Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 020335 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1135 PM EDT FRI AUG 1 2014 .SYNOPSIS... A STATIONARY FRONT EXTENDED FROM OFF THE NORTH CAROLINA COAST TO SOUTHERN GEORGIA THIS AFTERNOON WITH HIGH PRESSURE WEDGED FROM NEW JERSEY INTO THE WESTERN CAROLINAS. LITTLE CHANGE IN THE WEATHER PATTERN IS EXPECTED OVERNIGHT. SATURDAY THE WEDGE ERODES AND THE COASTAL FRONT REMAINS TO THE SOUTHEAST. && .NEAR TERM /THROUGH SATURDAY/... AS OF 1135 PM EDT FRIDAY... VERY MINOR UPDATE FOR POPS GIVEN MOST OF RAIN HAS MOVED TO THE NORTHEAST...AND HAVE CONTINUED TO TREND DOWN MUCH OF THE REST OF THE NIGHT GIVEN LATEST HRRR EVEN DRIER OVERNIGHT. SOME TEMPS...ESPECIALLY IN THE PIEDMONT HAVE DROPPED A COUPLE MORE DEGREES SO NEEDED TO PULL MINS DOWN IN SOME LOCATIONS ANOTHER NOTCH. SPREAD SOME OF THE FOG/DRIZZLE BACK A LITTLE FARTHER WEST IN SPOTS AND MADE SURE ENTIRE BLUE RIDGE WAS INCLUDED. PREV DISCUSSION AS OF 930 PM EDT FRIDAY... COVERAGE OF SHOWERS CONTINUES TO WANE AS THE UPPER WAVE IS NOW SHIFTING EAST OF THE FCST AREA. STEADIER AREA OF LIGHT RAIN WILL BE EAST OF OUR AREA BEFORE MIDNIGHT...LEAVING ONLY VERY LIGHT SCATTERED SHOWERS OR DRIZZLE ALONG THE BLUE RIDGE AND EAST. EVENING SOUNDINGS STILL SHOW ABOVE NORMAL PRECIP WATER VALUES AND THERE IS STILL A GOOD LOW LEVEL EASTERLY COMPONENT SEEN IN THE SOUNDINGS AND VWP FROM THE RADAR...SO CANNOT RULE OUT VERY SHALLOW UPSLOPE DRIZZLE OR SHOWERS ALTHOUGH THEY MAY BE HARD TO DETECT ON RADAR. WE BEGIN TO LOSE THE EASTERLY COMPONENT AT THE RIDGE TOP LEVEL LATE TONIGHT ACCORDING TO SOUNDING FCSTS...BUT THINK LOW LEVEL WEDGE WILL BE HOLDING STRONG AND SO WORTH KEEPING MENTION OF DRIZZLE AND AREAS OF FOG ALL NIGHT. BUT GIVEN THESE TRENDS AND THE LATEST HRRR AND RAP MODEL RUNS WHICH ARE HANDLING THINGS PRETTY WELL NOW AND SHOW ONLY VERY LITTLE IN THE WAY OF SCT SHWRS HERE AND THERE ACROSS NORTHERN PART OF FCST AREA...HAVE GENERALLY LOWERED POPS EVEN MORE FOR REST OF OVERNIGHT TO LOW TO MID CHC BLUE RIDGE AND EAST...AND NOTHING OR JUST SLIGHT CHC WEST. OTHER CHANGE FOR OVERNIGHT WAS TO LOWER MIN TEMPS IN PARTS OF THE PIEDMONT GIVEN FACT THAT CURRENT TEMPS IN A FEW SPOTS WERE ALREADY AS LOW AS PREVIOUSLY FCST MINS...ALTHOUGH DON`T THINK IN MOST CASES CURRENT TEMPS WILL DROP MORE THAN A FEW MORE DEGREES FROM WHAT THEY ARE NOW...IF ANYTHING. PRELIM LOOK AT TOMORROW SUGGESTS WEDGE WILL TRY TO BREAK DURING THE DAY...BUT MAY HOLD ON AS LONG AS POSSIBLE OVER NRV AND PARTS OF PIEDMONT...WHILE BREAKING EARLY ACROSS SOUTHWEST AND FAR WEST. TEMPS WILL BE TRICKY GIVEN THE BREAKING WEDGE...AND THINK BEST CHANCE FOR SHOWERS AND STORMS WILL BE THESE FAR WESTERN FRINGES WERE SUN IS OUT THE LONGEST. WARMER AT BLF LIKELY AGAIN COMPARED TO LYH. NO CHANGES IN THAT PERIOD YET THOUGH AS WE AWAIT MORE GUIDANCE FROM OVERNIGHT. PREV DISCUSSION AS OF 614 PM EDT FRIDAY... CURRENT RADAR SUGGESTS THAT MAIN LIFT WITH UPPER WAVE THAT IS MOVING NORTHEAST OUT OF WRN NORTH CAROLINA IS SHIFTING INTO THE PIEDMONT AREAS AND WHAT UPSLOPE ALONG THE BLUE RIDGE EXISTS THIS EVENING IS PRODUCING RELATIVELY SMALL AREAS OF LIGHT RAIN AND DRIZZLE. MOST OF THE NEAR TERM GUIDANCE THAT IS SIMILAR TO THE RADAR NOW SUGGESTS MUCH OF THIS WILL GRADUALLY WEAKEN BY LATE EVENING WHILE THE MORE MODERATE RAINFALL IN THE EAST QUICKLY SHIFTS OFF TO THE NORTHEAST. HARD TO SEE ANY REASONING FOR MUCH OF ANY SHOWER ACTIVITY DEVELOPING ON THE WEST EDGE OF THE CWA AND THE WEDGE GIVEN THAT DAYTIME INSTABILITY WILL BE LOST SOON. THUS AM LOWERING POPS FOR MOST OF THE WEST TO SLIGHT CHC WITH SOME LOW CHC REMAINING UP ACROSS GREENBRIER IN CASE ANY SHALLOW CONVECTION FARTHER NORTH BACKBUILDS...AND GRADUALLY LOWER THE LIKELY POPS ALONG THE BLUE RIDGE THE CHC OF SHOWERS AND DRIZZLE BY LATE EVENING INTO THE OVERNIGHT. CATEGORICAL FAR EAST FOR JUST ANOTHER COUPLE HOURS THEN DROPPING OFF TO MID CHC...AND WILL DETERMINE LATE IF WE NEED TO DROP THAT EVEN MORE FOR MUCH OF THE OVERNIGHT WHEN THIS UPPER WAVE HAS MOVED OFF...LEAVING WEAKENING UPSLOPE ALONG BLUE RIDGE AS 850 FLOW TURNS MORE SW BEHIND IT. DON`T THINK THIS SW FLOW WILL BE ABLE TO ERODE THE WEDGE OVERNIGHT HOWEVER...SO AM KEEPING CLOUDS AND AREAS OF DRIZZLE AND FOG IN ALL NIGHT. MADE SOME MINOR ADJUSTMENTS TO SKY COVER ON WESTERN FRINGE WHERE SOME PARTIAL CLEARING HAS TAKEN PLACE ON THE EDGE OF THE WEDGE...BUT THIS MAY FILL BACK IN AFTER DARK. ALSO PULLED MENTION OF HEAVY RAINFALL FROM THE HWO AS THERE ARE NOT ANY EXPECTATIONS OF RAINFALL RATES HIGH ENOUGH TO CAUSE EVEN MINOR ISSUES EXCEPT FOR SOME PONDING IN LOW-LYING STREETS IN THE EAST. PREV DISCUSSION AS OF 340 PM EDT FRIDAY... TWO DISTINCT SHORT WAVES SEEN ON THE WATER VAPOR LOOP THE FIRST MOVING ACROSS WEST VIRGINIA AND VIRGINIA HELPED GENERATE THE LARGE SHIELD OF RAIN FROM THIS MORNING. THE SECOND VORTICITY MAXIMUM WAS APPROACHING SOUTH CAROLINA AND WAS FORECAST TO MOVE INTO VIRGINIA OVERNIGHT. BUFKIT FORECAST SOUNDINGS SHOWED NORTHEAST WINDS AT THE SURFACE EAST OF THE BLUE RIDGE...20-25 KNOT EAST TO SOUTHEAST 850 MB WINDS TONIGHT AND SOUTHWEST WINDS ALOFT. THIS TRANSITIONS TO SOUTHWEST WINDS AT 850 MB AS THE WEDGE AND MOISTURE BECOMES SHALLOW ON SATURDAY. THE COMBINATION OF LIFT FROM THE CAROLINA WAVE AND UPSLOPE FLOW WILL RESULT IN RAIN ALONG AND EAST OF THE BLUE RIDGE TONIGHT. MOST OF THE SHORT TERM GUIDANCE HAD THE MORE WIDESPREAD AND STEADIER LIGHT TO MODERATE RAIN MOVING NORTHEAST OUT OF THE FORECAST AREA AFTER MIDNIGHT. THEN OVERNIGHT...PRECIPITATION WILL BE MORE SPOTTY LIGHT RAIN AND DRIZZLE. ALSO ADDED AREAS OF FOG IN THE TYPICAL AREAS WHERE THE WEDGE IS IN PLACE. TEMPERATURES ON SATURDAY WILL BE DEPENDENT ON WHEN WEDGE ERODES. EXPECTING TYPICAL SOUTHWEST TO NORTHEAST PROGRESSION...WITH LYNCHBURG AND THE NORTHEAST COUNTIES OF THE FORECAST AREA THIS LAST TO BREAK OUT. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... AS OF 250 PM EDT FRIDAY... THROUGHOUT MOST OF THIS PORTION OF THE FORECAST...THE AXIS OF THE ESTABLISHED UPPER LEVEL TROUGH WILL REMAIN POSITIONED JUST WEST OF THE FORECAST AREA. THIS WILL CONTINUE TO ALLOW FOR A GOOD MOISTURE FETCH OFF THE ATLANTIC TO PROGRESS INTO THE REGION. THE INTERPLAY OF UPSLOPE CONDITIONS ALONG AND NEAR THE CREST OF THE BLUE RIDGE AND WEAK DISTURBANCES ROUNDING THE BASE OF THE MAIN TROUGH AXIS...WILL KEEP THE CHANCE OF SHOWERS AND AFTERNOON/EARLY EVENING ISOLATED THUNDERSTORMS ACROSS OUR AREA DURING THIS PERIOD. WHILE THE MAIN UPPER TROUGH WILL REMAIN TO OUR WEST...THERE WILL BE A CHANGE IN JUST HOW THIS FEATURE IS MATERIALIZED. THROUGH ROUGHLY FRIDAY MORNING...THE FEATURE WILL BE THE BASE OF A CLOSED LOW SYSTEM NEAR HUDSON BAY CANADA. THIS LOW HOWEVER WILL SHIFT EAST BY THE START OF THE WEEKEND...ALLOWING THIS MAIN UPPER TROUGH TO FADE IN INTENSITY ONLY BRIEFLY. BY SUNDAY...THE REMNANT OF THIS FIRST UPPER TROUGH WILL BE STRENGTHENED BY A SHORTWAVE TROUGH PROGRESSING EASTWARD INTO THE TENNESSEE AND OHIO VALLEYS FROM THE WEST. DESPITE THIS FLUCTUATION...THE OVERALL FORECAST WILL BE AS DESCRIBED ABOVE. THE TIME PERIOD WHEN PRECIPITATION CHANCES WILL BE AT THEIR LOWEST IS MONDAY NIGHT WHEN THE LATEST GUIDANCE OFFERS A SOLUTION OF BROADENING THE WIDTH OF THE TROUGH...AND SHIFTING THE AXIS A LITTLE FARTHER EAST. THIS IS EXPECTED TO HAVE THE RESULT OF LIKEWISE SHIFTING THE BEST CHANCES OF PRECIPITATION EAST OF THE FORECAST AREA. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 1230 PM EDT FRIDAY... AT THE SURFACE TUESDAY...HIGH PRESSURE SITS OVER WEST VIRGINIA WHILE A SLOW MOVING COLD FRONT IS ACROSS THE OHIO VALLEY. TS BERTHA OR WHAT IS REMAINING OF IT IS FORECAST TO REMAIN WELL OFF SHORE AND WILL NOT BE A FACTOR IN OUR REGION NEXT WEEK. AN UPPER LEVEL TROUGH REMAINS SITUATED ACROSS THE EASTERN US. THE UPPER LEVEL FLOW WILL BECOME MORE ZONAL BY THE END OF THE PERIOD. THE FRONT ACROSS THE OHIO VALLEY WILL SLOWLY DRIFT AND PARTIALLY STALL OUT ACROSS NORTHERN PORTIONS OF OUR CWA BY THURSDAY INTO FRIDAY. WHILE PWATS ARE NOT IMPRESSIVE...GENERALLY 0.75-1.25 INCHES DEPENDING ON THE LOCATION...EXPECT ISOLATED TO SCATTERED THUNDERSTORMS EACH AFTERNOON BEGINNING DURING PEAK HEATING AND TAPERING OFF AROUND SUNSET. FOCUS OF THE LOW CHANCE POPS ARE ACROSS THE MOUNTAINS AND GENERALLY NORTH OF ROUTE 460. SURFACE TEMPS WILL BE RIGHT AROUND NORMAL FOR THE PERIOD. 850MB TEMPS OF +15-17C WILL CORRESPOND TO SURFACE HIGHS OF MID TO UPPER 80S EAST OF THE BLUE RIDGE AND LOWER 80S ACROSS THE MOUNTAINS. DEWPTS IN THE UPPER 50S TO LOWER 60S WILL KEEP NIGHT TIME TEMPS UP A BIT. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... AS OF 745 PM EDT FRIDAY... EXPECT SFC WEDGE TO HOLD EAST OF THE BLUE RIDGE...AND ANY AREAS WEST TO THE ALLEGHANY FRONT THAT HAVE SEEN WEAK EROSION OF THE WEDGE LATE THIS AFTERNOON...WILL LIKELY SEE IT FILL IN DURING THE NEXT FEW HOURS. MEANWHILE...THE MAIN DISTURBANCE THAT BROUGHT THE WIDESPREAD LIGHT RAIN TO THE EASTERN 2/3RD OF THE REGION THIS MORNING...HAS SHIFTED EAST OF THE REGION. THE LAST REMNANTS OF THE ASSOCIATED RAINFALL WAS PULLING OUT OF THE PIEDMONT AT THIS TIME. SOME WEAK WAVES MAY TRAVERSE THE AREAS EAST OF THE BLUE RIDGE OVERNIGHT...ENOUGH TO SUPPORT CONTINUED TO MENTION OF -RA AT TIMES FOR A FEW MORE HOURS AT KDAN/KLYH/KROA...BUT MOSTLY FROM THIS POINT THROUGH THE OVERNIGHT HOURS...THE WEDGE COMBINED WITH THE LACK OF DYNAMICS AND MOIST/RELATIVELY COOL GROUND IN MOST AREAS WILL YIELD TO AREAS OF -DZ AND BR/FG OVERNIGHT. THE EXCEPTION WILL BE KLWB...WHERE RAIN DID NOT FALL EARLIER AND LATE DAY CLOUDS HAVE CLEARED OUT. THIS SHOULD SET UP KLWB FOR ANOTHER NIGHT OF LOCALLY DENSE GROUND FOG. GIVEN MOIST LOWER ATMOSPHERE IN PLACE AND PRESENCE OF WEDGE...POTENTIAL FOR KLWB TO DROP TO 0SM TONIGHT. ELSEWHERE...EXPECT ANY VFR CIGS THIS EVENING TO TREND QUICKLY TO MVFR AND THEN LIKELY IFR AFT 06Z IN MOST AREAS EAST OF THE ALLEGHANY FRONT. VSBYS WILL RANGE FROM VFR AT 00Z DOWNWARD TO MOSTLY MVFR IN -DZ OR -RA OVERNIGHT/EARLY SAT. IFR CIGS WILL IMPROVE TO MVFR CIGS BY MID OR LATE MORNING...WITH POTENTIAL FOR VFR CIGS WEST O THE BLUE RIDGE BY AFTERNOON. VSBYS SHOULD IMPROVE TO VFR AFT 15Z SAT. WINDS...MOSTLY NE-SE THROUGH THE TAF VALID PERIOD AT SPEEDS OF 5-8KTS...EXCEPT WEST OF THE ALLEGHANY FRONT...I.E. KLWB AND KBLF...WHERE WINDS WILL BE LIGHT NE IN THE MORNING LIKELY BECOMING LIGHT SE TO SW DURING THE AFTERNOON. WITH RESPECT TO TSRA POTENTIAL SAT AFTERNOON...THAT SHOULD BE LITTLE TO NONE AT THIS POINT BECAUSE OF VERY STABLE AIR MASS EAST OF THE ALLEGHANY FRONT...AND LIMITED DYNAMICS TO THE WEST. IF ANY TSRA DEVELOPED...THEY WOULD LIKELY ONLY IMPACT BLF AND/OR LWB. MEDIUM CONFIDENCE IN CIGS AND VSYB THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN WIND DIR...MEDIUM TO HIGH CONFIDENCE IN WIND SPD THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... THE BROAD UPPER TROUGH OF LOW PRESSURE WILL LINGER ACROSS THE EASTERN UNITED STATES THROUGH SUNDAY. LATEST MODEL INDICATIONS ARE THAT THE TROUGH WILL BEGIN TO SHIFT BACK TO THE EAST BY SUNDAY/MONDAY...MOVING THE BEST POTENTIAL FOR ANY SHRA/TSRA MAINLY EAST OF THE REGION WITH TIME. HOWEVER...AN INCREASINGLY WARM/HUMID AIR MASS ACROSS THE REGION SHOULD LEAD TO AT LEAST SLIGHTLY BETTER POTENTIAL FOR SCT AFTERNOON/EVENING SHRA/TSRA ACROSS THE REGION BY SUN-MON...FAVORING EITHER THE MOUNTAINS OR AREAS EAST OF THE BLUE RIDGE. FOR MONDAY AND TUESDAY...THE AIR MASS WILL SLOWLY BECOME WARMER AND MORE UNSTABLE. HOWEVER...DYNAMICS AND FORCING ARE WEAK AT BEST. MAINLY ISOLD SHRA/TSRA ARE EXPECTED DURING THE AFTERNOON...WITH BRIEF/LOCALIZED MVFR-IFR VSBYS/CIGS IN SHRA/TSRA...MAINLY AFTERNOON/EARLY EVENING. LATE NIGHT/EARLY MORNING FOG WILL REMAIN A PROBLEM EACH DAY...ESPECIALLY AT THE USUAL SITES...SUCH AS LWB...BCB...AND LYH. BY WEDNESDAY...A WEAK COLD FRONT MOVES SLOWLY SOUTH FROM THE OHIO VALLEY ACROSS THE MID ATLANTIC REGION BRINGING SCT SHRA/TSRA TO THE REGION...MOST NUMEROUS WEST OF THE ALLEGHANY FRONT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS NEAR TERM...AMS/SK SHORT TERM...DS LONG TERM...CF AVIATION...RAB

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