Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 292345 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 745 PM EDT TUE JUL 29 2014 .SYNOPSIS... AN UPPER LEVEL TROUGH OF LOW PRESSURE AND A DRY...COOL AREA OF SURFACE HIGH PRESSURE WILL REMAIN ACROSS THE REGION THROUGH WEDNESDAY. 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 INCREASE OF SHOWERS AND STORMS. && .NEAR TERM /THROUGH WEDNESDAY/... AS OF 245 PM EDT TUESDAY... AN UPPER LEVEL LONGWAVE TROUGH WAS STILL CENTERED OVER THE REGION. SURFACE HIGH PRESSURE WAS ALSO CENTERED OVER THE AREA AND IS EXPECTED TO STRENGTHEN OVERNIGHT. A SHORTWAVE IS PROGRESSING THROUGH THE MAIN LONGWAVE PATTERN AND IS CURRENTLY CROSSING THE AREA OF OH/PA/MD/WV. THIS FEATURE ALONG WITH DAYTIME HEATING MAY STILL HELP PRODUCE SOME ADDITIONAL ISOLATED SHOWERS THE REMAINDER OF THIS AFTERNOON THAT WILL LAST TO JUST PRIOR TO SUNSET. MOST AREAS WILL BE PRECIPITATION-FREE. OVERNIGHT...DRIER AIR WILL CONTINUE TO FILTER INTO THE REGION. THIS WILL HELP LIMITED OVERNIGHT FOG DEVELOPMENT TO A SHORT PERIOD TOWARDS DAYBREAK...MAINLY IN SOME OF THE DEEPER MOUNTAIN VALLEY AND SOME OF THE RIVER VALLEY. ANY FOG THAT DEVELOPS LATE TONIGHT SHOULD BURN OFF QUICKLY WEDNESDAY MORNING. LOW TEMPERATURES TONIGHT WILL RANGE FROM THE UPPER 40S TO LOWER 50S ACROSS THE MOUNTAINS TO THE MID 50S ACROSS THE PIEDMONT. SOME AREAS ARE EXPECTED TO REACH OR BE NEAR RECORD LOW READINGS. SEE THE CLIMATE SECTION OF THIS DISCUSSION FOR DETAILS. FOR WEDNESDAY...WE EXPECT A SIMILAR DAY BUT WITH TEMPERATURES RECOVERING A BIT HIGHER. LOWER 80S FOR HIGHS WILL BE COMMON ACROSS THE PIEDMONT...WITH A MIX OF MID TO UPPER 70S ACROSS THE MOUNTAINS. THE NEXT SHORTWAVE TROUGH TO ROUND THE BASE OF THE LONGWAVE TROUGH LOOKS TO HAVE A TRACK A BIT FARTHER NORTH...AND THUS THE FOCUS FOR ISOLATED SHOWERS WILL ALSO BE FARTHER NORTH. THE FORECAST WILL REFLECT THE POTENTIAL ACROSS THE SOUTHERN ALLEGHANY HIGHLANDS AND NEAR THE CREST OF THE BLUE RIDGE. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... AS OF 325 PM EDT TUESDAY... 500 MB HEIGHTS GRADUALLY RISE THROUGH THURSDAY AS UPPER TROF RETROGRADES. THIS LEAVES FORECAST AREA IN BROAD SOUTHWEST FLOW ON THURSDAY NIGHT AND FRIDAY. AT THE SURFACE A WEAK COASTAL FRONT WILL BE STATIONARY FROM THE DELMARVA TO FLORIDA PANHANDLE. LITTLE IN THE WAY OF LIFT OR FORCING FOR THE COUNTY WARNING AREA UNTIL A SHORT WAVE COMES THROUGH THE SOUTHWEST FLOW ON FRIDAY. BUFKIT FORECAST SOUNDINGS FOR 00Z THURSDAY/8PM WEDNESDAY AND AGAIN THURSDAY AFTERNOON SHOWED A RELATIVELY HIGH BASED STRATOCUMULUS WITH A SMALL LAYER OF INSTABILITY...THEN DRIER AIR ABOVE AT MID LEVEL AND BELOW NEAR THE SURFACE. DEEPER MOISTURE RETURNS BE FRIDAY. A SHORT WAVE TRACKING FROM SOUTHWEST TO NORTHEAST WILL PROVIDE SOME LIFT SO THIS WILL BE MOST THE DAY WITH A BETTER PROBABILITY OF SHOWERS AND THUNDERSTORMS IN THE AFTERNOON. CLOUD COVER ON THURSDAY NIGHT WILL LIMIT DROP IN TEMPERATURES. AIR MASS GRADUALLY WARMS THROUGH THE PERIOD. BY FRIDAY 850 MB TEMPERATURES WILL BE BACK UP TO ABOUT +14. DEPENDING ON THE AMOUNT OF CLOUDS AND PRECIPITATION. FRIDAY WILL BE THE WARMEST DAY AS FAR AS MAXIMUM TEMPERATURES SO FAR THIS WEEK. && .LONG TERM /FRIDAY NIGHT 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 /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 735 PM EDT TUESDAY... UPPER TROUGH AND CYCLONIC FLOW WILL CONTINUE ACROSS THE FORECAST AREA THROUGH THE WEEK. WEAK SHORT WAVES WILL ROTATE THROUGH THE BASE OF THE TROUGH AND BRING PERIODS OF CLOUDS AND ISOLD -SHRA TO MAINLY AREAS WEST OF THE BLUE RIDGE AFTER THIS EVENING. THE CLOUD COVER AND -SHRA WILL BE AMPLIFIED DURING THE NORMAL DIURNAL HEATING CYCLE...PEAKING IN THE 18Z-22Z TIME FRAME. ISOLD -SHRA EAST OF THE BLUE RIDGE THIS EVENING CURRENTLY SUPPORTED BY WEAK UPPER SHORT WAVE MOVING THROUGH THAT REGION. THIS ACTIVITY WILL DISSIPATE QUICKLY BY 01Z. MOST CLOUDS OF CONSEQUENCE OVERNIGHT WILL BE WEST OF THE BLUE RIDGE...AND EVEN MORE SO WEST OF THE ALLEGHANYS. CIGS MOSTLY LOW END VFR WEST OF THE BLUE RIDGE...TRENDING TOWARD MVFR OVERNIGHT/EARLY THU. DID INCLUDE -SHRA FOR LWB/BLF WED AFTERNOON WITH EVIDENCE OF A SLIGHTLY STRONGER SHORT WAVE ROTATING THROUGH THAT REGION DURING PEAK HEATING. NOT MUCH CONCERN WITH VSBYS...EXPECT POTENTIALLY AT LWB IF CLOUDS CAN CLEAR ENOUGH AND WIND DECOUPLE. NOT EXPECTING ANY VSBYS WORSE THAN MVFR AT THIS POINT. WINDS MOSTLY WNW 5-7KTS THROUGH THE TAF VALID PERIOD...WITH MORE TENDENCY FOR VRB OR LIGHT SW WINDS ACROSS THE PIEDMONT. MEDIUM CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN WIND DIR THROUGH THE TAF VALID PERIOD...HIGH CONFIDENCE IN WIND SPD THROUGH THE TAF VALID PERIOD. 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. 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 30TH RECORD LOWS: ROANOKE......54...1997 BLUEFIELD....50...1981 DANVILLE.....60...1972/81/83/2013 LEWISBURG....46...2013 LYNCHBURG....52...1997 BLACKSBURG...50...1973/81 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. PHONE COMPANY IS WORKING ON IT. THE RADIO IS NOT EXPECTED TO BE BACK IN SERVICE ANY SOONER THAN WEDNESDAY MORNING. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...DS NEAR TERM...DS SHORT TERM...AMS LONG TERM...AMS AVIATION...DS/RAB CLIMATE...PH EQUIPMENT...DS

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