Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 302358 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 758 PM EDT WED JUL 30 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. THE RESULT THROUGH THE WEEKEND AND INTO THE EARLY PART OF NEXT WEEK WILL BE AN INCREASED CHANCE OF SHOWERS AND STORMS ACROSS OUR REGION STARTING ON THURSDAY. CURRENTLY...FRIDAY INTO SATURDAY LOOKS TO BE THE TIME WINDOW WITH THE GREATEST POTENTIAL FOR THE ENTIRE AREA. && .NEAR TERM /THROUGH THURSDAY/... AS OF 320 PM EDT WEDNESDAY... WE WILL CONTINUE TO WATCH TWO POTENTIAL AREAS OF CONVECTION HEADING INTO THE EARLY EVENING HOURS. THE ONE WILL BE CENTERED JUST SOUTHEAST OF THE FORECAST AREA...BUT ITS INFLUENCE MAY BE EXTEND FAR ENOUGH NORTH FOR SOME ISOLATED SHOWERS AND STORMS IN AREAS AROUND...EAST AND SOUTH OF DANVILLE VA THROUGH ROUGHLY 800 PM. THE OTHER AREA WILL BE IN ASSOCIATION WITH SOME INSTABILITY THAT HAS DEVELOPED JUST WEST OF THE SOUTHEAST WEST VIRGINIA PORTION OF THE FORECAST AREA. WHILE AREAS AROUND AND WEST OF LEWISBURG WV MAY SEE A STRAY SHOWER BETWEEN NOW AND ROUGHLY 500 PM...CHANCES WILL INCREASE AS WE APPROACH 700 PM. A DISTURBANCE WITH AN AREA OF STEEP LAPSE RATE AIR IS CURRENTLY MOVING THROUGH OHIO...AND SHOULD BE APPROACHING THE AREA TOWARD THE EARLY EVENING. BOTH THE HRRR AND RNK WRF-ARW OFFER SOLUTIONS THAT BRING THE ACTIVITY TO OUR DOORSTEP AND THEN HAVE IT DISSIPATE. HAVE ALLOWED FOR THE POTENTIAL FOR SOME ISOLATED THUNDERSTORMS THIS EVENING IN AREAS NEAR AND NORTH OF INTERSTATE 64 IN WV AND VA. OTHER ISOLATED SHOWERS WILL BE POSSIBLE NEAR THE CREST OF THE BLUE RIDGE FROM THE LATE AFTERNOON INTO THE EARLY EVENING. WHILE INSTABILITY IS NOT STRONG IN THIS AREA...CONVERGENCE WITHIN THIS AREA MAY BE ENOUGH FOR A FEW SHOWERS TO FORM. THE MAIN FOCUS WILL BE ACROSS THE FAR NORTHWEST AND FAR SOUTHEAST PARTS OF THE REGION. A HIGH PRESSURE RIDGE AXIS WAS SITUATED WEST-EAST ACROSS THE AREA CURRENTLY. EASTERLY FLOW ON THE SOUTH SIDE OF THIS FEATURE HAS HELPED ADVECT HIGHER DEW POINTS IN THE LOWER 60S BACK TOWARD THE AREA AS CLOSE AS ROXBORO NC AND SOUTH HILL VA. THE CENTER OF THE HIGH IS PROGGED TO START SHIFTING EASTWARD TONIGHT. THIS WILL HELP ALLOW FOR A GRADUAL TREND TOWARDS LOW LEVEL WINDS WITH A GREATER SOUTHERLY COMPONENT ACROSS THE REGION. IN TURN...HIGHER DEW POINT AIR IS EXPECTED TO CONTINUE ITS PROGRESSION TOWARDS AND THEN INTO THE AREA. BY DAYBREAK THURSDAY...SOME OF THIS MOISTURE WILL BECOME BANKED AGAINST THE CREST OF THE BLUE RIDGE WITH INCREASED CLOUD COVER OVER NORTHWEST NORTH CAROLINA AND NEIGHBORING SECTIONS OF SOUTHWEST VIRGINIA. LOW TEMPERATURES TONIGHT SHOULD BE MILDER AS COMPARED TO THOSE OF THIS MORNING. READINGS AROUND 50 TO THE LOWER 50S ARE EXPECTED ACROSS THE MOUNTAINS WITH A MIX OF MID TO UPPER 50S ACROSS THE PIEDMONT. A FEW SPOTS ACROSS SOUTHSIDE VIRGINIA AND NEIGHBORING NORTH CENTRAL NORTH CAROLINA CAN EXPECT LOWS AROUND 60. OF OUR SIX CLIMATE SITES...LEWISBURG HAS THE POTENTIAL OF BEING CLOSE TO A RECORD LOW TONIGHT. SEE THE CLIMATE SECTION OF THIS DISCUSSION FOR DETAILS. ON THURSDAY...THE TREND TOWARDS E-SE LOW LEVEL FLOW AND GREATER MOISTURE WILL CONTINUE. INCREASING CLOUDS WILL BE THE NORM THROUGHOUT THE DAY WITH UPSLOPE RAIN SHOWERS DEVELOPING AND GROWING IN COVERAGE. THE GREATEST CONCENTRATION WILL BE ACROSS THE NORTHERN MOUNTAINS OF NORTH CAROLINA...NORTHEAST ALONG THE CREST OF THE BLUE RIDGE TO NEAR FLOYD VA. HIGH TEMPERATURES WILL RANGE FROM THE MID 70S TO AROUND 80 IN THE MOUNTAINS TO THE LOW TO MID 80S ACROSS THE PIEDMONT. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... AS OF 330 PM EDT THURSDAY... MODELS CONSISTENT BRINGING A SHORT WAVE THROUGH THE SOUTHWEST FLOW ALOFT THURSDAY NIGHT THROUGH FRIDAY NIGHT. THURSDAY NIGHT AND FRIDAY THERE IS ALSO SOME SUPPORT FROM THE DIFFLUENT AREA OF THE UPPER JET. MAY KEEP PROBABILITY OF THUNDERSTORMS LOW SINCE GUIDANCE IS SHOWING LITTLE CAPE AND INSTABILITY OVER MUCH OF THE FORECAST AREA. BY FRIDAY MORNING...PRECIPITABLE WATER VALUES WILL BE BACK IN THE 1.0 TO 1.5 INCH RANGE WITH SURFACE DEW POINTS IN THE 60S. WPC 24 HOUR QPF FROM 12Z FRIDAY TO 12Z SATURDAY OF 0.25 TO 0.50 INCHES LOOKS REASONABLE. HOWEVER...MODELS DO NOT HAVE A PARTICULARLY GOOD CONSENSUS OF WHERE THE HEAVIEST AMOUNTS WILL BE. EASTERLY COMPONENT OF LOW LEVEL WINDS FAVORS THE EASTERN SLOPES OF THE BLUE RIDGE. PUTTING THE HIGHEST PROBABILITY OF PRECIPITATION IN FROM LATE THURSDAY NIGHT THROUGH LATE MORNING ON FRIDAY. WIDE RANGE IN GUIDANCE FOR MAXIMUM TEMPERATURES ON FRIDAY. WITH ALL THE CLOUDS AND PRECIPITATION EXPECTED...HAVE TRENDED TOWARD THE COOLER BIAS CORRECTED MAV NUMBERS. && .LONG TERM /SATURDAY 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 /00Z THURSDAY THROUGH MONDAY/... AS OF 745 PM EDT WEDNESDAY... GENERALLY VFR CONDITIONS EXPECTED THROUGH THE TAF VALID PERIOD...WITH THE EXCEPTION BEING POTENTIAL FOR BR HZ DURING THE LATE NIGHT/EARLY MORNING HOURS AT THE USUAL SPOTS...BUT ESPECIALLY WEST OF THE BLUE RIDGE. UPPER TROUGH WILL CONTINUE ACROSS THE REGION. A DISTURBANCE...NOW LOCATED IN THE SOUTHERN PLAINS WILL MOVE THROUGH THE BASE OF THE TROUGH THU...THEN BEGIN TO APPROACH THE REGION FROM THE SOUTHWEST THU NIGHT/FRI. LINE OF THUNDERSTORMS ACROSS WESTERN WV NORTHWARD INTO CENTRAL PA WILL DISSIPATE PER ALL MODEL SOLUTIONS AS IT MOVES TOWARD THE APPALACHIANS NOT AFFECTING ANY TAF SITES. HOWEVER...CI SHIELD MAY AFFECT LWB FOR A WHILE THIS EVENING. OTHERWISE...SCT AC/SC WILL DISSIPATE OVER THE NEXT COUPLE OF HOURS. MVFR BR CAN BE EXPECTED AGAIN TONIGHT AT LWB/BCB AND POTENTIALLY DAN/LYH...WITH LWB LIKELY SEEING A PERIOD OF IFR-LIFR ONCE AGAIN IN THE 08Z-13Z TIME FRAME. FOG IS NOT EXPECTED AT ROA OR BLF AT THIS TIME. FOR THU...LAYER OF MOISTURE WILL PERSIST IN THE 040-060 RANGE...RESULTING IN CONTINUATION OF SCT-BKN CU/SC/AC DURING THE MID DAY/AFTERNOON. LATE IN THE DAY...CI SHIELD WILL SPREAD NORTHEASTWARD TOWARD THE REGION FROM THE SOUTHEAST STATES. WILL HOLD OFF ON MENTIONING ANY SHRA/TSRA THIS TAF VALID PERIOD AS IT APPEARS TO REACH NO FURTHER THAN NW NC LATE IN THE DAY. WINDS...MOSTLY SW THROUGH THE TAF VALID PERIOD...BUT BCB/LYH/DAN/LWB WILL LIKELY SEE CALM WINDS MUCH OF THE NIGHT. SPEEDS THU REMAINING MOSTLY 5KTS OR LESS EVEN AFT 14Z. MEDIUM TO HIGH CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN VSBYS THROUGH 14Z...THEN HIGH CONFIDENCE IN VFR CONDITIONS. MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH THE TAF VALID PERIOD. 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 ISOLD 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 CAPES EXCEEDING 1000 J/KG 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. 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 NEAR TERM...DS SHORT TERM...AMS LONG TERM...AMS AVIATION...RAB CLIMATE...PH EQUIPMENT...DS

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