Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 312216 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 616 PM EDT THU JUL 31 2014 .SYNOPSIS... AN UPPER TROUGH OF LOW PRESSURE WILL CONTINUE TO 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 THIS EVENING INTO THE WEEKEND. && .NEAR TERM /THROUGH FRIDAY/... AS OF 600 PM EDT THURSDAY... SHOWERS AND ISOLATED TSRA SPREAD FROM SRN WV INTO THE MTN EMPIRE EAST TOWARD THE NRV...THEN SPREADING NEWD ACROSS THE NC/VA FOOTHILLS AND PIEDMONT. MADE SOME ADJUSTMENTS TO POPS AS COVERAGE IS MORE SCATTERED OR ISOLATED ATTM. MODEST INSTABILITY RESIDES ACROSS THE PIEDMONTS WITH SFC LI OF -3 TO -5. OVERALL THOUGH EXPECT THUNDER THREAT TO BE DIMINISHING THIS EVENING WITH SKIES SOCKED IN WITH CLOUDS...AND DEPARTING UPPER VORT WHICH IS PROVIDING SOME LIFT. OTHER FORECAST GRIDS ON TARGET...THOUGH MADE SOME HOURLY ADJUSTMENTS TO SKY COVER TO ACCOUNT FOR LATEST SAT TRENDS. PREVIOUS VALID DISCUSSION... WINDS ALOFT ARE LIGHT...WHICH WILL MAKE FOR SLOW CELL MOVEMENT AND THE POSSIBILITY OF LOCALLY HEAVY RAIN DURING THE EVENING. PRECIP WILL NOT GO AWAY ALTOGETHER AS DEEPER MOISTURE ARRIVES FROM THE CAROLINA COAST TO INTERACT WITH AN APPROACHING UPPER LEVEL DISTURBANCE. AS THE DISTURBANCE NEARS FROM THE CENTRAL MISSISSIPPI RIVER VALLEY...EXPECT RAIN COVERAGE TO INCREASE AGAIN...WITH HIGHEST RAINFALL CHANCES EXPECTED TOWARD DAWN ACROSS THE MOUNTAINS AS SOUTHEASTERLY FLOW FORCES THE MOIST AIR INTO THE HIGHER TERRAIN. RAINFALL WILL BE WIDESPREAD ON FRIDAY...THOUGH WITH OCCASIONAL BREAKS...AS THE UPPER LEVEL DISTURBANCE PASSES ACROSS OUR AREA. WITH HIGH PRESSURE STILL HUGGING THE SURFACE TO CREATE A STABLE LAYER IN THE ATMOSPHERE...BELIEVE THAT THUNDERSTORMS WILL BE MAINLY ISOLATED...ALTHOUGH A FEW MAY DEVELOP ABOVE THE HIGH PRESSURE WEDGE. REGARDLESS...LOCALLY HEAVY RAIN WILL STILL BE POSSIBLE...WITH AN INCH PER HOUR RATES IN A FEW AREAS ALONG THE BLUE RIDGE. THAT STATED...MUCH OF OUR AREA HAS BEEN DRY LATELY...AND THE GROUND IS VERY CAPABLE OF ABSORBING PERIODS OF HEAVY RAIN. AS SUCH...DO NOT BELIEVE THERE IS A MAJOR CONCERN FOR MORE THAN ISOLATED MINOR FLOODING THROUGH FRIDAY EVENING. THE HIGH PRESSURE WEDGE AND RAINFALL WILL ALSO KEEP A CAP ON HEATING...AND DO NOT SEE FRIDAY AFTERNOON TEMPERATURES WARMING MUCH...ESPECIALLY ACROSS THE NORTH CAROLINA MOUNTAINS WHERE THE CHANGE IN TEMPERATURES FROM EARLY MORNING LOWS MAY BE ONLY 2 TO 4 DEGREES. AS SUCH...MAY WANT TO KEEP A LIGHT JACKET HANDY AS HIGHS RANGE FROM THE MID 60S TO THE MID 70S AREAWIDE. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... AS OF 315 PM EDT THURSDAY... SHORT WAVE DIGS DOWN THE WEST SIDE OF THE UPPER TROF FRIDAY NIGHT AND SATURDAY OVER THE OHIO VALLEY. MODELS BRING THE BEST VORTICITY ADVECTION WITH THIS FEATURE INTO THE COUNTY WARNING ON SUNDAY. THERE SHOULD BE A BRIEF BREAK IN THE INTENSITY AND AREAL COVERAGE OF THE PRECIPITATION ON FRIDAY NIGHT AND SATURDAY. THEN THE PROBABILITY OF PRECIPITATION INCREASES AGAIN FOR SATURDAY NIGHT AND SUNDAY. MODELS SHOWING BEST UPPER DIFFLUENCE AND JET SUPPORT LATE SATURDAY INTO SUNDAY TOO. LARGEST PRECIPITATION AMOUNTS WILL BE GREATLY INFLUENCED BY THE AMOUNT...OF LACK OF...UPSLOPE...EFFICIENT RAIN PROCESSES WITH HIGH PRECIPITABLE WATER VALUES AND THE IMPACT OF THE COAST FRONT AND PRECIPITATION ALONG THAT BOUNDARY. BUFKIT AND MIXED LAYER LIFTED INDEX SHOWED A STABLE LAYER NEAR THE SURFACE ON FRIDAY NIGHT THEN BETTER INSTABILITY ON SATURDAY. IN-SITU WEDGE IS NOT AS PRONOUNCED BY THEN AND GFS SHOWED SOME INSTABILITY BY SATURDAY AFTERNOON. ENOUGH TO KEEP THUNDER IN FOR SATURDAY AFTERNOON AND AGAIN ON SUNDAY. LITTLE CHANGE IN THE AIR MASS THIS TIME FRAME WITH 850 MB TEMPERATURES FROM +14 TO +16 AND PRECIPITABLE WATER VALUES AS HIGH AS 2.0 INCHES IN THE FAR SOUTHEAST COUNTY WARNING AREA ON SUNDAY. NOTHING EXTREME SO GUIDANCE WILL HAVE A GOOD HANDLE ON HIGHS AND LOWS. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AS OF 330 PM EDT THURSDAY... MONDAY THROUGH WEDNESDAY THE TROFFING IN THE EAST FLATTENS. A SURFACE COLD FRONT COMES SOUTH THROUGH NEW ENGLAND MONDAY TUESDAY...BUT WILL ONLY MOVE SO FAR SOUTH WITH THE BOUNDARY PARALLEL TO THE UPPER FLOW. THIS WILL KEEP THE FORECAST AREA ON THE WARM UNSTABLE AIR MASS ON THE SOUTH SIDE OF THE FRONT THROUGH THURSDAY. DEEPEST MOISTURE AND BEST LIFT WILL BE FOCUSED ALONG THE COAST FRONT ACROSS THE CAROLINAS AND GEORGIA. NOT SEEING ANY ORGANIZED FORCING FOR THE COUNTY WARNING AREA. TEMPERATURES WILL BE NEAR NORMAL THROUGH THE PERIOD. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... AS OF 200 PM EDT THURSDAY... SATELLITE IMAGERY INDICATES MID AND HIGH CLOUDS INCREASING AS THE BROAD UPPER LEVEL TROUGH EXTENDING FROM NEAR HUDSON BAY RETROGRADES WESTWARD FROM THE APPALACHIAN CHAIN...CAUSING UPPER LEVEL FLOW ACROSS THE MID ATLANTIC TO SHIFT SOUTHWESTERLY. AT THE SAME TIME...HIGH PRESSURE ACROSS THE MID ATLANTIC CONTINUES TO GRADUALLY SHIFT EAST...WITH WINDS AROUND THE BACKSIDE OF THE HIGH BEGINNING TO DRAW ATLANTIC MOISTURE INTO THE AREA FROM THE COASTAL CAROLINAS. THROUGH THE REMAINDER OF THURSDAY...EXPECT VFR CONDITIONS FOR THE MOST PART...ALBEIT WITH GRADUALLY LOWERING CEILINGS. SHOWER AND ISOLATED THUNDERSTORM ACTIVITY MOVING IN FROM THE SOUTH WILL PROVIDE THE ONLY SUB-VFR CONDITIONS...AS HEAVY RAIN WITHIN THE STRONGER ACTIVITY WILL LOWER VISIBILITIES TO LESS THAN 1SM FOR BRIEF PERIODS OF TIME. COVERAGE OF SHOWER AND THUNDERSTORM ACTIVITY WILL BE ISOLATED TO WIDELY SCATTERED THROUGH MID EVENING...WITH COVERAGE INCREASING TOWARD MIDNIGHT. OVERNIGHT...CEILINGS WILL CONTINUE TO LOWER AS DEEPER MOISTURE RIDES IN FROM THE SOUTHEAST. EXPECT MVFR CEILINGS TO DEVELOP AFTER MIDNIGHT AS THE SOUTHEASTERLY FLOW PUSHES MOISTURE INTO THE HIGHER TERRAIN. ALSO EXPECT VISIBILITIES TO LOWER TO MVFR/OCCASIONAL IFR AS RAINFALL BECOMES WIDESPREAD. RAINFALL WILL TRANSITION FROM SHOWERY TO PROLONGED STRATIFORM THROUGH THE NIGHT AS THE DEPARTING HIGH PRESSURE TAKES ON WEDGE CHARACTERISTICS AGAINST THE MOUNTAINS...LEADING TO OVERRUNNING CONDITIONS. FLYING CONDITIONS WILL CONTINUE TO DETERIORATE LATE FRIDAY MORNING AS A STRONG UPPER LEVEL DISTURBANCE APPROACHES FROM THE SOUTHWEST. EXPECT RAINFALL TO BECOME WIDESPREAD AND HEAVY AT TIMES...MAKING FOR REDUCED VISIBILITIES. CEILINGS WILL ALSO CONTINUE TO DROP... WITH IFR CONDITIONS EXPECTED TO BE COMMON ACROSS THE REGION BY EARLY AFTERNOON. MAY SEE A FEW ELEVATED THUNDERSTORMS DEVELOP... HOWEVER THE WEDGE WILL KEEP MUCH OF THE AREA STABLE...SO DO NOT HAVE ENOUGH CONFIDENCE TO MENTION TSRA IN THE TAFS AT THIS TIME. EXTENDED AVIATION DISCUSSION... THE BROAD UPPER TROUGH OF LOW PRESSURE WILL LINGER ACROSS THE EASTERN UNITED STATES THROUGH SUNDAY.CONTINUING TO RETROGRADE FROM THE EASTERN/CENTRAL GREAT LAKES TO THE WESTERN GREAT LAKES BY THE WEEKEND. FOR SATURDAY AND SUNDAY...THE AIR MASS WILL SLOWLY BECOME WARMER AND MORE UNSTABLE. SCT SHRA/TSRA EXPECTED AGAIN SATURDAY WITH ONLY LIMITED INSTABILITY EVIDENT. FOR SUNDAY...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 SATURDAY AND MORE LIKELY SUNDAY 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. && .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...NF NEAR TERM...NF/WP SHORT TERM...AMS LONG TERM...AMS AVIATION...JH/NF EQUIPMENT...DS

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