Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 311903 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 303 PM EDT SUN AUG 31 2014 .SYNOPSIS... THE REGION WILL STAY BETWEEN A LARGE HIGH PRESSURE SYSTEM OVER THE SOUTHEAST UNITED STATES AND A COMPLEX LOW PRESSURE SYSTEM CROSSING THE GREAT LAKES. DISTURBANCES PASSING BETWEEN THESE TWO FEATURES WILL COMBINE WITH HEAT AND HUMIDITY TO RESULT IN PERIODIC CHANCES OF SHOWERS AND STORMS INTO EARLY WEEK. A COLD FRONT FINALLY ARRIVES FROM THE NORTH WEDNESDAY INTO THURSDAY. && .NEAR TERM /THROUGH MONDAY/...
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AS OF 220 PM EDT SUNDAY... SHALLOW CONVECTION STARTING TO SLOWLY INCREASE OVER THE WEST THIS AFTERNOON WHERE AIDED BY CONVERGENCE/DIFFERENTIAL HEATING WESTERN SLOPES...AND ALONG THE SOUTHERN BLUE RIDGE PER THETA-E POOLING. THIS AHEAD OF SHORTWAVE ENERGY THAT WILL PASS TO THE NW THIS EVENING FOLLOWED BY ANOTHER WEAKER IMPULSE OVERNIGHT. HOWEVER LOTS OF UPSTREAM DEBRIS CLOUD PUSHING INTO THE MOUNTAINS AS WELL WHICH MAY TEND TO INHIBIT ALREADY WEAK INSTABILITY FAR WEST...WITH HIGHER 2K J/KG CAPES EAST OF THE BLUE RIDGE. APPEARS ENOUGH COVERAGE TO CONTINUE LOW LIKELY TO HIGH CHANCE POPS WEST THIS EVENING...BUT QUESTIONS INTO HOW FAR EAST TO TAKE SHRA/TSRA PER BETTER DYNAMICS WEST/NW...AND LESS FOCUS DESPITE STRONGER INSTABILITY PIEDMONT. LATEST NAM/GFS/EC TEND TO CONFINE ADDED SHOWERS TO MAINLY THE WEST OR NW THROUGH MIDNIGHT...WITH THE HRRR/NSSL WRF AND CMC TAKING SOME CONVECTION OUT EAST. FOR NOW GIVEN POTENTIAL FOR OUTFLOW TO SNEAK OUT OFF THE MOUNTAINS AS MIXING FADES...PLAN TO KEEP SOME BRIEF LOW CHANCE POPS EAST TO THE PIEDMONT. SECONDARY FAINT IMPULSE MAY ALSO KEEP OR HELP DEVELOP ANOTHER AREA OF SHRA WEST AFTER SUNSET...OTRW GRADUALLY DIMINISHING POPS FROM NORTH TO SOUTH BY MORNING. TEMPS AGAIN SLOW TO FALL PER CLOUDS/MOISTURE SO STAYED CLOSER TO THE WARMER MET MOS ALLOWING SOME EASTERN SPOTS TO STAY ABOVE 70. SHORTWAVES WILL BE EXITING BY EARLY MONDAY LEAVING THE REGION IN DECENT WEST/SW FLOW ALOFT BUT WITHOUT MUCH FORCING WELL IN ADVANCE OF THE NEXT UPSTREAM 5H TROF/COLD FRONT TO THE NW. FORECAST SOUNDINGS SHOW QUITE A DEEP WESTERLY FLOW WHICH RESULTS IN DRYING ALOFT/LOWERING PWATS ESPCLY WEST MONDAY AFTERNOON AND A LEE TROUGH ACROSS THE PIEDMONT. MOST GUIDANCE SOLUTIONS SHOW A LACK OF MUCH CONVECTION IN THIS REGIME WITH ANY FOCUS PROVIDED BY OROGRAPHICS DUE TO WESTERLY CONVERGENCE AND PERHAPS LATE DAY LOW LEVEL BACKING SE. THUS WILL LEAVE IN SOME LOW POPS MAINLY WEST AS APPEARS A SUBTLE WAVE ALOFT COULD SNEAK THROUGH AROUND THE TIME OF MAX HEATING. OTRW EXPECT WEAK LAPSES...LACK OF DEEP INSTABILITY AND EASTERN DOWNSLOPE TO LIMIT OVERALL COVERAGE WITH MUCH OF THE DAY LIKELY DRY AFTER EARLY MID DECK/FOG ERODE. COULD BE ONE OF THE WARMEST DAYS SEEN IN A WHILE WITH 85H TEMPS PUSHING +21C OVER DECENT DOWNSLOPE AND UNDER AMPLE AFTERNOON SUN. THIS WOULD SUPPORT SOME MID 90S PIEDMONT...WITH UPPER 80S/LOW 90S BLUE RIDGE... AND LOW/MID 80S WESTERN ELEVATIONS IF CAN GET A TEMP JUMP AFTER A WARM START IN THE MORNING.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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AS OF 230 PM EDT SUNDAY... WITH WEAK HIGH PRESSURE BUILDING IN FROM THE SOUTH...EXPECT TO HEAD INTO LATE MONDAY NIGHT WITH MOSTLY CLEAR SKIES AND LIGHT WINDS. AS SUCH...WOULD NOT BE SURPRISED TO SEE PATCHY FOG DEVELOP IN SOME OF THE MOUNTAIN VALLEYS EARLY MORNING...WHICH WILL BURN OFF QUICKLY SHORTLY AFTER 9 AM. DURING TUESDAY AFTERNOON...SHOWER AND THUNDERSTORM ACTIVITY WILL INCREASE AS AN UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT APPROACH FROM THE WEST. ACTIVITY WILL START OFF ACROSS THE MOUNTAINS...SPOTTY AT FIRST DUE TO THE WESTERLY DOWNSLOPE FLOW...AND THEN WILL SPREAD EAST ACROSS THE PIEDMONT DURING THE EVENING AS THE UPPER LEVEL ENERGY SHIFTS EAST. LIGHT WINDS AND WARM TEMPERATURES ALOFT WILL LIMIT INSTABILITY...AND BELIEVE STRONG THUNDERSTORMS WILL BE ISOLATED AND SHORT LIVED. SHOWER AND THUNDERSTORM ACTIVITY WILL THEN DIMINISH THROUGH THE NIGHT WITH THE LOSS OF HEATING. BY WEDNESDAY MORNING...WILL HAVE A WEAK BOUNDARY SITUATED ACROSS OUR AREA...WHICH WILL EXHIBIT LITTLE MORE THAN A SHIFT IN WIND DIRECTION FROM ONE SIDE TO THE OTHER AS THE TRULY COOLER AND DRIER AIR WILL REMAIN WELL NORTH OF OUR AREA. REGARDLESS...THE LOW LEVEL CONVERGENCE ALONG THE BOUNDARY WILL BE ENOUGH TO TRIGGER ANOTHER ROUND OF SPOTTY SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON AND EVENING. BETTER CHANCES FOR RAINFALL WILL BE FOUND SOUTH OF HIGHWAY 460. TEMPERATURES HEADING INTO THE MIDDLE OF THE WEEK WILL BE WARMER THAN NORMAL THANKS TO UPPER LEVEL RIDGING ACROSS THE SOUTHEAST STATES. LOOK FOR HIGHS TO RANGE FROM THE LOW/MID 80S ACROSS THE MOUNTAINS... TO THE LOW/MID 90S ACROSS THE SOUTHSIDE. OVERNIGHT LOWS WILL RANGE FROM THE MID 60S WEST TO THE LOW 70S EAST.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 330 PM SATURDAY... UPPER LEVEL RIDGING WILL SHIFT NORTHWARD FROM THE SOUTHEAST STATES OVER THE MID ATLANTIC DURING THE SECOND HALF OF THE WEEK...RESULTING IN BOTH WARMER TEMPERATURES AND WEAKER WINDS ALOFT. THIS WILL MAKE FOR MORE STABLE CONDITIONS THAT WILL KEEP SHOWER AND THUNDERSTORM ACTIVITY DISORGANIZED THROUGH THE PERIOD. ANY RAINFALL WHICH DEVELOPS WILL BE DRIVEN MAINLY BY DAYTIME HEATING...WHICH WILL ALLOW THIS ACTIVITY TO FIZZLE AFTER SUNSET. HIGH PRESSURE WILL PASS OFF THE NEW ENGLAND COAST ON THURSDAY... RESULTING IN A WEAK WEDGING PATTERN WITH EASTERLY FLOW OFF THE ATLANTIC. THIS WILL LIKELY BE THE DRIEST DAY OF THE PERIOD. WINDS WILL SHIFT SOUTHWESTERLY AGAIN ON FRIDAY AS ANOTHER COLD FRONT SINKS SOUTH FROM THE GREAT LAKES. STRONGER FLOW OFF THE ATLANTIC WILL RESULT IN INCREASED MOISTURE...AND WILL EXPECT SPOTTY SHOWER AND THUNDERSTORM ACTIVITY DURING THE AFTERNOON AND EVENING. EXPECT TEMPERATURES TO REMAIN SLIGHTLY ABOVE NORMAL FOR THE PERIOD. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... AS OF 1255 PM EDT SUNDAY... OVERALL VFR CONDITIONS WILL BE DETERIORATING FROM WEST TO EAST THROUGH THE REST OF THE AFTERNOON AS AN AXIS OF LOWER CLOUDS JUST ENTERING THE MOUNTAINS PUSHES EAST. THIS SHOULD BRING A FEW HOURS OF MVFR TO KLWB/KBLF THE REMAINDER OF THE AFTERNOON WITH PASSING SHRA/ISOLATED TSRA POSSIBLY RESULTING IN LOCAL MVFR VSBYS INTO EARLY THIS EVENING. CANOPY LIKELY TO DIMINISH SOME HEADING EAST TO THE BLUE RIDGE SO KEEPING ELSW VFR WHILE DELAYING TIMING OF ANY SHRA/TSRA A COUPLE HOURS AT KBCB/KROA/KLYH...AND LEAVING OUT MENTION AT KDAN FOR NOW. LATEST GUIDANCE SUGGESTS THAT THE BEST COVERAGE OF CONVECTION WILL BE OVER THE NW THIS EVENING WITH PERHAPS A BAND MOVING EAST OFF THE RIDGES BEFORE FADING BY MIDNIGHT. THUS LEFT IN EITHER HIGH END MVFR TO LOW END VFR CIGS OVER THE WEST THIS EVENING WITH SOME PREVAILING VFR/MVFR VSBYS IN SHRA POSSIBLE. OTRW WILL KEEP A VCSH MENTION FOR A FEW HOURS THIS EVENING THEN TREND TOWARD MORE PATCHY FOG/STRATUS OVERNIGHT. HOWEVER LATEST SREF PROGS SUGGEST LIMITED DENSE FOG COVERAGE GIVEN MID CLOUDS SO ONLY LOWERING KLWB TO IFR BY MORNING WITH BRIEF MVFR AT MOST OTHER LOCATIONS EXCLUDING KROA BY DAYBREAK MONDAY. LAST MID LEVEL WAVE WILL PASS TO THE NW BY EARLY MONDAY LEAVING THE AREA IN BETWEEN THIS FEATURE AND THE NEXT UPSTREAM COLD FRONT. DEEP WESTERLY FLOW COMBINED WITH LACK OF FOCUS AND DECENT MIXING SHOULD INHIBIT MUCH CONVECTION DURING MONDAY ESPCLY IF EARLY MID DECK PERSISTS. THIS SUPPORTS GOOD FLYING CONDITIONS FOR MUCH OF MONDAY AFTER EARLY LOW CLOUDS/FOG FADE WITH ONLY ISOLATED CONVECTION LIKELY. EXTENDED DISCUSSION... UPPER TROUGH AND ITS ASSOCIATED COLD FRONT WILL APPROACH FROM THE NORTHWEST TUESDAY WITH SIMILAR ISOLATED SHOWERS/STORMS EXPECTED DURING THE DAY AHEAD OF THE BOUNDARY. FRONT SETTLES CLOSER TUESDAY NIGHT INTO WEDNESDAY...WHEN BETTER COVERAGE OF SHRA/TSRA IS EXPECTED...AND THEN ACROSS THE SOUTH THURSDAY WHERE THE BOUNDARY STALLS. HOWEVER LOW CONFIDENCE ON THE TIMING AND SOUTHWARD POSITION OF THE BOUNDARY AT THIS POINT. THUS APPEARS MAINLY VFR ON TUESDAY...WITH PERIODS OF MVFR WEDNESDAY-THURSDAY IN MORE ORGANIZED MAINLY AFTERNOON/EVENING CONVECTION...AND MVFR/IFR UNDER EARLY MORNING FOG IN THE VALLEYS AND WHERE EARLIER HEAVY RAIN OCCURRED. FRONT WASHES OUT TO THE SOUTH OF THE AREA FRIDAY WITH MORE DIURNAL NATURE SHOWERS AND STORMS...OTRW VFR. && .EQUIPMENT... AS OF 730 AM EDT FRIDAY ... THE VISIBILITY SENSOR AT KDAN...DANVILLE REGIONAL AIRPORT...WILL BE OUT OF SERVICE UNTIL FURTHER NOTICE. A PART HAS BEEN BACK-ORDERED. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS/JH NEAR TERM...JH SHORT TERM...NF LONG TERM...NF AVIATION...AMS/JH EQUIPMENT...AMS

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