Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 300516 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 116 AM EDT WED JUL 30 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 TODAY/... AS OF 1135 PM EDT TUESDAY... ENOUGH LOW LVL THETA-E INTO THE SOUTHERN VA PIEDMONT AS WELL AS 9.0C/KM LOW LVL LAPSE RATES EARLY THIS EVENING WERE ENOUGH TO PROPEL SHOWERS INTO LATE EVENING. NOT EVERYONE IS SEEING RAIN BUT THOSE THAT ARE...WERE GETTING UP TO ONE HALF INCH PER RADAR ESTIMATES. THE MODELS ARE ALLOWING FOR THESE SHOWERS TO FADE THROUGH 2 AM...SO KEEPING POPS ISOLATED AT BEST TOWARD SOUTH BOSTON/YANCEYVILLE AND CHARLOTTE COURT HOUSE ANOTHER 1-2 HOURS. APPEARS SKIES SHOULD CLEAR OUT SOME OVERNIGHT. NO OTHER CHANGES NEEDED WITH THIS UPDATE. PREVIOUS VALID DISCUSSION... 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. OVERNIGHT...DRIER AIR WILL CONTINUE TO FILTER INTO THE REGION. THIS WILL HELP LIMIT 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 /TONIGHT 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 /05Z WEDNESDAY THROUGH SUNDAY/... AS OF 100 AM EDT WEDNESDAY... PATCHY SHOWERS JUST SOUTH/SE OF KDAN SHOULD FINALLY EXIT IN THE NEXT HOUR OR TWO LEAVING MAINLY VFR CIGS EAST OF THE BLUE RIDGE AND SCATTERED CLOUDS OVER THE WEST. COULD SEE KDAN DROP DOWN TO HIGH END MVFR FOR A FEW HOURS BEFORE SUNRISE OTRW KEEPING CIGS MAINLY IN THE 4-7K FT RANGE FROM KROA EAST OVERNIGHT. WEAK WAVE ALOFT RESPONSIBLE FOR THE SHOWERS AND CLOUDS SHOULD FINALLY KICK OUT BY EARLY WEDNESDAY ALLOWING MORE CLEARING ESPCLY WEST BY DAWN. THIS MAY LEAD TO PATCHY VALLEY FOG GIVEN GOOD RADIATIONAL CONDITIONS WITH MVFR POSSIBLE AT KLWB/KBCB AND AN OUTSIDE CHANCE OF SEEING IFR AT KLWB. HOWEVER LOWER CIGS AT KBLF AND KLWB LOOK LESS LIKELY NOW WITH ANY LOW CIGS LIKELY DUE TO FOG/STRATUS FORMATION LATE. UPPER TROUGH UNDERCUT BY WEAK SURFACE HIGH PRESSURE WILL REMAIN IN PLACE WEDNESDAY WITH SCATTERED CU/AC EARLY INCREASING TO BKN 4-6K FT CLOUD BASES MOST SPOTS WITH HEATING. AN ISOLATED SHRA WILL BE POSSIBLE MAINLY WESTERN THIRD GIVEN THE APPROACH OF ANOTHER WAVE FROM THE NW BUT TOO IFFY TO INCLUDE ANY MENTION. OTRW KEEPING IT VFR FROM MID MORNING ON WITH GOOD FLYING CONDITIONS LINGERING INTO WEDNESDAY NIGHT WITH ANY CIGS LIKELY TO FADE WITH LOSS OF HEATING. 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...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 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/WP SHORT TERM...AMS LONG TERM...AMS AVIATION...DS/JH/RAB CLIMATE...PH EQUIPMENT...DS

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