Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 270508 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 108 AM EDT SUN JUL 27 2014 .SYNOPSIS... A WEAK WARM FRONT LIFTS NORTHEAST ACROSS THE AREA TONIGHT IN ADVANCE OF A STRONG UPPER DISTURBANCE APPROACHING FROM THE WEST LATE. THUNDERSTORMS WILL DEVELOP WITH THIS FEATURE ALONG THE FRONTAL BOUNDARY ACROSS THE MIDWEST THIS EVENING AND SPREAD EAST TOWARD OUR AREA BY EARLY SUNDAY. A STRONG COLD FRONT SHOULD MOVE ACROSS THE REGION LATER SUNDAY NIGHT INTO MONDAY...WITH COOLER WEATHER INTO THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TODAY/... AS OF 100 AM EDT SUNDAY... RADAR INDICATES SHOWERS AND SOME THUNDERSTORMS FILLING IN ACROSS WEST VIRGINIA AS UPPER LEVEL ENERGY ENCOUNTERS THE LIFT PROVIDED BY THE APPALACHIAN CHAIN. SUFFICIENT INSTABILITY REMAINS TO KEEP THESE SHOWERS GOING AS THEY PASS ACROSS THE PIEDMONT NORTH OF HIGHWAY 460...BUT GREATER UNCERTAINTY REMAINS FURTHER SOUTH. THE DECAYING THUNDERSTORM COMPLEX PASSING ACROSS KENTUCKY MAY PROVIDE SOME GUSTY WINDS AS IT ENTERS OUR AREA BUT BELIEVE THE THREAT OF SEVERE WEATHER IS MINIMAL NOW. WOULD BE MORE CONCERNED WITH THE POTENTIAL OF LOCALLY HEAVY RAIN...AND WILL KEEP AN EYE ON RADAR AND AREA RAIN GAUGES...BUT BELIEVE THE RAINFALL WILL BE MORE BENEFICIAL THAN PROBLEMATIC DUE TO THE RECENT DRY SPELL. HAVE INCREASED RAIN CHANCES FOR THE MOUNTAINS OVERNIGHT IN THE LATEST FORECAST UPDATE. AS OF 210 PM EDT SATURDAY... BIGGEST UNCERTAINTY REMAINS IN THE SUNDAY-SUNDAY EVENING PERIOD IN REGARDS TO THE EVOLUTION OF THE INITIAL MCS AND LATER DEVELOPMENT OF PERHAPS ANOTHER SYSTEM JUST TO OUR SW BEFORE MORE CONVECTION ARRIVES WITH THE ACTUAL COLD FRONT SUNDAY EVENING. GUIDANCE SPREAD REMAINS QUITE LARGE WITH SOLUTIONS VARYING FROM PUNCHING A WEAKENING SYSTEM ACROSS NORTH OF HIGHWAY 460 SUNDAY MORNING PER GFS/NCEP WRF...TO KEEPING THE CORE TO THE NW SIMILAR TO THE NAM/CMC...TO RIDING THE FEATURE SOUTH DOWN THE WESTERN SLOPES LIKE THE ECMWF TO WHERE BETTER INSTABILITY WILL RESIDE. FOR NOW WILL LEAN MORE TOWARD THE GFS GIVEN FAST MOVEMENT/BACKING FLOW AND BRING ACTIVITY FARTHER EAST ACROSS THE NORTH SOONER ALONG THE RESIDUAL WARM FRONT...FOLLOWED BY A LULL CENTRAL/EASTERN SECTIONS IN THE AFTERNOON AS A STRONG MID LEVEL DRY PUNCH ON DEEP WESTERLY FLOW ARRIVES IN ITS WAKE. HOWEVER LIKELY TO SEE ANOTHER MCS TAKE SHAPE OVER THE FAR SW AND WESTERN SECTIONS INTO WEST VA ON THE TAIL OF THE RESIDUAL EARLIER OUTFLOW SO SOMETHING TO WATCH. DEGREE OF DEBRIS CLOUDS AND MIXING TO DETERMINE IF ADDED CLUSTERS OF STORMS REDEVELOP NORTH HALF DURING THE LULL SUNDAY AFTERNOON...AND PERHAPS FARTHER SOUTH INTO SOUTHSIDE VA/NW NC WHERE MAY GET MISSED BY MUCH OF THE ACTIVITY OUTSIDE THE MOUNTAINS INTO SUNDAY NIGHT. USED A BLEND OF HIGHS RANGING FROM THE COOLER MET MOS NW UNDER THE CLOUDS/PRECIP TO THE VERY WARM MAV VALUES SOUTH WHERE LIKELY MORE SUNSHINE AIDED COMPRESSIONAL WARMING LIKELY TO PUSH THE MID 90S. THUS WILL GO WITH A PERIOD OF CAT/LIKELY POPS INCLUDING GUSTY WINDS/HEAVY RAIN MENTION NW INTO EARLY AFTERNOON SUNDAY...AND ALONG THE WESTERN SLOPES INTO SW VA THROUGH LATE IN THE DAY. HOWEVER WILL HOLD OFF ON A FLOOD WATCH AT THIS POINT GIVEN QPF UNCERTAINTY AND DRY ANTECEDENT CONDITIONS. ELSW...GOING WITH MORE CHANCE NATURE POPS FOR NOW AND CAN BUMP UP LATER IF THINGS TREND FARTHER SOUTH THAN EXPECTED. ACTUAL COLD FRONT ALONG WITH BETTER DYNAMICS AND COLDER AIR ALOFT ARRIVE SUNDAY NIGHT WITH PERHAPS ANOTHER BAND OF CONVECTION ATTEMPTING TO CROSS THE WESTERN SLOPES. THUS KEPT LIKELY POPS SUNDAY EVENING FAR WEST AND CHANCE BLUE RIDGE BUT ONLY SLIGHT COVERAGE EAST PER CONTINUED DOWNSLOPE. WINDS WILL TURN GUSTY FROM THE NW LATE SUNDAY NIGHT AS THE 85H FRONT CROSSES AND THE JET MIXES DOWN UNDER THE INCREASING COOL ADVECTION. MAV/MET MOS SIMILAR AND FOLLOWED FOR LOWS WHICH WILL STILL BE QUITE MILD...MOSTLY 60S SUNDAY NIGHT UNDER MIXING. && .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... AS OF 200 PM EDT SATURDAY... SHORT TERM PERIOD WILL BE CHARACTERIZED BY UPPER TROFFING AND COLD ADVECTION AS SURFACE HIGH PRESSURE BUILDS SLOWLY SOUTHEAST FROM OUT OF THE UPPER MIDWEST. UPSLOPING CLOUDS ALONG THE WESTERN FLANKS OF THE APPALACHIANS WILL BE COMMON...ALONG WITH THE THREAT FOR DIURNALLY DRIVEN SHOWERS...AND POSSIBLY AN ISOLATED LATE AFTERNOON/EVENING THUNDERSHOWER DUE TO COOLER AIR ALOFT CLOSER TO TROF AXIS...AND INFLUENCE OF WEAK FORCING PROVIDED BY SERIES OF WEAK SHORT WAVE TROFS EMBEDDED IN UPPER FLOW TO IMPACT AREA BOTH MONDAY AND ON TUESDAY. TEMPERATURES IN THE MOUNTAINS WILL BE UNSEASONABLY COOL...WITH DAYTIME HIGHS NOT LIKELY TO CLIMB OUT OF THE 60S ON EITHER MONDAY OR TUESDAY ACROSS THE HIGHEST TERRAIN WHERE UPSLOPING CLOUDS WILL BE MAXIMIZED. EAST OF THE BLUE RIDGE...INFLUENCE OF COLD ADVECTION WILL BE OFFSET SOMEWHAT BY DOWNSLOPING/COMPRESSIONAL WARMING AND BETTER INSOLATION TO SUPPORT HIGHS REACHING INTO THE 80S...YET STILL A BIT LOWER THAN CLIMATOLOGICAL AVERAGES. NIGHTTIME LOWS WILL BE LARGELY GOVERNED BY EXTENT OF MIXING AND CLOUD COVER. HIGHER ELEVATIONS WHERE/IF CLOUDS CAN CLEAR...AND ESPECIALLY THE MOUNTAIN VALLEYS WHERE BOUNDARY LAYER DECOUPLING WILL MORE READILY OCCUR SHOULD EXPERIENCE READINGS DOWN INTO THE 40S...PERHAPS WELL DOWN INTO THE 40S...ESPECIALLY LATE TUESDAY NIGHT AS SURFACE RIDGE PRESSES CLOSER INTO THE AREA AND AS GRADIENT WINDS RELAX. READINGS EAST OF THE BLUE RIDGE WILL BE A BIT MILDER...MAINLY 50S...YET STILL 8-10F BELOW CLIMATOLOGICAL AVERAGES. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 1230 PM EDT SATURDAY... THE PERIOD STARTS OFF WITH A COLD FRONT WELL OFF THE ATLANTIC COAST. A 1020MB SURFACE HIGH OVER SE MO SHIFTS TO THE NE STATES THURSDAY AND FRIDAY. AT THE MID LEVELS...A RIDGE WILL PERSIST ACROSS THE WESTERN US...WHILE A TROUGH WILL PERSIST ACROSS THE EASTERN US. VERY LITTLE MOISTURE IS AVAILABLE FOR WEDNESDAY AND THURSDAY. THE ONLY PLACE THAT MAY BE ABLE TO SQUEAK OUT A SHOWER OR TWO IS ACROSS THE FAR SW...OTHERWISE MUCH OF THE REGION WILL REMAIN DRY. MOISTURE AND LOW LEVEL CONVERGENCE INCREASE FOR FRIDAY AND SATURDAY...THUS INCREASING THE THREAT FOR SHOWERS AND THUNDERSTORMS. GREATEST CHANCE POPS ARE ACROSS THE WEST WHERE THE CONVERGENCE IS MAXIMIZED. 850MB TEMPS OF +13-15C AND A PERSISTENT WEDGING EASTERLY WIND WILL ALLOW SURFACE HIGH TEMPS TO BE 5-10 DEGREES BELOW NORMAL. THURSDAY WILL BE THE COOLEST MORNING OF THE PERIOD WITH UPPER 40S POSSIBLE ACROSS SOME OF THE MOUNTAIN VALLEY LOCATIONS. LOW TEMPS WILL MODERATE FRIDAY THROUGH THE WEEKEND AS SURFACE DEWPTS INCREASE. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... AS OF 745 PM EDT SATURDAY... MANY UNCERTAINTIES REGARDING CONVECTIVE POTENTIAL FOR SUNDAY...BUT THROUGH 06Z...EXPECT VFR TO CONTINUE ALL SITES. EXTENSIVE HIGH CLOUD SHIELD SPREADING ACROSS THE REGION IN ADVANCE OF FIRST MCS MOVING ESE OUT OF OH/WV...MAINLY ACROSS NORTHERN WV. DO NOT EXPECT ANY SHRA OR TSRA WITH THIS FIRST SYSTEM AT ANY OF THE TAF SITES. MID-LEVELS REMAIN VERY DRY AND STABLE ACROSS THE REGION AT THIS TIME. SECOND COMPLEX OF TSRA ACROSS IN/IL LIKELY TO REACH WV TAF SITES IN THE 08Z-12Z TIME FRAME. WHILE THIS CONVECTION WILL BE DYING...EXPECT POTENTIAL GUSTY WINDS AND OCCASIONAL CG LIGHTNING ALONG WITH MVFR VSBYS IN -SHRA/-TSRA. HOWEVER...DO NOT EXPECT CIGS TO DROP BELOW LOW END MVFR AT THIS POINT WITH THIS ACTIVITY. REMNANT -SHRA AND OCCASIONAL -TSRA WILL LINGER WITH THE MORNING ACTIVITY AS IT TRANSLATES AND DISSIPATES ACROSS THE PIEDMONT. THIS ACTIVITY WILL ALSO LEAVE NUMEROUS OUTFLOW BOUNDARIES ACROSS THE REGION...ESPECIALLY EAST OF THE ALLEGHANY FRONT...AS THE NEXT AND STRONGER UPPER IMPULSE DIVES SOUTHEASTWARD FROM THE OH VALLEY. THIS SHOULD ALLOW CONVECTION TO REFIRE AROUND 18Z THROUGH THE EVENING/REMAINDER OF THE TAF VALID PERIOD. THERE ARE MANY UNCERTAINTIES PRESENTED BY THE MODELS AS TO THE LOCATION OF THIS ADDITIONAL CONVECTION...WITH MANY OF THE MODELS SHOWING ONLY LIMITED CONVECTION EAST OF THE BLUE RIDGE OR ACROSS THE PIEDMONT/SOUTHSIDE AREA. HAVE LEFT THUNDER OUT OF KDAN FOR NOW...BUT INCLUDED VCTS ELSEWHERE. MOST SIGNIFICANT AREAS OF CONVECTION MAY TRANSLATE ACROSS NORTHERN VA...NORTH OF I-64 AND SOUTHWARD THROUGH FAR SW VA/E TN...WEST OF I-77. OVERALL EXPECT MOSTLY VFR CIGS/VSBYS OUTSIDE CONVECTIVE ACTIVITY SUNDAY. WINDS SSW-SW 5-8KTS OVERNIGHT...POSSIBLY STRONGER BLF. AFT 13Z SUN...EXPECT SW-WSW WINDS 10-15KTS WITH GUSTS TO 25KTS WEST OF THE BLUE RIDGE. STRONGER/GUSTY WINDS POSSIBLE IN EARLY MORNING THUNDERSTORMS BLF/LWB AND AGAIN LOCALLY WITH AFTERNOON THUNDERSTORMS SUN. MEDIUM CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN WIND DIR/SPD THROUGH THE TAF VALID PERIOD. EXTENDED AVIATION DISCUSSION... THE SURFACE COLD FRONT WILL BE MOVING ACROSS BY SUNDAY NIGHT INTO MONDAY...SO THREAT OF SUB VFR THROUGH MONDAY EXPECTED ACROSS SE WEST VA PER NW FLOW...BUT LESS ELSEWHERE GIVEN DOWNSLOPE. SOME GUSTY NW WINDS BEHIND THE FRONT LIKELY ESPCLY ALONG THE RIDGES LATE SUNDAY NIGHT INTO MONDAY WITH DRIER AIR PUSHING IN FOR TUE- WED...AND MAINLY VFR. CANNOT RULE OUT LATE NIGHT FOG KBCB/KLWB BUT LOW LVLS MAY STAY DRY ENOUGH FOR LESS FOG COVERAGE. VARIABLE CIGS EXPECTED UNDER ANOMALOUS UPPER LOW THROUGHOUT THE WEEK. A FEW -SHRA NOT COMPLETELY OUT OF THE QUESTION ACROSS EASTERN WV...ALONG WITH OCCASIONAL MVFR CIGS. TYPICAL FOG POTENTIAL LESS THAN NORMAL FOR THIS TIME OF YEAR THROUGHOUT THE WEEK BECAUSE OF TURBULENT MIXING AND PREVAILING CYCLONIC FLOW. TOWARD THE END OF THE WEEK...AS THE UPPER LOW RETROGRADES JUST WEST OF THE REGION...INCREASING POTENTIAL FOR SHRA/TSRA...ESPECIALLY IN THE FRI-SUN TIME FRAME. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/WP NEAR TERM...NF/RCS SHORT TERM...WERT LONG TERM...CF AVIATION...JH/RAB

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