Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 050556 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 156 AM EDT SAT SEP 5 2015 .SYNOPSIS... A BACKDOOR COLD FRONT WILL STALL OVER THE SOUTHERN PORTION OF THE REGION ON SATURDAY. 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 TODAY/... AS OF 1140 PM EDT FRIDAY... A LONE THUNDERSTORM NORTH OF LYH...WITH ISOLATED SHOWERS ACROSS THE ALLEGHANY HIGHLANDS INTO THE SOUTHERN SHENANDOAH VLY. NOT SEEING A LOT OF SIGNALS FOR GOOD COVERAGE OVERNIGHT SO KEPT POPS IN THE ISOLATED REALM MOSTLY ALONG AND EITHER SIDE OF THE BLUE RIDGE. THE 00Z NAM IS COMING IN TOO HOT...SHOWING EXCESSIVE COVERAGE IN THE QPF FIELDS IN THE PIEDMONT 03-06Z. SO LEANED MORE TOWARD LATEST HRRR/RAP...THEN BLENDED TOWARD OFFICIAL FORECAST BY DAWN...INCREASING POPS TO CHANCE IN THE SOUTHERN AND SOUTHWEST CWA BY MID MORNING...CLOSER TO THE UPPER IMPULSE. SHOULD SEE SOME VARIABLY CLOUDY SKIES AFTER MIDNIGHT...MIX OF LOW AND HIGH CLOUDS...THEN EASTERLY FLOW WILL SET UP MORE LOWER CLOUDS FOR MUCH OF THE AREA BY DAWN. FOG IS EXPECTED AS WELL...ESPECIALLY IN THE MOUNTAINS...ALONG THE BLUE RIDGE PEAKS...LIKE FANCY GAP. PREVIOUS VALID DISCUSSION... 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 /TONIGHT 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 /06Z SATURDAY THROUGH WEDNESDAY/...
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AS OF 145 AM EDT SATURDAY... BACKDOOR COLD FRONT...LIKELY AIDED BY EVENING CONVECTION...APPEARS TO BE NEAR A CRW- TRI- CLT LINE...DRIFTING SLOWLY WEST. HOWEVER...THE TRUE BACKDOOR FRONT APPEARS TO BE NEAR THE BLUE RIDGE. EVENING SHRA/TSRA ACTIVITY HAS GENERALLY DISSIPATED...BUT AN ISOLATED SHRA/TSRA PERSISTS BETWEEN LYH AND ROA NEAR THE TRUE BACKDOOR FRONTAL BOUNDARY. CANNOT TOTALLY RULE OUT AN ISOLD SHRA TRACKING WEST TO NEAR ROA/BCB OVER THE NEXT FEW HOURS...BUT NOT ENOUGH CONFIDENCE TO INCLUDE IN THE TAF. OTHERWISE...WITH LOSS OF DAYTIME HEATING...NOT EXPECTING MUCH MORE OVERNIGHT EXCEPT FOR AN OCCASIONAL SPRINKLE EAST OF THE BOUNDARY. MARITIME FLOW WILL CONTINUE TO ADVECT INTO THE AREA FROM THE EAST AND IS EXPECTED TO RESULT IN DETERIORATING CEILINGS IN THE 08Z-12Z TIME FRAME FROM EAST TO WEST...ESPECIALLY EAST OF THE BLUE RIDGE. WIDESPREAD MVFR CIGS ARE EXPECTED TO BE IN PLACE FOR ROA/LYH/DAN IN THIS TIME FRAME...LINGERING INTO THE MID/LATE MORNING HOURS BEFORE IMPROVING TO LOW END VFR CIGS. TO THE WEST...EARLIER RAINFALL AND RADIATIONAL COOLING UNDER CURRENTLY MOSTLY CLEAR SKIES AT LWB WILL ALLOW FOR DEVELOPMENT OF DENSE FOG...PAR FOR THE COURSE IN RECENT DAYS. THIS WILL EVOLVE INTO AN MVFR CIG AFT 14Z...LINGERING THROUGHOUT MUCH OF THE DAY. SIMILAR CONDITIONS EXPECTED AT BCB...ALTHOUGH CONFIDENCE IN IFR-LIFR BR/FG LESS. FOR BLF...SKIES ARE CURRENTLY CLEAR...BUT EAST FLOW SHOULD RESULT IN DEVELOPMENT OF MVFR CIGS BY DAYBREAK...LINGERING THROUGHOUT MUCH OF THE DAY. FOG DEVELOPMENT APPEARS LESS LIKELY THERE GIVEN EAST WINDS. FINALLY...INSTABILITY/DEWPOINT BOUNDARY WILL RESIDE NEAR THE I-77 CORRIDOR BY PEAK AFTERNOON HEATING...WHICH COULD SUPPORT THUNDERSTORMS IN THAT PART OF THE STATE AGAIN THIS AFTERNOON. WINDS GENERALLY NE-E 6-10KTS WITH LOW END GUSTS AFTER DAYBREAK. MEDIUM CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN TSRA POTENTIAL WEST THIS AFTERNOON. 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 PARTS OF THE AREA. THIS MOISTURE WILL BEGIN TO RETURN NORTH AND EAST BY MONDAY WITH CHANCES FOR SHOWERS AND THUNDERSTORMS INCREASING THROUGH MID-WEEK AS INSTABILITY INCREASES AND A COLD FRONT APPROACHES FROM THE WEST. PAST SATURDAY...CEILINGS AND VISIBILITIES WILL PRIMARILY BE VFR OUTSIDE EARLY MORNING PATCHY DENSE FOG AND AFTERNOON SHOWERS/THUNDERSTORMS.
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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/WP NEAR TERM...DS/WP SHORT TERM...NF LONG TERM...NF AVIATION...DS/RAB/WP HYDROLOGY...PC

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