Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 310730 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 330 AM EDT THU JUL 31 2014 .SYNOPSIS... AN UPPER TROUGH OF LOW PRESSURE WILL RETROGRADE WEST TO THE MISSISSIPPI RIVER VALLEY...AND THE CENTER OF SURFACE HIGH PRESSURE WILL SHIFT TO OUR EAST INTO FRIDAY. THIS WILL RESULT IN A RETURN OF MOISTURE TO THE REGION ALONG WITH INCREASING CHANCES OF SHOWERS AND THUNDERSTORMS LATER TODAY INTO THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 235 AM EDT THURSDAY... TRANSITION FROM THE DRY/COOL CONDITIONS OF LATE TO A WETTER SCENARIO TO BEGIN TODAY AS THE LINGERING 5H TROUGH STARTS TO SHIFT WEST WHILE THE PARENT SURFACE HIGH PRESSURE HEADS SLOWLY OFFSHORE. THIS WILL ALLOW FOR DEEPER MOISTURE TO RETURN WITH INCREASING SOUTH/SW FLOW ALOFT WITH THE UPPER TROUGH...AND LOW LEVEL SOUTH/SE FLOW ALONG THE BACKSIDE OF THE EXITING SURFACE RIDGE. HOWEVER FORCING TODAY REMAINS RATHER FAINT GIVEN A WEAK BUBBLE HIGH LINGERING ALONG THE MOUNTAINS AND MOST MID LEVEL ENERGY STILL BACK TO THE SW UNDER THE BASE OF THE COOL POOL. MODELS DO GRADUALLY BRING HIGHER DEWPOINTS UP FROM THE SOUTH WITH SE FLOW PROVIDING CONVERGENCE ALONG THE SOUTHERN BLUE RIDGE...AND PERHAPS FARTHER EAST IN THE PIEDMONT WHERE SOME GUIDANCE FEEDS AN AXIS OF LOW LEVEL MOISTURE IN FROM THE SE PER FORECAST RIBBON OF HIGHER THETA-E. THIS IN CONJUNCTION WITH HEATING AT LEAST THROUGH HIGH CLOUDS SHOULD ALLOW FOR INCREASING COVERAGE OF SHOWERS MAINLY SW EARLY ON...THEN EXPANDING NORTH AND EAST BY THIS EVENING. APPEARS THUNDER LIMITED TO THE FAR SOUTH AND SE GIVEN WEAK INSTABILITY BUT SUGGESTED BY A FEW SOLUTIONS INCLUDING THE SPC WRF AND NCEP WRF/NAM. THUS INCLUDED MENTION LATER WITH BUMP IN CHANCE POPS A BIT MAINLY SOUTH OF HIGHWAY 460...WITH ONLY SLIGHT POPS FARTHER NORTH WHERE MORE SUN LIKELY TODAY. HIGHS PERHAPS A LITTLE BELOW MOS SOUTH AND BLUE RIDGE GIVEN CLOUDS AND SE FLOW BUT OVERALL SIMILAR TO PREVIOUS...UPPER 70S/LOW 80S. MAY SEE A DECREASE IN CONVECTIVE COVERAGE THIS EVENING BEFORE THE SHORTWAVE CURRENTLY PRODUCING THE SHRA OVER OKLAHOMA ROUNDS THE TROUGH AND APPROACHES FROM THE SW LATE TONIGHT. SEVERAL MODELS SHOWING QUITE AN ENHANCEMENT TO THE PRECIP AFTER MIDNIGHT WITH GOOD OVERRUNNING RESULTING IN WIDESPREAD SHOWERS INTO A DEVELOPING LOW LEVEL WEDGE. APPEARS SOME HEAVY RAIN POSSIBLE NW NC MOUNTAINS TOWARD DAYBREAK WITH THE AIDED UPSLOPE FLOW AND STRONG MOISTURE TRANSPORT OF 1.5 INCH PWATS INTO THE EASTERN SLOPES OF THE BLUE RIDGE. SHOULD BE ENOUGH LIFT FOR SHOWERS TO SPREAD NE ACROSS THE ENTIRE CWA BY DAYBREAK WITH THE HEAVIEST BLUE RIDGE AND SW...BUT WITH ANY THUNDER BEING ELEVATED/ISOLATED AND MAINLY SW OF THE AREA GIVEN THE BETTER LIFT SOUTH OF THE LOW LEVEL COOL POOL. THUS RUNNING WITH HIGH LIKELY/LOW CAT POPS FROM THE NEW RIVER VALLEY AND POINTS SW ALONG WITH HIGH CHANCES ELSW FOR NOW. LOW TEMPS A BIT MORE WARM/HUMID AS MOISTURE SURGES BACK WITH MOST ONLY DROPPING INTO THE LOW/MID 60S OVERNIGHT. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... AS OF 314 AM EDT THURSDAY... VERY LITTLE CHANGE IN THE WEATHER PATTERN THROUGH THE WEEKEND...AS A BERMUDA HIGH SETS UP SHOP IN THE WESTERN ATLANTIC. BY FRIDAY MORNING ...A HYBRID WEDGE WILL LAY ACROSS THE MID ATLANTIC REGION. MEANWHILE...AN UPPER LEVEL TROUGH WILL REMAIN OVER THE GREAT LAKES AND UPPER MISSISSIPPI VALLEY. SHORT WAVES ROUNDING THIS TROUGH WILL RIDE OVER THE WEDGE...BRINGING A LONG PERIOD OF GRAY DREARY WEATHER TO THE REGION INTO THE WEEKEND. IT WILL NOT RAIN ALL THE TIME...BUT IT WILL RAIN/DRIZZLE MOST OF THE TIME. THE BEST CHANCE FOR AREA-WIDE RAIN WILL BE FRIDAY MORNING AND SATURDAY AFTERNOON. WITH AN EASTERLY FLOW...HIGHEST RAINFALL AMOUNTS WILL BE ALONG THE BLUE RIDGE WITH AMOUNTS NEAR 2 INCHES FOR THE 3 DAYS. THE WEDGE SHOULD KEEP THE AREA STABLE ON FRIDAY...HOWEVER THERE EXIST SOME INSTABILITIES ALOFT FOR AN ISOLATED RUMBLE OF THUNDER. BETTER INSTABILITIES ARE POSSIBLE SATURDAY AFTERNOON...ESPECIALLY IF THE WEDGE IS ALLOWED TO ERODE. WITH A WEDGE AND EASTERLY FLOW IN PLAY THROUGH THE PERIOD...TEMPERATURES WILL RUN WELL BELOW NORMAL. WITH THE ADDITION OF RAIN AND/OR DRIZZLE...I UNDERCUT GUIDANCE BY 3F-5F...PRODUCING AFTERNOON HIGHS AROUND 15F COLDER THAN NORMAL EACH DAY. OVERNIGHT TEMPERATURES WILL NOT DROP MUCH WITH READINGS IN THE 60S. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... AS OF 330 PM EDT THURSDAY... FRONT AT THE SURFACE REMAINS ALONG THE COAST SATURDAY NIGHT THROUGH MONDAY. ON TUESDAY AND WEDNESDAY...A COLD FRONT WILL PUSH INTO THE REGION FROM THE NORTHWEST. UNTIL THIS FRONT GOES THROUGH...THERE WILL BE A DAILY THREAT OF SHOWERS AND THUNDERSTORMS EACH AFTERNOON AND EVENING. CHALLENGING TO NARROW DOWN WHICH DAY OF TIME FRAME WILL BE MORE FAVORABLE FOR PRECIPITATION...ALTHOUGH MODELS SUGGEST A SHORT WAVE COMING THROUGH THE OHIO VALLEY ON SUNDAY MAY BRING A MORE ORGANIZED AREA OF SHOWERS AND THUNDERSTORMS TO THE COUNTY WARNING AREA. POCKET OF WARMER 850 MB AIR WITH +20 TEMPERATURES COMES OUT OF THE MISSISSIPPI VALLEY...REACHING THE FORECAST AREA ON WEDNESDAY BASED ON THE ECMWF. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... AS OF 1255 AM EDT THURSDAY... OVERALL VFR CONTINUES OVERNIGHT WITH SOME INCREASE IN HIGH CLOUDS FROM THE SW THROUGH DAYBREAK ALONG WITH PASSING MID DECK ACROSS THE NW. THIS MAY TEND TO MITIGATE FOG TO SOME EXTENT BUT STILL EXPECTING A PERIOD OF IFR/LIFR AT KLWB BEFORE DAWN...AND MVFR TO BRIEF IFR AT KBCB PENDING DEGREE OF CLOUD COVER. SOME SPOTTY OCNL MVFR ALSO POSSIBLE IN THE EAST AT KLYH/KDAN AROUND SUNRISE WITH MORE COVERAGE AROUND KLYH AT THIS POINT IF AT ALL. ANY LOW CONDITIONS SHOULD FADE BY MID MORNING WITH ANOTHER ROUND OF DEVELOPING 4-6K FT CU FIELDS UNDERNEATH A CI CANOPY INTO THURSDAY AFTERNOON. APPEARS MORE IN THE WAY OF BKN CLOUDS ACROSS THE SW EARLY ON WITH THIS SPREADING NE TO KBLF/KBCB AND KROA THIS AFTERNOON. A FEW SHRA AND ISOLATED TSRA MAY ALSO DEVELOP ALONG THE BLUE RIDGE BUT COVERAGE LACKING AND LIKELY NOT FAR ENOUGH NORTH TO AFFECT MOST TAF SITES LATER THURSDAY SO LEAVING OUT SHOWER MENTION FOR NOW. OTRW VFR WITH WINDS TURN MORE SOUTH TO SW AT 5-10 KTS THIS AFTERNOON. IMPULSE ROUNDING IN FROM THE SW SUPPORTS INCREASING MID CLOUDS THURSDAY EVENING WITH BASES LOWERING OVERNIGHT AS DEEP MOISTURE RETURNS. THIS MAY BRING WIDESPREAD MVFR CIGS TO MUCH OF THE REGION AFTER MIDNIGHT THURSDAY NIGHT WITH IFR IN SHOWERS POSSIBLE ESPCLY ALONG THE BLUE RIDGE BY FRIDAY MORNING. EXTENDED AVIATION DISCUSSION... A BROAD TROUGH OF LOW PRESSURE WILL BE ACROSS THE EASTERN UNITED STATES THROUGH SUNDAY. IT WILL SLOWLY RETROGRADE FROM THE EASTERN/CENTRAL GREAT LAKES TO THE WESTERN GREAT LAKES BY THE WEEKEND. THIS WILL BEGIN TO TURN THE UPPER FLOW TO THE SOUTHWEST WITH TIME. THE AFOREMENTIONED DISTURBANCE COMING FROM THE SE STATES THU...WILL MOVE NORTHEASTWARD ACROSS THE REGION FRI. EXTENSIVE OVERRUNNING LIKELY WITH EMBEDDED ISOLD TSRA. SFC AIR MASS REMAINS QUITE STABLE...ESPECIALLY EAST OF THE ALLEGHANY FRONT...SO THUNDER APPEARS ISOLATED AT THIS POINT. HOWEVER...WIDESPREAD MVFR CIGS/VSBYS WILL BE POSSIBLE FRI WITH THIS SCENARIO IN -RA -DZ BR. FOR SAT-SUN...AIR MASS WILL SLOWLY BECOME WARMER AND MORE UNSTABLE. SCT SHRA/TSRA AGAIN SAT WITH ONLY LIMITED INSTABILITY EVIDENT. FOR SUN...BETTER CHANCE OF TSRA WITH BETTER INSTABILITY ACROSS MUCH OF THE CWA...SW FLOW ALOFT...AND INCREASING MOISTURE LEVELS. THUS...BRIEF PERIODS OF MVFR-IFR CIGS/VSBYS EXPECTED IN SHRA/TSRA SAT AND MORE LIKELY SUN AFTERNOON. SOME DRYING WITH A RETURN TO OVERALL VFR POSSIBLE MONDAY AS ANOTHER WEAK COOL FRONT SWEEPS IN FROM THE NW AND TAKES MOST MOISTURE TO THE SE OF THE REGION. OTHERWISE...POTENTIAL FOR LATE NIGHT/EARLY MORNING IFR- LIFR BR/FG INCREASES THROUGH THE PERIOD...BUT MAINLY AT THE USUAL SITES...LWB/BCB/LYH. && .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. TECHNICIANS ARE WAITING ON DELIVERY OF PARTS TO MAKE REPAIRS. THE EARLIEST THE RADIO WILL BE WORKING AGAIN IS FRIDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...DS/JH NEAR TERM...JH SHORT TERM...RCS LONG TERM...AMS AVIATION...JH/RAB CLIMATE...PH EQUIPMENT...DS

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