Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 121747 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 147 PM EDT SAT JUL 12 2014 .SYNOPSIS... HIGH PRESSURE STRETCHED FROM NEW ENGLAND TO THE MID ATLANTIC STATES EARLY THIS MORNING. A STRONG COLD FRONT WILL APPROACH THE REGION FROM THE WEST SUNDAY THROUGH TUESDAY...THEN WILL CROSS TO THE EAST COAST BY LATE WEDNESDAY. HIGH PRESSURE FOLLOWS THE FRONT FOR THE END OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1245 PM EDT SATURDAY... ISOLATED SHOWERS ARE STARTING TO FORM ACROSS PARTS OF THE NORTHERN MOUNTAINS OF NORTH CAROLINA AND NEIGHBORING SECTIONS OF THE MOUNTAIN EMPIRE REGION OF SOUTHWEST VIRGINIA...SOUTHWEST OF WYTHEVILLE. THIS GIVES GOOD VERIFICATION AS TO WHERE TODAY/S ONSET OF PRECIPITATION WAS EXPECTED TO BE AND WHEN. NOW...WE ARE EXPECTING COVERAGE TO INCREASE THROUGHOUT THE AFTERNOON WITH THE FOCUS OF ACTIVITY NEAR THE CREST OF THE BLUE RIDGE...WITH LESSER COVERAGE FARTHER WEST THROUGHOUT THE MOUNTAIN REGION. TEMPERATURES ACROSS THE AREA ON TRACK FOR EARLIER FORECAST HIGHS...SO NO CHANGES THERE. HAVE ONLY TWEAKED HOURLY TEMPERATURE AND DEW POINT VALUES BASED UPON THE LATEST OBSERVATIONS AND EXPECTED TRENDS THROUGH THE AFTERNOON. AS OF 950 AM EDT SATURDAY... ONGOING FORECAST STILL LOOKS ON TRACK WITH THE EXPECTATION OF ISOLATED TO SCATTERED SHOWERS FORMING ALONG AND WEST OF THE CREST OF THE BLUE RIDGE EARLY THIS AFTERNOON. AS THE AFTERNOON PROGRESSES AND TEMPERATURE RISE...THERE MAY BE ENOUGH INSTABILITY FOR SOME OF THE SHOWERS TO DEVELOP INTO THUNDERSTORMS. NO SIGNIFICANT CHANGES WERE MADE. HAVE ONLY INCORPORATED THE LATEST TEMPERATURES AND DEW POINTS INTO THE CURRENT GRIDS WITH ADJUSTMENTS THESE VALUES THE NEXT FEW HOURS BASED UPON ANTICIPATED TRENDS. AS OF 410 AM EDT SATURDAY... EASTERN EXTENT OF 594 DM UPPER RIDGE OVER THE CENTRAL AND SOUTHERN PLAINS COVERS THE REGION TODAY...THEN HEIGHTS FALL IN THE CENTRAL UNITED STATES TONIGHT AND RIDGE RETREATS BACK TO THE CENTRAL ROCKIES. TYPICAL OF A DIFFUSE SUMMER PATTERN...TAIL OF A SUBTLE SHORT WAVE OVER THE GREAT LAKES AND THE ASSOCIATED UPPER JET STREAK WILL CROSS THE FORECAST AREA THIS AFTERNOON. THIS MODEST FORCING PLUS WEAK SOUTHEAST TO SOUTH SURFACE AND LOW LEVEL WINDS WILL SUPPORT ISOLATED THUNDERSTORMS THIS AFTERNOON. STARTING OUT DRY PER 00Z AND BUFKIT FORECAST SOUNDINGS...AND WATER VAPOR LOOP AT MID AND UPPER LEVELS THEN MOISTURE RETURNS ABOVE 700 MB LATE TONIGHT. ENOUGH MOISTURE TODAY BELOW 700MB FOR STRATOCUMULUS TO DEVELOP. SOME OF THE DRY AIR WILL MIX DOWN TO THE SURFACE...BUT DEEP ENOUGH ALONG THE BLUE RIDGE TO KEPT THE PROBABILITY OF SHOWERS AND THUNDERSTORMS THIS AFTERNOON. WITH A WEAK BOUNDARY IN SOUTHERN NORTH CAROLINA...BEST CHANCE OF STORMS WILL BE IN THE NORTH CAROLINA MOUNTAINS. MOST LOCATIONS WILL HAVE FOG THIS MORNING WHICH WILL DISSIPATE QUICKLY AFTER SUNRISE. MAXIMUM TEMPERATURES WILL BE SLIGHTLY ABOVE NORMAL. STAYED CLOSER TO THE WARMER MAV GUIDANCE FOR HIGHS. LOWS TONIGHT WILL BE MILD. EVEN THOUGH MORE CLOUD COVER DOES NOT ARRIVE UNTIL LATE TONIGHT...DEW POINTS IN THE 60S WILL LIMIT TEMPERATURE DROP.
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&& .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... AS OF 330 AM EDT SATURDAY... DIURNALLY DRIVEN SCATTERED SHOWERS AND THUNDERSTORMS EXPECTED SUNDAY MAINLY IN THE MOUNTAINS INTO THE FOOTHILLS AS RETURN UPSLOPE FLOW ON THE BACKSIDE OF DEPARTING SURFACE RIDGE IMPACTS THE EAST SLOPES OF THE APPALACHIANS...WHILE SOUTHWEST WINDS IMPINGE UPON THE WEST SLOPES SETTING UP A BROAD ZONE OF LOW LEVEL CONFLUENCE. WEAK FORCING COMBINED WITH SLOWLY INCREASING MOISTURE AND DIFFERENTIAL HEATING WILL BE SUFFICIENT TO OVERCOME WEAKENING CAPPING INVERSION. SWODY2 PLACED SLIGHT SEVERE THUNDERSTORM THREAT TO OUR NORTHWEST OVER PARTS OF THE OHIO VALLEY TO GREAT LAKES WITH STRONGER INSTABILITY AND HIGHER MLCAPES AROUND 2500 J/KG. THE ADJMAVBC CAPTURED SUNDAY HIGHS WITH READINGS FROM THE LOWER 80S IN THE MOUNTAINS TO THE LOWER 90S IN THE PIEDMONT. KEPT THE HIGHEST POPS IN THE NORTHWEST FOR SUNDAY NIGHT. USED A BLEND OF MOS GUIDANCE FOR LOW TEMPERATURES SUNDAY NIGHT WITH VALUES FROM THE MID 60S IN THE WEST TO AROUND 70 DEGREES IN THE EAST. APPROACH OF A VERY STRONG AND DEEPENING LONG WAVE TROF DIGGING SOUTH INTO THE UPPER GREAT LAKES WILL BEGIN TO IMPACT OUR REGION MONDAY INTO MONDAY NIGHT. BACKING OF LOW LEVEL WINDS IN ADVANCE OF THE COLD FRONT AND THETA-E ADVECTION WILL ERODE ANY LINGERING CAP...EVEN ACROSS THE PIEDMONT. WITH A SOUTHWEST LOW LEVEL FLOW...ANY UPSTREAM CONVECTION DEVELOPING NEAR THE WESTERN FLANKS OF THE APPALACHIANS WILL BE MORE LIKELY TO CROSS EAST OF THE BLUE RIDGE BY MID-LATE AFTERNOON INTO THE EVENING. INCREASING THERMODYNAMICS AND SHEAR WARRANTS AN INCREASING CONCERN FOR PRE-FRONTAL SEVERE WEATHER ON MONDAY AFTERNOON/EVENING. SUFFICIENT CONCERN EXISTS THAT THE STORM PREDICTION CENTER HAS HIGHLIGHTED PORTIONS OF THE AREA IN A POTENTIAL SEVERE WEATHER THREAT (SLIGHT RISK REGION) ON MONDAY. LOOKS LIKE THE POTENTIAL FOR SEVERE THUNDERSTORMS WITH HIGH WINDS BEING THE MAIN THREAT. THE FORECAST IS MADE MORE COMPLEX GIVEN A DIFFUSE FRONT THAT WILL PRECEDE THE STRONGER COLD FRONT...AND THERE ARE MODEL DIFFERENCES AS TO THE STRENGTH AND TIMING OF CYCLOGENESIS ALONG THE TRAILING FRONT. HIGH TEMPERATURES MONDAY AFTERNOON WILL RANGE FROM THE LOWER 80S IN THE MOUNTAINS TO THE LOWER 90S IN THE PIEDMONT. A FEW MID 90S COULD BE POSSIBLE DEPENDING ON CLOUD COVER AND CONVECTION. IN THE WEST MONDAY NIGHT...THE COLD FRONT AND ASSOCIATED CONVERGENCE AND BETTER JET DYNAMICS SHOULD MAINTAIN CHANCE OF ONGOING OR REDEVELOPING NEW CONVECTION THROUGHOUT THE NIGHT WEST OF THE BLUE RIDGE. LOW TEMPERATURES MONDAY NIGHT WILL BE NEAR SEASONAL FROM THE MID 60S IN THE MOUNTAINS TO THE LOWER 70S IN THE PIEDMONT. A STRONG COLD FRONT WILL PUSH EAST ACROSS OUR REGION ON TUESDAY. MU CAPE VALUES AROUND 1 TO 2K J/KG...30KT MEAN LAYER FLOW...AND MODEST LAPSE RATES WILL ALLOW SHOWERS AND THUNDERSTORMS TO DEVELOP AHEAD OF THE FRONT. QUESTIONS REMAIN ON THE EXACT TIMING OF FRONT WITH SOME DIFFERENCES BETWEEN THE GFS AND ECMWF SOLUTIONS. SHAPED TIMING OF FRONTAL BOUNDARY TOWARDS HPC ENSEMBLE BLEND. WITH CLOUDS AND CONVECTION...HIGHS ON TUESDAY WILL BE COOLER WITH VALUES FROM THE MID 70S IN THE MOUNTAINS TO THE UPPER 80S IN THE PIEDMONT. IN THE WAKE OF THE COLD FRONT...HIGH PRESSURE WILL BUILD SOUTH INTO OUR REGION TUESDAY NIGHT INTO WEDNESDAY MORNING. LEANED TOWARDS HPCGUIDE COOLER LOW TEMPERATURES TUESDAY NIGHT FROM THE LOWER 50S IN THE MOUNTAINS TO THE MID 60S IN THE PIEDMONT. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... AS OF 1230 PM EDT FRIDAY... AFTER THE COLD FRONT PASSES THROUGH THE AREA A 1020MB SURFACE HIGH BUILDS IN ALONG WITH MUCH COOLER TEMPERATURES. A NOTICEABLE DROP IN HUMIDITY WILL BE FELT AS DEWPTS CRASH INTO THE 40S AND 50S. HIGH TEMPS WILL BE SEVERAL DEGREES BELOW NORMAL WEDNESDAY AND THURSDAY WITH LOW TO MID 70S ACROSS THE MOUNTAINS AND NEAR 80 EAST OF THE BLUE RIDGE. NIGHT TIME LOWS WILL ALSO BE BELOW NORMAL...WILL NOT BE SURPRISED TO SEE A FEW MOUNTAIN LOCATIONS DROP INTO THE MID TO UPPER 40S ON THURSDAY MORNING...DEPENDING ON CLOUD COVER. && .AVIATION /18Z SATURDAY THROUGH FRIDAY/...
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AS OF 135 PM EDT SATURDAY... ISOLATED TO SCATTERED SHOWERS ARE EXPECTED TO CONTINUE TO DEVELOP ALONG AND WEST OF THE CREST OF THE BLUE RIDGE THROUGH THE REMAINDER OF THE AFTERNOON. WHILE NO TAF SITE IS CARRYING WX IN EITHER A PREVAILING AND TEMPORARY GROUP WITHIN THE TAFS...KROA AND KBCB ARE THE MOST LIKELY TAF LOCATIONS TO POTENTIALLY HAVE SHOWERS OR STORMS NEAR THEM THIS AFTERNOON. WILL UPDATE ACCORDINGLY AS NEED BE. ANY CONVECTION WILL BE MAINLY SUNSHINE DRIVEN TODAY...SO ANY ACTIVITY SHOULD QUICKLY DISSIPATE AROUND SUNSET. THROUGH THE NIGHT...MOST AREA WILL REMAIN VFR. HOWEVER...ANY LOCATIONS THAT RECEIVES RAIN TODAY WILL HAVE A INCREASED CHANCE OF SOME MVFR FOG AND/OR CEILINGS FOR ABOUT A FOUR HOUR PERIOD TONIGHT ENDING AROUND 12Z/8AM SUNDAY. SUNDAY WILL BE COMPARABLE TODAY WITH MAINLY VFR CONDITIONS...BUT POTENTIALLY HAVE GREATER COVERAGE OF SHOWERS AND STORMS WITH A SLIGHTLY EARLY START TIME. TODAY AND TOMORROW...ANY HEAVY CELLS COULD POTENTIALLY CAUSED SOME VERY BRIEF AND LOCALIZED SUB-VFR CONDITIONS. EXTENDED AVIATION DISCUSSION... SUNDAY AFTERNOON...COVERAGE OF SHOWERS AND STORMS WILL CONTINUE TO INCREASE COMPARED TO THE CONDITIONS JUST PRIOR TO 18Z/2PM. THE ACTIVITY WILL AGAIN BE MAINLY SUNSHINE DRIVEN...SO ANTICIPATE THE ACTIVITY TO DISSIPATE AROUND SUNSET. MONDAY NIGHT THROUGH TUESDAY NIGHT...A BETTER CHANCE OF SHOWER AND THUNDERSTORM ACTIVITY...ALONG WITH THE POTENTIAL FOR A GREATER COVERAGE OF SUB-VFR CONDITIONS WILL EXIST THANKS TO AN UPPER LEVEL LOW/TROUGH AND ITS ASSOCIATED DYANAMICS PROGRESSING EASTWARD THROUGH THE GREAT LAKES REGION AND THEN INTO NEW ENGLAND. ITS ASSOCIATED SURFACE FEATURES WILL OFFER A COLD FRONTAL PASSAGE TUESDAY AFTERNOON OR EVENING ALONG WITH A SLIGHT CHANCE OF SEVERE WEATHER AS OFFERED BY THE STORM PREDICTION CENTER. HIGH PRESSURE WILL TRY TO WORK ITS WAY INTO THE AREA WEDNESDAY INTO THURSDAY. THERE IS SOME QUESTION AS TO JUST HOW FAR SOUTH OF THE AREA THE COLD FRONT WILL MAKE IT BEFORE THE REGION IS ON THE WEST SIDE OF THE HIGH...AND THUS WE RETURN TO A SOUTHERLY FLOW OF MOISTURE INTO THE AREA. EITHER WAY...LOW LEVEL MOISTURE WILL LIKELY NOT COMPLETELY DRY OUT...AND THE POTENTIAL FOR OVERNIGHT IFR/MVFR FOG IS PROMISING...ESPECIALLY FOR AREAS THAT RECEIVE THE MOST RAINFALL MONDAY INTO TUESDAY. BY FRIDAY...MOST GUIDANCE IS IN AGREEMENT THAT A WAVE WILL MOVE ALONG THE STALLED FRONT AND BRING ANOTHER SUBSTANTIAL ROUND OF SHOWERS AND STORMS TO THE AREA.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS NEAR TERM...AMS/DS SHORT TERM...KK LONG TERM...CF/KK AVIATION...DS

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