Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201858 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 258 PM EDT SUN JUL 20 2014 .SYNOPSIS...
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A WEAK WEDGE OF HIGH PRESSURE WILL REMAIN OVER THE AREA THIS EVENING BEFORE SLIDING OFF THE MID ATLANTIC COAST OVERNIGHT. A RESIDUAL WEAK FRONTAL BOUNDARY AND UPPER DISTURBANCE ACROSS THE CAROLINAS WILL LIFT SLOWLY NORTH INTO THE REGION EARLY NEXT WEEK. THIS WILL RESULT IN CONTINUED UNSETTLED WEATHER INTO MID WEEK AHEAD OF A STRONGER COLD FRONT THAT IS EXPECTED TO ARRIVE ON THURSDAY.
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&& .NEAR TERM /THROUGH MONDAY/...
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AS OF 220 PM EDT SUNDAY... JULY WEDGE CONTINUES TO LINGER IN PLACE WITH THE WEAK PARENT SURFACE HIGH PRESSURE TO THE NE AND A SMALLER BUBBLE HIGH ALONG THE BLUE RIDGE. THIS COMBO WITH EXTENSIVE CLOUD COVER KEEPING HEATING TO A MINIMUM AGAIN AND EXPECTING ONLY A SLOW INCREASE IN FAR WESTERN SHRA COVERAGE OVER THE NEXT FEW HOURS AS INSTABILITY SLOWLY INCREASES ON THE PERIMETER OF THE WEDGE. HOWEVER LATEST SHORT TERM GUIDANCE INDICATES THAT A FAINT SHORTWAVE WILL EDGE EAST ACROSS WESTERN SECTIONS THIS EVENING WITH PERHAPS A FEW MORE SHRA/ISOLD TSRA WEST PENDING ANY ADDED HEATING THROUGH SUNSET. OTRW EXPECTING THE WEDGE TO ENHANCE A BIT AGAIN OVERNIGHT GIVEN WEAK SE FLOW UNDER THE LINGERING COOL POOL. UPPER SUPPORT LACKING EXCEPT FOR ANOTHER WAVE THAT WILL BE APPROACHING FROM THE SW UNDER WHATS LEFT OF THE 5H TROF CROSSING THE APPALACHIANS LATE. APPEARS ENOUGH WEAK LIFT AND PERHAPS UPSLOPE TO KEEP SOME LOW CHANCE TO SLIGHT POPS IN MAINLY SOUTHERN TIER AFTER COVERAGE FADES WITH THE WEAK WAVE THIS EVENING. FOG AND PATCHY -DZ ALSO POSSIBLE MAINLY BLUE RIDGE WITH LOWS AGAIN MAINLY 60S...BUT A DEGREE OR SO WARMER THAN LAST NIGHT AS DEWPOINTS NUDGE UP. RATHER CUTOFF MID LEVEL WAVE REMAINS OVER THE SE STATES ON MONDAY WITH DEEPER MOISTURE LIFTING BACK NORTH WITH THE RESIDUAL BOUNDARY PASSING THROUGH N CAROLINA MONDAY AFTERNOON. ALTHOUGH LITTLE SUPPORT ALOFT...RISING PWATS AND THETA-E RIDGING ALONG WITH A BETTER EAST/SE TRAJECTORY UNDER A WEAK DIFFLUENT PATTERN ALOFT SHOULD COMBO WITH A BIT MORE HEATING TO PRODUCE MORE SHRA ESCPLY SOUTH INTO LATE MONDAY. APPEARS BEST LOW LEVEL FOCUS SRN BLUE RIDGE WHERE KEPT A SLITHER OF LIKELY POPS OTRW MAINLY CHANCE COVERAGE FOR NOW. HOWEVER MAY ONLY SEE CLOUDS AND ISOLATED SHRA NORTH HALF WITH MOST DEEPER CONVECTION POSSIBLE EXTREME SOUTH AND WEST WHERE FORECAST INSTABILITY IS A BIT MORE PENDING DEGREE OF ISOLATION. HIGH TEMPS REMAIN TRICKY GIVEN POTENTIAL FOR CLOUDS TO LINGER BEFORE MORE SHRA DEVELOP...SO AGAIN LEANED TOWARD THE COOLER MET MOS SINCE APPEARS BEST WITH THE RESIDUAL WEDGING.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... AS OF 430 AM EDT SUNDAY... FOCUS THROUGH THIS PERIOD WILL EVOLVE AROUND A PERSISTENT TROUGH ALONG THE SOUTHEAST U.S. COAST LEFT BEHIND FROM THE CURRENT UPPER TROUGH AS IT LIFTS OUT. WITH TIME...THIS SYSTEM ASSUMES A PSEUDO TROPICAL CHARACTERISTIC AND DRIFTS SLOWLY NORTHWESTWARD AS A MAMMOTH UPPER RIDGE BUILDS ACROSS THE WESTERN U.S. AND RIDGES EASTWARD TOWARD THE GREAT LAKES WHILE ANOTHER UPPER RIDGE AMPLIFIES IN THE WEST ATLANTIC. THIS WILL FORCE THIS FEATURE TO RETROGRADE FROM THE GA/SC COAST NORTHWESTWARD TOWARD THE SOUTHERN APPALACHIANS THROUGH THE PERIOD. FINALLY...THE LONG RANGE MODELS HAVE COME INTO REASONABLY GOOD AGREEMENT ON THE EVOLUTION AND TRACK OF THIS SYSTEM. AS THIS SYSTEM DRIFTS NORTHWEST TOWARD THE REGION DURING THE FIRST HALF OF THE WEEK...PWS WILL RISE TO NEAR 2.0 INCHES. THIS ALONG WITH INCREASING HEAT AND INSTABILITY SHOULD SUPPORT AN INCREASE IN DIURNAL CONVECTION. THE BEST CHANCES FOR SUCH SHOULD REMAIN FOCUSED ACROSS NW NC/FAR SW VA WHERE MOIST SOUTHEAST UPSLOPE FLOW WILL BE ENHANCED ALONG THE BLUE RIDGE. EXPECT SCATTERED DIURNAL CONVECTION AREA WIDE...WITH NUMEROUS AFTERNOON/EVENING SHRA/TSRA ACROSS NW NC AND FAR SW VA THROUGH THE PERIOD. CONSEQUENTLY...HAVE ADVERTISED HIGH CHC TO LOW LIKELY POPS IN THESE AREAS THROUGH THE PERIOD DURING THE AFTERNOON HOURS. FOR MUCH OF THE AREA THIS WILL RESULT IN INCREASING CHANCES OF BENEFICIAL RAIN...BUT SLOW MOVING/TRAINING THUNDERSTORMS...ESPECIALLY ACROSS THE MOUNTAINS TERRAIN OF NW NC/FAR SW VA COULD BECOME MORE PROBLEMATIC AS THE WEEK PROGRESSES. ALTHOUGH INSTABILITY WILL BE HIGH...DYNAMICS/SHEAR ARE WEAK. HOWEVER...AN ISOLATED PULSE SEVERE WITH STRONG WIND GUSTS COULD NOT BE COMPLETELY RULED OUT THROUGH THE PERIOD ANYWHERE IN THE CWA FOR THAT MATTER. 850MB TEMPS WILL BE ON THE INCREASE AS HEIGHTS ALOFT RISE AS WELL. HOWEVER...INCREASING DEWPOINTS/PWS AND PERSISTENT TROUGHINESS ACROSS THE REGION WILL TEMPER ANY EXCESSIVE HEAT AND SHOULD KEEP MOST AREAS IN THE 80S FOR HIGHS...70S IN THE MOUNTAINS...NEAR 90 ACROSS THE PIEDMONT. WEDNESDAY WILL BE THE WARMEST DAY IN ADVANCE OF THE FRONT/UPPER TROUGH APPROACHING FROM THE NORTHWEST. && .LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 445 PM EDT SATURDAY... UPPER RIDGE IS FORECAST TO REMAIN OVER THE WESTERN CONUS THROUGH THE LONG TERM...WITH A PERSISTENT UPPER TROUGH OVER THE EASTERN CONUS. A STRONG SHORT WAVE TRACKS FROM SOUTH CENTRAL CANADA ATOP THE UPPER RIDGE TOWARD THE GREAT LAKES. THIS DRIVES A FRONTAL SYSTEM INTO THE EASTERN U.S. AND OUR REGION BY THURSDAY. ECMWF/GFS ARE IN REASONABLE AGREEMENT ON THE PROGRESSION AND TIMING OF THESE FEATURES. THE FRONT SHOULD PUSH JUST SOUTH OF THE AREA BY FRI...ALTHOUGH AT THIS TIME OF YEAR THERE IS ALWAYS SOME UNCERTAINTY AS TO HOW FAR SOUTH THE FRONT WILL GO BEFORE STALLING. THE STRENGTH OF THE NORTHWEST FLOW ALOFT IN OUR REGION OWING TO THE STRONG UPPER RIDGE OUT WEST SHOULD SUPPORT THE FRONT PUSHING SOUTH OF THE CWA AT A MINIMUM. THE GREATEST CHANCE FOR SHOWERS/STORMS WILL BE THURSDAY AND THERE IS SOME CHANCE THAT THE LINGERING PSEUDO TROPICAL SYSTEM ACROSS THE CENTRAL/SOUTHERN APPALACHIANS AND ASSOCIATED MOISTURE COULD ENHANCE SHRA/TSRA CHANCES ALONG THE FRONT. FRIDAY STILL LOOKS LIKE A DRY DAY WITH THE FRONTAL BOUNDARY SOUTH OF THE CWA. MOISTURE COULD RETURN TO WESTERN AREAS BY SAT...BUT HAVE KEPT POPS LOW AT THIS POINT WITH TOO MUCH UNCERTAINTY ON ANY UPSTREAM NW FLOW DISTURBANCES. AFTER A VERY WARM DAY WED...THURSDAY WILL BE A TRANSITION DAY WITH THE FRONTAL PASSAGE...FOLLOWED BY A 4 TO 7 DEGREE DOWNWARD TREND IN TEMPERATURES FOR FRIDAY AND SATURDAY. USED A GFS/ECMWF MOS MODEL BLEND THROUGH THE PERIOD. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... AS OF 1235 PM EDT SUNDAY... WEDGE WILL CONTINUE TO KEEP LOWER MVFR CIGS LOCKED IN OVER THE WESTERN LOCATIONS THIS AFTERNOON WITH GRADUAL IMPROVEMENT TO VFR UNDER SOME BREAKS IN THE EAST. EXPECT MOST SHOWERS TO REMAIN CONFINED TO THE KBLF/KLWB AREAS THIS AFTERNOON WITH PERIODS OF MVFR POSSIBLE INCLUDING AN ISOLATED -TSRA AS WEAK INSTABILITY DEVELOPS AND A WEAK WAVE ALOFT CROSSES. OTRW OTHER THAN A VICINITY MENTION...KEEPING SHRA OUT OF THE TAFS THE REST OF THE AFTERNOON UNDER A LIGHT SE WIND. IMPULSE PASSES TO THE NORTH LATER TONIGHT WHICH SHOULD HELP TAPER OFF ANY SIGNIFICANT LEFTOVER SHRA OVER THE WEST OVERNIGHT. HOWEVER CONTINUED SE FLOW COMBINED WITH DEEP MOISTURE BETWEEN THE SFC-7H WILL CAUSE CIGS TO AGAIN LOWER...WITH WIDESPREAD MVFR EXPECTED ESPCLY AFTER MIDNIGHT. COULD ALSO SEE PERIODS OF IFR/LIFR AT KLWB AND ALONG THE BLUE RIDGE WHERE SOME PATCHY -DZ AND FOG POSSIBLE. ISOLATED SHRA MAY TEND TO LIMIT LOWER CLOUD FORMATION ACROSS THE SE AS WELL AS AROUND KBLF WHERE WILL SEE WEAK DOWNSLOPING. WAVE TO THE SOUTH WILL CAUSE THE FLOW TO TURN MORE EASTERLY ON MONDAY ALLOWING THE WEDGE TO ENHANCE A BIT MORE. THIS MAY KEEP AT LEAST MVFR CIGS AROUND ESPCLY BLUE RIDGE WEST INTO THE AFTERNOON BUT EXPECT MOST SHOWERS TO BE CONFINED TO SOUTHERN AREAS MAINLY KTNB-KUKF TO KDAN. MORE BREAKS ALONG WITH VFR EXPECTED A BIT SOONER ACROSS THE NORTH ALONG THE KLWB-KLYH CORRIDOR BY MONDAY AFTERNOON WITH A MIX OF MVFR/VFR AT KBCB/KROA TO KBLF LIKELY. EXTENDED AVIATION DISCUSSION... UPPER SYSTEM IN THE BASE OF THE FADING SE TROUGH WILL WEAKEN AND LIFT NORTH TUESDAY INTO WEDNESDAY IN ADVANCE OF AN APPROACHING COLD FRONT FOR THU. THIS WILL RESULT IN MORE WIDESPREAD DIURNAL CONVECTION EACH DAY WITH EARLY FOG IN SPOTS GIVING WAY TO BRIEF VFR...THEN PERIODIC MVFR IN CLOUDS/SHRA EACH AFTERNOON/EVENING. 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...EXPECT POSSIBLY KDAN. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...JH SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...JH/PC/RAB

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