Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 270100 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 900 PM EDT SUN JUL 26 2015 .SYNOPSIS...
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A WEAK COLD FRONT WILL APPROACH THE REGION FROM THE NORTHWEST LATE TONIGHT INTO MONDAY BEFORE WASHING OUT OVER THE REGION INTO MIDWEEK. ANOTHER FRONT WILL MOVE INTO THE AREA FROM THE WEST THURSDAY...THEN STALL JUST TO THE SOUTHEAST OF THE REGION FRIDAY INTO THE WEEKEND...BRINGING A BETTER CHANCE OF SHOWERS AND THUNDERSTORMS TO THE AREA. OTHERWISE...IT WILL REMAIN WARM AND HUMID THROUGHOUT THE WEEK WITH MORE DIURNAL NATURE SHOWERS AND STORMS.
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&& .NEAR TERM /THROUGH MONDAY/...
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AS OF 830 PM EDT SUNDAY... HEAVIER SLOW MOVING CONVECTION HAS BEEN CONFINED MOSTLY TO OROGRAPHICS THIS EVENING WITH CELLS POPPING UP OFF THE RIDGES THEN REDEVELOPING WITH OUTFLOW ALLOWING SLOW PROPAGATION. HOWEVER MOST ONLY PRODUCING HEAVY RAIN WITH LITTLE LIGHTNING AS SUPPORTED BY SHALLOW INSTABILITY OFF EVENING SOUNDINGS AND STILL SOME CAPPING ABOVE 7H THEREBY LIMITING DEPTH TO MOST CELLS. BETTER WINDS ALOFT REMAIN TO THE NW CLOSER TO THE FRONT AND WITH AN APPARENT WEAK WAVE THAT WILL SLIDE TO THE NORTH OF THE CWA LATE TONIGHT. THIS MAY ALLOW FOR SOME ADDED COVERAGE TO REDEVELOP OVER THE NORTH AFTER MORE DIURNAL SHOWERS FADE IN THE NEXT FEW HOURS. THIS SIMILAR TO THE LATEST HRRR/NAM SO ADDING IN MORE LOW POPS OVER THE FAR NORTH/NE OVERNIGHT...WITH ISOLATED COVERAGE NEAR THE BLUE RIDGE UNTIL RESIDUAL INSTABILITY FADES BY MIDNIGHT. ALSO APPEARS DEBRIS CLOUDS LIKELY A BIT MORE OVERNIGHT WHICH SHOULD LIMIT FOG TO POCKETS WHERE HEAVIER RAINFALL OCCURRED AND IN THE VALLEYS FOR THE MOST PART. OTRW MORE OF A WARMER AND MORE HUMID OVERNIGHT WITH MOIST PWATS IN PLACE...AND HIGH DEWPOINTS SUPPORTING LOWS CLOSER TO 70-73 EXCEPT FOR 60S WESTERN VALLEYS. PREVIOUS DISCUSSION AS OF 330 PM EDT SUNDAY... SURFACE HIGH REMAINS OVER THE REGION WITH WEAK SOUTHERLY FLOW ACROSS THE PIEDMONT AND SOUTHEASTERLY FLOW ACROSS THE FOOTHILLS AND BLUE RIDGE. THERE STILL EXIST AN UPPER LEVEL TROUGH WITH WEAK STEERING CURRENTS FROM THE WEST-NORTHWEST. THIS PATTERN IS SIMILAR TO YESTERDAY. EXPECT ISOLATED AFTERNOON SHOWERS AND THUNDERSTORMS TO DEVELOP ACROSS THE MOUNTAINS...MORESO ALONG THE BLUE RIDGE...THEN DRIFT EASTWARD INTO THE FOOTHILLS AND POSSIBLY THE PIEDMONT THIS EVENING. ANY OF THESE DIURNAL STORMS THIS AFTERNOON/EVENING SHOULD REMAIN SMALL BUT COULD PRODUCE VERY LOCALIZED HEAVY DOWNPOURS AS PWATS HAVE INCREASED TO OVER AN INCH. MODELS ARE AGGRESSIVE WITH BRINGING FRONTAL SHOWERS...CURRENTLY OVER THE OHIO VALLEY...IN ACROSS CENTRAL AND NORTHERN VIRGINIA OVERNIGHT. WITH VERY LITTLE UPPER LEVEL SUPPORT AND LACK OF MOVEMENT FROM CURRENT CONVECTION...WILL LOWER CHANCES FOR PRECIPITATION OVERNIGHT AND KEEP A MAINLY DIURNAL THEME. THIS FRONT MAY WASHOUT BEFORE CROSSING OVER THE AREA ON MONDAY. IF THIS IS FACT...WE WILL HAVE ANOTHER DAY OF DIURNALLY DRIVEN SHOWERS AND THUNDERSTORMS FOR THE AREA. COVERAGE SHOULD BE MORE WIDESPREAD ON MONDAY COMPARED TO THIS WEEKEND. WITH NO FRONTAL PASSAGE AND JUST EXPECTING DIURNAL CONVECTION...INCREASED TEMPERATURES A FEW DEGREES WITH MORE SUNSHINE EXPECTED.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... AS OF 333 PM EDT SUNDAY... WILL SEE THE HEAT RETURN AND ESPECIALLY THE HUMIDITY AS 5H HEIGHTS BUILD FROM THE SOUTHERN PLAINS RIDGE. WILL SEE A WEAK FRONTAL BOUNDARY WITH SHORTWAVE IMPULSE SET UP FROM THE OHIO VALLEY INTO THE CAROLINAS THIS PERIOD. QUESTION WILL BE STRENGTH OF WARMING ALOFT AND WEAKENING OF CAP IN THE EVENING FOR STORM DEVELOPMENT. MODELS ALL ADVERTISE SCATTERED CONVECTION ACROSS MOST OF THE FA MONDAY EVENING BEFORE WEAKENING OVERNIGHT. TUESDAY WILL SEE THE IMPULSE WORK SWD INTO KY/NE TN AND NC...WITH THE GFS/ECMWF HINTING AT CONVECTION FIRING UP ACROSS THE SRN CWA....WHILE THE 12Z NAM IS SCATTERED WITH CONVECTIVE FEEDBACK BULLSEYES ACROSS THE MTNS. WILL MAINTAIN CLOSE TO WHAT THE ECMWF/GFS SHOW WITH 30-40 POPS SOUTH OF HIGHWAY 460 AND ROANOKE RIVER WITH LOWER THREAT NORTH. CONVECTION WANES TUESDAY NIGHT WITH HEIGHTS BUILDING MORE THAN TUESDAY AND THINK WEDNESDAY WILL BE OUR HOTTEST DAY THIS WEEK WITH LESS CONVECTION. WILL LIMIT STORMS TO THE MOUNTAINS...MAINLY SW VA/NW NC. BY WED NIGHT THE UPPER LOW OVER CENTRAL CANADA WORKS EAST TOWARD THE JAMES BAY AREA WITH TROUGH OFFERING LOWER HEIGHTS AND PUSH OF FRONTAL BOUNDARY TOWARD THE OHIO VALLEY BY 12Z THURSDAY. WILL KEEP A FEW EVENING STORMS AROUND IN THE SW...THEN DRY LATE...THINKING ANY FRONTAL CONVECTION WILL WAIT TIL THURSDAY. && .LONG TERM /THURSDAY THROUGH SUNDAY/... AS OF 220 PM EDT SUNDAY... OVERALL NOT TOO MUCH CHANGE IN THE FORECAST THIS PERIOD. LOOKS LIKE FRONT WILL SLIDE SOUTHEAST THROUGH OUR AREA BY FRIDAY MORNING. QUESTION ARISES ON HOW FAR SOUTHEAST THIS FRONT GETS AS UPPER FLOW WEAKENS AND BECOMES PARALLEL TO THE FRONT. MODELS SHOWING SEVERAL WAVES OF LOW PRESSURE THIS WEEKEND GOING FROM THE GULF COAST TO THE SOUTHEAST COAST...SUCH THAT THIS COULD PUSH THE FRONT NW TOWARD CENTRAL NC. SWING IN THE UPPER TROUGH FAVORS MOST OF THE DEEPER MOISTURE TO STAY OVER THE ATLANTIC COAST INTO THE COASTAL PLAINS SOUTHWEST TOWARD UPSTATE SC. STILL WILL MAINTAIN LOW CHANCE POPS THIS WEEKEND MAINLY FROM THE SOUTHEAST TO UP ACROSS THE BLUE RIDGE OF VA...WITH LITTLE TO NO CHANCE IN THE VIRGINIA/WEST VIRGINIA MOUNTAINS. PRIOR TO THIS...FRONT SWINGS IN AND BOOSTS OUR THREAT OF SHRA/STORMS THURSDAY INTO THURSDAY NIGHT. MAIN IMPACT LOOKS WEAK AS BETTER JET DYNAMICS STAYS WELL NORTH OVER THE MID ATLANTIC/NORTHEAST...SO FORCING WILL BE JUST WITH THE FRONT. SVR THREAT LOOKS LOW WITH THIS FEATURE AND MODELS HAVE BACKED OFF ON RAINFALL AMOUNTS. TEMPS THIS PERIOD WILL START OUT AT OR SLIGHTLY ABOVE NORMAL THURSDAY THEN START TO GET AT OR JUST BELOW NORMAL FOR THE WEEKEND AS WE STAY ON THE NORTHWEST SIDE OF THE FRONTAL BOUNDARY. DEWPOINTS MAY SINK INTO THE 50S BY SATURDAY MORNING INTO WV/ALLEGHANYS. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... AS OF 800 PM EDT SUNDAY... CURRENT RADAR IMAGERY INDICATES A FEW SLOW MOVING SHOWERS... DEVELOPING MAINLY ALONG/NEAR THE CREST OF THE BLUE RIDGE. HEAVY DOWNPOURS ARE OCCURRING BENEATH THESE CELLS HOWEVER...AND WILL REDUCE VISIBILITIES TO ABOUT 1SM FOR UP TO AN HOUR UNTIL THE CELL EXITS. OUTSIDE CONVECTION...VFR CONDITIONS OBSERVED AREAWIDE WITH LIGHT SOUTHERLY WINDS. OVERNIGHT...MAY SEE A FEW SHOWERS LINGER AS LATE AS 27/03Z. WE CAN EXPECT LOCALIZED MVFR/IFR CONDITIONS AS PATCHY FOG REDEVELOPS... PARTICULARLY IN THE DEEPER MOUNTAIN RIVER VALLEYS AND ACROSS SPOTS THAT RECEIVED SIGNIFICANT RAINFALL THIS EVENING. ANY SUB VFR CONDITIONS WILL IMPROVE RAPIDLY AFTER 27/13Z AS DAYTIME HEATING RAMPS UP. CU FIELD WILL REDEVELOP DURING LATE MORNING...MAINLY MOUNTAINS FIRST BEFORE SPREADING ACROSS THE PIEDMONT. BELIEVE WE WILL SEE WIDER COVERAGE OF SHOWER/THUNDERSTORM ACTIVITY ON MONDAY THANKS TO INCREASED SURFACE CONVERGENCE AND INSTABILITY AS A COLD FRONT APPROACHES FROM THE NORTH. CONVECTION WILL STILL BE PULSEY IN NATURE...CAPABLE OF PRODUCING PROLONGED LOCALIZED HEAVY DOWNPOURS AND GUSTY WINDS. STRONGER UPPER LEVEL WINDS WILL OFFER BETTER SUPPORT HOWEVER...AND MAY SEE A COUPLE STORMS BECOME STRONG TO SEVERE FOR SHORT PERIODS OF TIME. BEST COVERAGE WILL OCCUR ACROSS THE MOUNTAINS...BEGINNING EARLY AFTERNOON...WITH SOME SHOWERS/ STORMS DRIFTING EAST SOUTHEAST ACROSS THE PIEDMONT BY LATER AFTERNOON/EARLY EVENING. EXTENDED AVIATION FORECAST... MODELS APPEAR IN DECENT AGREEMENT THAT THE COLD FRONT WILL STALL JUST NORTH OF THE FORECAST AREA MONDAY EVENING...BEFORE RETREATING BACK TO THE NORTH ON TUESDAY. EXPECT MAINLY VFR CONDITIONS THROUGH THE WORKWEEK OUTSIDE OF SPOTTY CONVECTION EACH AFTERNOON/ EVENING...AND LOCALIZED FOG/STRATUS EARLY EACH MORNING. SHOWER AND THUNDERSTORM CHANCES INCREASE TOWARD THE END OF THE WEEK AS ANOTHER COLD FRONT APPROACHES. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/RCS NEAR TERM...JH/RCS SHORT TERM...WP LONG TERM...WP AVIATION...NF/RCS

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