Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 301122 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 722 AM EDT SUN AUG 30 2015 .SYNOPSIS... A SERIES OF WEAK UPPER LEVEL DISTURBANCES WILL LIFT NORTH ALONG THE APPALACHIAN CHAIN THIS AFTERNOON INTO EARLY MONDAY...BRINGING A GREATER CHANCE FOR SHOWERS TO THE REGION. UPPER LEVEL HIGH PRESSURE WILL THEN STRENGTHEN AND KEEP US IN A RATHER STAGNANT PATTERN...MAINTAINING A CHANCE FOR AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS THROUGH THE MIDDLE OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 715 AM EDT SUNDAY... RADAR INDICATING LIGHT RETURNS ACROSS NORTH CAROLINA APPROACHING OUR AREA THIS MORNING. VERY LITTLE OF THIS IS REACHING THE GROUND...HOWEVER RAISED RAIN CHANCES SLIGHTLY DURING THE MORNING TO ACCOUNT FOR ANY INCREASES IN THE COVERAGE OF SHOWER ACTIVITY. OTHERWISE...THE EARLY MORNING FORECAST REMAINS ON TRACK. AS OF 345 AM EDT SUNDAY... STARTING THE MORNING OFF WITH A BROAD BUT WEAK UPPER LEVEL TROUGH SITUATED FROM THE GREAT LAKES SOUTHWARD ALONG THE MISSISSIPPI RIVER VALLEY...WHILE SUBTROPICAL RIDGING REMAINS PARKED OFF THE ATLANTIC COAST OF THE SOUTHEAST STATES. THIS PATTERN IS MAKING FOR SOUTHWESTERLY WINDFLOW ALOFT FOR THE MID ATLANTIC...WHICH WILL CARRY A SERIES OF WEAK DISTURBANCE NORTHWARD ALONG THE APPALACHIAN CHAIN. FOR TODAY...EXPECT THE MID AND HIGH CLOUDS CURRENTLY IN PLACE TO LINGER THROUGH THE DAY...ALTHOUGH BRIEF BREAKS WILL OCCUR AT TIMES. SOUTH SOUTHEASTERLY WINDS NEAR THE SURFACE WILL CONTINUE TO DRAW MOISTURE INTO THE MOUNTAINS...AND EXPECT WE WILL SEE SHOWERS DEVELOP DURING EARLY AFTERNOON ALONG THE RIDGES. THE MID AND HIGH CLOUDS WILL KEEP INSTABILITY QUITE LIMITED...SO DO NOT REALLY MORE THAN VERY ISOLATED AND BRIEF THUNDERSTORMS TO DEVELOP. AFTERNOON TEMPERATURES WILL RANGE FROM THE MID 70S TO AROUND 80 ACROSS THE MOUNTAINS...AND REACH INTO THE LOW/MID 80S ACROSS THE PIEDMONT. SLIGHTLY BETTER CHANCES FOR SHOWER ACTIVITY ARE EXPECTED HEADING INTO LATE SUNDAY EVENING AS A STRONGER UPPER LEVEL DISTURBANCE APPROACHES FROM THE SOUTH. EVEN THEN...WEATHER FORECAST MODELS ARE CALLING FOR THE BRUNT OF RAINFALL TO MISS OUR AREA TO THE SOUTHEAST...AND BELIEVE THE PASSAGE OF THIS SYSTEM WILL AMOUNT TO SPOTTY SHOWERS FOR THE MOUNTAINS...AND PERHAPS THE PIEDMONT SOUTH OF HIGHWAY 460. SUNDAY NIGHT LOWS WILL RANGE FROM THE UPPER 50S AND LOW 60S WEST...TO THE MID 60S EAST.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... AS OF 400 AM EDT SUNDAY... A WEAK UPPER LOW AND ASSOCIATED TROPICAL MOISTURE ASSOCIATED WITH FORMER TROPICAL SYSTEMS DANNY AND ERIKA...WILL BE LIFTING NORTHEAST ACROSS THE REGION MONDAY ON THE WESTERN PERIPHERY OF A BUILDING SUBTROPICAL RIDGE ACROSS THE WESTERN ATLANTIC. MODEST LOW-LEVEL MOISTURE INCREASE IS INDICATED WITH PRECIPITABLE WATER VALUES CREEPING INTO THE 1.5/1.6 RANGE ACROSS MUCH OF THE CWA. AT THE SAME TIME...HOWEVER...THE UPPER TROUGH IS WEAKENING AND SHEARING OUT. ON THE OTHER END OF THE CWA A DIFFUSE AND STALLING FRONT BOUNDARY WILL BE LOCATED JUST TO OUR NORTH WITH THE ASSOCIATED UPPER AIR SUPPORT HAVING LIFTED WELL NORTHEAST OF THIS REGION. DESPITE THESE WEAK SYSTEMS...THE UNDERLYING THEME WILL BE A BROAD SUBTROPICAL RIDGE BUILDING ACROSS MUCH OF THE EASTERN 2/3RDS OF THE U.S. SUFFICIENT MOISTURE...INSTABILITY...AND DYNAMICS...GIVEN THE FRONT TO THE NORTH AND UPPER TROUGH LIFTING ACROSS THE REGION... SHOULD BE PRESENT MONDAY TO SUPPORT ISOLATED TO SCATTERED DIURNAL CONVECTION...WITH A FEW SPRINKLES OR LIGHT SHOWERS EVEN POSSIBLE DURING THE MORNING...TYPICAL FOR A POCKET OF REMNANT TROPICAL MOISTURE DRIFTING ACROSS THE REGION. AM NOT CONCERNED ABOUT A HEAVY RAIN THREAT GIVEN THE LACK OF ANY FOCUSING MECHANISM AND NOTING THAT THE PLUME OF DEEP TROPICAL MOISTURE REMAINS GENERALLY OFF THE EAST COAST. MODEL QPF IS VERY LACKLUSTER...GENERALLY 1/4 INCH AMOUNTS AT BEST. THIS AGREES WELL WITH WPC. FOR TUE-WED...THE MAIN STORY WILL BE THE BUILDING UPPER RIDGE. ANY VESTIGE OF THE TROPICAL SYSTEMS...FRONTAL BOUNDARY...AND UPPER TROUGH IS COMPLETELY GONE IN THIS TIME FRAME WITH 588DM OR GREATER HEIGHTS ENCOMPASSING MOST OF THE U.S. SOUTH OF THE CANADIAN BORDER...WEST TO THE ROCKIES. A VERY WEAK UPPER LOW TROUGH WILL LINGER ACROSS THE WESTERN TN VALLEY INTO THE SOUTHERN PLAINS. LINGERING TRAPPED TROPICAL MOISTURE AND DIFFERENTIAL HEATING ACROSS THE MOUNTAINS WILL LIKELY BE SUFFICIENT EACH AFTERNOON TO TRIGGER ISOLATED CONVECTION...BUT LITTLE TO SUPPORT MORE THAN 30 POPS AT THIS TIME. BY WED AFTERNOON...THE GFS AND ECMWF BOTH DEPICT A POTENTIAL BACKDOOR FRONT SLIPPING INTO THE REGION FROM THE NORTHEAST...WITH A SLIGHT INCREASE IN CONVECTION POSSIBLE ACROSS THE NORTHERN AREAS AS A RESULT. TEMPERATURES WILL BE ON THE INCREASE THROUGH THE PERIOD AS 850MB TEMPS RISE FROM THE CURRENT LEVELS AROUND +14C TO +16C TOWARD +20C DURING THE PERIOD. THIS WILL SUPPORT HIGHER MAX TEMPS...WITH SOME AREAS ACROSS THE PIEDMONT APPROACHING 90 DEGREES...WITH 75 TO 80 MOUNTAINS AND 80S ELSEWHERE. MIN TEMPS WILL ALSO BE ON THE INCREASE WITH HIGHER DEWPOINTS/RH/PWATS IN PLACE THROUGH THE PERIOD. OVERALL MIN TEMPS WILL AVERAGE 10 DEGREES ABOVE NORMAL THROUGH THE PERIOD WITH MAX TEMPS ABOUT 5 DEGREES ABOVE AVERAGE. && .LONG TERM /THURSDAY THROUGH SATURDAY/... AS OF 415 AM EDT SUNDAY... THE EXTENDED PERIODS CONTINUE TO BE LARGELY DOMINATED BY A BROAD LATE SUMMER UPPER RIDGE ACROSS THE EASTERN HALF OF THE U.S. INCREASING TROUGHING ALONG THE WEST COAST WILL ALLOW THE UPPER RIDGE TO PUSH FURTHER EAST...QUICKLY ERASING ANY MIDWEEK EFFECTS OF A BACKDOOR FRONT AND WEAK SHORTWAVE TRAVERSING THE NORTHEASTERN PERIPHERY OF THE UPPER RIDGE. TROPICAL MOISTURE WILL LINGER ACROSS THE REGION WITH NO CHANGE IN AIR MASS EXPECTED. ON THE OTHER HAND...THERE IS SIMPLY NO SYNOPTIC/DYNAMIC TRIGGERING MECHANISM. THIS LEAVES CONVECTION TO BE DRIVEN ENTIRELY BY DIFFERENTIAL DIURNAL HEATING THROUGH THE END OF THE WORK WEEK. TEMPERATURES ARE EXPECTED TO CONTINUE ABOVE NORMAL THROUGH THE PERIOD WITH HIGHS 75 TO 80 MOUNTAINS AND 80S ELSEWHERE...NEAR 90 ACROSS THE PIEDMONT. MIN TEMPS WILL BE MORE SIGNIFICANTLY ABOVE NORMAL WITH MAINLY 60S TO NEAR 70 PIEDMONT. THESE READINGS ARE 5 TO 10 DEGREES ABOVE NORMAL. LOOKING AHEAD...SOME MODELS ARE ADVERTISING PERHAPS THE FIRST FALL COLD FRONT INTO THE FOLLOWING WEEK...BUT ENTIRELY TOO FAR OUT TO PUT ANY CREDIBILITY IN AT THIS POINT. && .AVIATION /11Z SUNDAY THROUGH THURSDAY/... AS OF 200 AM EDT SUNDAY... FOR THE OVERNIGHT...MAINLY MID/HIGH CLOUDS WILL CONTINUE MOVING IN FROM THE SOUTH. LOW LEVELS REMAIN DRY ENOUGH HOWEVER FOR SUFFICIENT RADIATIONAL COOLING TO ALLOW FOR SOME LIGHT FOG/MIST ACROSS THE AREA...DROPPING VISIBILITIES TO 4SM IN SPOTS. MAY ALSO SEE RIVER VALLEY FOG DEVELOP ACROSS THE MOUNTAINS...WHICH MAY LOWER VISIBILITIES IN THE IMMEDIATE AREA TO LESS THAN 1SM. ANY FOG DEVELOPING OVERNIGHT WILL DISSIPATE QUICKLY AFTER 30/14Z SUNDAY WITH INCREASED DAYTIME HEATING...RESULTING IN VFR CONDITIONS THROUGH THE DAY. WITH AN UPPER LEVEL DISTURBANCE APPROACHING...SHOWER COVERAGE WILL BE INCREASED SUNDAY AFTERNOON... BUT STILL EXPECT ONLY A SCATTERED THREAT. AS SUCH...BELIEVE ANY REDUCTIONS IN VISIBILITIES WILL BE LIMITED TO THOSE IN RAINFALL... WHICH SHOULD BE BRIEF. WITH SHORT WAVE ENERGY LIFTING NORTHWARD FROM THE GULF COAST REGION...WILL SEE MORE WIDESPREAD CONVECTION SUNDAY NIGHT INTO MONDAY MORNING. EXTENDED AVIATION DISCUSSION... GENERALLY EXPECT THE BEST CHANCES FOR MVFR/IFR TO BE LATE NIGHT/EARLY MORNING DUE TO FOG AND STRATUS DEVELOPMENT FROM THE BLUE RIDGE WEST ESPECIALLY AT KLWB/KBCB. WILL THEN REMAIN IN A WEAKLY FORCED SYNOPTIC ENVIRONMENT THROUGH MIDWEEK WITH CHANCES FOR DIURNAL CONVECTION MAINLY FROM THE BLUE RIDGE WEST...AND SOME MVFR/IFR FOG/STRATUS DEVELOPMENT AT NIGHT ESPECIALLY AT KBCB AND KLWB. && .EQUIPMENT... AS OF 400 PM EDT SATURDAY... THE DEW POINT READING AT KJFZ...RICHLANDS VA AWOS...IS INCORRECT. AT THIS TIME WE DO NOT KNOW WHEN THIS SENSOR WILL BE REPAIRED. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...NF SHORT TERM...RAB LONG TERM...AMS/RAB AVIATION...NF/WP EQUIPMENT...

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