INTO THE CWA...AND ESPECIALLY WHETHER OR NOT IT WILL MOVE SOUTH OF THE CWA...AS THE FLOW IS LARGELY ZONAL AND BLOCKED BY THE UPPER RIDGE. IT MAY TAKE UNTIL LATE IN THE WEEK OR NEXT WEEKEND BEFORE ANOTHER PUSH BY A NORTHWEST U.S. UPPER TROUGH ALLOWS THE FRONT TO PENETRATE FAR ENOUGH SOUTH TO GET THROUGH OUR AREA. CONFIDENCE IN PRECIPITATION CHANCES THROUGH THIS PERIOD IS LOW. FOR THE MOST PART...IT APPEARS TO BE DRIVEN ALMOST ENTIRELY BY DIURNAL AND DIFFERENTIAL HEATING...FOCUSED LARGELY TOWARD THE WESTERN MOUNTAINS. THERE ARE SOME NOTABLE DIFFERENCES IN THE ECMWF/GFS REGARDING POTENTIAL RETURN ATLANTIC MOISTURE FROM OFF THE SC/NC COAST. IT APPEARS THAT THIS MOISTURE COULD ACTUALLY BE ASSOCIATED WITH THE REMNANTS OF FORMER TROPICAL STORM ERIKA. IT IS UNCLEAR WHETHER OR NOT THIS MOISTURE WILL PENETRATE FAR ENOUGH WEST TO REACH OUR CWA. HAVE PREFERRED TO LEAN TOWARD THE CONSENSUS OF SYNOPTIC SCALE MODELS WHICH KEEP THIS DEEP TROPICAL MOISTURE EAST OF OUR CWA...CLOSER TO THE COAST. TEMPERATURES WILL BE WARMING AGAIN THROUGH THE FIRST HALF OF NEXT WEEK...REMAINING WELL ABOVE NORMAL FOR THE MOST PART. TEMPERATURE DEPARTURES WILL BE MOST NOTABLE WITH RESPECT TO MINS...WITH LOWS IN THE LOW TO MID 60S...SOME 7-10 DEGREES ABOVE NORMAL. MAX TEMPS WILL START OUT OVER THE WEEKEND NEAR NORMAL...BUT CREEP BACK UP TO ABOVE NORMAL LEVELS FOR THE FIRST HALF OF NEXT WEEK...WITH MOSTLY 80S WEST TO NEAR 90 EAST...EXCEPT 70S MOUNTAINS. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 135 PM EDT THURSDAY... MAINLY VISUAL FLIGHT RULE CONDITIONS EXIST ACROSS THE REGION CURRENTLY. THE EXCEPTION WILL BE UNDER THE HEAVIER CORES OF THE ISOLATED TO SCATTERED SHOWERS AND STORMS THAT ARE PROGRESSING SOUTH THROUGH PARTS OF THE REGION. AS THE REGION CONTINUES TO DESTABILIZE WITH DAYTIME HEATING...CONFIDENCE HAS INCREASED ENOUGH TO INCLUDE SUCH A LOWERING OF FLIGHT CATEGORIES AT ROANOKE BETWEEN 19Z/3PM AND 20Z/4PM WITH THE CLUSTER OF SHOWERS AND STORMS THAT IS CURRENTLY PROGRESSING SOUTH THROUGH ALLEGHANY COUNTY VIRGINIA. FOR THE OTHER TERMINAL SITES SAVE DANVILLE...HAVE INCLUDED ONLY VICINITY OF SHOWERS OR VICINITY OF THUNDER THROUGH THIS AFTERNOON. IF CONFIDENCE INCREASES THE ACTIVITY TO PASS OVER A GIVEN AIRPORT...AN ADMENDMENT WILL BE ISSUED. COVERAGE IS EXPECTED TO INCREASE AS THE AFTERNOON PROGRESSES...AND GRADUALLY ENTER INTO EASTERN AND SOUTHEASTERN PARTS OF THE REGION BY THE LATE AFTERNOON AND EARLY EVENING. AT THIS POINT COVERAGE WILL BEGIN TO WANE...LEAVING ISOLATED COVERAGE BY THE LATE EVENING. OVERNIGHT AND INTO EARLY FRIDAY...THE LOW LEVEL FLOW WILL BEGIN TO TREND NORTHEAST OR EAST...EVENTUALLY ALLOWING FOR A MOISTURE FETCH OFF THE ATLANTIC. THIS WILL HELP ADVECT CLOUD COVER INTO THE REGION AND ALSO ALLOW FOR UPSLOPE CLOUD DEVELOP ALONG THE CREST OF THE BLUE RIDGE. SHOWER AND THUNDERSTORM DEVELOPMENT IS EXPECTED TO INITIATE BY THE LATE MORNING TO AROUND NOONTIME ON FRIDAY. CEILINGS WILL MOSTLY BE VISUAL FLIGHT RULES WITH POCKETS OF MARGINAL VISUAL FLIGHT RULES. MOUNTAIN AND RIVER VALLEY FOG OR MIST IS AGAIN EXPECTED LATE TONIGHT INTO EARLY FRIDAY...WITH COVERAGE MORE LIKELY WHERE PRECIPITATION OCCURS THE AFTERNOON AND EVENING. EXTENDED AVIATION DISCUSSION... WILL SEE A WEAK FLOW PATTERN WITH AN UPPER TROUGH EXTENDING FROM EAST-WEST OVER OUR AREA FRIDAY INTO SUNDAY. THIS ALONG WITH HIGH PRESSURE TO THE NORTHEAST WILL CAUSE THE LOW LEVEL FLOW TO TURN MORE EASTERLY IN TIME. AS OF NOW...THE TERMINALS WILL BE VFR DURING THE DAY...WITH POSSIBLE MVFR OR WORSE WITH FOG AT NIGHT INTO FRIDAY NIGHT. THE EASTERLY FLOW EXPECTED BY SATURDAY WILL BRING LOWER CLOUDS IN AND POTENTIAL FOR MVFR CIGS AT LEAST FOR THE MOUNTAINS...AND LOW END VFR AT KROA/KLYH/KDAN. WITH THIS UPPER TROUGH THERE WILL BE A DAILY THREAT OF SHOWERS...SO SUB VFR IN THESE WILL BE POSSIBLE. BY SUNDAY-MONDAY THE WEAK TROUGH ALOFT MOVES OVER THE SOUTHEAST COAST WHILE UPPER RIDGING ELONGATES OVER THE MID ATLANTIC. WE WILL SEE SOME DRYING TAKE PLACE SO VFR SHOULD OCCUR SUNDAY-TUESDAY WITH THE STILL A THREAT OF FOG AT NIGHT AT KBCB/KLWB. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...DS/JH SHORT TERM...RAB LONG TERM...AMS/RAB AVIATION...DS/JH

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