Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 261645 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1245 PM EDT SAT JUL 26 2014 .SYNOPSIS... A WEAK WARM FRONT LIFTS NORTHEAST ACROSS THE AREA THIS AFTERNOON ALLOWING A MORE WEST TO SOUTHWEST TRAJECTORY TO DEVELOP. THUNDERSTORMS WILL DEVELOP ALONG THIS FRONTAL BOUNDARY IN THE OHIO VALLEY BY EVENING AND SPREAD SOUTHEAST TOWARD OUR AREA BY EARLY SUNDAY. A STRONG COLD FRONT SHOULD MOVE ACROSS THE MID ATLANTIC AND SOUTHERN APPALACHIANS BY MONDAY...WITH COOLER WEATHER INTO THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 940 AM EDT SATURDAY... MID LEVEL WAVE PASSING TO THE NE HAS ALLOWED A GOOD PUNCH OF DRY AIR INTO THE AREA FROM THE WEST THIS MORNING PER VAPOR LOOP. THIS ALSO SEEN VIA MORNING RAOBS WITH VERY DRY AIR ALOFT CAPPED BY A MID LEVEL INVERSION AND DEEP WEST TO NW FLOW THROUGH THE COLUMN. LATEST PWATS OFF RAOBS AND THE LOCAL IPW ALSO SHOW SOME DECREASE IN MOISTURE WITH THE PASSAGE OF THE WAVE WHICH SUPPORTS A MAINLY DRY AFTERNOON WITH NEXT ROUND OF LIFT WELL TO THE NW. THIS IN LINE WITH MOST SHORT TERM SOLUTIONS SHOWING LITTLE CONVECTION THROUGH EARLY THIS EVENING. HOWEVER CANT TOTALLY RULE OUT SOMETHING ISOLATED POPPING FAR SOUTH-SE WHERE THE AXIS OF HIGH LOW LEVEL THETA-E PER MSAS...AND THE WARM FRONT MAY INTERACT WITH CAPES AROUND 2K J/KG LATER ON. FOR NOW GIVEN WEAK SUBSIDENCE AND LACK OF SHRA OFF THE 12Z NAM WILL LEAVE OUT POPS AND RUN MAINLY SUNNY UNDER A DEVELOPING CU FIELD ONCE THE CURRENT PATCHY FOG FADES. SURGE IN 85H TEMPS TO BACK OVER +20C AND WEST/SW FLOW UNDER STRONG HEATING SUPPORTS HIGHS REACHING THE LOW 90S PIEDMONT...AND 85-90 BLUE RIDGE...WITH ONLY THE FAR WESTERN ELEVATIONS STAYING IN THE LOW/MID 80S. TONIGHT...WILL BE WATCHING UPSTREAM AS MCS IS EXPECTED FOR THE OHIO VALLEY AND MODELS SHIFT THIS AREA EAST AND SOUTH TOWARD SE WV/FAR SW VA BY SUNDAY MORNING. MODELS IN DECENT AGREEMENT THROUGH 12Z SUNDAY IN HITTING SRN OHIO TO ERN KY AND WRN WV WITH BEST COVERAGE...WITH HIGHER THETA-E RIDGE SITUATED ACROSS THIS REGION. GIVEN THAT SYSTEMS TEND TO BE FASTER THAN MODEL FORECAST WILL HAVE POPS UP TO LIKELY IN THE FAR WEST BY MORNING TAPERING TO SLIGHT CHANCE TO THE BLUE RIDGE AND NORTH OF LYH. CONVECTION IS LIKELY TO BE WEAKENING TOWARD MORNING GIVEN LACK OF THERMAL INSTABILITY BUT WIND FIELDS ARE FAVORABLE FOR A FEW STRONG GUSTS. THE STORM PREDICTION CENTER IS KEEPING THE MAIN THREAT OUT OF OUR AREA UNTIL AFTER 12Z SUNDAY...WHICH IS COVERED IN THE NEXT SECTION OF THIS DISCUSSION. LOWS TONIGHT WILL BE MUGGY AS DEWPOINTS INCREASE...MAINLY IN THE 60S CWA WIDE....AROUND 70 SOUTHEAST. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... AS OF 240 AM EDT SATURDAY... SUNDAY INTO SUNDAY NIGHT CONTINUES TO LOOK LIKE A VERY ACTIVE WEATHER DAY ACROSS AT LEAST THE WESTERN AND NORTHERN PARTS OF THE REGION...WITH A POTENTIAL THUNDERSTORM COMPLEX ENTERING AND MOVING THROUGH THE AREA DURING THE AFTERNOON AND EVENING HOURS. THE NEW DAY 2 CONVECTIVE OUTLOOK BY THE STORM PREDICTION CENTER HAS THE CENTER OF A MODERATE RISK OF POTENTIAL SEVERE WEATHER NEAR THE KY/WV BORDER...WITH THE EASTERN EDGE OF THE MODERATE AREA JUST TOUCHING GREENBRIER COUNTY WV SOUTHWEST INTO TAZEWELL COUNTY VA. THE REMAINDER OF THE FORECAST AREA IS WITHIN THE NEW DAY 2 SLIGHT RISK AREA. DAMAGING WINDS AND LARGE HAIL ARE EXPECTED TO BE THE MAIN THREATS ACROSS THE REGION...WITH AN ISOLATED TORNADO POTENTIAL WITHIN THE MODERATE RISK AREA. THIS SYSTEM WILL BE IN ADVANCE OF A SHORTWAVE TROUGH/LOW THAT WILL HEAD SOUTHEAST THROUGH THE GREAT LAKES REGION SUNDAY NIGHT. IT WILL BE THIS FEATURE THAT MERGES WITH A SOUTHEAST CANADIAN AREA OF LOW PRESSURE THAT YIELDS A LONGWAVE TROUGH ACROSS MOST OF THE EASTERN THIRD OF CONUS...CENTERED OVER OUR REGION...BY MONDAY AFTERNOON. A DECENT GRADIENT WILL EXIST AROUND THE SOUTHERN WAVE FOR THIS TIME OF YEAR TO PRODUCE 850 MB WINDS ON THE ORDER OF 35 TO 45 KTS ACROSS THE AREA LATE SUNDAY...SUNDAY NIGHT...AND EARLY MONDAY TO ALLOW FOR SURFACE GUSTS IN THE 20 TO 30 MPH RANGE AT HIGHER ELEVATIONS DURING THIS PERIOD. WEAK DISTURBANCES WITH IN THE FLOW OF THE PARENT LONGWAVE TROUGH WILL PERIODICALLY PROGRESS TROUGH OUR AREA MONDAY INTO TUESDAY. THE FIRST OF THESE WILL ALLOW FOR SOME SCATTERED SHOWER AND PERHAPS AN ISOLATED THUNDERSTORM ON MONDAY...ESPECIALLY ACROSS THE MOUNTAINS. A LEE TROUGH WILL DEVELOP THANKS TO STRONG W-NW FLOW. AFTERNOON DEVELOPMENT WILL BE POSSIBLE JUST EAST OF THIS TROUGH WHERE LOW LEVEL WINDS WILL BACK SOUTHWEST...AND YIELD A CONVERGENCE LINE ALONG THE TROUGH. MONDAY NIGHT...THE ACTIVE WILL SLOWLY WANE...BUT NOT COMPLETELY END ACROSS THE MOUNTAINS WHERE LINGERING UPPER SUPPORT...AND A NORTHWEST UPSLOPE FLOW WILL HELP MAINTAIN SOME ISOLATED SHOWERS. ON TUESDAY...ANOTHER WEAK DISTURBANCE HEADS SOUTH THROUGH THE AREA...BUT BY THIS TIME...SURFACE HIGH PRESSURE WILL ALSO BE ACROSS THE AREA. WILL LIMIT PRECIPITATION COVERAGE TO ISOLATED SHOWERS ACROSS MAINLY WESTERN AND SOUTHERN PARTS OF THE AREA. THIS ACTIVITY IS EXPECTED TO END BY TUESDAY EVENING. TEMPERATURES DURING THIS PORTION OF THE FORECAST WILL TREND COOLER EACH DAY. TEMPERATURES BY TUESDAY AND TUESDAY NIGHT WILL BE SOME 10 TO 15 DEGREES COOLER THAN THOSE EXPECTED SUNDAY AND SUNDAY NIGHT. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... 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 /16Z SATURDAY THROUGH WEDNESDAY/... AS OF 1220 PM EDT SATURDAY... VFR EXPECTED TO PREVAIL THROUGH EARLY TONIGHT WITH BKN CU FIELDS AROUND KDAN THIS AFTERNOON AND INCREASING HIGH CLOUDS OVER THE FAR WEST. MAIN AVIATION ISSUE WILL BE WITH A COMPLEX OF STORMS PROGGED TO IMPACT THE KBLF/KLWB AREA BY 12Z/8AM SUNDAY. CONVECTION MAY BE FASTER AND WIDESPREAD ENOUGH TO INCLUDE PREVAILING MVFR VSBYS/CIGS AT BOTH SITES AROUND 10Z/6AM AND KBCB/KROA BEFORE 14Z/10AM BUT LOWER CONFIDENCE THERE. STORMS WILL DEFINITELY IMPACT THE KBLF/KLWB AND OVER TOWARD ROA/KBCB/KLYH INTO EARLY AFTERNOON SUNDAY...AS MODELS ZIP THIS FEATURE EAST WHILE WEAKENING UPON CROSSING EAST OF THE BLUE RIDGE. THUS WILL ONLY INCLUDE A VCSH MENTION AT KLYH FOR NOW AND LEAVE OUT OF KDAN AS APPEARS MOST CONVECTION WILL STAY JUST NORTH OF THAT AREA. STILL AVIATION INTERESTS SHOULD BE WARY OF POTENTIAL SUB VFR CIGS/VSBYS WITH HEAVY RAIN AND THUNDERSTORMS/WINDS ESPCLY OVER THE MOUNTAINS SUNDAY MORNING. MAY SEE A LULL IN COVERAGE AS THIS IMPULSE PASSES MID/LATE SUNDAY AFTERNOON WITH PERIODIC MVFR CONDITIONS AFFECTING BOTH KBLF AND KLWB INTO THE EVENING WITH A SECOND WAVE ALONG THE FRONT. ELSW MIXING AND WEAK SINKING MOTION BEHIND THE INITIAL FEATURE MAY TREND MOST SPOTS TOWARD VFR DURING THE AFTERNOON AS WE SLIP IN BETWEEN THE EARLY IMPULSE AND THE UPSTREAM COLD FRONT THAT WONT ARRIVE UNTIL SUNDAY NIGHT. 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. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/WP NEAR TERM...JH/WP SHORT TERM...DS LONG TERM...CF AVIATION...JH/WP

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