Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 191000 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 600 AM EDT TUE AUG 19 2014 .SYNOPSIS...
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SPOTTY SHOWERS AND THUNDERSTORMS CAN BE EXPECTED THIS AFTERNOON AND EVENING AS AN UPPER LEVEL DISTURBANCE APPROACHES FROM THE NORTHWEST. NORTHWESTERLY FLOW ALOFT WILL ALLOW A SERIES OF UPPER LEVEL DISTURBANCES TO PUSH ACROSS THE REGION THROUGH THE WEEK. A STRONG DISTURBANCE IS EXPECTED TO PASS ACROSS THE AREA THURSDAY NIGHT...POTENTIALLY BRINGING SEVERE WEATHER AND HEAVY RAIN.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 415 AM EDT TUESDAY... WARM MUGGY CONDITIONS PERSIST THIS MORNING AS A FRONTAL BOUNDARY IS STALLED FROM CHARLOTTE COUNTY NORTHWEST NEAR ROANOKE AND LEWISBURG. HAVE BEEN KEEPING AN EYE ON A BAND OF SHOWERS TRAINING ALONG THE FRONT ACROSS SOUTHEAST WEST VIRGINIA...HOWEVER RAINFALL RATES ARE NOT HEAVY ENOUGH FOR THESE SHOWERS TO CAUSE MUCH TROUBLE. ELSEWHERE...MAINLY A MIXTURE OF LOW CLOUDS AND LOCALLY DENSE FOG WHICH IS REDUCING VISIBILITIES ANYWHERE FROM 3 MILES TO A FEW HUNDRED FEET WHERE IT IS OCCURRING. AFTER SUNRISE...LACK OF DENSE UPPER LEVEL CLOUD COVER WILL ALLOW FOR STRONGER HEATING TODAY...CAUSING FOG TO BURN OFF QUICKLY AFTER 9 AM. WILL ALSO SEE CLOUDS GRADUALLY LIFT THROUGH THE REMAINDER OF THE MORNING...WITH POSSIBLY A FEW RAYS OF SUNSHINE BREAKING THROUGH THE OTHERWISE MOSTLY CLOUDY SKIES. SPOTTY SHOWERS AND A FEW THUNDERSTORMS WILL DEVELOP WITH DAYTIME HEATING BY EARLY AFTERNOON...WITH THIS ACTIVITY BECOMING MORE WIDESPREAD DURING THE EVENING AS ANOTHER UPPER LEVEL DISTURBANCE APPROACHES FROM THE NORTHWEST. THE THREAT FOR SEVERE THUNDERSTORMS AGAIN APPEARS MINIMAL...ALTHOUGH ONE OR TWO STRONG STORMS WILL BE POSSIBLE. OF GREATER CONCERN WILL BE THE POSSIBILITY OF LOCALLY HEAVY RAIN THIS AFTERNOON AND EVENING DUE TO THE ABUNDANCE OF TROPICAL MOISTURE AND THE SLOW MOVING FRONTAL BOUNDARY TO HELP FOCUS THE CONVECTION. SHOWERS AND THUNDERSTORM WILL DIMINISH IN COVERAGE TUESDAY EVENING WITH SUNSET AND LOSS OF HEATING. WE CAN THEN EXPECT A REPEAT OF WARM AND MUGGY CONDITIONS...WITH SCATTERED LOW CLOUDS AND PATCHY DENSE FOG. STUCK CLOSER TO MAV GUIDANCE FOR TEMPERATURES TODAY...WHICH IS PRETTY CLOSE TO SEASONAL NORMALS. BREAKS IN THE CLOUD COVER AND A LATER START TO SHOWER AND THUNDERSTORM ACTIVITY WILL HELP AFTERNOON TEMPERATURES CLIMB INTO THE UPPER 70S AND LOW 80S ACROSS THE MOUNTAINS...WHILE THE SOUTHSIDE AND NORTH CAROLINA PIEDMONT CAN EXPECT TO REACH INTO THE MID 80S. OVERNIGHT LOWS WILL AGAIN RANGE FROM THE MID 60 TO THE LOW 70S.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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AS OF 500 AM EDT TUESDAY... WAVY FRONTAL BOUNDARY WILL STRETCH FROM THE CENTRAL/SOUTHERN PLAINS TO THE MID ATLANTIC COAST. SCATTERED SHOWERS/THUNDERSTORMS WILL BE FOUND ALONG THIS BOUNDARY WITH POTENTIAL FOR ORGANIZED MESOSCALE CONVECTIVE SYSTEMS IN ADDITION TO THE DIURNALLY DRIVEN ACTIVITY. CURRENTLY ENTERTAINING CHANCE POPS THROUGH THE WEEK. WITH THE FRONTAL BOUNDARY STALLED OVER THE AREA...CAN EASILY EXPERIENCE A SHOWER AT MOST ANYTIME DAY OR NIGHT. THERE ARE A COUPLE OF TIME FRAMES HOWEVER WHERE MODEL CONSENSUS SUGGESTS A HIGHER PROBABILITY OF SHOWERS PER POTENTIAL FOR ORGANIZATION...DETAILS AS FOLLOWS... LOOKING AT WEDNESDAY SPECIFICALLY...AN UPPER LOW OVER THE GREAT LAKES WILL BE MOVING INTO NEW ENGLAND. VORT AXIS OR VORT TAIL ASSOCIATED WITH THIS TROF IS PROGGED TO PASS OVERHEAD MID-DAY WEDNESDAY. THE BETTER LIFT ASSOCIATED WITH THIS FEATURE IS EXPECTED TO PASS WELL NORTH OF OUR FCST AREA INTO PA/NY. NEVER THE LESS...THERE WILL BE AN ENHANCED AREA OF LIFT TRAILING SOUTH INTO THE MID ATLANTIC THAT SHOULD ENHANCE THE DEVELOPMENT OF SHOWERS. SHOWERS/STORMS THAT DEVELOP WITH THIS FEATURE SHOULD BE TRANSIENT AND PASS QUICKLY EAST OF THE AREA WEDNESDAY EVENING. BY THURSDAY...THE WEATHER PATTERN BEGINS TO AMPLIFY JUST A BIT WITH A 595 DM HIGH BECOMING ESTABLISHED OVER THE GULF COAST STATES...THE RIDGE AXIS BUILDING NORTH THROUGH THE MISSISSIPPI VALLEY AND INTO THE UPPER MID WEST. THIS WILL TIGHTEN THE PRESSURE GRADIENT OVER THE OHIO VALLEY AND STRENGTHEN THE ADVECTION OF VERY WARM MOIST AIR INTO THE OHIO VALLEY AND MID ATLANTIC REGION...A POOLING OF THIS AIRMASS TAKING PLACE OVER THE STATIONARY SURFACE FRONT THAT BISECTS THE REGION FROM THE MID ATLANTIC INTO THE UPPER MIDWEST. THIS SET- UP...PATTERN RECOGNITION...SUGGESTS ENVIRONMENT THAT WILL BE FAVORABLE FOR ROBUST THUNDERSTORM DEVELOPMENT WITH CAPES EXCEEDING 2500 J/KG. ATTM MODELS SUGGEST STORMS WILL DEVELOP VCNTY OF THE FRONT OVER THE MIDWEST AND LOWER GREAT LAKES THURSDAY...THEN BECOME ORGANIZED INTO AN MCS...MESOSCALE CONVECTIVE SYSTEM...THIS FEATURE MOVING SOUTHEAST ACROSS THE OHIO VALLEY THURSDAY AFTERNOON AND INTO THE MID ATLANTIC THURSDAY EVENING...FOLLOWING THE FRONTAL BOUNDARY. CONFIDENCE IS BEGINNING TO INCREASE THAT WE WILL BE DEALING WITH SEVERE STORMS LATE THURSDAY AND HAVE ADDED THIS TO THE HAZARDOUS WEATHER OUTLOOK. IN ADDITION...THE PATTERN THAT IS EMERGING WITH THE BUILDING RIDGE AXIS JUST TO OUR WEST ALSO SUGGEST THERE MAY BE THE POTENTIAL FOR EXCESSIVE RAINFALL. POSITION OF THE UPPER RIDGE AXIS...WHICH WILL BE JUST TO OUR WEST...WILL HELP ORIENT THE LOW LEVEL WINDS...LOW LEVEL 850 MB JET AXIS...UP THROUGH THE TN AND INTO THE LOWER OHIO VALLEY...BISECTING THE FRONT SOMEWHERE NEAR THE I-64 CORRIDOR ACROSS WV. IT IS THIS REGION WHERE STORMS MAY HAVE A TENDENCY TO BACKBUILD AS THE MCS CROSSES THE FORECAST AREA. THAT BEING SAID...HAVE ALSO HIGHLIGHTED POTENTIAL FOR EXCESSIVE RAINFALL IN THE HAZARDOUS WEATHER OUTLOOK FOR THURSDAY NIGHT. TEMPERATURES DURING THIS INTERIM FORECAST PERIOD ARE EXPECTED TO BE NEAR NORMAL WEDNESDAY...TIPPING THE SCALE TO THE SLIGHTLY ABOVE NORMAL SIDE FOR THURSDAY. PENDING CLOUD COVER...THURSDAY LOOKS LIKE IT WILL BE THE WARMEST DAY WITH 85H TEMPS TESTING +20 DEG C...THE EMERGING UPPER RIDGE TO OUR WEST FORCING SOME VERY WARM AIR OVER THE MOUNTAINS THURSDAY AFTERNOON.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 100 PM EDT MONDAY... TREND OF BUILDING UPPER RIDGE INTO GREAT LAKES REGION SPREADING INTO OHIO VALLEY WITH DEEPENING AMPLITUDE TROUGH OVER NEW ENGLAND AND ALONG MID ATLANTIC COAST IS STILL ADVERTISED BY EXTENDED MODELS...AND TREND LAST 24 HRS HAS BEEN A BIT DEEPER AMPLITUDE AND POSSIBLY A BIT OF RETROGRESSION OF THE TROUGH BY LATE IN WEEKEND. AT LEAST A GOOD BET THAT FLOW WILL BECOME BLOCKED AND CONFIDENCE A LITTLE HIGHER THAT MUCH OF BLACKSBURG CWA WILL BE INFLUENCED BY BACK DOOR PUSH OF FRONTAL BOUNDARY OFF TO THE SOUTH BY AS EARLY AS FRI OR AT LEAST BY SAT AND THUS WEDGE OF COOLER AIR FOR MUCH OF WEEKEND AND POSSIBLY INTO MONDAY. SO WHILE STRONG RIDGE AND MORE TYPICAL AUGUST LIKE TEMPERATURES WILL BE ON OUR DOOR STEP AND AT TIMES THIS WARMER AIRMASS MAY INFLUENCE PARTS OF THE SOUTHWEST FCST AREA...LOOKS LIKE MOST LOCATIONS WILL BE BACK IN THE WELL BELOW NORMAL REGIME AGAIN. NEVERTHELESS TEMP FCST STILL TRICKY SINCE BACK DOOR FRONT COULD TAKE DEEPER MOISTURE SOUTH AND THUS DRY THINGS OUT ENOUGH TO GET MORE SUN THAN OTHERWISE MIGHT. FCST TEMPS IN GENERAL CLOSER TO ECMWF GUIDANCE...BUT LATEST 12Z MEX/GFS GUIDANCE SHOWING THE LOWERING TREND COMPARED TO PREVIOUS 00Z GUIDANCE. THE PRECIP FCST ALSO REMAINS CHALLENGING THROUGH THIS PERIOD...ALL DEPENDENT ON HOW FAR SOUTH BOUNDARY PUSHES AND TIMING OF UPSTREAM SHORT WAVE ENERGY FROM NORTHWEST. CHANCES ARE HIGHER FRIDAY INTO SATURDAY WITH BOUNDARY CLOSER TO SW PART OF FCST AREA AND WILL CONTINUE CARRYING A MID CHANCE POP FOR MTNS...LINGERING INTO OVERNIGHT GIVEN THIS BOUNDARY AND UNKNOWN TIMING OF DISTURBANCES COMING FROM NW. BUT WILL THEN INDICATE SOMEWHAT LOWERING CHANCES SUNDAY AND ESPECIALLY BY MONDAY AS BOUNDARY LIKELY TO PUSH WELL SOUTH...BUT KEEPING A SLIGHT CHANCE SINCE BY THIS TIME RIDGING COULD ACTUALLY BUILD BACK IN TO THE WEST...WHICH OF COURSE IS ANOTHER CHALLENGE FOR TEMPERATURES AS WELL. OVERALL...STILL A FAIR AMOUNT OF UNCERTAINTY WITH THIS PATTERN...AND WOULD ALMOST LIKE TO SEE A RETURN TO RIDGE AND TYPICAL DIURNAL PATTERN TO CONVECTION...AT LEAST FROM A FCST CHALLENGE PERSPECTIVE...AND THERE ARE SOME GOOD SIGNS OF THAT HAPPENING AS WE GET FARTHER INTO NEXT WEEK. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... AS OF 200 AM EDT TUESDAY... SURFACE OBSERVATIONS INDICATE MVFR/IFR CEILINGS ARE WIDESPREAD THIS MORNING ACROSS THE REGION AS TROPICAL MOISTURE POOLS JUST SOUTH OF A STATIONARY FRONT SITUATED ALONG A LINE FROM KLWB/KROA/KAVC. LOCALLY DENSE FOG IS ALSO BEING OBSERVED ACROSS THE MOUNTAINS AND FOOTHILLS IN THE FEW LOCATIONS WHERE CLOUDS HAVE SCATTERED. LOW CLOUDS AND PATCHY DENSE FOG WILL PERSIST OVERNIGHT...ALTHOUGH CEILINGS AND VISIBILITIES WILL FLUCTUATE UP AND DOWN AT TIMES. VISIBILITIES WILL IMPROVE QUICKLY AFTER 13Z AS DAYTIME HEATING INCREASES...WITH CLOUD BASES ALSO GRADUALLY IMPROVING THROUGH THE REMAINDER OF THE MORNING. EXPECT A MIXTURE OF BROKEN LOW END VFR CLOUDS AND HIGH MVFR CLOUDS TO AFFECT THE AREA DURING THE AFTERNOON. WILL ALSO SEE A REDEVELOPMENT OF SPOTTY SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE MOUNTAINS BY 16Z AS ANOTHER UPPER LEVEL DISTURBANCE APPROACHES THE REGION. THIS ACTIVITY WILL SPREAD EAST THROUGH LATE AFTERNOON TO AFFECT THE PIEDMONT. SHOWER ACTIVITY WILL LINGER INTO MID EVENING BEFORE DIMINISHING WITH THE LOSS OF DAYTIME HEATING. EXPECT A RETURN OF MVFR AND IFR CEILINGS TUESDAY NIGHT...ALONG WITH PATCHY DENSE FOG. EXTENDED AVIATION... A SURFACE FRONT IS EXPECTED TO REMAIN STALLED NORTH OF THE AREA THROUGH THE MIDDLE OF THE WEEK AS A SERIES OF UPPER LEVEL DISTURBANCES TRACK FROM WNW-ESE ACROSS THE REGION...TRIGGERING SHOWERS AND THUNDERSTORMS...WITH BEST CHANCES OCCURRING DURING THE AFTERNOON AND EVENING. ABUNDANT TROPICAL MOISTURE AND MOIST SOIL CONDITIONS WILL ALSO RESULT IN LATE NIGHT/EARLY MORNING IFR-LIFR CONDITIONS IN FOG AND LOW CLOUDS AT THE USUAL SITES...LWB/BCB/LYH... WITH MVFR POSSIBLE AT OTHER LOCATIONS. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...NF SHORT TERM...PM LONG TERM...SK AVIATION...NF/RCS

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