Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 280829 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 429 AM EDT FRI AUG 28 2015 .SYNOPSIS...
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HIGH PRESSURE WILL MOVE EAST TOWARD NEW ENGLAND TODAY...SHIFTING WINDS FROM THE SOUTHEAST BY THIS EVENING. A WEAK UPPER LEVEL DISTURBANCE WILL SLIDE NORTH ALONG THE APPALACHIANS SUNDAY INTO MONDAY...BRINGING BETTER CHANCES OF SHOWERS AND STORMS...MAINLY TO THE MOUNTAINS. HIGH PRESSURE WILL THEN STRENGTHEN IN THE WAKE OF THIS FEATURE...RESULTING IN DRIER AND WARMER WEATHER BY THE MIDDLE OF NEXT WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 400 AM EDT FRIDAY... THE UPPER LEVEL TROUGH WHICH HELD IN PLACE ACROSS THE EASTERN PORTION OF THE COUNTY CONTINUES TO WEAKEN THIS MORNING...WHILE SUBTROPICAL RIDGING GRADUALLY NUDGES ITS WAY OVER THE SOUTHEAST AND MID ATLANTIC STATES. IN THE LOW LEVELS...HIGH PRESSURE CONTINUES TO SHIFT EAST ACROSS THE LOWER GREAT LAKES...MAKING FOR LIGHT NORTHEAST WINDFLOW ACROSS OUR AREA. WHILE OUR ATMOSPHERE IS DRY FOR THE MOST PART...DO HAVE A THIN LAYER OF MOISTURE A FEW THOUSAND FEET OFF THE SURFACE...MAKING FOR PARTLY TO MOSTLY CLOUDY SKIES ACROSS MUCH OF THE MOUNTAINS AND FOOTHILLS. THESE CLOUDS ARE ACTING TO BOTH KEEP TEMPERATURES A LITTLE WARMER COMPARED TO THE PREVIOUS FEW MORNINGS...AND ALSO KEEP VALLEY FOG FORMATION TO A MINIMUM. AS HIGH PRESSURE SHIFTS TOWARD NEW ENGLAND...EXPECT OUR WINDS TO BECOME EASTERLY BY LUNCHTIME...AND SOUTHEASTERLY DURING THE EVENING. THE MORE EASTERLY DIRECTION WILL CONTINUE TO DRAW ATLANTIC MOISTURE INTO OUR AREA...PUSHING IT UPSLOPE INTO THE MOUNTAINS. AS SUCH...WE CAN EXPECT ISOLATED TO WIDELY SCATTERED SHOWERS TO DEVELOP DURING THE AFTERNOON ACROSS THE RIDGES. OTHERWISE...EXPECT PARTLY CLOUDY SKIES...PERHAPS BECOMING MOSTLY CLOUDY AT TIMES ACROSS THE MOUNTAINS. SLIGHTLY WARMER TODAY AS WELL THANKS TO THE INCREASED INFLUENCE FROM THE SUBTROPICAL RIDGE. AFTERNOON HIGH TEMPERATURES WILL RANGE FROM THE MID/UPPER 70S ACROSS THE MOUNTAINS TO THE LOW/MID 80S ACROSS THE PIEDMONT. SOUTHEASTERLY WINDFLOW WILL REMAIN FOR TONIGHT...PUSHING MARINE MOISTURE INTO THE MOUNTAINS. AS SUCH...EXPECT PARTLY TO MOSTLY CLOUDY SKIES TO REDEVELOP ACROSS THE MOUNTAINS AND FOOTHILLS... POSSIBLY WITH AN ISOLATED BRIEF SHOWER. OVERNIGHT TEMPERATURES WILL FALL INTO THE MID 50S TO LOW 60S.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
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AS OF 400 AM EDT FRIDAY... FORECAST BECOMES INCREASINGLY UNCERTAIN DURING THIS PERIOD...FOCUSED PRIMARILY AROUND THE TRACK AND INTENSITY OF TROPICAL STORM ERIKA LATE IN THE PERIOD. SEVERAL WEAK FEATURES DRIVING THE SYNOPTIC CONDITIONS AT THE BEGINNING OF THE PERIOD. A BROAD...REMNANT UPPER TROUGH LINGERS ACROSS THE EASTERN U.S...WHILE A NEW UPPER TROUGH DRIFTS INTO THE OHIO VALLEY. BOTH SYSTEMS UNDERLIE A BROAD UPPER RIDGE PRESENT AND BUILDING ACROSS MUCH OF THE REGION...BOTH FROM THE WESTERN ATLANTIC AND THE CENTRAL U.S. MEANWHILE...A TROUGH/EARLIER WEEK FRONTAL PASSAGE...LINGERS ALONG THE NC/SC COAST INTO THE SOUTHEAST STATES. WEAK REMNANTS OF FORMER HURRICANE DANNY EVIDENT ACROSS THE EASTERN GULF COASTAL REGION. THE TROUGH TO THE WEST WILL SLOWLY APPROACH THE REGION...BUT WILL WEAKEN AND LIFT NORTH AS IT APPROACHES THE ALLEGHANYS SUN...WITH ONLY A WEAK REMNANT TROUGH LINGERING ACROSS THE NORTHERN PORTIONS OF THE AREA BY MON. MEANWHILE...SOUTHERLY FLOW BETWEEN THE WESTERN ATLANTIC RIDGE AND THE BROAD UPPER LOW PERSISTING ACROSS THE MID-SOUTH...WILL ALLOW GULF/TROPICAL MOISTURE TO GRADUALLY BE DRAWN NORTHWARD INTO THE REGION THROUGH THE WEEKEND. WITH EASTERLY FLOW AND MOISTURE POOLED/UPLIFTED ACROSS THE MOUNTAINS IN THE SOUTHWEST PART OF THE CWA...WE SHOULD START TO SEE SLIGHTLY BETTER COVERAGE EACH DAY OF SHOWERS AND THUNDERSTORMS IN THAT REGION. EASTERN AREAS WILL SEE GREATER SUBSIDENCE AND DRIER/MORE STABLE NORTHEAST FLOW...CONSEQUENTLY LITTLE TO NO PRECIPITATION EXPECTED. ALL OF THIS IS BEST REPRESENTED BY SLIGHT CHANCE POPS WESTERN MOUNTAINS SATURDAY...INCREASING TO CHANCE POPS AND CREEPING SLIGHTLY EASTWARD TOWARD THE BLUE RIDGE BY MONDAY. 850MB TEMPS WILL BE ON THE INCREASE THROUGH THE PERIOD AS BROAD UPPER RIDGING DEVELOPS ACROSS MUCH OF THE EASTERN 2/3RD OF THE U.S. 850MB TEMPS RISE FROM THEIR CURRENT LEVELS IN THE +10C TO +15C RANGE...CLOSER TO +20C BY EARLY NEXT WEEK. WITH DEWPOINTS ALSO ON THE INCREASE...MIN TEMPS WILL RANGE FROM MID TO UPPER 50S MOUNTAINS TO MID 60S EAST...WITH HIGHS 70S MOUNTAINS TO MID AND UPPER 80S PIEDMONT.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/...
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AS OF 415 AM EDT FRIDAY... THE FORECAST BEYOND MONDAY IS LARGELY DEPENDENT ON THE TRACK AND INTENSITY OF ERIKA. CURRENT MODEL TRENDS ARE ALL OVER THE PLACE WITH THE CANADIAN SHOWING A MAJOR HURRICANE TRACKING NORTHWEST INTO OUR CWA WITH ASSOCIATED WIND/RAIN...WHILE THE GFS/ECMWF HAVE LITTLE MORE THAN A TROPICAL LOW...POTENTIALLY SHEARED INTO TWO PARTS...ONE WHICH REMAINS OFF THE ATLANTIC COAST AND THE OTHER TRACKING WESTWARD...EITHER INTO THE MID-SOUTH OR POSSIBLY INTO THE TN VALLEY. WITH THE CONSIDERABLE DEGREE OF UNCERTAINTY IN PLACE...SIMPLY CANNOT INCLUDE ANY EFFECTS IN THE GRIDS AT THIS POINT. LATEST NHC TRENDS ARE FOR A WEAKER SYSTEM AND MUCH WILL DEPEND ON ITS INITIAL INTERACTION WITH THE CARIBBEAN ISLANDS BEFORE IT EVEN REACHES THE U.S. MAINLAND. HAVE MADE ONLY MINOR ADJUSTMENTS TO POPS BEYOND DAY 5...WHICH GENERALLY ADVERTISED JUST SLIGHT CHANCE/CHANCE POPS...HIGHLY DIURNAL IN NATURE...ALL SUBJECT TO CHANGE BASED ON THE EVENTUAL TRACK AND FATE OF ERIKA. TEMPS BASICALLY A PERSISTENCE FORECAST THROUGH THE PERIOD UNDER WEAK SURFACE HIGH PRESSURE AND BROAD RIDGING ALOFT...THUS LITTLE CHANGE IN THE AIRMASS EXCEPT FOR SLOWLY INCREASING MOISTURE. OVERALL...MIN AND MAX TEMPS SHOULD BE SLIGHTLY ABOVE NORMAL WITH 850MB TEMPS HOVERING NEAR +20C THROUGH THE PERIOD. EXPECT LOWS MOSTLY IN THE 60S...A FEW 50S MOUNTAINS...WITH HIGHS 70S MOUNTAINS TO MID AND UPPER 80S PIEDMONT.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... AS OF 200 AM EDT FRIDAY... HIGH PRESSURE IS PASSING EAST ACROSS THE LOWER GREAT LAKES THIS MORNING...SHIFTING WINDS ACROSS THE MID ATLANTIC INCREASINGLY FROM THE NORTHEAST. CURRENTLY OBSERVING SCT TO BKN CLOUDS FROM THE BLUE RIDGE WESTWARD...MAINLY VFR WITH BASES IN THE 4KFT TO 6KFT RANGE. EXPECT CEILINGS TO DROP IN SPOTS ACROSS THE MOUNTAINS TOWARD DAWN...RESULTING IN SPOTTY MVFR BASES IN THE 2KFT TO 3KFT RANGE. WILL ALSO SEE RIVER VALLEY FOG DEVELOP IN SPOTS THAT REMAIN CLOUD- FREE FOR EXTENDED PERIODS OF TIME. FOG WILL DISSIPATE AND CEILINGS LIFT AFTER 28/14Z AS DAYTIME HEATING INCREASES. WINDS WILL SHIFT INCREASINGLY EASTERLY THROUGH LATE MORNING...BECOMING SOUTHEASTERLY DURING EARLY EVENING...WITH SPEEDS IN THE 5KT TO 10KT RANGE. WITH WIND DIRECTION BECOMING UPSLOPE...EXPECT A FEW SHOWERS TO DEVELOP ACROSS THE RIDGES WITH MAXIMUM AFTERNOON HEATING...HOWEVER LACK OF DEEP MOISTURE IN THE AREA WILL KEEP COVERAGE LIMITED. OTHERWISE...EXPECT SCT CU ACROSS THE PIEDMONT...AND SCT TO BKN CU ACROSS THE MOUNTAINS...AGAIN WITH BASES IN THE 4KFT TO 6KFT RANGE. EXTENDED AVIATION DISCUSSION... AS OF 200 AM EDT FRIDAY... EXPECT A MAINLY VFR FORECAST INTO SUNDAY. MOISTURE GRADUALLY INCREASES BY THE WEEKEND WITH ISOLATED TO SCATTERED CONVECTION POSSIBLE...WITH BRIEF PERIODS OF MVFR CIGS/VSBYS POSSIBLE. TYPICAL LATE NIGHT/EARLY MORNING MVFR TO LIFR FOG THREAT AT LWB/BCB/LYH THROUGH THE PERIOD. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...NF SHORT TERM...RAB LONG TERM...JH/RAB AVIATION...DS/NF

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