Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201144 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 744 AM EDT SUN JUL 20 2014 .SYNOPSIS... WEAK SURFACE FEATURES AND A SLOW-MOVING UPPER LEVEL TROUGH OVER THE EASTERN U.S. WILL ALLOW A CHANCE FOR SHOWERS TODAY AND INTO THE EARLY PART OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 330 AM EDT SUNDAY... UPPER LEVEL TROUGH OVER THE EASTERN U.S. WILL REMAIN IN PLACE TODAY AND TONIGHT WITH WEAK RIDGING FROM NEW ENGLAND CONTINUING TO MAINTAIN A WEAK EASTERLY LOW-LEVEL WIND COMPONENT INTO THE MID- ATLANTIC AND CENTRAL APPALACHIANS PRODUCING SUBTLE COOL-AIR DAMMING. WITH VERY LITTLE FORCING EXPECTED AT THE SURFACE AND ALOFT THERE SEEMS TO BE LITTLE OBVIOUS TRIGGER FOR SHOWER ACTIVITY BUT THE AIR MASS THE OVERHEAD WILL REMAIN QUITE MOIST WITH PWATS HOLDING NEAR 1.5 INCHES ACROSS MOST OF THE CWA...00Z/20 RAOB FROM KRNK HAD 1.48 INCHES WHICH IS ABOUT THE 75TH PERCENTILE FOR DATE IN JULY...ALSO RIGHT AT THE CLIMATOLOGICAL MAXIMA FOR THE YEAR. THAT SAID THE QUESTION REMAINS WHETHER WE CAN DEVELOP ANY CONVECTION AT ALL TODAY AND THAT MAY DEPEND ON SOME BREAKS IN THE PERSISTENT OVERCAST. BEST CHANCES FOR ANY SHOWERS OR EVEN A THUNDERSTORM TO DEVELOP WILL BE IN FAR WEST WHICH WILL BE LESS UNDER THE INFLUENCE OF THE WEDGE. MODEL CAPES FROM ARW_RNK REACH 1000 J/KG BY LATE AFTERNOON AT BLUEFIELD SO PUT ISOLATED THUNDER CHANCES IN THE WEST ALONG WITH CHANCE POPS GENERALLY FROM BLUE RIDGE WESTWARD AND ONLY SLIGHT CHANCE EAST. BEST SYNOPTIC FORCING FOR PRECIPITATION WILL BE WELL SOUTH OF OUR CWA IN ASSOCIATION WITH SHORT-WAVE AND WEAK LOW DOWN ALONG THE GULF COAST. SOME OF THIS ACTIVITY MAY REACH OUR SOUTHERN COUNTIES BUT AMOUNTS SHOULD BE QUITE MODEST...GENERALLY UNDER 0.25 INCHES ON A MEAN AREAL BASIS. TEMPS TRICKY AS WELL TODAY WITH CLOUDS/JULY SUN GAME IN FULL SWING. USED MODEL BLEND BUT A FEW HOURS OF EXTRA HEATING COULD PLAY HAVOC WITH CURRENT MID-70S WEST TO LOW 80S EAST FORECAST. && .SHORT TERM /MONDAY 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 /12Z SUNDAY THROUGH THURSDAY/... AS OF 735 AM EDT SUNDAY... GENERALLY POOR AVIATION CONDITIONS EXPECTED TO CONTINUE WEST OF THE BLUE RIDGE...WITH MARGINAL AVIATION CONDITIONS EAST OF THE BLUE RIDGE. UPPER TROUGH WILL LINGER ACROSS THE EASTERN U.S. THROUGH THE PERIOD. A PSUEDO TROPICAL UPPER DISTURBANCE WILL DEVELOP ALONG THE GA/SC COAST TODAY INTO MONDAY...THEN RETROGRADE NW BETWEEN EXPANDING WESTERN ATLANTIC UPPER RIDGE AND WESTERN CONUS UPPER RIDGE. SYSTEM WILL REMAIN TRAPPED ACROSS THE SOUTHERN-CENTRAL APPALACHIANS THROUGH MID-WEEK. LATEST MODEL RUNS SUPPORT -SHRA SKIRTING KDAN THROUGH MID-MORNING WITH LOW END VFR OR HIGH END MVFR CIGS...LIKELY VFR VSBYS. BY AFTERNOON...EXPECT SHRA AND EVEN A FEW TSRA TO DEVELOP ACROSS THE ALLEGHANYS...INCLUDING LWB/BLF/BCB...SPREADING EAST TOWARD ROA AROUND SUNSET. FOR NOW...HAVE CONFINED MENTION OF TSRA TO BLF WHERE BEST INSTABILITY WILL EXIST. OVERNIGHT...THIS ACTIVITY SHOULD GRADUALLY DISSIPATE...BUT EXPECT LOWERING CIGS/VSBYS MOST AREAS AFT 06Z IN STRATUS/FOG TO MVFR...WITH POTENTIAL FOR IFR BCB/BLF/LWB AFT 08Z. DEEPER MOISTURE SPREADING NORTH AND WEAK SE FLOW SHOULD PROMOTE DRIZZLE THROUGH THE NEW RIVER...GREENBRIER...AND POTENTIALLY EVEN THE ROANOKE VALLEYS LATE TONIGHT/EARLY MON. WINDS THROUGH THE PERIOD REMAINING LIGHT SE 5KTS OR LESS. MEDIUM CONFIDENCE IN CIGS AND VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN TSRA POTENTIAL THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND SPD/DIR THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... THE AFOREMENTIONED UPPER DISTURBANCE WILL TRACK TOWARD NW NC MON AND STALL/SHEAR OUT ACROSS THE SOUTHERN-CENTRAL APPALACHIANS TUE-WED IN ADVANCE OF AN APPROACHING COLD FRONT FOR THU. EXPECT SCT-NMRS DIURNAL CONVECTION EACH DAY...WITH THE BEST CHANCE/COVERAGE THROUGH THE ALLEGHANYS AND WEST OF THE BLUE RIDGE. FRONTAL SYSTEM THU WILL BRING MORE WIDESPREAD SHRA/TSRA TO ALL AREAS. PERIODS OF MVFR WITH LOCALIZED IFR CIGS CAN BE EXPECTED THROUGH THU. THE HIGH MOISTURE CONTENT IN THE ATMOSPHERE AND DAILY -SHRA WILL PROMOTE DEVELOPMENT OF LATE NIGHT/EARLY MORNING FOG...ESPECIALLY IN THE USUAL SUCH PRONE LOCATIONS...NAMELY LWB/BCB/LYH. IMPROVED AVIATION CONDITIONS ARE EXPECTED FRIDAY BEHIND THE FRONT WITH CLEARING SKIES AND LITTLE TO NO PRECIPITATION...EXPECT POSSIBLY KDAN. && .CLIMATE... THE PERSISTENT LOW CLOUD COVER...DRIZZLE AND EASTERLY FLOW COMBINED TO PRODUCE THREE NEW RECORD LOW MAXIMA FOR THE DATE YESTERDAY JULY 19 2014. BLACKSBURG...LEWISBURG AND BLUEFIELD ALL SET NEW DATE RECORDS...BY 6 DEGREES F IN THE CASE OF BLACKSBURG. SEE WBCRERRNK FOR DETAILS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PC NEAR TERM...PC SHORT TERM...RAB LONG TERM...PM/RAB AVIATION...PC/RAB CLIMATE...PC

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