Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 301941 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 341 PM EDT WED JUL 30 2014 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH THURSDAY/...
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AS OF 320 PM EDT WEDNESDAY... WE WILL CONTINUE TO WATCH TO 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 WES 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.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
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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.
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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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.
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&& .AVIATION /20Z 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...
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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.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...DS NEAR TERM...DS SHORT TERM...AMS LONG TERM...AMS AVIATION...DS/MBS CLIMATE...PH EQUIPMENT...DS

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