Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 192007 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 407 PM EDT TUE AUG 19 2014 .SYNOPSIS...
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A WEAK STATIONARY FRONT WILL REMAIN IN THE AREA THROUGH THE REST OF THE WEEK. UPPER LEVEL DISTURBANCES TRACKING EAST AND SOUTHEAST ACROSS THE BOUNDARY WILL BRING SCATTERED SHOWERS AND STORMS TO THE REGION EACH DAY.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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AS OF 250 PM EDT TUESDAY... SHOTGUN PATTERN OF SHRA/ISOLATED TSRA CONTINUES LATE THIS AFTERNOON WITH LOCAL CONVERGENCE ZONES OVER THE SOUTH AND WEST PER MSAS MAKING FOR A FEW CLUSTERS OF HEAVIER RAINFALL. HOWEVER INSTABILITY RATHER WEAK WITH ANALYSIS SHOWING CAPES OF ONLY 500-1000 J/KG AND THIS COMBO WITH DRIER AIR ALOFT SHOULD LIMIT DEEP CONVECTION FOR THE MOST PART INTO THIS EVENING. STILL APPEARS POCKETS OF HEAVY RAIN THE MAIN CONCERN SO RUNNING WITH MOSTLY CHANCE POPS INTO THIS EVENING INCLUDING SPOTTY LIKELY POPS IN THE VERY NEAR TERM WHERE COVERAGE REMAINS BEST. EXPECT A GRADUAL DECREASE IN COVERAGE AFTER SUNSET WITH RESIDUAL OUTFLOW AND LOW LEVEL MOISTURE PERHAPS KEEPING LINGERING COVERAGE AROUND ESPCLY MOUNTAINS INTO LATE EVENING. OTRW WEAK SUBSIDENCE AND LOSS OF HEATING SHOULD MAKE FOR A PERIOD OF LITTLE POP FROM LATE EVENING INTO THE EARLY MORNING HOURS BEFORE SHORTWAVE ENERGY FROM THE NW APPROACHES LATE. GUIDANCE DIFFERING ON TIMING OF ARRIVAL OF THE LEADING AXIS OF DEEPER MOISTURE BUT MOST SHOW SOME WEAK WESTERN SLOPE CONVERGENCE AND INSTABILITY TOWARD DAYBREAK. THIS SUPPORTS RETURNING CHANCE POPS OVER THE FAR WEST LATE BUT LITTLE OUT TOWARD THE BLUE RIDGE AND POINTS EAST. OTRW MAINLY PC WITH PATCHY FOG AROUND AGAIN AND LOWS MOSTLY IN THE 60S. NEXT MID LEVEL WAVE SLIDES EAST AND CROSSES THE REGION FROM THE WEST UNDER THE NEXT PASSING 5H TROUGH WELL TO THE NORTH WEDNESDAY. BEST SUPPORT/DYNAMICS SLIPS TO THE NORTH WHILE A TRAILING VORT LOBE WORKS EAST OF THE BLUE LATER IN THE AFTERNOON. APPEARS BETTER INSTABILITY PER MORE INSOLATION WOULD SUPPORT SOME SORT OF BROKEN BAND OF SHRA/TSRA EITHER SLIDING ACROSS OR DEVELOPING ALONG THE BLUE RIDGE AND MOVING EAST DURING THE AFTERNOON. WITH BETTER HEATING...TRENDING TOWARD THE SLOWER 12Z ECMWF SOLUTION WHICH WOULD HAVE MOST COVERAGE JUST ARRIVING IN THE WEST MORNING/EARLY AFTERNOON AND THEN ALONG AND EASTWARD FROM THE BLUE RIDGE LATER IN THE DAY. HOWEVER WILL HOLD ON GOING ANY HIGHER THAN DECENT CHANCE POPS AT THIS POINT GIVEN UNCERTAINTY BUT PERHAPS ENOUGH OF A MID LEVEL JET AND STRONG LAPSE RATES TO SUPPORT AN ISOLATED SEVERE THREAT MAINLY NORTH/EAST. KEPT HIGHS CLOSER TO THE WARMER MAV MOS EAST AND A BLEND OF THE MET/MAV AND 2M ECMWF VALUES WEST WHERE LIKELY MORE CLOUDS/SHRA EARLIER.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
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AS OF 355 PM EDT TUESDAY... SHORT WAVE IS EXPECTED TO EXIT TO THE EAST DURING THE EVENING AND SHOULD ALLOW A MAINLY DRY NIGHT FOR THE REGION...ASIDE FROM MAYBE SOME LINGERING UPSLOPE AIDED SHOWERS IN THE FAR WEST. MOST LIKELY THIS WAVE WILL BE TAKING AN AREA OF ZONE OF SCATTERED CONVECTION EAST OF THE FCST AREA BY EVENING...BUT LEFT SOME LOW CHANCE POPS IN FAR EAST DURING THE EVENING IN CASE THIS SLOWS DOWN. TIMING SUBTLE WAVES IS TRICKY AND MOST MODELS IMPLY ANOTHER WEAK ONE COULD ARRIVE BY THURSDAY MORNING TO KEEP SOME LINGERING SHOWERS AND MAYBE EVEN A THUNDERSTORM IN THE WEST. NAM SOUNDINGS SHOW CONTINUE INSTABILITY OVERNIGHT SO DONT WANT TO RULE THAT OUT...BUT MORE SIGNIFICANT WAVE ARRIVES LATE IN THE DAY THURS TO EARLY EVENING FOR MUCH BETTER CHANCE FOR WIDESPREAD OR ORGANIZED CONVECTION...MAINLY IN THE WEST BUT SOME ACTIVITY COULD SPREAD INTO PIEDMONT DESPITE NW FLOW GIVEN UPPER SUPPORT. DONT SEE ENOUGH INSTABILITY TO SUPPORT MUCH SEVERE THREAT REACHING INTO AREA...UNLESS TIMING IS A LITTLE FASTER BUT COULD BE ORGANIZED LINE OR BOW ECHO TYPE STRUCTURES COMING THROUGH OHIO VALLEY AND INTO WV SO WILL NEED TO KEEP AN EYE ON. MORE CONCERNED ABOUT HIGHRAINFALL RATES AND SOME AREAS GETTING MORE THAN ONE ROUND OF SHOWER/THUNDERSTORM ACTIVITY...BUT CONFIDENCE NOT HIGH ENOUGH YET TO CONSIDER ANY KIND OF HEADLINE FOR FLOOD POTENTIAL....WHICH WOULD BE CONFINED TO WESTERN SLOPES OF APPALACHIANS. FRIDAY COULD BE A REPEAT IN SOME REGARDS...BUT AT THIS POINT UPSTREAM SHORT WAVE NOT LOOKING AS POTENT...IF ANYTHING AT ALL. STILL COULD BE DIURNAL CONVECTION...AGAIN MAINLY WEST WITH NW FLOW. AS PATTERN AMPLIFIES...MORE LIKEY FRI NIGHT AND INTO SAT...BACK DOOR FRONT COULD SNEAK DOWN FROM NORTHEAST...BUT LOOKS LIKE THAT WILL HOLD OFF UNTIL OVERNIGHT. THUS HAVE KEPT TEMPERATURE WARM AGAIN FOR FRIDAY BUT STILL UNDER GFS MOS DUE TO LIKELY LOTS OF CLOUD COVER. TRENDING UP THOUGH FROM PREV FCST SINCE BACK DOOR FRONT IS EXPECTED AFTER DAY TIME. MAY NOT BE QUITE AS WARM AS THURSDAY THOUGH...WHERE HAVE LOWER 90S GOING IN EAST WITH MORE SUNSHINE AND DOWNSLOPE. GOING CLOSER TO ECMWF GUIDANCE FOR HIGHS BOTH THURS AND FRIDAY AS GFS HAS MID 90S THURSDAY AND LOWER 90S FRI IN PIEDMONT.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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AS OF 130 PM EDT TUESDAY... THE WEEKEND THROUGH EARLY NEXT WEEK WILL BE CHARACTERIZED BY THE BATTLE BETWEEN LARGE UPPER RIDGE TO OUR WEST TRYING TO BUILD INTO SOUTHERN APPALACHIANS...WHILE TROUGH OFF NEW ENGLAND COAST DEEPENS WHILE CLOSING OFF AND CONTINUES TO APPEAR THAT IT WILL SET UP CLOSE ENOUGH TO COAST TO PUSH BACK DOOR FRONT THROUGH AND WELL SOUTH OF THE AREA THROUGH THE WEEKEND...BEFORE LIKELY WEAKENING AND ALLOWING MORE INFLUENCE OF THE RIDGE TO BE FELT BY TUES...ESPECIALLY ACROSS WESTERN PARTS OF THE AREA IF WEAK/SHALLOW BOUNDARY LAYER WEDGE IS IN PLACE EARLY IN THE DAY BEFORE MIXING OUT OVER THE EAST. WHILE SURFACE WEDGE FRONT MAY BE WELL TO THE SOUTH DURING MUCH OF THIS PERIOD...WITH STRONGEST SOUTHWARD PUSH ON SATURDAY...THE 850 BOUNDARY AND MOST LIKELY TRACK FOR UPPER S/WV ENERGY FROM THE NW IS LIKELY TO BE RIGHT OVER THE BLACKSBURG FORECAST AREA...AND THUS GOOD CHANCE FOR SHOWERS/THUNDERSTORMS THROUGH THIS ENTIRE PERIOD. TIMING MOST LIKELY WINDOWS REMAINS TRICKY...AS MANY OF THESE WAVES ARE STRONGLY INFLUENCE BY CONVECTIVE COMPLEXES THAT WILL DEVELOP WELL UPSTREAM. LIKE THE TRENDS OVERALL THAT 12Z GFS IS TAKING...NOT ONLY WITH RETURN TO SHARPER AMPLITUDE PATTERN...BUT IDEA OF TWO DISTINCT WAVES HEADING FOR THE WESTERN PART OF OUR FORECAST AREA...ONE SATURDAY AND ANOTHER ONE SUNDAY. EXACT TIMES MAY HELP DETERMINE IF THERE WILL BE ENOUGH INSTABILITY...WHICH WOULD LIKELY BE LIMITED TO THE FAR WEST NEAR EDGE OF WEDGE BOUNDARY...BUT PERHAPS THE BIGGER CONCERN IS RAINFALL THAT IS LIKELY TO IMPACT THE SAME AREAS AT LEAST A COUPLE OF DAYS IN A ROW. THERE COULD BE ANOTHER WAVE FOR MONDAY...BUT AS RIDGE ATTEMPTS TO BUILD IN AND TROUGH TO THE EAST AND ASSOCIATED WEDGE WEAKEN WHAT MAY TEND TO OCCUR IS MORE DIURNAL POP-UP CONVECTION ALONG AND NEAR THE WESTERN PERIPHERY OF THE WEDGE BOUNDARY IN OUR WESTERN FORECAST AREA AS THE ATMOS DESTABILIZES MORE. BY TUESDAY THE SUPPORT TO KEEP WEDGE IN PLACE SHOULD BE WEAKENING AS TROUGH LIFTS AND SFC HIGH SHIFTS MORE EAST OF THE AREA...AND OVERALL IT LOOKS A LITTLE DRIER...BUT NOT SURE ALL POPS CAN BE REMOVED. GIVEN PATTERN WE`VE BEEN IN...REALLY DON`T HAVE CONFIDENCE TO DRY IT OUT OR WARM IT UP TOO FAST...SO WILL LEAN TOWARD STRONGER INFLUENCE OF THE WEDGE THROUGH THIS PERIOD AND BETTER CHANCES FOR PRECIP...WHICH WILL HELP STRENGTHEN THE WEDGE TOO. UNDERCUT EVEN COOLER ECMWF A LITTLE BIT FOR HIGHS...WITH A BIT MORE WARMING FOR TUESDAY. BUT IN THE FAR SOUTHWEST THINGS MAY BE ABLE TO WARM UP VERY QUICKLY A DAY OR TWO EARLIER THAN THIS IF THE WEDGE CAN BREAK AND SOME OF THE INFLUENCE OF THE BIG UPPER RIDGE CAN BE REALIZED. THIS WILL EVENTUALLY RESULT IN A SIGNIFICANT WARM UP FOR OUR ENTIRE AREA...BUT AM THINKING IT WILL NOT COME UNTIL MIDDLE OF NEXT WEEK.
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&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/... AS OF 100 PM EDT TUESDAY... STAGNANT WEATHER PATTERN CONTINUES TODAY AS CLOSED UPPER LOW SLOWLY WORKS THROUGH THE GREAT LAKES REGION AND A STALLED FRONT MEANDERS IN OUR VICINITY AT THE SURFACE. ANOTHER PULSE OF SHORT WAVE ENERGY IS ROTATING THROUGH THE FLOW AND WILL INTERACT WITH LOW LEVEL INSTABILITY TO GET SOME DIURNAL SHOWERS AND THUNDERSTORMS GOING. RADAR AND MESO MODELS INDICATE ACTIVITY WILL WARRANT MORE THAN A VICINITY SO WILL USE TEMPO EARLY ALL SITES EXCEPT KLYH WHERE ACTIVITY IS OFF TO A SLOWER START. MODEL SOUNDINGS SHOW LINGERING INSTABILITY WELL INTO THE NIGHT SO BELIEVE LINGERING SHOWERS WILL BE AROUND WELL INTO THE OVERNIGHT...THOUGH COVERAGE WILL BECOME SPARSE. NEXT IMPULSE IS ON OUR DOORSTEP AROUND 12Z SO WILL REINTRODUCE SOME SHOWERS. OUTSIDE OF ANY PRECIPITATION CONDITIONS SHOULD BE JUST ON THE PLUS SIDE OF VFR BUT IT WILL BE RIGHT ON THE EDGE WEST OF THE BLUE RIDGE. HOWEVER EXPECTING IFR/LIFR CONDITIONS TO BE DEVELOPING OVERNIGHT MAINLY DUE TO CIGS BUT THERE WILL BE SOME FOG AROUND AS WELL. NO SIGNIFICANT WIND ISSUES EXPECTED THROUGH THIS TAF PERIOD. EXTENDED AVIATION... AVIATION CONDITIONS WILL CONTINUE TO BE UNSETTLED AND VARIABLE FOR THE NEXT FEW DAYS AS THE PATTERN REMAINS SLUGGISH WITH WAVES OF ENERGY MOVING THROUGH WITH A LOT OF MOISTURE TO WORK WITH. THERE WILL BE A DIURNAL FLAVOR TO THINGS WITH LOW CLOUDS AND FOG AT NIGHT WITH IFR/LIFR THEN SOME AFTERNOON SHOWERS AND THUNDERSTORMS. BEST CHANCE FOR VFR WILL BE LATE MORNING TO EARLY AFTERNOON AFTER FOG/LOW CLOUDS BURN OFF AND BEFORE CONVECTION BEGINS. WILL ALSO HAVE TO WATCH FOR POSSIBILITY OF CONVECTION DEVELOPING UPSTREAM AND AFFECTING TAF SITES AT NIGHT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF/SK NEAR TERM...JH SHORT TERM...SK LONG TERM...SK AVIATION...MBS

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