Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 031443 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1043 AM EDT FRI JUL 3 2015 .SYNOPSIS...
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A LOW PRESSURE SYSTEM WILL MOVE THIS AFTERNOON ALONG A FRONTAL BOUNDARY. THROUGH THE HOLIDAY WEEKEND OUR WEATHER WILL REMAIN UNSETTLED...WITH A SERIES OF UPPER LEVEL DISTURBANCES BRINGING A CHANCE FOR SHOWERS AND THUNDERSTORMS.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1030 AM EDT FRIDAY... UPDATED FORECAST TO FOLLOW A BLEND OF RADAR TRENDS COMBINED WITH THE LATEST RAP/12Z HRRR. SHOULD SEE SMALL AREA OF SHOWERS ACROSS SE WV TO THE INTERSTATE 81 CORRIDOR NEAR ROANOKE SHIFT NE THROUGH MIDDAY...WITH ONLY ISOLATED COVERAGE ELSEWHERE. NEXT UPSTREAM CONVECTION LIES ALONG THE FRONTAL ZONE IN SOUTHEAST KENTUCKY AND WE WILL SEE THIS AREA MOVE INTO OUR WRN COUNTIES AFTER NOON-1PM. TAPERED POPS OFF SOME THROUGH EARLY AFTERNOON GIVEN RADAR TRENDS. THUNDER CHANCES WILL REMAIN AS WE GET BETTER UPPER SUPPORT FROM THE WAVE MOVING OUT OF TN/KY THIS AFTERNOON...THOUGH INSOLATION WILL BE CLOSED OFF DUE TO EXTENSIVE CLOUD COVER. CANNOT RULE OUT SOME THIN SPOTS AT TIMES THOUGH. 12Z RNK SOUNDING SHOWS A VERY MOIST PROFILE. MODIFIED FOR SOME INCREASE TEMPS AND DEWPOINTS FAVORS SBCAPES OVER 1000 J/KG. SO CUT BACK THUNDER TO SCATTERED COMPARED TO LIKELY/NUMEROUS. LOOKS LIKE AXIS OF DEEP CONVECTION WILL GET GOING INTO WV/SW VA THIS AFTERNOON MOVING ENE INTO THE FOOTHILLS AND PIEDMONT. STILL NOT EXPECTING A LONG LIVED HEAVY RAIN EVENT...SO NO WATCHES FOR NOW...BUT WILL MONITOR FOR ISOLATED FLOOD POTENTIAL. WILL CONTINUE TO HIGHLIGHT THE POTENTIAL FOR HEAVY RAIN AND POSSIBLE HYDRO ISSUES IN THE HWO. IN ADDITION THERE IS SOME FOG AROUND THANKS TO COOL STABLE LAYER EARLY ON OVER THE MTNS AND RAIN KEEPING RH NEAR 100 PERCENT. THINK FOG TO FADE TOWARD EARLY AFTERNOON EXPECT HIGHER PEAKS ALONG THE BLUE RIDGE. CUT BACK HIGH TEMPS A FEW DEGREES BUT STILL MAINLY 70S AREA WIDE. PREVIOUS VALID DISCUSSION... ACTIVITY MOVING OUT AND WINDING DOWN THIS EVENING/EARLY TONIGHT. AS THE LOW MOVES OFF TO OUR NORTHEAST TONIGHT THE FRONTAL BOUNDARY WILL SWING BACK THROUGH THE REGION AS A COLD FRONT. THIS WILL YIELD SOME LINGERING SHOWERS WEST OF THE BLUE RIDGE WITH SOME IMPROVEMENT TO THE EAST LOWS TONIGHT RANGE FROM THE UPPER 60S EAST TO LOWER 60S WEST.
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&& .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
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AS OF 415 AM EDT FRIDAY... THE BROAD UPPER TROUGH PLAGUING THE EASTERN U.S. WILL UNDERGO SOME SUBTLE MODIFICATIONS DURING THIS PERIOD. SAT-SUN...THE UPPER TROUGH WILL TAKE ON A POSITIVE TILT AS A SHORT WAVE RIDGE BUILDS INTO THE GREAT LAKES/PA REGION. MEANWHILE...THE SOUTHERN END BECOMES CUTOFF ACROSS THE CAROLINAS AND LINGERS ACROSS THAT REGION SUN...THEN GRADUALLY DRIFTS BACK NORTHWARD INTO EASTERN VA MON AND NORTHERN VA TUE. THUS...THE AREA REMAINS UNSETTLED AND WET...BUT WITH A GRADUAL SHIFT OF THE BETTER COVERAGE OF SHOWERS AND THUNDERSTORMS TOWARD THE EASTERN PART OF THE CWA WITH TIME. FOR SATURDAY...YET AGAIN...POTENTIAL FOR WIDESPREAD SHOWERS AND EMBEDDED THUNDERSTORMS TO START OFF THE DAY...JUST AS HAS BEEN THE CASE THE PAST TWO DAYS. HOWEVER...CONFIDENCE IN THIS IS LOW AT THIS POINT AS IT WILL LARGELY BE BASED ON UPSTREAM CONVECTIVE COMPLEXES...TRACK...AND INTENSITY. HOWEVER...FEEL THAT CONFIDENCE IN ONGOING PRECIPITATION AT 12Z IS SLIGHTLY GREATER THAN THE PAST TWO DAYS AS THE UPPER TROUGH SHIFTS EAST MOVING THE CURRENT CORRIDOR OF PRECIPITATION ACROSS THE TN VALLEY EASTWARD INTO OUR REGION. THE EXTENT OF CLOUDS AND PRECIPITATION IN THE MORNING WILL DETERMINE THE DEGREE OF INSTABILITY AND HENCE CONVECTIVE COVERAGE LATER IN THE DAY. UPPER FLOW TENDS TO BECOME MORE SOUTHWEST INSTEAD OF NORTHWEST DURING THIS PERIOD GIVEN THE TRANSITION OF THE WEAK UPPER LOW TO THE SOUTH OF THE REGION. THIS SHOULD BE ENOUGH TO SUPPORT HIGH CHANCE TO LIKELY POPS INTO THE AFTERNOON/EVENING. SPC CURRENTLY ONLY HAS GENERAL THUNDER ACROSS THE REGION GIVEN THE LACK OF INSTABILITY. WITH FAIRLY WET ANTECEDENT CONDITIONS...THE MAIN CONCERN WILL BE HEAVY RAINFALL AND LOCALIZED FLOODING. HOWEVER...IT APPEARS UNLIKELY THAT FFG WILL BE EXCEEDED AS RAINFALL AMOUNTS WOULD NEED TO EXCEED 2-2.5 INCHES IN 1-3 HRS MOST LOCATIONS FOR THIS TO OCCUR. PROJECTED RAINFALL FOR THE THREE DAY PERIOD TODAY THROUGH SUNDAY IS MOSTLY 1.5 TO 2.5 INCHES. FOR SUNDAY...THE WEAK UPPER LOW DRIFTS BACK NORTH INTO THE CWA. WIDESPREAD SHOWERS AND THUNDERSTORMS APPEAR LIKELY...BUT THE EXTENSIVE CLOUD COVER WILL AGAIN LIMIT INSTABILITY. ONCE AGAIN...LOCALIZED HEAVY RAINFALL WILL BE THE MAIN CONCERN...BUT GIVEN THAT THE HEAVIEST RAINFALL SHOULD REMAIN MOSTLY EAST OF THE MOUNTAINS...THIS FURTHER REDUCES CONCERNS OF FLOODING. HOWEVER...THE PATTERN DOES ONCE AGAIN SUPPORT LIKELY POPS ACROSS MUCH OF THE CWA...ESPECIALLY EASTERN SECTIONS. MONDAY PROMISES TO BE YET ANOTHER WET DAY AS THE REMNANT UPPER LOW DRIFTS INTO NORTHERN VA. ONCE AGAIN...THE BEST COVERAGE OF PRECIPITATION SHOULD BE ACROSS THE EASTERN SECTIONS...BUT DIFFERENTIAL HEATING ACROSS THE MOUNTAINS SHOULD RESULT IN AN UPTICK OF AFTERNOON CONVECTION THERE AND FURTHER NORTH COMPARED TO SUN. AGAIN...HIGH CHANCE TO LIKELY POPS APPEAR IN ORDER. INSTABILITY ONCE AGAIN APPEARS MARGINAL AND THE MAIN CONCERN WILL REMAIN THAT OF LOCALIZED HEAVY RAINFALL. MAX TEMPS SHOULD REMAIN WELL BELOW NORMAL THROUGH THE PERIOD THANKS TO CLOUD COVER AND PRECIPITATION...WITH HIGHS MOSTLY IN THE 70S...TO LOWER 80S EAST IF A FEW BREAKS IN THE OVC CAN OCCUR. ON THE OTHER HAND...LOW TEMPERATURES WILL REMAIN ABOVE NORMAL THANKS TO HIGH PWATS/DEWPOINTS AND CONSIDERABLE CLOUD COVER.
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&& .LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 430 AM EDT FRIDAY... BY TUESDAY...THERE IS FAIRLY GOOD AGREEMENT AMONG THE MODELS THAT THE CUT OFF UPPER LOW LINGERING ACROSS THE REGION WILL SPLIT IN TWO...WITH THE PART ACROSS NORTHERN VA LIFTING NORTHEAST TOWARD NY/NEW ENGLAND...AS THE PARENT UPPER LOW SINKS SOUTHWARD TOWARD THE FL PANHANDLE/SOUTH GA. MEANWHILE...A SHORT WAVE AND ASSOCIATED FRONT WILL APPROACH FROM THE NORTHWEST BY TUESDAY...THEN DRIFT INTO THE REGION AND STALL WED-THU. AT THIS POINT...TUE SHOULD BE THE DAY WITH THE LOWEST POPS OVERALL...AND LIKELY LOWER THAN ANY PRIOR DAYS OR SUCCEEDING DAYS. ONCE THE FRONT DRIFTS INTO THE REGION WED AND STALLS...WAVES OF LOW PRESSURE WILL RIDE ALONG THE FRONT AND KEEP GOOD CHANCES OF SHOWERS/THUNDERSTORMS ACROSS THE REGION. HOWEVER...COMPARED TO THE CURRENT WEEK WITH NORTHWEST FLOW...UPPER FLOW WILL BE MORE WEST-SOUTHWEST AS BROAD UPPER RIDGING IS NOTED ACROSS THE SOUTHERN STATES. PRECIPITATION OVERALL SHOULD BE SLIGHTLY MORE DIURNAL IN NATURE...I.E...LESS NOCTURNAL...AS A RESULT AND TEMPERATURES WILL CERTAINLY BE TRENDING WARMER...BUT REMAIN MOSTLY 70S MOUNTAINS AND 80S PIEDMONT AS 850MB TEMPS TOP OUT IN THE +16C TO +18C RANGE. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... AS OF 730 AM EDT FRIDAY... POOR AVIATION CONDITIONS EXPECTED THROUGH THE TAF VALID PERIOD AS BROAD UPPER TROUGH AND EMBEDDED DISTURBANCES CONTINUE TO TRACK ACROSS THE REGION. CONFIDENCE IS LOW IN TIMING OF CONVECTIVE COMPLEXES AND DEGREE OF INSTABILITY FOR HEAVIER AFTERNOON/EVENING CONVECTION GIVEN WIDESPREAD MORNING SHOWERS. AREA OF SHOWERS AND EVEN A FEW THUNDERSTORMS AT THIS HOUR SPREADING TO THE WESTERN PART OF THE REGION ALREADY. MODELS SHOW THIS TRACKING FROM SOUTHWEST TO NORTHEAST THROUGH THE MORNING...THEN ANOTHER AREA OF CONVECTION...POSSIBLY STRONGER...ARRIVING DURING THE AFTERNOON/EVENING...BEFORE SHIFTING TO THE EAST OF THE CWA BY SATURDAY MORNING. HAVE ADVERTISED WIDESPREAD MVFR CIGS AND VSBYS EAST OF THE BLUE RIDGE IN SHRA AND OCCASIONAL TSRA THROUGH THE EVENING...WITH MVFR-IFR CIGS/VSBYS WEST OF THE BLUE RIDGE THROUGH THE EVENING. OVERNIGHT...HEAVIER PRECIPITATION SHOULD SHIFT EAST...BUT LINGERING SHOWERS WILL REMAIN. IN ADDITION...CONDITIONS APPEAR FAVORABLE FOR WIDESPREAD IFR-LIFR CIGS/VSBYS IN FOG AND LOW CLOUDS...ESPECIALLY BLF/LWB/BCB. WINDS GENERALLY NE-SE 3-7KTS THROUGH THE DAY IN ADVANCE OF A WEAK AREA OF SFC LOW PRESSURE TRACKING ALONG THE QUASI-STATIONARY FRONT DRAPED ACROSS THE REGION. WINDS SHOULD BECOME SSW-SW 3-6KTS BEHIND THE HEAVIER SHRA/TSRA ACTIVITY THIS EVENING. LOW TO MEDIUM CONFIDENCE IN CIGS AND VSBYS THROUGH THE TAF VALID PERIOD. LOW TO MEDIUM CONFIDENCE IN THUNDERSTORM POTENTIAL THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN WIND DIRECTION/MEDIUM TO HIGH CONFIDENCE IN WIND SPEED THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... POOR AVIATION CONDITIONS LIKELY TO CONTINUE INTO EARLY NEXT WEEK...BUT WINDOWS OF OPPORTUNITY FOR VFR CONDITIONS INCREASE AS WE MOVE INTO MON/TUE. UPPER LOW/TROUGH WILL LINGER WEST OF THE VA/NC COASTAL PLAIN INTO THE SOUTHEAST STATES THROUGH THE WEEKEND...THEN BEGIN TO DRIFT INTO NORTHERN VA BY MON. MEANWHILE...A COLD FRONT WILL APPROACH FROM THE OH VALLEY BY WED. THIS LEAVES A VERY UNSETTLED/WET PATTERN ACROSS THE REGION THROUGH THE PERIOD. EXPECT WIDESPREAD LATE NIGHT/EARLY MORNING LOW CLOUDS/FOG WITH IFR-LIFR CIGS/VSBYS. OVERALL...CONDITIONS SHOULD IMPROVE TO MVFR-VFR OUTSIDE SHRA/TSRA ACTIVITY DURING THE AFTERNOONS. AT THIS POINT...TUESDAY APPEARS TO OFFER THE BEST OPPORTUNITY FOR MORE WIDESPREAD VFR CONDITIONS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...MBS/WP NEAR TERM...MBS/WP SHORT TERM...RAB LONG TERM...RAB/RCS AVIATION...MBS/NF/RAB

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