Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 271446 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1046 AM EDT SUN JUL 27 2014 .SYNOPSIS...
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UPPER DISTURBANCES WILL CONTINUE TO WORK INTO THE AREA THIS AFTERNOON AND EVENING IN ADVANCE OF A STRONG COLD FRONT THAT WILL BE APPROACHING FROM THE NORTHWEST THIS EVENING. THESE FEATURES MAY TRIGGER STRONG TO POTENTIALLY SEVERE THUNDERSTORMS THIS AFTERNOON INTO EARLY TONIGHT. THE COLD FRONT WILL MOVE ACROSS THE REGION BY EARLY MONDAY...RESULTING IN COOLER WEATHER INTO THE MIDDLE OF THE WORK WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1020 AM EDT SUNDAY... FORECAST REMAINS COMPLICATED INTO THIS EVENING GIVEN TIMING ISSUES OF IMPULSES ALOFT AND MODEL UNCERTAINTY WITH THESE FEATURES. CURRENT SHORTWAVE CROSSING THE REGION THAT CAUSED THE EARLIER ARRIVAL OF SHRA/TSRA EARLY THIS MORNING CONTINUES TO PRODUCE BANDS OF SHOWERS AND STORMS OVER THE WEST BUT ALSO A QUITE EXTENSIVE AREA OF CLOUD COVER WITHIN THE APPARENT LEFTOVER COOL POOL. NEXT UPSTREAM VORT AHEAD OF THE FRONT THAT LOOKS TO BE THE MAIN PLAYER FOR STRONGER STORMS LATER ON WILL WORK AROUND THE UPSTREAM UPPER TROF THIS AFTERNOON AND EVENTUALLY MERGE WITH THE SURFACE COLD FRONT EARLY TONIGHT. FORECAST SHEAR AND HELICITY QUITE LARGE AS WELL AS LAPSES BUT ALL DEPENDENT UPON INSTABILITY WHICH WILL BE THE DRIVING FORCE FOR ORGANIZED COVERAGE LATER ON. LATEST 12Z GUIDANCE CONTINUES TO SHIFT THE BETTER LIFT TO LATER IN THE DAY AND MORESO THIS EVENING AS WILL LIKELY TAKE LONGER TO GET AT LEAST DECENT HEATING AND CAPES REACHING 1-2K J/KG. THUS MAY HAVE A SITUATION WHERE INITIALLY WILL SEE MORE ELEVATED CONVECTION ESPCLY NORTH/CENTRAL SECTIONS...WITH MORE SURFACE BASED STORMS TAKING SHAPE ACROSS THE FAR SW PER BETTER THETA-E AND HEATING UNDER THE INCREASING SW JET. OTRW COMBO OF WESTERLY FLOW ALOFT AND EARLY CLOUDS/SHRA LIKELY TO CAUSE LESS EARLY ON...SO LOWERED POPS SOUTHERN/EAST TO INIT...THEN INCREASED WEST FOR LEAST MORE SHRA EARLY AFTERNOON AHEAD OF THE NEXT MCS BEFORE THINGS PERHAPS COME TOGETHER FOR DEEPER CONVECTION ESPCLY WEST- NORTH LATE IN THE DAY. CONSIDERED A FLOOD WATCH OVER THE FAR WEST/NW WHERE 12Z GUIDANCE SHOWING IN EXCESS OF AN INCH OF RAIN BUT GIVEN UNCERTAINTY AND LIGHT AMOUNTS OVERNIGHT WILL CONTINUE TO HOLD OFF FOR NOW. TEMPS REMAIN QUITE TRICKY AS SEEING LITTLE RISE ATTM AND WITH LATEST LAV MO COOLER...EXPECT MORE LATE DAY HIGHS SO LOWERED A CAT OR SO MOST SPOTS WHICH MAY NOT BE COOL ENOUGH OVER THE NW. PREVIOUS DISCUSSION 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.
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&& .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 /14Z SUNDAY THROUGH THURSDAY/... AS OF 720 AM EDT SUNDAY... WIDELY SCATTERED SHOWERS WILL CREATING SPOTTY AREAS OF MVFR CIGS AND VSBYS THIS MORNING. THIS FIRST ROUND OF PRECIPITATION WILL DIMINISH BY LATE MORNING. WIND GUSTS TO 30 MPH IN THE NORTHWEST NC MOUNTAINS AND FAR SOUTHWEST VIRGINIA EARLY THIS MORNING WILL GRADUALLY DIMINISH AS THE MORNING PROGRESSES. WHILE VFR CONDITIONS ARE EXPECTED THROUGH MUCH OF THE MORNING...A COMPLEX OF STORMS IN KENTUCKY WILL SPREAD MID AND HIGH CLOUDS OVER THE REGION...AS WELL AS SCATTERED SHOWERS AND STORMS...ESPECIALLY IN NW NORTH CAROLINA. THE GREATEST THREAT TO AVIATORS TODAY WILL BE YET ANOTHER COMPLEX OF STORMS THAT WILL ENTER OUR AREA FROM THE NORTHWEST LATE THIS AFTERNOON AND THIS EVENING...IN ADVANCE OF A STRONG UPPER LEVEL DISTURBANCE MOVING INTO THE OHIO VALLEY.THERE STILL IS SOME UNCERTAINTY ABOUT HOW MUCH INSTABILITY WILL BE IN PLACE BY EARLY AFTERNOON...WHICH WILL DEPEND ON HOW MUCH CLOUD COVER REMAINS FROM THE MORNING CONVECTION. REGARDLESS...WITH AN IMPRESSIVE WIND FIELD ALOFT...CONFIDENCE IS GROWING THAT THIS LARGE COMPLEX OF STORMS WILL IMPACT OUR AREA AND MANY TAF SITES...BUT MOST LIKELY KBLF...KLWB...KBCB AND KROA. AS A RESULT...INTRODUCED THUNDER WITH PROB30 OF WIND GUSTS TO 30-40KTS. IFR CONDITIONS WITH LOW CIGS/VSBYS EXPECTED WITH THIS COMPLEX. A COLD FRONT PASSES TONIGHT...LEAVING VFR CONDITIONS...BUT GUSTY NORTHWEST WINDS...ESPECIALLY IN THE MOUNTAINS. EXTENDED AVIATION DISCUSSION... THREAT OF SUB VFR THROUGH MONDAY EXPECTED ACROSS SE WEST VA PER NW FLOW...BUT LESS ELSEWHERE GIVEN DOWNSLOPE. DRIER AIR PUSHING IN FOR TUESDAY-WEDNESDAY WILL BRING MAINLY VFR CONDITIONS...BUT 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...JH/NF NEAR TERM...JH/NF SHORT TERM...PH LONG TERM...CF AVIATION...NF/PH/RAB

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