Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 211856 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 256 PM EDT MON JUL 21 2014 .SYNOPSIS...
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A WEAK WEDGE OF HIGH PRESSURE ALONG THE MID ATLANTIC COAST WILL CONTINUE TO EXTEND INLAND ACROSS THE AREA TONIGHT INTO TUESDAY. EAST TO SOUTHEAST WINDS AROUND THE HIGH WILL COMBINE WITH DEEP MOISTURE LIFTING NORTH WITH A RESIDUAL FRONTAL BOUNDARY TO PRODUCE SCATTERED SHOWERS AND THUNDERSTORMS INTO TUESDAY EVENING. A STRONGER COLD FRONT WILL APPROACH THE REGION FROM THE NORTHWEST WEDNESDAY...AND PUSH THROUGH THE AREA THURSDAY...RESULTING IN MORE WIDESPREAD SHOWERS AND STORMS.
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&& .NEAR TERM /THROUGH TUESDAY/...
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AS OF 200 PM EDT MONDAY... RESIDUAL FRONT ACROSS THE CAROLINAS CONTINUES TO FOCUS BEST LIFT ALONG AN EAST-WEST CORRIDOR JUST SOUTH OF THE CWA THIS AFTERNOON WITH MUCH OF THIS SHRA/TSRA NOT MAKING MUCH NORTHWARD PROGRESS INTO THE DRIER AIR ALOFT ATTM. LATEST GUIDANCE KEEPS THIS TREND GOING FOR THE MOST PART INTO EARLY THIS EVENING WITH MAINLY WIDELY SCATTERED COVERAGE OVER THE SOUTH PER OUTFLOW FROM THIS MORE CONCENTRATED AREA OF SHRA...AND OVER THE FAR WEST WHERE HEATING HAS BEEN BEST. HOWEVER LOW LEVEL INSTABILITY REMAINS RATHER WEAK GIVEN THE LINGERING WEDGE...CAP ALOFT...AND SHARP EDGE TO SUPPORT TO THE SOUTH. FOR NOW WILL GO AHEAD AND MAINTAIN HIGHER POPS ALONG THE FAR SOUTHERN CWA BORDER FOR A WHILE LONGER...AND KEEP SCATTERED CHANCES ELSW FOR POP UP COVERAGE UNTIL SUNSET. MODELS BASICALLY FIZZLE ANY CONVECTION SHORTLY AFTER LOSS OF HEATING WITH THE LOW LEVEL WEDGE REDEVELOPING TO SOME DEGREE LATE. FLOW DOES REMAIN WEAK UPSLOPISH ABOVE THE SURFACE AND GIVEN THE COMBO OF A WAVE ALOFT...OUTFLOW AND POTENTIAL FOR LATE NIGHT CONVERGENCE BLUE RIDGE...DECIDED TO LEAVE IN A NOCTURNAL CHANCE POP MAINLY ACROSS THE SW OVERNIGHT WHICH HAS SOME SUPPORT FROM THE LATEST SREF. OTRW PREVIOUS FORECAST OF LOWERING CHANCES AND INCLUDING SOME PATCHY FOG/DZ LOOKS ON TRACK WITH MUGGY LOWS IN THE 60S TO LOW 70S. CUTOFF MID LEVEL LOW OVER THE SE WILL RETROGRADE OFF TO THE WEST ON TUESDAY LEAVING THE FAINT BOUNDARY TO LIFT NORTH INTO THE AREA BEFORE DISSIPATING WITH EVEN HIGHER PWATS AND MORE OF A SOUTHERLY TRAJECTORY LATE IN THE DAY. THIS SUPPORTS GOING WITH MORE DIURNAL COVERAGE OF STORMS THAN SEEN IN THE LAST COUPLE OF DAYS PER HIGHER FORECAST CAPES UNDER MORE INSOLATION. THIS SIMILAR TO THE LATEST GFS OUTPUT WITH BEST LOW LEVEL FOCUS SOUTHERN BLUE RIDGE AND OVER THE SW WHERE THE EDGE OF THE LEFTOVER FRONT WILL PIVOT NORTH INTO THE S/SE FLOW. THUS WILL RUN WITH A PERIOD OF LIKELY POPS THERE AFTER ANY MORNING COVERAGE FADES PER SOME MODEL CONSENSUS. ELSW MOSTLY MID TO HIGH CHANCES GIVEN SO MUCH MOISTURE AROUND BUT LIKELY LIMITED ACROSS THE NORTH/NE BY LINGERING DRY AIR ALOFT AND WEAK SUBSIDENCE. AGAIN WENT CLOSER TO THE SLIGHTLY COOLER MET MOS FOR HIGHS...BUT COULD SEE SOME SPOTS ZOOM CLOSER TO THE WARM MAV VALUES IF MORE SUN OCCURS EARLIER.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... AS OF 415 AM EDT MONDAY... MODELS IN GOOD AGREEMENT ON THE OVERALL SYNOPTIC PATTERN WITH A MAMMOTH NEAR 600DM RIDGE BUILDING ACROSS THE INTERMOUNTAIN WESTERN U.S....A SIMILAR RIDGE BUILDING ACROSS THE WESTERN ATLANTIC... AND AN UPPER TROUGH LINGERING ACROSS THE SOUTHEASTERN U.S. STUCK BETWEEN THE TWO AFOREMENTIONED UPPER RIDGES. THIS PATTERN WILL KEEP THE HOT WEATHER WELL TO OUR WEST. THE PERSISTENT SE U.S. UPPER TROUGH WILL DRIFT/RETROGRADE TO THE NW WITH TIME IN RESPONSE TO THE BUILDING WESTERN ATLANTIC UPPER RIDGE. THIS SYSTEM HAS SOME PSEUDO TROPICAL CHARACTERISTICS WITH PWS NEARING 2.0 INCHES IN THE ASSOCIATED AIR MASS. AS THIS SPREADS NORTHWEST TUE-WED...EXPECT AN INCREASE IN DIURNALLY DRIVEN CONVECTION...ESPECIALLY ALONG THE EAST FACING SLOPES OF THE BLUE RIDGE FROM NW NC NORTHEASTWARD INTO SOUTHWEST/SOUTH CENTRAL VA. WITH SUCH HIGH PWS AND WEAK STEERING CURRENTS ALOFT...THE THUNDERSTORMS WILL BE VERY EFFICIENT RAIN PRODUCERS AND AS SUCH COULD RESULT IN LOCALIZED FLOODING. FORTUNATELY...MUCH OF THE CWA IS IN A MILD DROUGHT...SO THE RAINFALL WILL BE WELCOME. BUT IN MOUNTAINOUS TERRAIN...AN INCH OR TWO IN AN HOUR CAN BECOME PROBLEMATIC RATHER QUICKLY. HOWEVER...CERTAINLY NOT ENOUGH CONCERN FOR ANY FLOOD/FLASH FLOOD WATCH AT THIS POINT DUE TO THE LOCALIZED NATURE OF THE EXPECTED THUNDERSTORMS. HOWEVER...A MENTION OF LOCALIZED HEAVY RAIN IN THE HWO ACROSS MAINLY THE NC COUNTIES IN COLLABORATION WITH OUR NEIGHBORS IS WARRANTED. MEANWHILE...THE SEVERE THREAT SHOULD BE NEAR NIL WITH AN INCREASING TROPICAL AIR MASS...HENCE MOIST ADIABATIC SOUNDING...AND VERY WEAK WINDS ALOFT. NEVER CAN TOTALLY RULE OUT AN ISOLD WET DOWNBURST...BUT NOT ENOUGH CONFIDENCE TO EVEN MENTION IN THE HWO AT THIS POINT. THE BEST FOCUS FOR CONVECTION TODAY SHOULD BE ACROSS NORTHWEST/NORTH CENTRAL NC INTO THE ADJACENT COUNTIES OF SOUTHWEST/SOUTH CENTRAL VA...SHIFTING MORE TOWARD SW VA/SE WV ON THU. FOR THU...MODELS GENERALLY IN GOOD AGREEMENT IN BRINGING A FRONT INTO THE REGION FROM THE NORTHWEST AS A STRONG UPPER DISTURBANCE TRACKS ATOP THE WESTERN/CENTRAL U.S. UPPER RIDGE TOWARD THE GREAT LAKES. THE LINGERING DISTURBANCE ACROSS THE SOUTHERN/CENTRAL APPALACHIANS WILL SHEAR OUT IN ADVANCE OF THIS FEATURE...BUT LEAVE AMPLE MOISTURE FOR THE FRONTAL SYSTEM TO ACT UPON. FOR A CHANGE...THE ECMWF IS ACTUALLY SLIGHTLY FASTER THAN THE GFS IN BRINGING THIS SYSTEM THROUGH THE CWA...WITH MOST FAVORED TIMING TO ENTER THE WESTERN SECTIONS WED NIGHT/EARLY THU...TRACKING ACROSS THE CWA THU...SHIFTING TO THE SOUTH OF THE AREA FRI. AGAIN...THE MAIN CONCERN WITH THIS FRONT WILL BE LOCALIZED HEAVY RAINFALL AS IT INTERACTS WITH THE VERY MOIST AIR MASS IN PLACE ACROSS THE REGION. OVERALL PROGGED INSTABILITY AND SHEAR SUGGEST THAT THE SEVERE THREAT IS MINIMAL AND CURRENTLY SPC DOES NOT HAVE ANY AREAS OUTLOOKED. EVEN SO...USUALLY THE DYNAMICS/BETTER FORCING EVIDENT ALONG A FRONT OFFER AT LEAST A SLIGHT INCREASE IN THE SEVERE THREAT. WITH RESPECT TO TEMPERATURES...850MB TEMPS WILL CREEP UP SLIGHTLY INTO THE +18C RANGE AS 500MB HEIGHTS RISE TOWARD 590DM. HOWEVER...INCREASING MOISTURE CONTENT...ABUNDANT CLOUD COVER...AND SCT-NMRS SHRA/TSRA EACH AFTERNOON SHOULD KEEP TEMPERATURES FROM BECOMING OPPRESSIVELY HOT. HOWEVER...HUMIDITY LEVELS WILL BE NOTABLY HIGHER THAN RECENT DAYS...SO EVEN WITH HIGHS MOSTLY IN THE 80S WEST TO NEAR 90 PIEDMONT...DEWPOINTS 65 TO 70 WILL YIELD SOME RATHER UNCOMFORTABLE AFTERNOONS COMPARED TO RECENT DAYS WITH RECORD LOW HIGHS IN THE 60S. WEDNESDAY SHOULD BRING THE WARMEST TEMPERATURES TO THE REGION IN ADVANCE OF THE FRONT...ESPECIALLY ACROSS THE PIEDMONT...WHICH SHOULD SEE A SLIGHT DECREASE IN CONVECTION AT THAT TIME...THUS POTENTIALLY SEEING MAX TEMPS IN THE LOW 90S LYH-DAN AND VICINITY. && .LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 445 AM EDT TUESDAY... FRONTAL SYSTEM SHOULD SHIFT JUST SOUTH OF THE REGION FRI...ALTHOUGH ALWAYS UNCERTAINTY IN MID-SUMMER REGARDING AS TO HOW FAR SOUTH THE FRONT WILL GO BEFORE STALLING. WITH STRONG UPPER RIDGE TO THE WEST AND STRONG NW FLOW ALOFT ACROSS OUR REGION AS A RESULT...FEEL IT WILL AT LEAST GET FAR ENOUGH SOUTH OF THE CWA TO ENSURE ONE MOSTLY DRY DAY. HAVE HELD ONTO SLIGHT CHC POPS ACROSS THE FAR SE COUNTIES...MAINLY THE NC COUNTIES...TO ACCOUNT FOR THE SLIGHTLY LESS SOUTHWARD MOVEMENT ADVERTISED BY THE ECMWF. DRYING AND COOLING BEHIND THE FRONT COMPARED TO THE PAST TWO SUCH EVENTS IS MINOR AND WE SHOULD STILL SEE HIGHS IN THE 80S...70S MOUNTAINS. HUMIDITY LEVELS/DEWPOINTS WILL DROP SLIGHTLY...BUT WITH PWS STILL NEAR 1.5 INCHES...SIGNIFICANT DRYING IS NOT EXPECTED WITH THIS FRONTAL PASSAGE. FOR THE WEEKEND AND INTO EARLY NEXT WEEK...THE AREA REMAINS VULNERABLE TO NW FLOW DISTURBANCES TRACKING AROUND THE LARGE WESTERN/CENTRAL U.S. UPPER RIDGE. THERE ARE SEVERAL SUCH STRONG DISTURBANCES NOTED IN THE MODELS DURING THIS TIME FRAME...THE MOST NOTABLE ON SUN...THAT COULD BRING THUNDERSTORMS BACK INTO THE AREA. HAVE RETAINED EXISTING CHC POPS THAT WERE ADVERTISED WITH EARLIER FORECAST PACKAGES...BUT CLEARLY THESE COULD POTENTIALLY BECOME LIKELY AT SOME POINT AS THE DEVELOPMENT OF AN UPSTREAM MCS BECOMES MORE APPARENT. BY EARLY THE FOLLOWING WEEK...MODELS IN GOOD AGREEMENT ON THE UPPER TROUGH REAMPLIFYING ACROSS THE EASTERN U.S...WHICH 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 COUNTY...FORTUNATELY. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... AS OF 1250 PM EDT MONDAY... SIMILAR TO SUNDAY...WIDESPREAD MVFR CIGS CONTINUE THIS AFTERNOON WITH THE EXCEPTION OF KBLF WHERE SEEING VFR ON THE WESTERN PERIMETER OF THE LOW LEVEL WEDGE. HOWEVER SHOWERS REMAIN VERY ISOLATED ATTM WITH MOST OF THE BEST LIFT AND COVERAGE JUST SOUTH OF THE REGION CLOSER TO THE OLD FRONT IN THE CAROLINAS. MOISTURE SPREADING NORTH FROM THIS ACTIVITY LIKELY TO KEEP LOWER CIGS IN PLACE THIS AFTERNOON WITH ONLY A SLOW IMPROVEMENT IN CLOUD BASES AS THE LOW LEVEL MOISTURE STAYS TRAPPED UNDER THE CANOPY HEADING IN FROM THE SOUTH. STILL SOME CHANCE AT SEEING BRIEF PERIODS OF VFR ESPCLY ACROSS THE WESTERN LOCATIONS...WHILE OCNL IFR COULD OCCUR NEAR OR WITHIN ANY DEVELOPING SHRA/TSRA THAT LOOK MOST LIKELY AROUND KDAN AND PERHAPS OVER THE FAR SW FROM KHLX TO KBLF. THUS WILL LEAVE IN THE GOING VICINITY SHRA/TSRA MENTION MOST SPOTS BUT LOW CONFIDENCE GIVEN ONLY SPOTTY HEATING AND FORCING ALOFT. ANY CONVECTION SHOULD BE DIURNAL AND FADE FOR THE MOST PART AFTER SUNSET...BUT LEAVE WIDESPREAD MVFR CIGS TRENDING TOWARD IFR AFT MIDNIGHT WITH POCKETS OF -DZ BR AS WELL AS LIFR NEAR THE BLUE RIDGE. ALSO SOME POTENTIAL TO SEE ADDED BANDS OF NOCTURNAL SHOWERS REDEVELOP ALONG THE SOUTHERN BLUE RIDGE TOWARD KDAN GIVEN THE SE FLOW AND OLD OUTFLOW UNDER SUCH DEEP MOISTURE. OTRW WINDS SOUTHEAST THROUGH THE TAF VALID PERIOD AT SPEEDS OF 5-7KTS...LESS AT NIGHT. WEDGE WILL WEAKEN A BIT MORE ON TUESDAY AS THE LOW LEVEL FLOW TURNS A LITTLE MORE SOUTHERLY PERHAPS ALLOWING LOW CIGS TO IMPROVE A BIT FASTER TO VFR THAN THE LAST COUPLE OF DAYS. HOWEVER ANY BREAKS WILL ONLY LEAD TO QUICKER DEVELOPMENT OF SHRA/TSRA BY TUESDAY AFTERNOON WITH DECENT COVERAGE LIKELY ESPCLY BLUE RIDGE...AND POINTS WEST ON TUESDAY...BUT MAINLY AFTER THE VALID TAF PERIOD. EXTENDED AVIATION DISCUSSION... UPPER SYSTEM IN THE BASE OF THE FADING SE TROUGH WILL CUTOFF AND SHIFT WESTWARD INTO WEDNESDAY IN ADVANCE OF AN APPROACHING COLD FRONT FOR THURSDAY. HOWEVER LEFTOVER DEEP MOISTURE WITH THE OLD FRONT AROUND WILL RESULT IN MORE WIDESPREAD DIURNAL CONVECTION WEDNESDAY AFTERNOON WITH EARLY FOG IN SPOTS GIVING WAY TO BRIEF VFR...THEN PERIODIC MVFR IN CLOUDS/TSRA. A COLD FRONT LOOKS TO PUSH THROUGH ON THURSDAY WITH BETTER COVERAGE OF MVFR/IFR PRODUCING SHOWERS AND STORMS. IMPROVED AVIATION CONDITIONS ARE EXPECTED FRIDAY BEHIND THE FRONT WITH CLEARING SKIES AND LITTLE TO NO PRECIPITATION INTO SATURDAY. && .EQUIPMENT...
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AS OF 245 PM EDT MONDAY... KFCX RADAR IS DOWN. TECHNICIANS WILL INVESTIGATE LATER TODAY. NO ESTIMATED TIME FOR RETURN TO SERVICE.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/NF NEAR TERM...JH SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...JH/NF/RAB EQUIPMENT...JH/CF

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