Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 252355 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 755 PM EDT MON MAY 25 2015 .SYNOPSIS... HIGH PRESSURE WILL CONTINUE ITS POSITION OFF THE COAST OF THE SOUTHEAST UNITED STATES. AN UPPER LEVEL TROUGH AND ASSOCIATED SURFACE COLD FRONT WILL MAKE GRADUAL PROGRESSION TOWARD OUR REGION FROM THE CENTRAL PART OF THE COUNTRY. THIS SCENARIO WILL PROVIDE FOR WARM AND HUMID CONDITIONS...WITH INCREASING CHANCES OF SHOWERS AND STORMS THROUGH AT LEAST THURSDAY. && .NEAR TERM /THROUGH TUESDAY/...
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AS OF 645 PM EDT MONDAY... HAVE BACKED OFF ON THE ALREADY LOW PROBABILITY OF PRECIPITATION THROUGH 11PM IN THE FAR SOUTHWEST PART OF THE COUNTY WARNING AREA AND THROUGH 2AM FOR THE REST OF THE WESTERN COUNTY WARNING AREA. ALSO RAISED DEW POINTS OVERNIGHT BASED ON THE LATEST TRENDS IN THE OBSERVATIONS AND SHORT TERM GUIDANCE. TONIGHT INTO TUESDAY THE TREND ACROSS THE AREA WILL BE FOR INCREASING MOISTURE LEVELS IN ADVANCE OF AN APPROACHING UPPER TROUGH...AND ANTI-CYCLONIC ONSHORE FLOW AROUND A SURFACE HIGH PARKED TO OUR EAST. THE RESULT WILL BE INCREASING DEW POINT VALUES AND HIGHER HUMIDITY. THAT MOISTURE TONIGHT IS EXPECTED TO GENERATE LOW LEVEL CLOUD COVER UNDER THE BASE OF THE NOCTURNAL INVERSION...SO THAT JUST ABOUT ALL LOCATIONS WILL BE MOSTLY CLOUDY TO CLOUDY BY SUNRISE TUESDAY. WESTERN PARTS OF THE AREA WILL BECOME CLOUDY FIRST. THIS WILL ALSO BE THE AREA TO WATCH FOR THE DEVELOPMENT OF ISOLATED TO SCATTERED SHOWERS DURING THE OVERNIGHT HOURS. PRECIPITATION WILL START LATER AND CONTINUE INTO TUESDAY MORNING. OVERNIGHT LOW WILL BE MILDER THAN THOSE OF THIS MORNING THANKS TO THE HIGHER DEW POINT LEVELS. LOOK FOR THE UPPER 50S TO AROUND 60 ACROSS THE MOUNTAINS...WITH LOW TO MID 60S ACROSS THE PIEDMONT. TUESDAY WILL BE A DAY WITH MORE CLOUD COVER AND BETTER CHANCES OF PRECIPITATION THAN THAT OF TODAY. FIRST...THE EARLY MORNING LOW LEVEL CLOUD COVER WILL MIX OUT AS THE DAY PROGRESSES. HOWEVER...IT WILL ONLY THEN REDEVELOP AS ADDITIONAL CLOUD COVER AT THE LIFTING CONDENSATION LEVEL BY THE AFTERNOON. SHOWERS WILL START TO DEVELOP BY THE LATE MORNING...WITH ISOLATED THUNDERSTORMS A BETTER POTENTIAL DURING THE AFTERNOON. COVERAGE WILL BE GREATEST ACROSS THE MOUNTAINS. WHILE WARM AIR ADVECTION WILL CONTINUE ACROSS THE AREA...THE ADDITIONAL CLOUD COVER AND GREATER CHANCES OF PRECIPITATION WILL KEEP HIGH TEMPERATURES COMPARABLE TO LEVELS OF TODAY. AREAS IN THE WEST MAY BE A FEW DEGREES COOLER. HIGHS WILL RANGE FROM THE MID 70S TO AROUND 80 ACROSS THE MOUNTAINS WITH LOW TO MID 80S ACROSS THE PIEDMONT.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... AS OF 300 PM EDT MONDAY... AXIS OF A HIGHLY AMPLIFIED 591 DM UPPER H5 RIDGE WILL BE CENTERED JUST OFF THE EAST COAST AT THE START OF THIS FORECAST PERIOD. THE RIDGE WILL RESIST DISPLACEMENT EASTWARD AS SHORT-WAVES CONTINUE TO EMERGE FROM THE TROUGH OVER THE CENTRAL U.S. BUT EVENTUALLY THE RIDGE BECOMES SUPPRESSED FAR ENOUGH TO ALLOW FOR MORE MOISTURE AND ENERGY TO RIDE NORTHWARD ALONG ITS WESTERN PERIPHERY. THUS WILL BE INCREASING POPS WITH A DISTINCT DIURNAL EMPHASIS THROUGH MUCH OF THE PERIOD AS THE DEEP SW FLOW CONTINUES. PWATS WILL SLOWLY INCREASE THROUGH THE PERIOD INCREASING THE EFFICIENCY OF RAINFALL IN WHAT LOOK TO BE MOSTLY PULSE-TYPE THUNDERSTORMS. SPC OUTLOOK FOR WEDNESDAY SHOWS ONLY GENERAL THUNDER CHANCES ACROSS THE CWA AS THE SHEAR AND STRONGEST DYNAMICS REMAIN TO THE WEST. THURSDAY-FRIDAY APPEAR TO BE SIMILAR AS THE SURFACE AND UPPER RIDGE REMAIN INFLUENTIAL IN DIRECTING MOISTURE AROUND THEIR WESTERN PERIPHERY TOWARD THE SOUTHERN APPALACHIAN REGION BUT BEST SUPPORT FOR MORE ORGANIZED STORMS PERSISTS CLOSER THE MEAN TROUGH OVER THE CENTRAL AND WESTERN PLAINS. AGAIN PULSE-TYPE AFTERNOON CONVECTION WILL BE LIKELY OR AT LEAST AT HIGH CHANCE WITH DIMINISHING NOCTURNAL TREND. RAINFALL AMOUNTS LIKELY TO BE HIGHLY VARIABLE AS WOULD BE EXPECTED IN THIS CONVECTIVE ENVIRONMENT BUT NOTHING AT THIS POINTS SUGGESTS WIDESPREAD ENOUGH FOR ANY SIGNIFICANT FLOODING. MAINLY ADVISORY LEVEL DOWNPOURS ARE POSSIBLE IN SLOW-MOVING OR STATIONARY STORMS. TEMPS WILL REMAIN WELL ABOVE NORMAL AS THE SOUTHWEST FLOW AND CONSIDERABLE CLOUDINESS DO NOT ALLOW FOR ANY INCURSIONS OF CONTINENTAL POLAR AIR OR OVERNIGHT RADIATIONAL COOLING...BUT DAYS SHOULD NOT BE EXTREMELY HOT. NIGHTTIME HIGHS WILLS RUN ABOUT +10 DEGREES ABOVE LATE MAY CLIMO WHILE DAILY HIGHS CLOSER TO +5 ABOVE CLIMO. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 300 PM EDT MONDAY... IN EXTENDED PERIOD THE SYNOPTIC SETUP DOES NOT REALLY CHANGE TOO MUCH. THE RIDGE OUT OVER THE ATLANTIC CONTINUES TO DIRECT A STEADY SUPPLY OF WARMTH AND MOISTURE INTO THE EASTERN SEABOARD. AT THE SAME THERE WILL BE A CHANCE FOR SOMEWHAT MORE ORGANIZED ACTIVITY ASSOCIATED WITH A SLOW-MOVING BOUNDARY TRAILING FROM A SURFACE LOW TRACKING INTO THE GREAT LAKES ON SATURDAY. THE ECMWF SHOWS THIS FEATURE BECOMING QUASI-STATIONARY TO OUR NORTH OH-PA-NJ AXIS ON LATE SATURDAY INTO MONDAY AND THEN POSSIBLY SLIDING FARTHER SOUTH INTO OUR AREA BY LATER MONDAY. GFS PERHAPS A BIT FURTHER NORTH WITH THIS FEATURE AND MORE PROGRESSIVE AND EVENTUALLY BUILDS HIGH PRESSURE OVER THE NORTHEAST WHICH PUSHES A BACKDOOR TYPE FRONT TOWARD THE AREA LATE SUNDAY. GFS ENSEMBLES SOLUTION THROUGH THIS PERIOD MOSTLY MAINTAIN THE RIDGE OVER THE SOUTHEAST IN A POSITION THAT WOULD HOLD THE BOUNDARY AND ASSOCIATED PRECIPITATION FURTHER NORTH. HPC GUIDANCE CLOSER TO EURO SOLUTION AND WAS BASICALLY FOLLOWED FOR THE EXTENDED. THIS ALL MEANS CONTINUED WELL ABOVE NORMAL TEMPERATURES...ESPECIALLY AT NIGHT...ALONG WITH ABUNDANT MOISTURE AND HIGH CHANCES FOR AT LEAST AFTERNOON/EVENING CONVECTION. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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AS OF 745 PM EDT MONDAY... UPPER RIDGE THAT HAS BEEN BLOCKING THE REGION FROM THE WARMTH AND HUMIDITY TO THE WEST WILL CONTINUE TO SHIFT SLOWLY EAST THROUGH MID-WEEK. LIKEWISE...SFC HIGH WILL REMAIN OFF MID-ATLANTIC COAST IN A POSITION TO ALLOW WARM/MOIST GULF AIR TO BEGIN TO SPREAD INTO THE REGION FROM THE SOUTHWEST. THIS WILL BE REALIZED NOT THROUGH INCREASING TD/RH VALUES...BUT IN THE FORM OF LOW CLOUDS. FEEL THERE IS A GOOD CHANCE OF MVFR CIGS DEVELOPING ACROSS MUCH OF THE AREA...BUT ESPECIALLY ALONG/WEST OF THE BLUE RIDGE AFT 08Z TUE. THESE CLOUDS WILL GRADUALLY LIFT INTO LOW END VFR RANGE BY LATE MORNING/EARLY AFTERNOON. THE CLOUDS WILL LIKELY PREVENT MUCH IN THE WAY OF FOG DEVELOPMENT...BUT CANNOT TOTALLY IGNORE THE HIGHER DEWPOINTS AND THE POTENTIAL FOR MVFR BR AT ANY SPOTS THAT DECOUPLE LATE TONIGHT/EARLY TUE...E.G. LWB/BCB. THE FIRST OF SEVERAL DISTURBANCES EMANATING FROM A BROAD UPPER LOW ACROSS THE SOUTHWEST/CENTRAL U.S. WILL MOVE INTO THE REGION FROM THE SOUTHWEST OVERNIGHT/EARLY TUE. THIS DISTURBANCE CURRENTLY SUPPORTING SHRA/TSRA ACROSS EASTERN AL/NORTHERN GA/EASTERN TN. CONFIDENCE IS LOW GIVEN EARLY MORNING ARRIVAL TIME OF THIS FEATURE THAT IT WILL NET MUCH MORE THAN SOME -SHRA OR SPRINKLES. HOWEVER...BY AFTERNOON...DEPENDING ON HOW EARLY AND TO WHAT EXTENT THE MORNING LOW CLOUDS BREAK...WOULD EXPECT SHRA/TSRA TO DEVELOP IN A MORE EARNEST FASHION THAN WE HAVE SEEN IN A WEEK. COVERAGE WILL BE GREATEST WEST OF THE BLUE RIDGE...FURTHEST AWAY FROM THE UPPER-LEVEL RIDGE AND ASSOCIATED SUBSIDENCE. BRIEF PERIODS OF MVFR CIGS/MVFR VSBYS WILL BE POSSIBLE IN/NEAR THUNDERSTORMS...BUT OVERALL MOSTLY VFR CIGS/VSBYS EXPECTED AFT 14Z TUE. WINDS BACKING TOWARD THE SSE OVERNIGHT 5-7KTS...THEN VEERING TO SSW 8-12KTS WITH GUSTS 16-20KTS AFT 14Z TUE. MEDIUM CONFIDENCE IN CIGS THROUGH THE TAF VALID PERIOD. MEDIUM TO HIGH CONFIDENCE IN VSBYS THROUGH THE TAF VALID PERIOD. HIGH CONFIDENCE IN WIND SPD THROUGH THE TAF VALID PERIOD...MEDIUM TO HIGH CONFIDENCE IN WIND DIR THROUGH THE TAF VALID PERIOD. MEDIUM CONFIDENCE IN TSRA POTENTIAL TUE AFTERNOON. EXTENDED AVIATION DISCUSSION... WEDNESDAY...A SIGNIFICANT UPPER DISTURBANCE...NOW ACROSS OK/TX AND GENERATING WIDESPREAD SEVERE WEATHER AND FLOODING IN THAT REGION...WILL REACH OUR REGION. THIS ALONG WITH A WEAK BOUNDARY...EVIDENT IN SEVERAL OF THE MODELS...SHOULD ENHANCE SHRA/TSRA ACTIVITY ACROSS THE REGION...ESPECIALLY WED AFTERNOON. THIS BOUNDARY DRIFTS INTO EASTERN VA THU BEFORE WASHING OUT...SO ACTIVITY COULD BE SOMEWHAT MORE FOCUSED ALONG-EAST OF THE BLUE RIDGE THU. FOR THE REMAINDER OF THE PERIOD...A MOIST UNSTABLE AIR MASS REMAINS ACROSS THE REGION WITH WEAK TRIGGERING MECHANISMS AND DYNAMICS. A FRONTAL SYSTEM WILL APPROACH FROM THE NORTH BY THE WEEKEND...BUT WILL LIKELY REMAIN WELL NORTH OF THE CWA. THUS...NO CHANGE IN AIR MASS OR THE OVERALL SYNOPTIC PATTERN IS EXPECTED THROUGH THE PERIOD. EARLY MORNING LOW CLOUDS/FOG AND ASSOCIATED IFR-LIFR CIGS/VSBYS BECOME INCREASINGLY MORE LIKELY THROUGH THE PERIOD...ESPECIALLY FOLLOWING ANY LATE DAY RAINFALL. OTHERWISE...EXPECT MOSTLY VFR-MVFR CIGS OUTSIDE HEAVIER SHOWERS/THUNDERSTORMS. WINDS REMAINING SW 5-10KTS THROUGH MUCH OF THE PERIOD...EXCEPT VARIABLE AND GUSTY IN/NEAR THUNDERSTORMS.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...DS NEAR TERM...AMS/DS SHORT TERM...PC LONG TERM...PC AVIATION...DS/RAB

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