Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 120827 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 427 AM 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/... 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. && .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 /08Z SATURDAY THROUGH WEDNESDAY/... AS OF 145 AM EDT SATURDAY... SATELLITE PICTURES SHOWED SCATTERED MID AND HIGH CLOUDS AT 05Z/1AM. STILL ENOUGH CLEARING THAT TEMPERATURES HAVE LOWERED CLOSE TO THE DEW POINT AT KLYH/KDAN/KLWB AND KBCB. MODERATE TO HIGH CONFIDENCE OF MVFR FOG FORMATION AT THESE LOCATIONS BY 09Z/5AM. LOWER CONFIDENCE THAT LIFR FOG WILL DEVELOP. MOST LIKELY LOCATIONS IF THAT DOES OCCUR WOULD BE AT KBCB AND KLWB. PLENTY OF DRY AIR ABOVE THE SURFACE BASED INVERSION THAT FOG WILL MIX OUT QUICKLY AFTER SUNRISE. SCATTERED TO BROKEN VFR STRATOCUMULUS...AROUND 4000 FT WILL DEVELOP DURING THE LATE MORNING. ISOLATED THUNDERSTORMS ARE EXPECTED ALONG THE BLUE RIDGE IN THE AFTERNOON. PROBABILITY OF OCCURRENCE IS TOO LOW AT ANY ONE AIRPORT TO INCLUDE IN THE TAF. EXTENDED AVIATION DISCUSSION... MOISTURE AND MORE WIDESPREAD SHRA/TSRA LIKELY TO RETURN FOR SUNDAY AND EARLY NEXT WEEK AS A BROAD UPPER TROUGH DIGS INTO THE GREAT LAKES REGION AND RESULTANT CYCLONIC FLOW PROVIDES INCREASINGLY UNSTABLE CONDITIONS ACROSS THE REGION. BEST CHANCE OF WIDESPREAD MVFR CIGS/VSBYS WILL BE LATE MONDAY AND INTO TUESDAY WITH THE PASSAGE OF A STRONG COLD FRONT WITH OCNL IFR CIGS/VSBYS IN WITH THE AFTERNOON/EVENING TSRA. PATCHY LATE NIGHT/EARLY MORNING FOG WILL RESULT IN LOCAL MVFR TO IFR CONDITIONS DURING THE LATE NIGHTS AND EARLY MORNINGS...ESPECIALLY IN VALLEY LOCATIONS AND WHERE EARLIER AFTERNOON RAINFALL OCCURRED. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...KK LONG TERM...CF/KK AVIATION...AMS/RAB

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