Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 270926 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 526 AM EDT SUN JUL 27 2014 .SYNOPSIS...
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SHOWERS AND THUNDERSTORMS WILL AFFECT THE REGION THIS MORNING AND EARLY AFTERNOON AS AN UPPER LEVEL DISTURBANCE PASSES ALONG THE APPALACHIAN CHAIN. ANOTHER STRONG UPPER LEVEL DISTURBANCE WILL APPROACH THE REGION THIS AFTERNOON FROM THE MIDWEST...TRIGGERING STRONG TO POTENTIALLY SEVERE THUNDERSTORMS FOR THIS EVENING. A STRONG COLD FRONT WILL MOVE ACROSS THE REGION EARLY MONDAY... RESULTING IN COOLER WEATHER INTO THE MIDDLE OF THE WORKWEEK.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 500 AM EDT SUNDAY... SHOWERS AND SCATTERED THUNDERSTORMS ARE OBSERVED ACROSS THE FORECAST REGION THIS MORNING AS AN UPPER LEVEL DISTURBANCE PASSES OVERHEAD. RAINFALL AMOUNTS HAVE BEEN OBSERVED AROUND A HALF INCH ACROSS SOUTHEAST WEST VIRGINIA...WITH AMOUNTS TAPERING DOWN TO A FEW HUNDREDTHS FURTHER EAST. IN ADDITION TO THE ACTIVITY CURRENTLY AFFECTING OUR AREA...ALSO KEEPING AN EYE ON TWO OTHER AREAS OF THUNDERSTORM ACTIVITY...ONE ENTERING WESTERN KENTUCKY AND ANOTHER OVER EASTERN ILLINOIS. RAPID UPDATE FORECAST MODELS APPEAR TO BE IN GOOD AGREEMENT THAT THE THUNDERSTORMS OVER WESTERN KENTUCKY WILL SHIFT EAST SOUTHEAST... PUSHING INTO THE NORTH CAROLINA MOUNTAINS LATE MORNING TO AROUND NOON. WHILE THE DISTURBANCE TRIGGERING THESE STORMS MAY REMAIN STRONG ENOUGH TO PRODUCE SOME GUSTY WINDS ACROSS THE MOUNTAINS... WONDERING IF THE CLOUD COVER IT PRODUCES WILL ALSO LIMIT INSTABILITY FOR AREAS SOUTH OF HIGHWAY 460 DURING THE AFTERNOON AS THE SECOND...MORE POTENT DISTURBANCE PUSHES EAST ALONG THE OHIO RIVER. THE SECOND DISTURBANCE WILL BRING WITH IT AN UNSEASONABLY STRONG MID LEVEL WINDS IN THE RANGE OF 50KT TO 60KT. WITH CLOUD COVER EXPECTED TO BE MORE DIMINISHED HEADING INTO THE AFTERNOON NORTH OF HIGHWAY 460...EXPECT GREATER INSTABILITY IN THIS AREA. MODELS ARE IN AGREEMENT ON BRINGING THE SECOND LINE OF STORMS INTO SOUTHEAST WEST VIRGINIA DURING THE 6PM TO 8PM TIME FRAME...WITH CONVECTION QUICKLY SPREADING EAST THEREAFTER. THE MAIN THREAT WITH THESE STORMS WILL BE POTENTIALLY DAMAGING WINDS AS THE DOWNDRAFTS PULL THE STRONG MID LEVEL WINDS TO THE SURFACE. HAIL WILL ALSO BE POSSIBLE IN SOME OF THE STRONGER CELLS...AS WILL BE LOCALLY HEAVY RAIN DUE TO THE UNUSUALLY HIGH ATMOSPHERIC MOISTURE POOLING AHEAD OF THE SYSTEM. DUE TO THE STRONG SHEAR PRESENTED BY THIS SYSTEM... CANNOT EVEN RULE OUT AN ISOLATED TORNADO...ALTHOUGH BELIEVE THE THREAT IS HIGHER WEST OF THE APPALACHIANS...OUTSIDE OUR FORECAST AREA. THUNDERSTORM ACTIVITY WILL BEGIN TO DIMINISH DURING LATE EVENING AS THE LINE PASSES EAST OF THE MOUNTAINS AND BEGINS TO MOVE DOWNSLOPE...ALTHOUGH SOME POTENTIAL FOR GUSTY WINDS WILL REMAIN THROUGH MIDNIGHT EAST OF THE BLUE RIDGE. WINDS WILL THEN SHIFT WESTERLY EARLY MONDAY AS A STRONG COLD FRONT MOVES EAST ACROSS THE FORECAST REGION...LEAVING ONLY UPSLOPE SHOWERS ACROSS THE MOUNTAINS. AS MENTIONED BEFORE...CLOUD COVER AND SHOWERS ARE ADDING TO THE UNCERTAINTY OF MANY ASPECTS OF THE FORECAST...INCLUDING AFTERNOON HIGHS. HAVE UNDERCUT MAV/MET GUIDANCE BY A FEW DEGREES...OPTING FOR THE COOLER MOS GUIDANCE. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 300 AM EDT SUNDAY... BY 12Z (8 AM EDT) MONDAY...THE DYNAMIC UPPER LEVEL SHORTWAVE WILL HAVE LIFTED INTO THE NORTHEAST U.S. LEAVING A DEEP LOW LEVEL NORTHWEST FLOW IN PLACE. FAIR PRESSURE RISES AND 40+ KT 850MB WINDS SHOULD GENERATE GUSTY WINDS...BUT SPEEDS REMAINING BELOW ADVISORY CRITERIA. RESIDUAL MOISTURE BELOW 4K FT SHOWN ON FORECAST SOUNDINGS FORCED UP ALONG THE WESTERN SLOPES...COMBINED WITH LAPSE RATES GREATER THAN 6.5 C/KM WILL HELP GENERATE UPSLOPE SHOWERS MONDAY AND INTO MONDAY EVENING. LEANED TOWARD THE COOLER GUIDANCE FOR HIGHS MONDAY...HOWEVER...WITH DOWNSLOPING WINDS...TEMPS EAST OF THE BLUE RIDGE WILL STILL MANAGE TO REACH WELL INTO THE 80S. CHANCE FOR UPSLOPE SHOWERS DIMINISH TUESDAY AND UPSLOPE FLOW WEAKENS AND LOW LEVEL DRYING CONTINUES. AS THE DOWNSLOPE FLOW EAST OF THE BLUE RIDGE ALSO WEAKENS...COOLING TREND CONTINUES AND WENT SLIGHTLY BELOW GUIDANCE FOR HIGHS TUESDAY. ENERGY ROUNDING THE BASE OF THE UPPER LEVEL EASTERN U.S. TROF HELPS DEVELOP A WEAK SFC LOW ACROSS THE CAROLINAS LATE TUESDAY. MODELS HINT THAT THIS MAY PRODUCE A WEAK EAST/NORTHEAST FLOW IN THE FAR EAST AND PERHAPS BRING SOME CLOUDS TO THIS REGION. ACROSS THE WEST...HOWEVER...SFC HIGH PRESSURE BUILDS WHICH SHOULD ALLOW TEMPS TUESDAY NIGHT TO DROP INTO THE 40S ACROSS PORTIONS OF THE MOUNTAINS. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... 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 /10Z SUNDAY THROUGH THURSDAY/... AS OF 200 AM EDT SUNDAY... SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS CONTINUE TO ENTER THE MOUNTAINS THIS MORNING AS AN UPPER LEVEL DISTURBANCE PASSES OVERHEAD. TRENDS SINCE MIDNIGHT HAVE INDICATED WEAKENING OF THE THUNDERSTORM COMPLEX OVER KY EVEN AS NEW SHOWERS DEVELOP AS THE ENERGY ENCOUNTERS THE OROGRAPHIC LIFT ALONG THE APPALACHIAN CHAIN FURTHER NORTH. WITH DECREASING INSTABILITY DUE TO LOSS OF DAYTIME HEATING...BELIEVE SHOWER ACTIVITY OVERNIGHT WILL REMAIN MOSTLY WEAK...WITH LOCALLY HEAVY RAIN PRODUCING BRIEF IFR VISIBILITIES. CEILINGS SHOULD REMAIN MOSTLY VFR IN THE SOUTHWESTERLY FLOW. ONCE CONVECTION OVER KENTUCKY EXITS...MODELS ARE PICKING UP ON ANOTHER DISTURBANCE BRINGING ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS FROM SOUTHERN IN/WESTERN KY THIS MORNING TO THE CENTRAL APPALACHIANS THIS AFTERNOON. UNSURE HOW MUCH INSTABILITY WILL BE IN PLACE BY EARLY AFTERNOON...WHICH WILL DEPEND ON HOW MUCH CLOUD COVER REMAINS FROM THE MORNING. CONSIDERING THE STRENGTHENING WEST WIND DURING THE AFTERNOON WHICH WILL HELP KEEP A LID ON CONVECTION...HAVE SHOWERS IN THE TAFS FOR NOW. FOCUS THEN SHIFTS TO THE EVENING...WHEN ANOTHER STRONGER DISTURBANCE WILL ARRIVE...BRINGING 50KT TO 55KT MID LEVEL WINDS. BELIEVE STORMS WITH THIS DISTURBANCE WILL ARRIVE IN SOUTHEAST WV AT OR AROUND 28/00Z IN THE FORM OF A LINE...AND THEN PASS QUICKLY ACROSS THE AREA THROUGH 28/03Z. HIGHEST THREAT OF SEVERE WEATHER WILL BE ACROSS THE MOUNTAINS...AND NORTHERN VA PIEDMONT...AFFECTING KLWB/KLYH/KROA/KBCB/KBLF. BELIEVE THE STORMS WILL WEAKEN AS THEY PASS THE BLUE RIDGE IN THE DOWNSLOPE WINDFLOW. STRONG WINDS WILL BE THE BIGGEST THREAT WITH THESE STORMS AS THEY PULL THE STRONGER WINDS ALOFT DOWN TO THE SURFACE. CANNOT RULE OUT HAIL...AND HEAVY RAIN WILL ALSO BE LIKELY WITH THE LINE...WHICH WILL PRODUCE IFR VISIBILITIES FOR EXTENDED PERIODS OF TIME. WEATHER IS EXPECTED TO QUIET DOWN TO RESIDUAL SHOWER ACTIVITY/ISOLATED STORMS AFTER 28/04Z AS THE MAIN ENERGY PASSES EAST. EXTENDED AVIATION DISCUSSION... 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 TUESDAY-WEDNESDAY...AND MAINLY VFR. CANNOT RULE OUT LATE NIGHT FOG KBCB/KLWB BUT LOW LVLS MAY STAY DRY ENOUGH FOR LESS FOG COVERAGE. VARIABLE CIGS EXPECTED UNDER ANOMALOUS UPPER LOW THROUGHOUT THE WEEK. A FEW -SHRA NOT COMPLETELY OUT OF THE QUESTION ACROSS EASTERN WV...ALONG WITH OCCASIONAL MVFR CIGS. TYPICAL FOG POTENTIAL LESS THAN NORMAL FOR THIS TIME OF YEAR THROUGHOUT THE WEEK BECAUSE OF TURBULENT MIXING AND PREVAILING CYCLONIC FLOW. TOWARD THE END OF THE WEEK...AS THE UPPER LOW RETROGRADES JUST WEST OF THE REGION...INCREASING POTENTIAL FOR SHRA/TSRA... ESPECIALLY IN THE FRI-SUN TIME FRAME. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...NF NEAR TERM...NF SHORT TERM...PH LONG TERM...CF AVIATION...NF/RAB

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