Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 191408 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1008 AM EDT TUE AUG 19 2014 .SYNOPSIS...
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A WEAK STATIONARY FRONT WILL REMAIN ACROSS THE REGION TODAY INTO THURSDAY. WEAK UPPER LEVEL DISTURBANCES TRACKING SOUTHEAST ALONG THE BOUNDARY WILL BRING SCATTERED SHOWERS AND STORMS TO THE REGION FOR MUCH OF THE WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 945 AM EDT TUESDAY... WEAK FRONT REMAINS STUCK ACROSS THE FAR NORTH AND NE SECTIONS OF THE AREA THIS MORNING IN THE WAKE OF THE EXITING WAVE FROM OVERNIGHT. PLENTY OF LEFTOVER LOW LEVEL MOISTURE HAS CONTINUED TO RESULT IN WIDESPREAD CLOUDS ESPCLY EAST CLOSER TO THE EXITING LOW AND OUT WEST WHERE SEEING A WEAK INVERTED SURFACE TROUGH. MORNING SOUNDINGS HAVE SHOWN A BIT OF DRYING ALOFT OVER THE MOUNTAINS WITH PWATS ALSO A BIT LOWER GIVEN THE WEAK WESTERLY FLOW AND FAINT SUBSIDENCE. HOWEVER ENOUGH WEAK CONVERGENCE IN THIS FLOW TO KEEP A NARROW BAND OF SHRA GOING ACROSS SE WEST VA ATTM...AND EXPECT THIS TO PERSIST A WHILE LONGER BEFORE THINGS START TO MIX OUT A BIT MORE. SHOULD FINALLY SEE ENOUGH HEATING TO ERODE THE CLOUD CANOPY EARLY THIS AFTERNOON MOST SPOTS ALTHOUGH THE FAR WESTERN SLOPES AND VA PIEDMONT MAY BE SLOWER TO SEE MORE SUN. LATEST MODIFIED RAOBS GIVING 1-2K J/KG CAPES PROVIDED MORE INSOLATION AS LATEST MODELS HAVE TRENDED SLOWER WITH RENEWED CONVECTION THIS AFTERNOON GIVEN THE SLOW START TO HEATING. HOWEVER CONSENSUS POINTS TO BEST COVERAGE ALONG THE BLUE RIDGE AND POINTS WEST BY MID/LATE AFTERNOON WHERE LIKELY TO SEE MORE DIFFERENTIAL HEATING AND WEAK CONVERGENCE UNDER A HIGHER RIBBON OF THETA-E INCLUDING A WEAK PASSING IMPULSE ALOFT. SEVERE THREAT LOOKS SMALL UNLESS A TSRA CAN TAP THE DRY AIR ABOVE AS EXPECT MORE SHALLOW NATURE CONVECTION GIVEN DRYING ALOFT BUT LIKELY AGAIN SLOW MOVING WITH ONLY 10-15 KTS OF STEERING. THUS HAVE TWEAKED THINGS FOR SLOWER DEVELOPMENT ACROSS THE CWA AND CONFINED THE GOING HIGHER POPS IN A SWATH ALONG THE MOUNTAINS SINCE ONLY EXPECTING A FEW HOURS OF SCATTERED COVERAGE. ALSO LOWERED POPS OUT EAST GIVEN MORE SUBSIDENCE/CLOUDS AND LACK OF FOCUS PER MORE OF A LIGHT N-NE TRAJECTORY. HIGHS AGAIN TRICKY PENDING INSOLATION AND GIVEN CURRENT TRENDS AND LATEST LAV MOS VALUES HAVE LOWERED HIGHS A FEW DEGREES IN SPOTS. SHOWERS AND THUNDERSTORM WILL DIMINISH IN COVERAGE THIS 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. OVERNIGHT LOWS WILL AGAIN RANGE FROM THE MID 60 TO THE LOW 70S.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... 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. && .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 /14Z TUESDAY THROUGH SATURDAY/... AS OF 800 AM EDT TUESDAY... STATIONARY FRONT EXTENDS FROM NORTHERN VIRGINIA INTO THE OHIO VALLEY. VERY MOIST AIR IS POOLED SOUTH OF THIS FRONT WHICH WILL PROVIDE FUEL FOR SCATTERED SHOWERS AND THUNDERSTORMS TODAY. COVERAGE TODAY WILL BE SCATTERED COMPARED TO THE WIDESPREAD NATURE YESTERDAY. NEVER THE LESS EXPECT LOCAL MVFR CONDITIONS ASSOCIATED WITH ANY OF THE SHOWER ACTIVITY AND LOCAL IFR CONDITIONS ASSOCIATED WITH THUNDERSTORMS. GREATEST COVERAGE WILL BE DURING THE PEAK HEATING THIS AFTERNOON AND EVENING. A MOIST BOUNDARY LAYER WILL PROMOTE AREAS OF FOG FORMATION AND STRATUS TONIGHT...WITH THE LOWEST VISIBILITIES DEVELOPING AFTER MIDNIGHT AND CONTINUING THROUGH DAYBREAK WEDNESDAY. EXTENDED AVIATION... A SURFACE FRONT IS EXPECTED TO REMAIN STALLED NORTH OF THE AREA THROUGH THURSDAY 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...JH NEAR TERM...JH/NF SHORT TERM...PM LONG TERM...SK AVIATION...NF/RCS

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