Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 251732 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 132 PM EDT SAT JUL 25 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD OVER THE REGION TODAY AND WILL REMAIN OVER THE AREA THROUGH SUNDAY. A BACKDOOR COLD FRONT WILL MOVE INTO THE AREA SUNDAY NIGHT AND MONDAY...THEN STALL...AND BE A FOCUS FOR SHOWERS AND THUNDERSTORMS INTO AT LEAST TUESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 100 PM EDT SATURDAY... SURFACE HIGH PRESSURE WILL REMAIN OVER THE AREA TODAY...KEEPING MOST LOCATIONS DRY. MOISTURE IS LIMITED AND BELOW 6500 FEET. ISOLATED SHOWERS THIS AFTERNOON WILL MOSTLY LIKELY BE ALONG THE EASTERN SLOPES OF THE BLUE RIDGE. ANY SHOWERS THAT DEVELOP IN SOUTHEASTERLY FLOW WILL NOT LAST LONG THIS EVENING AND WILL FADE WITH LOSE OF HEATING. UNDER PARTLY CLOUDY SKIES...TEMPERATURES THIS AFTERNOON WILL WARM TO NORMAL LEVELS. SINCE EXTREME SOUTHWEST VIRGINIA AND SOUTHEASTERN WEST VIRGINIA ALREADY HAVE A SOUTHERLY FLOW...THIS AFTERNOON`S TEMPERATURES WILL BE 3F-5F WARMER THAN NORMAL. AS OF 400 AM EDT SATURDAY... AS SURFACE HIGH PRESSURE BUILDS IN FROM THE OHIO VALLEY THIS MORNING...MOISTURE...WHICH IS TRAPPED UNDER AN INVERSION...IS RESULTING IN AREAS OF LOW CLOUDS. AREAS NOT BEING OVERCOME BY LOW TO MID CLOUDS HAVING PATCHY MORNING FOG...MAINLY IN MOUNTAIN VALLEYS AND LOW LYING AREAS. THE COVERAGE OF FOG AT THIS TIME IS LESS THAN YESTERDAY MORNING. THE MORNING FOG WILL BURN OFF QUICKER THAN ANY STRATUS DECK WHICH MAY FORM. WHILE SEVERAL OF THE MODELS SHOWED A WEAK SHORTWAVE DROPPING SOUTH IN THE NORTHWEST FLOW THIS AFTERNOON...BELIEVE POPS AND QPF ARE OVERDONE...ESPECIALLY ON NAM. LEANED TOWARDS GFS...LATEST 06Z HRRR AND RAP...WHICH INDICATE THAT A SOUTHEASTERLY UPSLOPE WINDS MAY HAVE ENOUGH MOISTURE TO PRODUCE A FEW ISOLATED SHOWERS AND MAYBE A THUNDERSTORM IN THE AFTERNOON...ESPECIALLY IN NORTHWEST NORTH CAROLINA ALONG BLUE RIDGE. HIGH TEMPERATURES THIS AFTERNOON WILL RANGE FROM THE THE MID TO UPPER 70S IN THE NORTHWEST MOUNTAINS TO NEAR 90 DEGREES IN THE PIEDMONT. SFC HIGH PRESSURE WILL CONTINUE TO SETTLE ALONG THE EAST COAST THROUGH TONIGHT...WITH WEAK SOUTHERLY RETURN FLOW INTO THE APPALACHIANS. ANY LINGERING ISOLATED MOUNTAIN SHOWERS SHOULD DISSIPATE THIS EVENING. LIGHT WINDS AND LOW LEVEL MOISTURE WILL RESULT IN PATCHY VALLEY FOG TONIGHT INTO SUNDAY MORNING. LOW TEMPERATURES TONIGHT WILL BE NEAR NORMAL WITH READINGS FROM AROUND 60 IN THE MOUNTAINS TO THE UPPER 60S IN THE PIEDMONT. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... AS OF 430 AM EDT SATURDAY... STRONG UPPER RIDGE ACROSS THE CENTRAL U.S. WILL DRIFT SLOWLY EASTWARD DURING THE PERIOD. WEAK NW-NNW FLOW WILL REMAIN OVER OUR REGION. THE MAIN FOCUS THROUGH THIS PERIOD WILL BE ON A WEAK NORTHWEST FLOW SHORT WAVE AND ASSOCIATED FRONT PROGGED TO DRIFT SOUTHWARD INTO THE NORTHWEST PART OF THE FORECAST AREA MONDAY...CONTINUING SLOWLY INTO THE PIEDMONT SECTION TUE. INSTABILITY PARAMETERS ARE FAIRLY WEAK FOR THIS TIME OF YEAR AND DYNAMICS ARE NIL. MOISTURE IS SOMEWHAT LIMITED COMPARED TO LAST WEEK...WITH DEWPOINTS IN THE MID 60S...AS OPPOSED TO UPPER 60S AND LOWER 70S...WITH PWATS GENERALLY 1.50 INCH OR LESS. THUS...CONDITIONS ARE FAR FROM IDEAL FOR WIDESPREAD SHOWERS/THUNDERSTORMS. HOWEVER...WITH DAYTIME HEATING AND AT LEAST SOME FOCUS GIVEN THE FRONTAL BOUNDARY...WOULD AT LEAST EXPECT TO SEE WIDELY SCATTERED TO SCATTERED SHOWERS AND THUNDERSTORMS. BY TUESDAY...WITH THE UPPER RIDGE BUILDING EASTWARD INTO THE TENNESSEE VALLEY AND THE FRONTAL BOUNDARY/UPPER TROUGH SHIFTING INTO THE SOUTHEAST STATES...THE FOCUS FOR CONVECTION SHOULD SHIFT MOSTLY SOUTH OF THE CWA. AT THIS POINT...NO SUPPORT TO ADVERTISE ANYTHING MORE THAN CHANCE POPS...WITH A STRONG DIURNAL SIGNAL. THE THREAT FOR SEVERE THUNDERSTORMS IS VERY LOW AND SPC CURRENTLY ONLY HAS GENERAL THUNDER THROUGH THE PERIOD. 850MB TEMPS HOVER NEAR +20C THROUGHOUT THE PERIOD...BUT GENERALLY DOES NOT EXCEED IT MUCH. AS HAS BEEN THE CASE RECENTLY...THE GFS GRIDDED TEMPS ARE MUCH WARMER THAN ANY OF THE OTHER MODELS ADVERTISING WIDESPREAD 90S...WHILE THE OTHER MODELS ARE MORE TEMPERATE WITH HIGHS IN THE 80S. LEANED TOWARD THE MODEL BLEND...WHICH KEEPS MOST AREAS IN THE 80S...UPPER 70S MOUNTAINS...AS OPPOSED TO THE HOT GFS. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... AS OF 445 AM EDT SATURDAY... STRONG UPPER RIDGE REMAINS ACROSS THE WESTERN TENNESSEE VALLEY...BUT EXTENDS NORTHEASTWARD INTO THE MID-ATLANTIC AND NORTHEAST U.S. GENERALLY A DRY PERIOD WEDNESDAY THROUGH THURSDAY. BY FRIDAY...THE UPPER RIDGE BACKS OFF INTO THE WESTERN U.S...ALLOWING AN UPPER TROUGH TRAVERSING THE GREAT LAKES AND NEW ENGLAND TO PUSH A WEAK COLD FRONT SOUTHWARD THROUGH THE REGION. FROM THIS POINT...THE MODELS DIVERGE SIGNIFICANTLY FROM EACH OTHER AND ALSO FROM RUN-TO-RUN AND CONFIDENCE IN THIS PORTION OF THE FORECAST IS QUITE LOW. FOR THE LAST SEVERAL CYCLES THE ECMWF AND ALSO THE CANADIAN HAVE ADVERTISED A SIGNIFICANT TROPICAL SYSTEM DEVELOPING OFF THE SC/NC COAST AND MOVING NORTHEASTWARD JUST OFF THE EAST COAST. THE GFS HAS FAILED TO SUPPORT THIS...OPTING FOR AN INLAND TROUGH/WEAK AREA OF LOW PRESSURE ELONGATED FROM SW-NE ALONG THE COAST...WITH A LAGGING UPPER TROUGH ACROSS THE SOUTHEAST STATES. THE 00Z ECMWF HAS NOW COME ON BOARD WITH THE LONG STANDING GFS SOLUTION...WHILE THE CANADIAN IS STILL ADVERTISING A TROPICAL SYSTEM. THE KEY WILL BE WHETHER OR NOT LOW PRESSURE DEVELOPS INLAND OR OVER THE WARM GULF STREAM WATERS. WHILE CONFIDENCE REMAINS LOW...THERE IS INCREASING CONSENSUS THAT A TROUGH OF LOW PRESSURE WILL BE ACROSS EASTERN VA/NC AND AREAS EAST OF THE BLUE RIDGE SHOULD SEE INCREASING CHANCES FOR PRECIPITATION DURING THIS PERIOD...WITH LESS TO THE WEST CLOSER TO THE UPPER RIDGE. A SHIFT IN THIS TROUGH AXIS WILL HAVE SIGNIFICANT IMPLICATIONS AS TO HOW MUCH MOISTURE WE RECEIVE. ALL IS SUBJECT TO CHANGE WITH LATER MODEL RUNS. GIVEN THE LOW CONFIDENCE AND RUN-TO-RUN INCONSISTENCIES...HAVE NOT MADE ANY CHANGES TO POPS/TEMPS BEYOND DAY 5. AS IN THE SHORT TERM PERIOD...850MB TEMPS HOVER NEAR OR SLIGHTLY ABOVE +20C MUCH OF THIS PERIOD...SO IT WILL REMAIN WARM TO HOT...WITH ANY COOLING A RESULT OF CLOUD COVER AND PRECIPITATION DURING THE LATER PORTION OF THE PERIOD. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 120 PM EDT SATURDAY... SURFACE HIGH PRESSURE WILL REMAIN OVER THE AREA INTO TONIGHT ...KEEPING MOST LOCATIONS DRY. MOISTURE IS LIMITED AND BELOW 6500 FEET. ISOLATED SHOWERS THIS AFTERNOON WILL MOSTLY LIKELY BE ALONG THE EASTERN SLOPES OF THE BLUE RIDGE. ANY SHOWERS THAT DEVELOP IN SOUTHEASTERLY FLOW WILL NOT LAST LONG THIS EVENING AND WILL FADE WITH LOSE OF HEATING. WITH CONVECTION ACTIVITY BEING ISOLATED THIS AFTERNOON/EVENING...CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE IN 18Z TAFS. HOWEVER...THEY MAY DISRUPT FLIGHT PATHS FOR THOSE TRAVELING PARALLEL TO THE BLUE RIDGE. SOME HI-RES MODELS SHOWING BLUE RIDGE CONVECTION DRIFTING EAST INTO THE FOOTHILLS THIS EVENING. LOOKING AT SATELLITE IMAGERY...THIS IS POSSIBLE...HOWEVER ACTIVITY WILL REMAIN ISOLATED. HIGH-END MVFR/LOW-END VFR CLOUDS MAY HANG AROUND THIS EVENING. AREAS THAT CLEAR OVERNIGHT...ESPECIALLY MOUNTAIN VALLEYS...WILL SEE PATCHY FOG SUNDAY MORNING. EXTENDED AVIATION FORECAST... A WEAK FRONTAL BOUNDARY WILL DRIFT INTO THE REGION SUNDAY WITH SCATTERED SHOWERS AND THUNDERSTORMS...MAINLY DURING THE AFTERNOON. THE FRONT WILL DRIFT SLOWLY SOUTHEAST THROUGH MONDAY...WITH THE CHANCE FOR SHOWERS AND THUNDERSTORMS SHIFTING MAINLY EAST OF THE BLUE RIDGE BY MONDAY. OUTSIDE MAINLY AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS AND LATE NIGHT/EARLY MORNING MAINLY VALLEY FOG...EXPECT MOSTLY VFR CONDITIONS. MOSTLY VFR CONDITIONS EXPECTED TUE-WED...BEFORE BETTER CHANCES FOR SHOWERS/THUNDERSTORMS RETURN BY THU/FRI WITH THE NEXT FRONTAL BOUNDARY AND A POTENTIAL DEEP FETCH OF GULF MOISTURE. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...KK NEAR TERM...KK/RCS SHORT TERM...RAB LONG TERM...RAB/WP AVIATION...RCS

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