Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 222009 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 409 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/... AS OF 205 PM EDT TUESDAY... WEAK SURFACE RIDGE ACROSS THE REGION THIS AFTERNOON COMBINING WITH LIMITED INSTABILITY AND LACK OF FORCING TO KEEP OVERALL CONVECTIVE COVERAGE AT A MINIMUM ATTM. BEST LOW LEVEL THETA-E ALSO SHOWING UP JUST SOUTH OF THE REGION WHICH COULD STILL INTERACT WITH RESIDUAL OUTFLOW TO PRODUCE A BIT BETTER COVERAGE OF MAINLY SHRA ACROSS THE SOUTH/SE INTO THIS EVENING. ELSW APPEARS ANY LATE DAY COVERAGE WILL BE QUITE ISOLATED AND PERHAPS ONLY OVER THE FAR NW ON THE EDGE OF THE CURRENT CLOUD SHIELD WHERE MORE HEATING HAS OCCURRED. THUS MAINTAINING THE HIGHEST POPS FAR SOUTH WITH MID TO LOW CHANCES ELSW INTO EARLY EVENING. UPPER LOW WELL TO THE SW WILL CONTINUE TO SHIFT WEST OVERNIGHT LEAVING THE REGION IN A MOIST ENVIRONMENT BUT WITH LACK OF MUCH SUPPORT FOR ADDED SHRA. IN ADDITION THE LOW LEVEL WEDGE WILL BE BREAKING DOWN AS THE SURFACE HIGH SHIFTS ACROSS AND TO THE SOUTH ALLOWING THE FLOW TO TURN LIGHT WESTERLY AFTER MIDNIGHT. THIS SHOULD LIMIT MUCH -DZ POTENTIAL WITH ONLY SOME WEAK LEFTOVER CONVERGENCE WESTERN SLOPES LATE TONIGHT. APPEARS MAY BE ABLE TO GO DRY AFTER THIS EVENING BUT WITH DEEPER MOISTURE STILL OVER THE SW LEFT IN A TOKEN POP THERE OVERNIGHT. LOWS AGAIN WARM/MUGGY WITH MOST IN THE 65-72 RANGE GIVEN HIGH DEWPOINTS AND PATCHY FOG AROUND. 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. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
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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.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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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.
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&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/... AS OF 1230 PM EDT TUESDAY... HEATING OF LOW LEVEL MOISTURE HAS RESULTED IN AN EXPANSIVE CU FIELD ACROSS THE REGION THIS AFTERNOON WITH BASES EXPECTED TO RISE TO MOSTLY VFR LEVELS IN THE NEXT COUPLE OF HOURS. HOWEVER SPOTTY CONVECTION DEVELOPING CLOSE TO KDAN MAY KEEP THEM MORE IN THE HIGH END MVFR LEVEL RANGE AS WELL AS KLYH WHERE PERIODS OF MVFR LIKELY. SOME ADDED SHRA OR TSRA MAY POP ALONG THE BLUE RIDGE BY MID OR LATE AFTERNOON SO LEAVING IN A VCSH/VCTS MENTION MAINLY WHERE ALREADY ONGOING WHICH EXCLUDES KBLF/KLYH FOR NOW. OTRW LOOKING AT OVERALL CLOUD BASES OF 3-5K FT THIS AFTERNOON/EARLY EVENING WITH SE WINDS LESS THAN 10 KTS. MOST CONVECTION WEAKENS/SUBSIDES SHORTLY AFTER SUNSET WITH ONLY ISOLATED SHRA/TSRA PERHAPS LINGERING MOUNTAINS BEFORE MIDNIGHT. FOG FORMATION LIKELY LATE EVENING INTO OVERNIGHT BUT GIVEN LESS OF A LOW LEVEL WEDGE AND LIGHT WEST WINDS NOT EXPECTING THE OVERALL MORE WIDESPREAD IFR/LIFR CONDITIONS SEEN THE LAST FEW NIGHTS. THINK THE VALLEY LOCATIONS SUCH AS KBCB AND KLWB HAVE THE BEST CHANCE OF SEEING IFR/LIFR CONDITIONS WITH IFR TO MVFR AT KLYH/KDAN BY EARLY WEDNESDAY MORNING. LOW LEVEL FLOW TURNS MORE WESTERLY AHEAD OF AN UPSTREAM COLD FRONT ON WEDNESDAY WHICH SHOULD ALLOW LOW CLOUDS/FOG TO SCOUR OUT A BIT SOONER WEDNESDAY MORNING. THUS EXPECTING A RETURN TO VFR AT ALL LOCATIONS BY MID OR LATE MORNING WEDNESDAY. HOWEVER HEATING WILL AGAIN LEAD TO ADDED SHRA/TSRA DEVELOPMENT ESPCLY ALONG THE SOUTHERN BLUE RIDGE DURING THE AFTERNOON AND ACROSS THE SE WEST VA SITES BY EARLY EVENING. THIS MAY RESULT IN INCREASING PERIODIC MVFR CONDITIONS OVER THE MOUNTAINS BUT MOSTLY VFR OUT EAST. 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 245 PM EDT TUESDAY... KFCX RADAR REMAINS DOWN. HOWEVER TECHNICIANS ARE CURRENTLY WORKING ON THE PROBLEM AND WE MAY SEE A RETURN TO SERVICE LATER THIS AFTERNOON. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/WP NEAR TERM...JH SHORT TERM...PM LONG TERM...PM AVIATION...JH/WP EQUIPMENT...JH/WP

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