Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 230129 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 929 PM EDT TUE JUL 22 2014 .SYNOPSIS... UPPER TROUGH OVER THE GULF COAST STATES SHIFTS WEST THROUGH WEDNESDAY LEAVING A RESIDUAL WEAK BOUNDARY AND LOW LEVEL MOISTURE OVER THE AREA INTO MID WEEK. A COLD FRONT WILL BE ARRIVING THURSDAY FROM THE NORTHWEST...THEN EXITING BY THURSDAY NIGHT. HIGH PRESSURE BUILDS IN ON FRIDAY. && .NEAR TERM /THROUGH WEDNESDAY/...
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AS OF 940 PM EDT TUESDAY... LOW LEVEL WEDGE THAT HAS BEEN IN PLACE FOR THE PAST FEW DAYS HAS SHOWN SIGNS OF BREAKING DOWN...AS SFC WINDS HAVE BEEN GRADUALLY VEERING TO THE SOUTH THIS EVENING. MODELS ARE IN GOOD AGREEMENT THAT AS AN UPPER LEVEL SHORT WAVE MOVES OVER THE GREAT LAKES BY 12Z WEDNESDAY...LOW LEVEL WINDS IN OUR AREA WILL CONTINUE TO VEER TO THE WEST/NORTHWEST OVERNIGHT. WITHOUT AN UPSLOPE FLOW TONIGHT CLOUD COVER SHOULD BE LIMITED AND ADJUSTED SKY CONDITIONS ACCORDINGLY IN THE FORECAST. PATCHY FOG IS STILL POSSIBLE TONIGHT WITH A MOIST AIRMASS IN THE LOW LEVELS...AS THE 00Z RNK SOUNDING SHOWING A FAIRLY MOIST ATMOSPHERE BELOW 700MB...AND LIGHT WINDS. WITH THE GSO SOUNDING SHOWING MUCH HIGHER PWATS (1.85 INCHES VS. 1.2 AT RNK)...CANNOT RULE OUT A STRAY SHOWER IN THE SOUTHERN PORTION OF THE FORECAST AREA OVERNIGHT. WITH LESS COVER...BROUGHT TEMPS DOWN A COUPLE OF DEGREES FOR TONIGHT. THE NEXT STRONG 5H TROF AND ASSOCIATED COLD FRONT WILL BE APPROACHING ON WED AS HIGH PRESSURE SHIFTS FARTHER SOUTH ALLOWING DEEPENING WESTERLY FLOW AND A SUBSEQUENT LEE TROF WELL EAST OF THE BLUE RIDGE. MODELS SPARK MOST AFTERNOON CONVECTION ALONG THE SOUTHERN BLUE RIDGE GIVEN THE WEAK BOUNDARY LAYER SW FLOW AND BETTER DIFFERENTIAL HEATING BUT STILL IFFY GIVEN WESTERLY FLOW ALOFT AND ONLY FAINT LIFT. ELSW APPEARS RATHER ISOLATED DESPITE LINGERING MOISTURE GIVEN DRY AIR ALOFT AND DOWNSLOPING WEST WINDS ACROSS THE EAST SO KEEPING SHOTGUN CHANCE POPS. HOWEVER THE UPSTREAM PRE- FRONTAL BAND OF TSRA WILL LIKELY BE NEARING THE NW SLOPES LATE. THUS KEPT IN LOW LIKELYS EXTREME WEST...BUT MOSTLY TOWARD SUNSET AT THIS POINT. SOME ISOLATED SEVERE POSSIBLE IF PULSE STORMS ORGANIZE MORE EARLY...AND UPSTREAM ACTIVITY MOVES INTO THE WEST IN MORE OF A LINE FEATURE...ALTHOUGH THIS MAY BE AFTER INSTABILITY IS STARTING TO FADE. OTRW SHOULD SEE CLOUDS BREAK QUICKER UNDER THE WESTERLY FLOW ALLOWING INSOLATION AND 85H TEMPS AROUND +20C TO AID WEAK COMPRESSION IN PUSHING HIGHS INTO THE 80S WEST AND 90-95 EAST.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... AS OF 345 PM EDT TUESDAY... WEDNESDAY NIGHT...PREFRONTAL MCS LIKELY TO IMPACT AT LEAST THE WESTERN HALF OF THE CWA...ACTIVITY FADING WITH LOSS OF DAYTIME HEATING. REMNANT OUTFLOW MAY REACH PIEDMONT BY DAYBREAK THURSDAY AND DEBRIS CLOUDINESS WILL LIKELY REMAIN TO START THE DAY THURSDAY. MODELS ARE IN AGREEMENT THE ACTUAL COLD FRONT WILL ENTER OUR SOUTHEAST WEST VIRGINIA COUNTIES LATE MORNING/EARLY AFTERNOON ON THURSDAY...AND CONTINUE EAST THROUGH THE DAY. ATTM THINK ABUNDANT CLOUDINESS EARLY THURSDAY MAY INHIBIT SOLAR INSOLATION...LIMITING INSTABILITY OVER ALL BUT THE FAR SOUTHEASTERN CWA...THE GREATEST CHC FOR SHOWERS/STORMS OCCURRING FROM OUR PIEDMONT EASTWARD INTO THE TIDEWATER OF VA/NC. FOR NOW WILL MAINTAIN HIGH POPS BOTH WEDNESDAY NIGHT AND THURSDAY...THEN END THE PRECIP THREAT QUICKLY FROM WEST TO EAST WITH THE PASSAGE OF THE FRONT...LEAVING MAINLY DRY CONDITIONS FOR THE AREA BY FRIDAY. WEAK HIGH PRESSURE WILL BUILD INTO THE AREA BEHIND THE FRONT...AND SHOULD PROVIDE A DAY...MAYBE TWO...OF PRECIP FREE CONDITIONS. TEMPERATURES THURSDAY WILL BE TEMPERED BY CLOUDS ASSOCIATED WITH THE FRONT...THEN TREND DOWN A FEW DEGREES FOR FRIDAY. THE AIRMASS CHANGE IS NOT OVERLY DRY NOR COOL...SO WHEN THE SUN POPS OUT FRIDAY...READINGS MAY FEEL JUST AS WARM AS THURSDAY...ALTHOUGH THE DEWPOINTS WILL NOT BE AS ROBUST. && .LONG TERM /SATURDAY THROUGH TUESDAY/... AS OF 400 PM EDT TUESDAY... FOR THE WEEKEND AND INTO EARLY NEXT WEEK...THE AREA REMAINS VULNERABLE TO NW FLOW DISTURBANCES TRACKING AROUND THE LARGE WESTERN/CENTRAL CONUS UPPER RIDGE. A PARTICULARLY STRONG DISTURBANCE...NOTED BY ALL THE MODELS...PROMISES TO AMPLIFY THE EASTERN LONG WAVE TROUGH...A FEATURE THAT SHOULD KEEP CONDITIONS UNSETTLED WITH NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES WHILE THE EXTREME HEAT REMAINS WELL TO OUR WEST AND WELL AWAY FROM OUR PART OF THE COUNTRY. THE BEST CHANCE FOR SHOWERS/STORMS LOOKS TO BE SUNDAY AS THE SURFACE FRONT ASSOCIATED WITH THE STRONG DISTURBANCE CROSSES THE FORECAST AREA FROM THE NORTHWEST. POTENTIAL EXISTS FOR STORMS TO BE ORGANIZED WITH UPSTREAM MCS IMPACTING THE FORECAST AREA. GENERALLY FOLLOWED HPC GUIDANCE THROUGH THE PERIOD. TRENDED POPS UP FOR SUNDAYS FROPA...THEN DOWN FOR A DAY OR TWO AFTER SUNDAYS FRONTAL PASSAGE. TENDENCY FOR FRONTAL PASSAGES IS TO BRING SOME DOWNTIME AS WITH RESPECT TO POPS BEFORE MOISTURE AND INSTABILITY CAN RETURN. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... AS OF 715 PM EDT TUESDAY... ONLY ISOLATED STORMS WERE NOTED ON RADAR...MAINLY NEAR KDAN AND ACROSS THE HIGHER TERRAIN OF SOUTHEAST WV. THIS SMALL AREA OF CONVECTION WILL DISSIPATE SHORTLY AFTER SUNSET...AND INCLUDED ONLY AN HOUR OR TWO OF VCSH AT KDAN/KLWB/KBLF THIS EVENING. AS WEAK HIGH PRESSURE CONTINUES TO BUILD SOUTHWEST...LIGHT SFC WINDS WILL VEER TO THE SOUTH AND SOUTHWEST. THIS SHOULD RESULT IS LESS CLOUD COVER COMPARED TO WHAT HAS BEEN EXPERIENCED FOR THE PAST FEW MORNINGS. HOWEVER...LIGHT WINDS AND A MOIST LOW LEVEL AIRMASS WILL LEAD TO THE DEVELOPMENT OF FOG AFTER 05Z. THOSE CLIMATOLOGICAL FAVORED AREAS...KLWB AND KBCB...WILL HAVE THE BEST CHANCE OF SEEING IFR VISIBILITIES LATE TONIGHT/EARLY TOMORROW DUE TO FOG. MVFR VISIBILITIES ARE POSSIBLE AT KLYH AND KDAN. ANY FOG WILL QUICKLY BURN OFF EARLY WEDNESDAY...THANKS TO A SOUTHWEST LOW LEVEL FLOW IN ADVANCE OF AN APPROACHING COLD FRONT. HOWEVER...THIS WILL USHER IN DEEPER MOISTURE AND EXPECT BETTER COVERAGE WITH AFTERNOON SHOWERS AND STORMS...ESPECIALLY ACROSS THE SOUTHERN BLUE RIDGE. AS A RESULT...INTRODUCED VCTS FOR THE MOUNTAIN TAF SITES WEDNESDAY AFTERNOON. EXTENDED AVIATION DISCUSSION... NEXT NORTHERN STREAM UPPER TROUGH AND ITS ASSOCIATED COLD FRONT WILL APPROACH WEDNESDAY NIGHT AND WORK THROUGH THE REGION ON THURSDAY. THIS WILL BRING THE BEST CHANCES OF MORE WIDESPREAD SHOWERS TO THE MOUNTAINS AND PERHAPS SOME DEEPER CONVECTION EAST OF THE BLUE RIDGE PENDING TIMING OF THE BOUNDARY THURSDAY AFTERNOON. AIRMASS WILL DRY OUT BEHIND THE FRONT GOING INTO FRIDAY- SATURDAY. OVERALL EXPECT SUB VFR AT TIMES THURSDAY WITH SHRA/TSRA AND MAYBE SOME FOG THU NIGHT...FOLLOWED BY VFR FRI- SAT OUTSIDE OF ANY VALLEY FOG AT KLWB/KBCB EACH MORNING. && .EQUIPMENT... AS OF 715 PM EDT TUESDAY... KFCX RADAR REMAINS DOWN. TECHNICIANS ARE STILL AT THE SITE WORKING ON THE PROBLEM...AND HOPE TO HAVE THE RADAR BACK ONLINE THIS EVENING. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/WP NEAR TERM...JH/PH SHORT TERM...PM LONG TERM...PM AVIATION...JH/PH/WP EQUIPMENT...JH/WP

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