Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201154 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 754 AM EDT WED AUG 20 2014 .SYNOPSIS... A WEAK STATIONARY FRONT WILL REMAIN IN THE AREA THROUGH THE REST OF THE WEEK. UPPER LEVEL DISTURBANCES TRACKING EAST AND SOUTHEAST ACROSS THE BOUNDARY WILL BRING SCATTERED SHOWERS AND STORMS TO THE REGION EACH DAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AS OF 445 AM EDT WEDNESDAY... AN UPPER LEVEL TROUGH OF LOW PRESSURE IS MOVING THROUGH THE GREAT LAKES WITH LOBE OF VORTICITY TRAILING SOUTH INTO THE OHIO VALLEY. THIS FEATURE HAS RESULTED IN A PERSISTENT AREA OF LIFT ASSOCIATED WITH SHOWERS AND THUNDERSTORMS. AS OF 08Z/4AM...NUMEROUS SHOWERS AND STORMS WERE OCCURRING FROM WESTERN PA INTO EASTERN OHIO AND NORTHEAST KY. OUTFLOW FROM THIS COMPLEX OF THUNDERSTORMS IS EXPECTED TO MAKE ITS WAY OVER THE MOUNTAINS TODAY. MODELS DO NOT SEEM OVERLY CONFIDENT THIS OUTFLOW WILL MAKE IT OVER THE MOUNTAINS...INDICATING WEAKENING AND A GRADUAL DEMISE OF ACTIVITY. MATTER OF FACT THE SYNOPTIC MODELS DON`T PRODUCE MUCH IN THE WAY OF RAINFALL AT ALL ACROSS OUR CWA...MOS POPS GENERALLY LESS THAN 40 PERCENT. ATTM PREFER NOT TO IGNORE THE OBVIOUS...WHICH IS A MODEST LOOKING UPPER LEVEL TROF...ASSOCIATED WITH A HEALTHY LOOKING AREA OF SHRA/TSRA...THE OUTFLOW OF WHICH SHOULD PASS THROUGH OUR FORECAST AREA TODAY. THE ONLY THING THAT KEPT ME FROM GOING WITH CATEGORICAL POPS IS THE POTENTIAL TIMING OF THE ACTIVITY AS IT CROSSES THE MOUNTAINS. BASED ON CURRENT PROGRESSION...SHOWERS WILL MOVE INTO THE WV MOUNTAINS DURING THE MORNING...THEN PROGRESS EAST REACHING THE BLUE RIDGE TOWARD NOON...THEN EAST OF THE MTNS EARLY THIS AFTERNOON. THIS EARLIER SORT OF TIMING SUGGESTS DEBRIS CLOUDS WILL OVERSPREAD THE CWA EARLY AND LIMIT FULL INSOLATION THUS LIMITING INSTABILITY. THAT SAID...THINK AREA OF SHOWERS WITH EMBEDDED THUNDER WILL CROSS THE FORECAST AREA...BUT IN A WEAKENED STATE. GREATEST COVERAGE WILL BE FROM THE VIRGINIAS NORTHWARD CLOSER TO THE UPPER SUPPORT FROM THE SHORT WAVE TROUGH...THE STRONGER DYNAMIC LIFT MOVING FROM THE OHIO VALLEY INTO PA/NY. HAVE PLACED THE HIGHEST POPS ACROSS WV/VA CLOSER TO THE SUPPORT FROM THE UPPER TROF...AND WHERE THE OUTFLOW WILL HAVE THE BEST CHANCE OF MAKING IT OVER THE MOUNTAINS AND HELP FOCUS RENEWED DEEP CONVECTION. FARTHER SOUTH...FROM THE VA/NC BORDER SOUTHWARD...COVERAGE WILL BE LESS AND MORE SCATTERED IN NATURE. WITH LESS COVERAGE COMES THE OPPORTUNITY FOR MORE SUN. MORE SUN SUGGESTS WARMER TEMPERATURES...AND WARMER TEMEPERATURES WILL YIELD GREATER INSTABILITY PROVIDING STRONGER UPDRAFTS. AS SUCH CAN`T RULE OUT A STRONG PULSE STORM OR TWO...ESPECIALLY WHERE MORE SUN MATERIALIZES. WENT BLO MOS GUIDANCE FOR TEMPERATURES ACROSS THE VIRGINIAS WHERE MORE CLOUD COVER IS ANTICIPATED TODAY. THE WARMEST TEMPERATURES WILL BE ACROSS NORTH CAROLINA WHERE MORE SUN IS ANTICIPATED. PASSAGE OF THE UPPER TROUGH WILL BRING AN END TO MOST OF THE STORM ACTIVITY THIS EVENING...FOLLOWED BY ANOTHER FOGGY NIGHT WITH AREAS OF FOG AND PATCHY DENSE FOG DEVELOPING ACROSS THE FORECAST AREA. IF SKIES CAN COMPLETELY CLEAR...THIS WOULD BE MOST IDEAL FOR RADIATION FOG. THERE WERE SEVERAL REPORTS IN THE NEW RIVER VALLEY WITH DENSE FOG EARLY WEDNESDAY MORNING. THINK IT WILL BE A REPEAT AGAIN EARLY THURSDAY MORNING. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... AS OF 330 AM WEDNESDAY... THE REGION WILL REMAIN IN AN ACTIVE WEATHER PATTERN DURING THIS PORTION OF THE FORECAST. A STRONG UPPER HIGH PRESSURE WILL BE SITUATED ACROSS THE MID-MISSISSIPPI VALLEY. A DEEPENING UPPER LOW/TROUGH WILL BE POSITIONED OFF THE COAST OF NEW ENGLAND. OUR AREA OF THE COUNTRY WILL BE SANDWICHED BETWEEN THE TWO WITHIN NW-SE ORIENTED MID-LEVEL BAROCLINIC ZONE...WITH AN ASSOCIATED SURFACE BACKDOOR COLD FRONT EITHER OVER...OR VERY CLOSE TO THE REGION BY THE START OF THE WEEKEND. THE ABOVE SCENARIO POINTS TOWARD A PERIOD WITH AT LEAST SCATTERED SHOWERS IN THE FORECAST EACH DAY AND NIGHT...AND SOME AFTERNOON AND EVENING STORMS. WHAT IS A LITTLE HARDER TO NAIL DOWN WILL BE THE WINDOWS OF OPPORTUNITY FOR LIKELY TO CATEGORICAL CHANCES OF PRECIPITATION IN ASSOCIATION WITH PERIODICAL UPPER LEVEL SHORTWAVE TROUGHS HEADING SOUTHEAST ALONG THIS BAROCLINIC ZONE AND THROUGH OUR REGION. EACH MODEL SEEMS TO HAVE A DIFFERENT TAKE ON TIMING AND TRACK. EYEBALLING A CONSENSUS OF THE GUIDANCE POINTS TOWARD THURSDAY AFTERNOON AND EVENING AS ONE POTENTIAL TIME THAT WOULD WARRANT HIGHER POPS...ESPECIALLY ACROSS THE WESTERN AND NORTHERN PARTS OF THE REGION. ANOTHER OPPORTUNITY MAY BE FRIDAY NIGHT ACROSS MAINLY NORTHERN AND EASTERN PARTS OF THE AREA. FINALLY...SATURDAY NIGHT MAY PROVE TO BE A THIRD OPPORTUNITY FOR ALL OF THE REGION...ESPECIALLY CENTRAL AND WESTERN PORTIONS. AT THIS TIME...CONFIDENCE IS NOT THERE TO OFFER A CATEGORICAL...75 PERCENT OR HIGHER...CHANCE OF PRECIPITATION FOR ANY ONE OF THE THREE SCENARIOS LISTED ABOVE. HOWEVER...WILL CONTINUE...OR ADD...A FORECAST OF LIKELY POPS TO THE FIRST AND SECOND SCENARIOS. FOR THE THIRD SCENARIO...WILL OFFER A FORECAST JUST SHY OF LIKELY POPS. TEMPERATURES THROUGH THE PERIOD ARE EXPECTED TO GRADUALLY COOL AS THE BAROCLINIC ZONE MAKES PROGRESS WESTWARD. THE COMBINATION OF MORE CLOUD COVER AND MORE PRECIPITATION...ALONG WITH LOWER HEIGHTS WILL CONTRIBUTE TO THIS. BY SATURDAY...THE SURFACE COLD FRONT MAY BE BISECTING THE REGION FROM NW-SE...THUS YIELDING NOTABLY COOLER TEMPERATURES AT LEAST FOR THE CENTRAL AND NORTHEAST PARTS OF THE AREA. && .LONG TERM /SUNDAY THROUGH TUESDAY/... AS OF 130 PM EDT TUESDAY... THE WEEKEND THROUGH EARLY NEXT WEEK WILL BE CHARACTERIZED BY THE BATTLE BETWEEN LARGE UPPER RIDGE TO OUR WEST TRYING TO BUILD INTO SOUTHERN APPALACHIANS...WHILE TROUGH OFF NEW ENGLAND COAST DEEPENS WHILE CLOSING OFF AND CONTINUES TO APPEAR THAT IT WILL SET UP CLOSE ENOUGH TO COAST TO PUSH BACK DOOR FRONT THROUGH AND WELL SOUTH OF THE AREA THROUGH THE WEEKEND...BEFORE LIKELY WEAKENING AND ALLOWING MORE INFLUENCE OF THE RIDGE TO BE FELT BY TUES...ESPECIALLY ACROSS WESTERN PARTS OF THE AREA IF WEAK/SHALLOW BOUNDARY LAYER WEDGE IS IN PLACE EARLY IN THE DAY BEFORE MIXING OUT OVER THE EAST. WHILE SURFACE WEDGE FRONT MAY BE WELL TO THE SOUTH DURING MUCH OF THIS PERIOD...WITH STRONGEST SOUTHWARD PUSH ON SATURDAY...THE 850 BOUNDARY AND MOST LIKELY TRACK FOR UPPER S/WV ENERGY FROM THE NW IS LIKELY TO BE RIGHT OVER THE BLACKSBURG FORECAST AREA...AND THUS GOOD CHANCE FOR SHOWERS/THUNDERSTORMS THROUGH THIS ENTIRE PERIOD. TIMING MOST LIKELY WINDOWS REMAINS TRICKY...AS MANY OF THESE WAVES ARE STRONGLY INFLUENCE BY CONVECTIVE COMPLEXES THAT WILL DEVELOP WELL UPSTREAM. LIKE THE TRENDS OVERALL THAT 12Z GFS IS TAKING...NOT ONLY WITH RETURN TO SHARPER AMPLITUDE PATTERN...BUT IDEA OF TWO DISTINCT WAVES HEADING FOR THE WESTERN PART OF OUR FORECAST AREA...ONE SATURDAY AND ANOTHER ONE SUNDAY. EXACT TIMES MAY HELP DETERMINE IF THERE WILL BE ENOUGH INSTABILITY...WHICH WOULD LIKELY BE LIMITED TO THE FAR WEST NEAR EDGE OF WEDGE BOUNDARY...BUT PERHAPS THE BIGGER CONCERN IS RAINFALL THAT IS LIKELY TO IMPACT THE SAME AREAS AT LEAST A COUPLE OF DAYS IN A ROW. THERE COULD BE ANOTHER WAVE FOR MONDAY...BUT AS RIDGE ATTEMPTS TO BUILD IN AND TROUGH TO THE EAST AND ASSOCIATED WEDGE WEAKEN WHAT MAY TEND TO OCCUR IS MORE DIURNAL POP-UP CONVECTION ALONG AND NEAR THE WESTERN PERIPHERY OF THE WEDGE BOUNDARY IN OUR WESTERN FORECAST AREA AS THE ATMOS DESTABILIZES MORE. BY TUESDAY THE SUPPORT TO KEEP WEDGE IN PLACE SHOULD BE WEAKENING AS TROUGH LIFTS AND SFC HIGH SHIFTS MORE EAST OF THE AREA...AND OVERALL IT LOOKS A LITTLE DRIER...BUT NOT SURE ALL POPS CAN BE REMOVED. GIVEN PATTERN WE`VE BEEN IN...REALLY DON`T HAVE CONFIDENCE TO DRY IT OUT OR WARM IT UP TOO FAST...SO WILL LEAN TOWARD STRONGER INFLUENCE OF THE WEDGE THROUGH THIS PERIOD AND BETTER CHANCES FOR PRECIP...WHICH WILL HELP STRENGTHEN THE WEDGE TOO. UNDERCUT EVEN COOLER ECMWF A LITTLE BIT FOR HIGHS...WITH A BIT MORE WARMING FOR TUESDAY. BUT IN THE FAR SOUTHWEST THINGS MAY BE ABLE TO WARM UP VERY QUICKLY A DAY OR TWO EARLIER THAN THIS IF THE WEDGE CAN BREAK AND SOME OF THE INFLUENCE OF THE BIG UPPER RIDGE CAN BE REALIZED. THIS WILL EVENTUALLY RESULT IN A SIGNIFICANT WARM UP FOR OUR ENTIRE AREA...BUT AM THINKING IT WILL NOT COME UNTIL MIDDLE OF NEXT WEEK. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 200 AM EDT WEDNESDAY... BKN LINE OF SHRA/TSRA WILL CROSS THE FORECAST AREA TODAY. SHRA/TSRA WILL PASS THROUGH THE MTNS THIS MORNING CROSSING BLF/LWB/BCB BETWEEN 12-15Z/8-11AM...THEN MOVE EAST OF THE MTNS AROUND MID-DAY WITH POTENTIAL FOR SHOWERS AND POSSIBLE THUNDERSTORM VCNTY OF ROA/LYH/DAN DURING THE EARLY/MID AFTERNOON. AN UPPER LEVEL TROF OF LOW PRESSURE WILL MOVE EAST ACROSS THE GREAT LAKES AND OHIO VALLEY TODAY...AND INTO NEW ENGLAND THURSDAY. THE TROF AXIS IS ASSOCIATED WITH A LINE OF SHOWERS AND THUNDERSTORMS WHICH WILL MOVE THROUGH THE MOUNTAINS THIS MORNING AND INTO THE PIEDMONT THIS AFTERNOON. STORMINESS SHOULD CLEAR THE FORECAST AREA BY 22Z/6PM THIS EVENING WITH ACTIVITY MOVING EAST. AREAS OF FOG WILL THEN RE-DEVELOP ACROSS THE AREA TONIGHT WITH AREAS OF MVFR AND POTENTIAL FOR IFR VSBYS AGAIN THURSDAY MORNING. EXTENDED AVIATION... WEATHER CONDITIONS WILL CONTINUE TO BE UNSETTLED AND HIGHLY VARIABLE FOR THE NEXT FEW DAYS AS A STATIONARY FRONT REMAINS STALLED OVER THE MID ATLANTIC. UPPER LEVEL DISTURBANCES WILL BE MOVING THROUGH PERIODICALLY 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 INDICATED THAT A DEEPER EASTERLY SORT OF WIND FLOW WILL SETUP FOR THIS UPCOMING WEEKEND. THIS SUGGEST 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.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...SK NEAR TERM...PM SHORT TERM...DS LONG TERM...SK AVIATION...PM

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