Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 040518 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 118 AM EDT FRI SEP 4 2015 .SYNOPSIS... A BACKDOOR COLD FRONT WILL APPROACH THE REGION FROM THE NORTH FRIDAY BEFORE STALLING OUT ACROSS THE AREA LATER FRIDAY NIGHT INTO SATURDAY. INCREASING MOISTURE AHEAD OF THE BOUNDARY WILL LEAD TO INCREASING COVERAGE OF SHOWERS AND STORMS LATER FRIDAY INTO FRIDAY NIGHT. HIGH PRESSURE WILL WEDGE IN FROM THE NORTHEAST SATURDAY NIGHT INTO SUNDAY...AND REMAIN IN PLACE THROUGH EARLY NEXT WEEK RESULTING IN SOMEWHAT COOLER WEATHER OVER THE HOLIDAY WEEKEND. && .NEAR TERM /THROUGH TODAY/... AS OF 800 PM EDT FRIDAY... THE COVERAGE OF SHOWERS AND STORMS HAS RAPIDLY FALLEN OFF WITH SUNSET AND ONLY A FEW ISOLATED SHOWERS ARE EXPECTED OVER THE NEXT FEW HOURS. A FEW SPOTS PICKED UP OVER AN INCH OF RAIN THIS AFTERNOON BUT MOST AREAS SAW LITTLE OR NOTHING. OVERNIGHT INTO FRIDAY...WE ARE EXPECTING THE LOW LEVEL FLOW TO TREND MORE NORTHEAST...AND EVENTUALLY MORE EASTERLY TOWARDS LATE IN THE DAY FRIDAY. THIS WILL HAVE THE INFLUENCE OF EVENTUALLY BRINGING INCREASING ATLANTIC MOISTURE INTO THE REGION. THE RESULT WILL BE A TREND TOWARDS MORE CLOUD COVER...AND PATCHY RAIN SHOWERS VERY LATE TONIGHT INTO EARLY FRIDAY MORNING BECOMING MORE NUMEROUS THROUGHOUT FRIDAY. TRAJECTORIES BY THE AFTERNOON WILL ALLOW FOR OROGRAPHIC INFLUENCE ALONG THE BLUE RIDGE...WITH LIKELY PROBABILITY OF PRECIPITATION BY THE LATE AFTERNOON. MOUNTAIN AND RIVER VALLEY FOG WILL DEVELOP AGAIN TONIGHT...ESPECIALLY IN THOSE AREA THAT RECEIVE RAIN TODAY AND THIS EVENING. TEMPERATURES WILL CONTINUE TO BE ON THE WARM/HOT SIDE TONIGHT AND THURSDAY. LOWS TONIGHT WILL RANGE FROM THE LOW TO MID 60S ACROSS THE MOUNTAINS TO THE MID TO UPPER 60S ACROSS THE FOOTHILLS AND PIEDMONT. HIGH TEMPERATURES FRIDAY WILL RANGE FROM THE MID 80S ACROSS THE MOUNTAINS TO THE UPPER 80S TO LOWER 90S ACROSS THE FOOTHILLS AND PIEDMONT. && .SHORT TERM /TONIGHT THROUGH SUNDAY/... AS OF 345 PM EDT THURSDAY... UPPER LOW OVER THE SOUTHEAST UNITED STATES AND WEDGE ALONG THE EAST SLOPES OF THE APPALACHIANS WILL RESULT IN DEEP EASTERLY WINDS FRIDAY NIGHT AND SATURDAY. WINDS WILL NOT BE PARTICULARLY STRONG BUT BUFKIT FORECAST SOUNDINGS AT LYNCHBURG AND DANVILLE INDICATE EAST WINDS FROM THE SURFACE THROUGH AT LEAST 500MB. BUFKIT WAS ALSO SHOWING SOME MID LEVEL DRYING ON SUNDAY NIGHT AND MONDAY BUT OVERALL MODELS WERE NOT AS AGGRESSIVE WITH THE PUSH OF DRIER AIR BEHIND THE BACKDOOR COLD FRONT AS IN PAST FEW RUNS. BEST LIFT THROUGH THE PERIOD WILL BE FROM THE UPSLOPE WITH VORTICITY ADVECTION AND INSTABILITY NOT AS MUCH OF A CONTRIBUTING FACTOR. THIS WILL MEAN THE HIGHEST PROBABILITY OF PRECIPITATION WILL BE ALONG THE BLUE RIDGE AND OVER THE FOOTHILLS. 12Z GFS WAS FARTHER EAST WITH RETURN OF LOW LEVEL MOISTURE INTO THE EASTERN COUNTY WARNING AREA ON SUNDAY. WILL BE FOLLOWING THE GFS TRENDS FOR CLOUD COVER ON SATURDAY NIGHT AND SUNDAY. WILL BE TRIMMING BACK THE CHANCE OF THUNDER ON SATURDAY NIGHT AND SUNDAY WITH THE GUIDANCE SHOWING THE STABLE AIR BEHIND THE FRONT WELL INTO THE FORECAST AREA. STAYED CLOSER TO COOLER MAV GUIDANCE NUMBERS FOR MAXIMUM AND MINIMUM TEMPERATURES IN THE WEDGE. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AS OF 100 PM EDT THURSDAY... STARTING WITH A BROAD UPPER LOW OVER THE SOUTHEAST UNITED STATES AND A STRONG RIDGE IN THE SOUTHERN PLAINS ON SUNDAY NIGHT. 500 MB HEIGHTS FALL OVER THE NORTHEAST UNITED STATES MONDAY THROUGH WEDNESDAY. BY THURSDAY THE NORTHERN STREAM BECOMES MORE DOMINANT WITH MORE TROUGHING ACROSS ALL OF THE EAST. AT THE SURFACE AND LOW LEVELS FORECAST AREA WILL BE IN A DEEP WEDGE COVERING THE EAST SIDE OF THE APPALACHIANS FRIDAY NIGHT THROUGH MONDAY WITH EAST TO SOUTHEAST WINDS. THE WEDGE WILL BREAK DOWN ON TUESDAY. THEN SOUTHWEST FLOW WILL BRING A RETURN OF MOISTURE AND WARMER 850 MB TEMPERATURES TUESDAY NIGHT AND WEDNESDAY. A WELL DEFINED COLD FRONT AND THE LEADING EDGE OF COOLER AIR WILL REACH THE FORECAST AREA ON THURSDAY. WAVES OF LOW PRESSURE ALONG THE FRONT IN THE CENTRAL UNITED STATES MAY SLOW DOWN THE TIMING AND THE EASTWARD MOVEMENT OF THE FRONT FOR WEDNESDAY AND THURSDAY. TEMPERATURES WILL AGAIN BE ABOVE NORMAL IN THE WARM SECTOR AHEAD OF THE COLD FRONT ON WEDNESDAY AND THURSDAY. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 100 AM EDT FRIDAY... FOG/STRATUS THE MAIN AVIATION CONCERN AGAIN OVERNIGHT WITH IFR/LIFR LIKELY TO DEVELOP IN THE VALLEYS AND IN SPOTS WHERE AFTERNOON RAINFALL OCCURRED NAMELY AT KBCB/KLWB. OTRW LOOKING AT SPOTTY MVFR IN FOG WITH ONLY SOME MID DECK AROUND WHERE STRATUS DOES NOT DEVELOP. A BACKDOOR COLD FRONT WILL SINK SOUTH TOWARD THE AREA ON FRIDAY PRECEDED BY ONSHORE FLOW AND STRONG INSTABILITY. THIS COMBINED WITH WEAK ENERGY ALOFT TO THE NW SHOULD LEAD TO MORE WIDESPREAD CONVECTION FROM MIDDAY INTO FRIDAY EVENING. APPEARS BEST COVERAGE EARLY ON WILL BE ALONG THE BLUE RIDGE WITH A GRADUAL SHIFT EAST ONCE THE BOUNDARY SLIDES SOUTH. THINK ENOUGH POTENTIAL TO INCLUDE A PREVAILING SHRA GROUP WITH EMBEDDED VCTS AT MOST LOCATIONS ALONG AND EAST OF THE BLUE RIDGE AND VCTS IN SE WEST VA FOR NOW. SHOWERS MAY LINGER ESPCLY SOUTH INTO THE EVENING SO KEPT MENTION IN PAST SUNSET. OTRW LOOKING AT MAINLY VFR CU FIELDS BY LATE MORNING...WITH 4-6K FT CU CIGS INTO THE AFTERNOON WITH MVFR/IFR WHERE BANDS/CLUSTERS OF STORMS DEVELOP. STRONG WINDS WILL ALSO BE POSSIBLE IN THE VICINITY OF STORMS BUT WILL HOLD OFF INCLUDING WITHIN THE TAFS FOR NOW GIVEN UNCERTAINTY IN STRENGTH/COVERAGE LATER ON. EXTENDED AVIATION DISCUSSION... WILL SEE A WEAK FLOW PATTERN WITH AN UPPER TROUGH EXTENDING FROM EAST-WEST OVER OUR AREA SATURDAY 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. && .HYDROLOGY... AS OF 745 PM EDT THURSDAY... THE WEEKLY UNITED STATES DROUGHT MONITOR ISSUED THIS MORNING 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/JH NEAR TERM...DS SHORT TERM...AMS LONG TERM...AMS AVIATION...DS/JH/PC HYDROLOGY...PC

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