Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 221148 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 748 AM EDT FRI AUG 22 2014 .SYNOPSIS... A STRONG UPPER LEVEL RIDGE OF HIGH PRESSURE IS CENTERED OVER THE LOWER MISSISSIPI RIVER VALLEY WITH A STATIONARY SURFACE FRONT EXTENDING FROM THE UPPER MIDWEST...THROUGH THE OHIO VALLEY AND INTO THE MID ATLANTIC STATES. THIS FRONT WILL BE THE FOCUS FOR PERIODIC ROUNDS OF SHOWERS AND STORMS FROM THE OHIO VALLEY INTO THE MID ATLANTIC TODAY AND TONIGHT. OVER THE WEEKEND THE FRONT IS EXPECTED TO MOVE SOUTH ALONG THE EAST COAST...TURNING INTO A BACKDOOR COLD FRONT WHICH WILL BRING COOLER AIR TO AREAS EAST OF THE APPALACHIANS...WHILE VERY WARM SULTRY WEATHER CONTINUES ACROSS THE MID SECTION OF THE UNITED STATES. && .NEAR TERM /THROUGH TONIGHT/... AS OF 530 AM EDT FRIDAY... FLASH FLOOD WATCH IN EFFECT TODAY AND TONIGHT FOR MUCH OF WEST VIRGINIA AND PARTS OF SOUTHWESTERN VIRGINIA. CLASSIC RING OF FIRE PATTERN SETTING UP AROUND THE PERIPHERY OF THE STRONG UPPER LEVEL RIDGE OF HIGH PRESSURE WHICH HAS NOW BECOME CENTERED OVER THE MISSISSIPPI VALLEY. A VERY RICH...MOISTURE LADEN AIRMASS...IS BEING PUMPED FROM THE GULF OF MEXICO NORTHWARD...AND IS POOLING ALONG A STATIONARY FRONT WHICH ARCS AROUND THE NORTHERN PERIPHERY OF THE RIDGE. THIS FRONT EXTENDS FROM THE UPPER MID WEST ACROSS THE OHIO VALLEY AND INTO THE MID ATLANTIC...THE NUMEROUS STORMS EVOLVING ALONG THIS BOUNDARY APPEARING AS A LARGE RING LIKE FEATURE WHEN YOU LOOK AT REGIONAL SATELLITE AND RADARS. IT ALSO GIVES THE IMPRESSION OF A TRAIN WITH STORMS APPEARING TO TRAVERSE THE SAME AREAS...FOLLOWING A PROVERBIAL RAILROAD TRACK. THIS OF COURSE IS PROBLEMATIC SINCE REPEATED DOWNPOURS OVER THE SAME AREA WILL ULTIMATELY LEAD TO FLOODING. MESOANALYSIS FROM THIS MORNING INDICATES THE MOST PRONOUNCED PART OF THE RAILROAD TRACK...STRONGEST PART OF THE BAROCLINIC ZONE... RUNS FROM NORTHERN IL/IN...THEN BENDS SOUTHEAST ACROSS OHIO AND INTO WV...BECOMING DIFFUSE ONCE YOU GET EAST OF THE MTNS. IN SPITE OF THE LARGER SCALE MODEL DIFFERENCES...WHICH UNDERPLAY THE QPF FROM THE MESOSCALE FEATURES...I AM MODERATE TO HIGHLY CONFIDENT STORMS WILL CONTINUE TO REGENERATE ALONG THE STRONGEST PART OF THE BAROLINIC ZONE...STORMS MOVING SOUTHEAST ALONG THIS RAILROAD TRACK FEATURE AND INTO OUR CWA AND PRODUCING HIGHER QPF. STRONG 85H MOISTURE TRANSPORT IS ONGOING ACROSS WV WITH PWATS STEADILY CLIMBING TOWARD 2.0. THIS SUGGESTS STORMS THAT PASS THROUGH THIS ENVIRONMENT WILL BE VERY RAIN EFFICIENT. GIVEN THE POTENTIAL FOR THESE STORMS TO REPEATEDLY MOVE OVER THE SAME AREA...A FLASH FLOOD WATCH SEEMS TO BE A GOOD HEADLINE FOR THE DAY. ATTM WILL FOCUS THE ATTENTION ON OUR WV COUNTIES AND ACROSS THE NEW RIVER VALLEY WHERE FLASH FLOOD GUIDANCE SUGGESTS ANY RAIN THAT EXCEEDS 1.5 TO 2.0 INCHES IN AN HOUR WILL REQUIRE A FLASH FLOOD WARNING. THESE NUMBERS ARE CERTAINLY ACHIEVABLE GIVEN THE ENVIRONMENT. SHOWERS AND STORMS ARE CERTAINLY POSSIBLE ELSEWHERE ACROSS THE CWA. SIMILAR TO YESTERDAY...NORTHWEST FLOW WILL RESULT IN A WEAKENING OF THE ACTIVITY AS IT CROSSES THE MOUNTAINS...THE STORMS BREAKING UP INTO CLUSTERS OR SHORT LINE SEGMENTS AS THEY QUICKLY TRAVERSE THE CWA. THESE STORMS WILL ALSO PRODUCE HEAVY RAIN...BUT I AM LESS CONFIDENT EAST OF THE MOUNTAINS THAT STORMS WILL EXHIBIT THE SAME SORT OF TRAIN EFFECTS AS AREAS TO THE WEST. WENT BLO GFS MOS GUIDANCE AND CLOSER TO THE MET GUIDANCE FOR TEMPERATURES TODAY AND TONIGHT. THE GFS SEEMED 3 TO 5 DEGREES TOO WARM GIVEN THE MOSTLY CLOUDY MOIST SHOWERY FORECAST. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... AS OF 400 AM EDT FRIDAY... DURING THIS PORTION OF THE FORECAST...THE MAIN ITEM OF FOCUS WILL BE A BACKDOOR COLD FRONT THAT ENTERS THE REGION SATURDAY NIGHT INTO SUNDAY AS HIGH PRESSURE BUILDS SOUTH OFF THE NEW ENGLAND COAST. PRIOR TO ITS ARRIVAL...THE WEATHER ON SATURDAY WILL BE COMPARABLE WITH THAT EXPECTED TODAY. THE AREA WILL BE WITHIN AN UNSTABLE ENVIRONMENT WITH UPPER LEVEL DISTURBANCES TRAVERSING THE REGION...PROVIDING ADDITIONAL SUPPORT FOR CONVECTION. HOWEVER...THE FOCUS FOR ANY OF THESE WILL BE SHIFTED ACROSS MORE OF THE SOUTHWEST PARTS OF THE REGION AS THE UPPER BAROCLINIC ZONE SHIFTS IN THAT DIRECTION AS WELL. SATURDAY NIGHT INTO SUNDAY...THE PASSAGE OF THE BACKDOOR COLD FRONT WILL ITSELF BE A FOCUS FOR SHOWER ACTIVITY. HOWEVER...ONCE IT HAS MOVED WEST OF A PARTICULAR AREA...LOW LEVEL WILL BECOME EASTERLY...AND THE ONSET OF A LEE SIDE DAMMING WEDGE WILL ENSUE. EXPECT AREAS ALONG AND WEST OF A LINE FROM ROUGHLY BLUEFIELD WV TO MARION VIRGINIA WILL REMAIN SOMEWHAT UNSTABLE WITH THE FRONT TAKING UP POSITION EITHER OVER...OR VERY CLOSE TO THAT AREA. IT WILL BE HERE WHERE ANY ADDITIONAL SHOWERS OR STORMS MAY DEVELOP ON SUNDAY. TEMPERATURES WITHIN THE AREA OF THE WEDGE WILL EXPERIENCE LITTLE RISE FROM SATURDAY NIGHT OVERNIGHT LOWS. WE STILL ANTICIPATE A COOL DAY SUNDAY WITHIN THE WEDGE WITH UPPER 60S TO AROUND 70 COMMON FOR HIGH TEMPERATURES. THE FAR WESTERN PARTS OF THE AREA ARE MORE LIKELY TO EXPERIENCE UPPER 70S TO LOWER 80S FOR HIGHS. PRECIPITATION WITHIN THE WEDGE WILL TRANSITION FROM SHOWERS TO MORE A LIGHT RAIN OR DRIZZLE SCENARIO. HEADING INTO MONDAY...AM RELUCTANT TO REMOVE THE INFLUENCE OF THE WEDGE TOO QUICKLY. HAVE CONTINUED WITH A MORE CLOUDY THAN CLEAR DAY WITH RESIDUAL...BUT REDUCED IN COVERAGE...LIGHT RAIN OR DRIZZLE WITHIN THE AREA OF THE WEDGE. BY MONDAY NIGHT...THE FORECAST WILL REFLECT DRIER AIR WORKING ITS WAY INTO THE AREA AS THE CENTER OF THE HIGH MOVES ONSHORE TO CENTRAL PENNSYLVANIA. STEERING ONSHORE FLOW AROUND THE HIGH WILL START ADVECTING LOW LEVEL MOISTURE SOUTH OF OUR REGION. LOW WILL RANGE FROM THE UPPER 50S ACROSS THE MOUNTAINS TO LOWER 60S ACROSS THE PIEDMONT. && .LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 1130 AM EDT THURSDAY... SURFACE HIGH PRESSURE WILL BE IN A FAVORABLE LOCATION OVER NEW ENGLAND TO WEDGE WELL DOWN THE EAST SLOPES OF THE APPALACHIANS SUNDAY NIGHT AND MONDAY. SUPPORT FOR THE WEDGE WEAKENS BY TUESDAY. HIGH PRESSURE WILL REMAIN OVER THE FORECAST AREA THROUGH WEDNESDAY. WEDNESDAY NIGHT AND THURSDAY A COLD FRONT WILL APPROACH THE AREA. LARGE 500 MB RIDGE ALOFT WILL COVER MUCH OF THE LOWER MISSISSIPPI VALLEY ACROSS THE EASTERN UNITED STATES THROUGH THE PERIOD. THE DEEPEST MOISTURE SHIFTS SOUTHWEST OUT OF THE FORECAST AREA ON MONDAY AND TUESDAY. WILL HAVE THESE DAYS DRY IN THE FORECAST. THE CHANCE OF PRECIPITATION RETURNS TO THE AREA ON WEDNESDAY AND THURSDAY AHEAD OF THE FRONT. EXPECT MAXIMUM TEMPERATURES TO BE WARMEST ON WEDNESDAY AND THURSDAY WITH THE WEDGE GONE AND MORE POTENTIAL TO MIX DOWN WARM 850 MB TEMPERATURES. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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AS OF 800 AM EDT FRIDAY... SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS CAN BE EXPECTED TODAY AND TONIGHT...WITH THE GREATEST COVERAGE OVER THE MOUNTAINS. FLYING CONDITIONS WILL BE HIGHLY VARIABLE WITH PRIMARILY MVFR/IFR CONDITIONS OVER THE MTNS...AND A MIX OF VFR/MVFR EAST OF THE MTNS THROUGH THE 24 HOUR TAF PERIOD. EXTENDED AVIATION... WEATHER CONDITIONS WILL REMAIN UNSETTLED THROUGH THE WEEKEND. UPPER LEVEL DISTURBANCES WILL BE MOVING THROUGH PERIODICALLY AND INTERACTING WITH A STATIONARY FRONT OVER THE AREA FOR THE NEXT FEW DAYS...RESULTING IN PERIODS OF SHOWERS AND THUNDERSTORMS. DUE TO THE HIGH MOISTURE CONTENT OF THE AIR...EXPECT STRATUS AND FOG DURING THE OVERNIGHT PERIODS WITH AREAS OF MVFR/IFR MOST PRONOUNCED BETWEEN MIDNIGHT AND 9AM EACH DAY. MODELS ARE INDICATING THAT A DEEPER EASTERLY SORT OF WIND FLOW WILL SETUP FOR THIS UPCOMING WEEKEND. THIS SUGGESTS THAT LOW CIGS MAY PERSIST EVEN DURING THE DAYTIME PERIODS...SATURDAY AND SUNDAY...WITH WIDESPREAD MVFR CONDITIONS ACROSS THE AREA THIS WEEKEND DUE TO MOISTURE BANKING UP AGAINST THE EAST SIDE OF THE APPALACHIANS. A BETTER PUNCH OF DRY AIR WITH HIGH PRESSURE BUILDING IN FROM THE NE MAY BE ENOUGH WITH MIXING/HEATING TO ALLOW FOR INCREASING VFR MONDAY INTO TUESDAY UNDER MAINLY DRY CONDITIONS.
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&& .EQUIPMENT... THE ASOS AT LYNCHBURG (LYH) VA REMAINS PARTIALLY INOP DUE TO A BOARD FAILURE. PARTS HAVE BEEN ORDERED WITH THE RETURN OF COMPLETE SERVICE UNKNOWN AT THIS TIME. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ007-009>014. NC...NONE. WV...FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR WVZ042>045. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...DS LONG TERM...AMS AVIATION...PM EQUIPMENT...PM

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