Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 300809 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 409 AM EDT WED JUL 30 2014 .SYNOPSIS... AN UPPER LEVEL TROUGH OF LOW PRESSURE ALONG WITH A COOL AREA OF SURFACE HIGH PRESSURE WILL REMAIN ACROSS THE REGION TODAY AND TONIGHT. FROM THURSDAY INTO THE WEEKEND...THE UPPER TROUGH WILL RETROGRADE WEST TOWARD THE MISSISSIPPI RIVER VALLEY. THIS WILL ALLOW FOR ATLANTIC MOISTURE TO MAKE ITS WAY BACK INTO THE AREA AND BRING AN INCREASING THREAT FOR SHOWERS AND STORMS. && .NEAR TERM /THROUGH TONIGHT/... AS OF 245 AM EDT WEDNESDAY... WEAK WESTERLY FLOW UNDER THE 5H TROUGH ALOFT WILL PERSIST OVER THE NEXT 24 HOURS ALLOWING ADDED WEAK SHORTWAVE ENERGY TO CROSS THE REGION THROUGH EARLY TONIGHT. INITIAL WAVE CAUSING SHRA OVER THE FAR SE SHOULD FINALLY EXIT EARLY THIS MORNING LEAVING BEHIND AREAS OF MID/LOW CLOUDS FROM THE BLUE RIDGE EAST UNDER A RESIDUAL WEAK SURFACE TROUGH AXIS. EXPECT THIS CLOUD COVER TO FADE TO AN INCREASING CU FIELD WITH HEATING THIS AFTERNOON WITH FORECAST RAOBS SHOWING A LAYER OF MOISTURE ALOFT BETWEEN 7H-85H. HOWEVER APPEARS ENOUGH WEAK SURFACE RIDGING TO KEEP ANY SHRA TO MINIMUM THROUGH EARLY AFTERNOON BEFORE A MID LEVEL WAVE UNDER THE COLD POCKET TO THE NW APPROACHES. THIS MAY COMBINE WITH JUST ENOUGH MOISTURE TO PRODUCE A FEW SHRA NORTH-NW BY MID TO LATE AFTERNOON ALTHOUGH MODELS REMAIN MEAGER WITH ANY PRECIP AS BASICALLY ONLY THE NAM SHOWS MUCH DEVELOPMENT. HOWEVER LAPSES WILL BE QUITE STEEP AND GIVEN THE WEAK FLOW UNDER HEATING APPEARS ENOUGH TO INCLUDE A 20-30 POP GREENBRIER/HIGHLANDS DOWN THE BLUE RIDGE WITH AN ISOLATED TSRA MENTION MAINLY NORTH. OTRW WILL CALL IT MAINLY PC FOR INTERVALS OF CLOUDS ESPCLY EARLY...AND AGAIN THIS AFTERNOON WITH HIGHS MOSTLY 70S MOUNTAINS AND LOW 80S SE PENDING CLOUDS. ANOTHER IMPUSLE ALOFT SWINGING UNDER THE BASE OF THE 5H COLD POOL WILL JET EAST CROSSING THE FAR SOUTHERN AREAS THIS EVENING. MOISTURE AGAIN LIMITED WITH THIS FEATURE ALTHOUGH MAY BE JUST ENOUGH WEAKNESS AND EARLY EVENING CONVERGENCE PER LOW LEVEL SW FLOW TO DEVELOP SHRA SE SIMILAR TO TONIGHT. THUS EXTENDED SLIGHT POPS FARTHER EAST INTO THE PIEDMONT MAINLY BEFORE MIDNIGHT. OTRW PASSING OF THIS SHORTWAVE SHOULD ALLOW MORE CLEARING MOUNTAINS WHILE MID DECK MAY AGAIN LINGER PIEDMONT OVERNIGHT AS SEEN VIA MOST MODEL RH SOLUTIONS ATTM. WILL AGAIN BE QUITE A COOL NIGHT ESPCLY IF CLEARING DEVELOPS SOONER AND DEWPOINTS DONT RISE TOO MUCH. HOWEVER BUT MAY HARD PRESSED TO REACH RECORDS AS EXPECT A BIT MORE VALLEY FOG LATE WITH SLIGHTLY HIGHER MOISTURE LEVELS TO KEEP READINGS ABOVE RECORDS FOR NOW. && .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... AS OF 345 AM EDT WEDNESDAY... THE LARGE UPPER LEVEL TROUGH AFFECTING THE EASTERN HALF OF THE NATION WITH COOLER THAN AVERAGE TEMPERATURES DURING THE EARLY HALF OF THE WEEK WILL BEGIN TO AMPLIFY WEST OF THE MISSISSIPPI RIVER ON THURSDAY. THIS WILL CAUSE WINDS ALOFT TO SHIFT FROM WESTERLY TO SOUTHWESTERLY...WHICH WILL BEGIN THE PROCESS OF RETURNING TROPICAL MOISTURE BACK INTO OUR AREA. REGARDLESS...THAT PROCESS WILL TAKE AT LEAST A DAY...AND EXPECT THURSDAY TO BE MOSTLY DRY...BUT WITH INCREASING CLOUDS. WITH THE 500MB HEIGHT RISES AS THE TROUGH RETROGRADES...EXPECT WARMER AFTERNOON TEMPERATURES...WITH HIGHS RANGING FROM THE MID 80S ACROSS THE SOUTHSIDE...TO THE MID/UPPER 70S ACROSS THE MOUNTAINS. AS HIGH PRESSURE IN THE LOW LEVELS CONTINUES TO PUSH OFFSHORE THURSDAY EVENING...RAIN WILL GRADUALLY WORK ITS WAY NORTH THROUGH THE CAROLINAS THURSDAY NIGHT...AND EXPECT TO START THE DAY FRIDAY WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS ACROSS OUR AREA. BELIEVE THAT THE MOUNTAINS...ESPECIALLY THE BLUE RIDGE...WILL HAVE THE HIGHEST RAINFALL CHANCES DUE TO THE SOUTHEASTERLY FLOW AT THE SURFACE FORCING THE MOISTURE INTO THE HIGHER TERRAIN. AND WITH PRECIPITABLE WATER VALUES QUICKLY RAMPING UP TO BETTER THAN 1.5 INCHES...BELIEVE THAT THE SHOWERS AND THUNDERSTORMS DURING THE MORNING AND AFTERNOON WILL BE EFFICIENT RAINFALL PRODUCERS. RAINFALL WILL DIMINISH FRIDAY NIGHT WITH THE LOSS OF DAYTIME HEATING...BUT DO NOT EXPECT SHOWERS TO GO AWAY COMPLETELY. MORE SHOWERS AND THUNDERSTORMS CAN BE EXPECTED ON SATURDAY AREAWIDE AS THE MID ATLANTIC REMAINS SITUATED IN A PATTERN OF DEEP SOUTHWEST FLOW ALOFT...CARRYING UPPER LEVEL DISTURBANCES ACROSS THE AREA TO INTERACT WITH TROPICAL MOISTURE RIDING NORTH ALONG THE APPALACHIAN CHAIN. RAINFALL AND WIDESPREAD CLOUD COVER WILL KEEP AFTERNOON HIGH IN THE MID 70S TO LOW 80S...WHILE OVERNIGHT LOWS WILL BE MILD... FALLING INTO THE UPPER 50S TO THE MID 60S. && .LONG TERM /SUNDAY THROUGH TUESDAY/... AS OF 325 PM EDT TUESDAY... UPPER LOW OVER THE NORTHEAST FLATTENS BY SUNDAY WITH A SHORT WAVE PASSING NORTH OF THE FORECAST AREA ON SUNDAY. ECMWF SUGGESTS ANOTHER COLD FRONT WILL APPROACH THE AREA FROM THE NORTH ON TUESDAY AND POSSIBLY MOVE ALL THE WAY THROUGH THE MID ATLANTIC REGION ON WEDNESDAY. NOT ALL THE EXTENDED GUIDANCE SUPPORTS A TROF AS AMPLIFIED AS THE ECMWF SO STILL QUESTIONABLE HOW FAR SOUTH FRONT WILL ADVANCE. AHEAD OF THAT FRONT FORECAST AREA STAYS IN TYPICAL AIR MASS FOR SUMMER WITH NEAR NORMAL TEMPERATURES AND ENOUGH MOISTURE AND INSTABILITY FOR A DAILY THREAT OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... AS OF 100 AM EDT WEDNESDAY... PATCHY SHOWERS JUST SOUTH/SE OF KDAN SHOULD FINALLY EXIT IN THE NEXT HOUR OR TWO LEAVING MAINLY VFR CIGS EAST OF THE BLUE RIDGE AND SCATTERED CLOUDS OVER THE WEST. COULD SEE KDAN DROP DOWN TO HIGH END MVFR FOR A FEW HOURS BEFORE SUNRISE OTRW KEEPING CIGS MAINLY IN THE 4-7K FT RANGE FROM KROA EAST OVERNIGHT. WEAK WAVE ALOFT RESPONSIBLE FOR THE SHOWERS AND CLOUDS SHOULD FINALLY KICK OUT BY EARLY WEDNESDAY ALLOWING MORE CLEARING ESPCLY WEST BY DAWN. THIS MAY LEAD TO PATCHY VALLEY FOG GIVEN GOOD RADIATIONAL CONDITIONS WITH MVFR POSSIBLE AT KLWB/KBCB AND AN OUTSIDE CHANCE OF SEEING IFR AT KLWB. HOWEVER LOWER CIGS AT KBLF AND KLWB LOOK LESS LIKELY NOW WITH ANY LOW CIGS LIKELY DUE TO FOG/STRATUS FORMATION LATE. UPPER TROUGH UNDERCUT BY WEAK SURFACE HIGH PRESSURE WILL REMAIN IN PLACE WEDNESDAY WITH SCATTERED CU/AC EARLY INCREASING TO BKN 4-6K FT CLOUD BASES MOST SPOTS WITH HEATING. AN ISOLATED SHRA WILL BE POSSIBLE MAINLY WESTERN THIRD GIVEN THE APPROACH OF ANOTHER WAVE FROM THE NW BUT TOO IFFY TO INCLUDE ANY MENTION. OTRW KEEPING IT VFR FROM MID MORNING ON WITH GOOD FLYING CONDITIONS LINGERING INTO WEDNESDAY NIGHT WITH ANY CIGS LIKELY TO FADE WITH LOSS OF HEATING. EXTENDED AVIATION DISCUSSION... A BROAD TROUGH OF LOW PRESSURE WILL BE ACROSS THE EASTERN UNITED STATES THROUGH SUNDAY. HOWEVER...IT WILL START CENTERED OVER THE REGION...AND THEN RETROGRADE WEST TO NEAR THE MISSISSIPPI RIVER BY SUNDAY. THIS TRANSITION WILL ALLOW FOR BETTER CHANCES OF SHOWERS...AND PERHAPS A FEW THUNDERSTORMS...TO OCCUR ACROSS THE REGION AS ATLANTIC MOISTURE WILL BE ABLE TO WORK ITS WAY INTO THE AREA. APPEARS COVERAGE WILL BE MORE ISOLATED ON THURSDAY...THEN INCREASING FROM FRIDAY INTO THE WEEKEND AS A DEEPER SOUTHERLY TRAJECTORY STARTS TO DEVELOP. ALONG WITH THIS MOISTURE WILL COME BETTER CHANCES FOR SUB- VFR CONDITIONS...ESPECIALLY UNDER ANY HEAVIER SHOWER OR STORM THAT FORMS...BUT ALSO DURING THE OVERNIGHT HOURS AS BOUNDARY LAYER MOISTURE GETS TRAPPED UNDER THE NOCTURNAL INVERSION. && .CLIMATE... JULY 30TH RECORD LOWS: ROANOKE......54...1997 BLUEFIELD....50...1981 DANVILLE.....60...1972/81/83/2013 LEWISBURG....46...2013 LYNCHBURG....52...1997 BLACKSBURG...50...1973/81 JULY 31ST RECORD LOWS: ROANOKE......49...1914 BLUEFIELD....49...1997 DANVILLE.....55...1966 LEWISBURG....48...1997 LYNCHBURG....49...1997 BLACKSBURG...44...1997 && .EQUIPMENT... THE NOAA WEATHER RADIO AT WYTHEVILLE VA...WZ2500...BROADCASTING ON A FREQUENCY OF 162.450 MHZ...IS OFF THE AIR...DUE TO PHONE LINE ISSUES. PHONE COMPANY IS WORKING ON IT. THE RADIO IS NOT EXPECTED TO BE BACK IN SERVICE ANY SOONER THAN WEDNESDAY MORNING. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...DS/JH NEAR TERM...JH SHORT TERM...NF LONG TERM...AMS AVIATION...DS/JH/RAB CLIMATE...PH EQUIPMENT...DS

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