Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 242338 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 738 PM EDT MON AUG 24 2015 .SYNOPSIS... A COLD FRONT WILL TRACK ACROSS THE AREA THIS EVENING...EXITING THE PIEDMONT BY MIDNIGHT TONIGHT. HIGH PRESSURE WILL THEN EXTEND EASTWARD FROM THE PLAINS TUESDAY INTO THURSDAY...BRING A DRIER AIRMASS. && .NEAR TERM /THROUGH TUESDAY/... AS OF 630 PM EDT MONDAY... KFCX 88D RADAR WAS DETECTING ISOLATED SHOWERS...AND EVEN MORE ISOLATED...THUNDERSTORMS ACROSS PARTS OF SOUTHSIDE VIRGINIA. THIS ACTIVITY WAS LOCATED ALONG AND EAST OF A COLD FRONT THAT IS MOVING THROUGH THE AREA...CURRENTLY NEAR A MARTINSVILLE TO LYNCHBURG LINE. THE CONVECTION WILL CONTINUE MAKING PROGRESS EASTWARD INTO THE EVENING HOURS...AND EXIT THE REGION BETWEEN 1000 PM AND 1100 PM. HAVE MADE MINOR ADJUSTMENTS TO THE FORECAST CHANCE OF PRECIPITATION FOR THE NEXT COUPLE OF HOURS. HAVE FOCUSED ON PUTTING HIGHER POPS IMMEDIATELY DOWNSTREAM OF THE CURRENT ACTIVITY WHERE CONFIDENCE IN A CONTINUATION OF THE PRECIPITATION IS HIGHEST. AS OF 310 PM EDT MONDAY... SURFACE COLD FRONT IN THE WESTERN MOUNTAINS THIS AFTERNOON WILL TRAVEL EAST THIS EVENING INTO TONIGHT. PRE-FRONTAL TROUGH IN THE PIEDMONT TRIGGERING SCATTERED CONVECTION IN THE MOIST UNSTABLE AIR. SPC MESOSCALE ANALYSIS AT 18Z INDICATED SFC BASED CAPES FROM 1 TO 2K J/KG EAST OF THE BLUE RIDGE MOUNTAINS. THE DEEP LAYER MOISTURE FLUX CONVERGENCE WAS ENHANCED JUST EAST OF BLUE RIDGE MOUNTAINS. THE DAY ONE CONVECTIVE OUTLOOK KEEPS OUR AREA IN GENERAL THUNDERSTORMS. THE BETTER THREAT FOR STRONGER AND MORE ORGANIZED CONVECTION REMAINS TO OUR NORTH WITH THE BETTER DYNAMICS. AN ISOLATED PULSE STRONG THUNDERSTORM MAY BE POSSIBLE IN THE EAST...BUT GIVEN MARGINAL INSTABILITY...LACK OF ROBUST UPDRAFTS AND WEST FLOW...SEVERE WEATHER IS NOT EXPECTED. DEEP LAYER SHEAR WILL REMAIN INSUFFICIENT FOR SEVERE CONVECTIVE ORGANIZATION. LEANED POPS TOWARDS HRRR FOR THIS AFTERNOON INTO THIS EVENING...THEN BLENDED ISC GRIDS TOWARDS SUPERBLEND FOR TONIGHT INTO TUESDAY. THE COLD FRONT WILL SLOW AND STALL TO OUR EAST ALONG THE COASTAL PLAIN TONIGHT INTO TUESDAY...AS A WAVE OF LOW PRESSURE LIFTS NORTHWARD ALONG THE BOUNDARY. HIGH PRESSURE WILL BUILD EAST INTO OUR REGION TONIGHT INTO TUESDAY. DRIER AIR WILL LAG A FEW HOURS AS USUAL BEHIND THE MAIN FRONT...BUT SHARP DEWPOINT DROPS NOTED IN THE OHIO VALLEY. SHAPED LOW TEMPERATURES IN THE WESTERN MOUNTAINS TO COOLER COOP MOS VALUES. IT SHOULD BE A GOOD NIGHT TO OPEN THE WINDOWS WITH LOW TEMPERATURES FROM THE UPPER 40S IN THE MOUNTAINS TO THE MID 60S IN THE PIEDMONT CLOSER TO FRONTAL BOUNDARY. ALOFT THE UPPER PATTERN CONTINUES WITH AN EASTERN TROF AND GREAT LAKES CLOSED LOW SLOWING TRAVELING EAST TUESDAY. UNDER PLENTY OF SUNSHINE...HIGH TEMPERATURES WILL BE BELOW NORMAL WITH READINGS FROM THE UPPER 60S IN THE NORTHWEST MOUNTAINS TO THE MID 80S IN THE PIEDMONT. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... AS OF 230 PM EDT MONDAY... LARGE LONGWAVE UPPER TROUGH FOR LATE AUGUST WILL BE SLIDING EAST ACROSS THE REGION DURING THE WEEK ALLOWING COOL SURFACE HIGH PRESSURE TO BUILD INTO AND NORTH OF THE AREA BY THURSDAY. THIS SHOULD KEEP OVERALL SUBSIDENCE IN PLACE PER DEEPER MOISTURE TO THE EAST ALONG THE RESIDUAL FRONT...WITH LOW LEVEL DRY AIR SUPPORTIVE OF COOL NIGHTS AND MOSTLY SUNNY DAYS THROUGH THE PERIOD. HOWEVER MID LEVEL SHORTWAVE ENERGY ROTATING THROUGH THE 5H TROUGH WILL HAVE TO BE WATCHED FOR POSSIBLE INTERACTION WITH MOISTURE TO THE EAST ESPECIALLY LATE IN THE PERIOD...AND EARLY ON FOR MORE UPSLOPE INDUCED CLOUDS WEST EARLY WEDNESDAY. GIVEN THAT LATEST FORECAST SOUNDINGS CONTINUE TO SHOW PLENTY OF LOW LEVEL DRY AIR IN PLACE WILL ONLY BOOST CLOUDS A BIT AND LEAVE OUT POPS FOR NOW. OTHERWISE TEMPS THE MAIN CONCERN GIVEN THE ARRIVAL OF THE COOLEST AIR ALOFT WEDNESDAY MORNING...AND SUBSEQUENT REINFORCING POCKETS OF 85H COOL ADVECTION INTO THURSDAY. HOWEVER TIMING OF SHORTWAVE ENERGY EARLY WEDNESDAY SUGGESTS PERHAPS MORE UPSLOPE CLOUDS FAR WEST AND SOME MIXING OUTSIDE OF THE VALLEYS GIVEN THE SURFACE HIGH STILL WELL UPSTREAM. THUS BUMPED UP LOWS A CATEGORY OR SO WEDNESDAY MORNING WITH ONLY THE DEEPEST VALLEYS SEEING A FEW 40S AND MAINLY 50S ELSEWHERE. NOT QUITE AS COOL THURSDAY MORNING BUT STILL 50S WEST TO LOW 60S EAST GIVEN A SLIGHT REBOUND IN DEWPOINTS OUT EAST. EXPECT HIGHS TO RECOVER TO JUST BELOW SEASONAL LEVELS PENDING HEATING OF DRY AIR SO TRENDED CLOSER TO THE LATEST MOS BLEND FOR HIGHS. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... AS OF 1245 PM EDT MONDAY... UPPER TROUGH WILL BE LIFTING OUT ACROSS THE REGION LATE IN THE WEEK RESULTING IN BRIEF ZONAL 5H FLOW BEFORE ANOTHER WEAKER SHORTWAVE TROUGH DROPS SE AROUND THE UPPER RIDGE TO THE WEST AND INTO THE AREA EARLY NEXT WEEK. THIS SHOULD ALLOW A RATHER LARGE AREA OF HIGH PRESSURE TO THE NORTH LATE IN THE WEEK TO SETTLE SOUTH AND OVERHEAD DURING THE WEEKEND BEFORE WEAKENING INTO NEXT WEEK. MOST MODELS DEPICT THIS SCENARIO IN KEEPING DEEPER MOISTURE WITH THE OLD FRONT NEAR THE COAST WITH PERHAPS THE REMNANT WAVE OF DANNY SPAWNING A WEAK LOW OFF THE SOUTHEAST COAST EARLY NEXT WEEK. HOWEVER GUIDANCE ALSO INDICATES JUST ENOUGH TROPICAL MOISTURE RETURN BY DAYS 6/7 UNDER THE WEAKENING SURFACE RIDGE AND SLIGHT COOLING ALOFT TO BRING A RETURN OF LEAST SOME DIURNAL ISOLATED/SCATTERED MAINLY MOUNTAIN CONVECTION FROM LATE SATURDAY INTO MONDAY. OTRW SHOULD BE MAINLY DRY WITH SEASONAL TEMPS EARLY IN THE PERIOD...THEN A REBOUND TOWARD HOTTER AND MORE HUMID CONDITIONS BY EARLY NEXT WEEK...WITH HIGHS 80S TO PERHAPS NEAR 90 SOUTHEAST AS RETURN FLOW DEVELOPS. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... AS OF 730 PM EDT MONDAY... GENERALLY VFR CONDITIONS EXPECTED THROUGH THE TAF VALID PERIOD. A DRY AIR MASS WILL SPREAD EASTWARD ACROSS THE REGION OVERNIGHT...WITH THE LAST VESTIGES OF THE HIGHER DEWPOINT/RH VALUES ACROSS THE PIEDMONT BEING PUSHED FURTHER EAST TOWARD THE COAST BY TUESDAY. ISOLATED SHRA/TSRA ASSOCIATED WITH THE PRE- FRONTAL TROUGH ACROSS THE PIEDMONT WILL DISSIPATE QUICKLY WITHIN THE NEXT HOUR. OTHERWISE...EXPECTING MOSTLY SKC/SCT250 OVERNIGHT...THEN SKC EAST TO FEW STRATOCUMULUS WEST IN THE 050-060 RANGE TUESDAY AFTERNOON. ONLY POSSIBILITY OF MARRING AN OTHERWISE VFR FORECAST THROUGH THE TAF VALID PERIOD IS PATCHY RADIATIONAL FOG LATE TONIGHT/EARLY TUESDAY MORNING. THIS HAS ONLY BEEN INTRODUCED FOR LWB AT THIS POINT...BUT WILL NEED TO KEEP AN EYE ON LYH/BCB AS THE NIGHT PROGRESSES. FOR LWB HAVE ONLY ADVERTISED MVFR...BUT GIVEN EXPECTED LOWS WELL DOWN INTO THE 50S/UPPER 40S...A BRIEF WINDOW OF IFR CANNOT BE COMPLETELY RULED OUT. WINDS...MOSTLY CALM/VRB03KT PIEDMONT AND WNW 3-5KTS WEST OF THE BLUE RIDGE OVERNIGHT...THEN WNW 5-9KTS ALL AREAS AFT 14Z TUE. HIGH CONFIDENCE IN A VFR FORECAST THROUGHOUT THE TAF VALID PERIOD...EXCEPT MEDIUM TO HIGH BECAUSE OF GROUND FOG POTENTIAL LWB/BCB/LYH 08Z-14Z TUE. MEDIUM TO HIGH CONFIDENCE IN WIND DIRECTION/SPEED THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... HIGH PRESSURE CONTROLS OUR WEATHER THROUGH MIDWEEK KEEPING IT VFR. MAY SEE SOME LATE NIGHT/EARLY MORNING PATCHY FOG THAT DISSIPATES QUICKLY AFTER SUNRISE IN THE FAVORED TERMINALS LWB/BCB. INCREASED CHANCES FOR SHOWERS/THUNDERSTORMS EARLY NEXT WEEK AS MOISTURE FROM THE SOUTHEAST STATES WORKS ITS WAY NORTHWARD INTO THE EASTERN U.S. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...KK/WP NEAR TERM...DS/KK SHORT TERM...JH LONG TERM...JH AVIATION...KK/RAB/WP

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