Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 301703 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 103 PM 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 1250 PM EDT WEDNESDAY... VIA LAPS DATA...WEAK INSTABILITY IS STARTING TO DEVELOP ON THE SOUTHEAST EDGE OF THE FORECAST AREA...SOUTH INTO CENTRAL NORTH CAROLINA...WITHIN THE REGION WHERE HIGHER DEW POINT AIR...UPPER 50S TO AROUND 60...WAS STARTING TO WORK ITS WAY BACK INTO THE REGION ON LIGHT EASTERLY WINDS. ANOTHER AREA OF INSTABILITY WAS JUST WEST OF THE NORTHWEST PART OF THE FORECAST AREA IN CENTRAL WEST VIRGINIA. BOTH THE LATEST OUTPUT FROM THE HRRR AND RNK WRF- ARW MODELS SHOW THESE REGIONS OF THE FORECAST AREA GAINING INCREASED INSTABILITY THROUGH THE AFTERNOON WITH ISOLATED SHOWERS DEVELOPING. ENOUGH INSTABILITY MAY YIELD A THUNDERSTORM OR TWO ACROSS THE FAR SOUTHEAST PARTS OF THE REGION. THERE ALSO...ALTHOUGH NOT AS ROBUST ALONG THE FAR NW AND SE PARTS OF THE REGION...SOME WEAK INDICATION THAT SOME ISOLATED SHOWERS MAY BE POSSIBLE ALONG AND NEAR THE CREST OF THE BLUE RIDGE THIS AFTERNOON. HAVE MADE ADJUSTMENTS DOWNWARDS TWO OR THREE DEGREES THE FORECAST HIGH TEMPERATURE FOR MUCH OF THE AREA. OUR ONGOING FORECAST HAD BEEN RUNNING A BIT WARM COMPARED TO REALITY. HAVE ALSO INCREASED DEW POINTS A BIT ACROSS THE SOUTHEAST PART OF THE AREA BASED UPON THE LATEST OBSERVATIONS AND EXPECTED TRENDS THROUGH THE AFTERNOON. AS OF 955 AM EDT WEDNESDAY... VISIBLE SATELLITE IMAGERY AND SURFACE OBSERVATIONS WERE STILL INDICATING POCKETS OF LIGHT FOG THIS MORNING OVER PARTS OF THE REGION. THE GREATEST CONCENTRATION WAS IN THE GREENBRIER VALLEY. THE TREND HAS BEEN FOR A QUICK DISSIPATION...AND THIS IS EXPECTED TO CONTINUE SO THAT LITTLE IF ANY FOG IS EXPECTED TO REMAIN BY 1100 AM. NO MAJOR ADJUSTMENTS TO THE FORECAST AT THIS TIME. STILL ANTICIPATE THE DEVELOPMENT OF ISOLATED SHOWERS THIS AFTERNOON...ESPECIALLY ACROSS THE NORTHERN QUARTER OF THE FORECAST AREA...AND POTENTIALLY SOUTH ALONG THE SPINE OF THE BLUE RIDGE. A MORE ROBUST AREA OF CONVECTION MAY APPROACH THE REGION FROM THE NORTH TOWARD THE EARLY EVENING. HAVE TWEAKED HOURLY TEMPERATURE...DEW POINT...WIND AND SKY COVER GRIDS TO REFLECT THE LATEST OBSERVATIONS AND ANTICIPATED TRENDS INTO THE EARLY AFTERNOON. 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 IMPULSE 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 /18Z WEDNESDAY THROUGH MONDAY/... AS OF 100 PM EDT WEDNESDAY... HIGH CONFIDENCE IN LIGHT WINDS THROUGH THE TAF PERIOD. MED/HIGH CONFIDENCE VFR EAST OF THE BLUE RIDGE. MEDIUM CONFIDENCE VFR YIELDING TO MVFR/IFR IN FOG/STRATUS TONIGHT WEST OF THE BLUE RIDGE. WEATHER THIS TAF PERIOD SHOULD BE QUITE SIMILAR TO WHAT WE HAD YESTERDAY AS ENERGY ROTATES AROUND THE UPPER TROF AND COMBINES WITH INSTABILITY IN THE COLD POOL OF AIR TO PRODUCE A GOOD CU FIELD AND SOME ISOLATED SHOWERS...ESPECIALLY FROM THE BLUE RIDGE WESTWARD. BELIEVE THE CU WILL BE A VFR SCT V BKN TYPE SITUATION. WILL LEAN OPTIMISTIC AND KEEP SCT EXCEPT FOR KBLF/KLWB WHERE BKN WILL BE MORE LIKELY DUE TO PROXIMITY TO SHORT WAVE ENERGY. WILL ALSO KEEP TAFS DRY SINCE EXTENT OF ANY SHOWERS WILL BE QUITE LIMITED. EXPECTING ANOTHER ROUND OF MVFR/IFR FOG AND STRATUS OVERNIGHT FOR KLWB/KBLF/KBCB BUT IF CU/SC CLOUD DECK LINGERS IT MAY DELAY ONSET AND ULTIMATELY LIMIT EXTENT OF FOG/STRATUS. WILL CHOOSE TO GO WITH QUICKER CU/SC DISSIPATION THIS EVE/TONIGHT AND MORE AGGRESSIVE FOG/STRATUS OVERNIGHT. MOISTURE WILL BE ON THE INCREASE FROM THE SOUTH TOMORROW AS MORE SHORT WAVE ENERGY ROUNDS THE BASE OF THE UPPER TROF BUT ANY SIGNIFICANT AFFECTS LOOK TO BE BEYOND THIS TAF ISSUANCE. 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 WITH LINGERING OVERALL VFR...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 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. TECHNICIANS ARE WORKING ON THE PROBLEM. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...DS/JH NEAR TERM...DS/JH SHORT TERM...NF LONG TERM...AMS AVIATION...DS/MBS CLIMATE...PH EQUIPMENT...DS

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