Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 231544 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA ISSUED BY NATIONAL WEATHER SERVICE RALEIGH NC 1144 AM EDT WED JUL 23 2014 .SYNOPSIS... CYCLONIC FLOW ALOFT WILL PREVAIL ACROSS THE EASTERN UNITED STATES THROUGH THURSDAY...DOWNSTREAM OF AN UPPER LEVEL RIDGE ANCHORED OVER THE ROCKIES. WEAK UNIDIRECTIONAL FLOW ALOFT WILL PREVAIL ON FRIDAY AND SATURDAY AS THE UPSTREAM RIDGE FLATTENS AND EXTENDS EASTWARD INTO THE CENTRAL MISSISSIPPI RIVER VALLEY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1140 AM EDT WEDNESDAY... AFTERNOON: LOW-TOPPED SHOWERS PROGRESSING TOWARD THE WV/VA BORDER THIS MORNING ARE A RESULT OF ORORGRAPHIC ASCENT VIA WEST/NW LOW- LEVEL FLOW AND A SMALL AMPLITUDE TROUGH AT 700 MB...IN THE PRESENCE OF 500-100 J/KG MLCAPE ASSOCIATED WITH A VERY MOIST BOUNDARY LAYER. EXPECT THIS ACTIVITY TO PERSIST ON THE HIGHER RIDGES ALONG THE WV/VA BORDER THROUGH EARLY AFTERNOON...WITH LITTLE OR NO ACTIVITY ELSEWHERE THROUGH MID AFTERNOON. EXPECT HIGHS IN THE UPPER 80S TO LOWER 90S IN THE NC/VA PIEDMONT. EVENING: STRENGTHENING CYCLONIC FLOW ALOFT OVER THE OH VALLEY AND WESTERN MID-ATLANTIC LATE THIS AFT/EVE WILL RESULT IN A GRADUAL INCREASE IN SYNOPTIC ASCENT FROM THE WEST VIA DPVA ASSOC/W SMALL AMPLITUDE SHORTWAVES AND STRENGTHENING CYCLONIC SHEAR VORTICITY. A COLD FRONT ATTENDANT THE AMPLIFYING UPPER LEVEL TROUGH EXTENDED SOUTHWEST FROM THE LOWER GREAT LAKES THROUGH CENTRAL IN AND SOUTHERN IL AT 15Z WILL PROGRESS SOUTHEAST INTO KY/WV AND SOUTHERN OH/PA BY 00Z THIS EVENING...WITH A PRONOUNCED PRE-FRONTAL TROUGH DEVELOPING EAST OF THE BLUE RIDGE IN VA/NC. WITH THE ABOVE IN MIND...EXPECT THE BEST CHANCE FOR CONVECTION IN THE RNK CWA TO BE LATE THIS AFT/EVE IN VICINITY OF THE WV/VA BORDER WHERE MODERATE DIURNAL DESTABILIZATION (1000-1500 J/KG) IS EXPECTED AS STEEP MID- LEVEL LAPSE RATES ADVECT EAST ATOP A SEASONABLY MOIST BOUNDARY LAYER IN THE PRESENCE OF STRENGTHENING SYNOPTIC ASCENT. EXPECT A MUCH LOWER POTENTIAL FOR CONVECTION EAST OF THE APPALACHIANS WHERE FORCING FOR ASCENT WILL BE CONFINED TO SHALLOW CONVERGENCE ASSOC/W THE PRE-FRONTAL TROUGH AND WHERE WEAK MID-LEVEL LAPSE RATES WILL TEMPER DESTABILIZATION. SEVERE POTENTIAL: RELATIVELY STEEP MID-LEVEL LAPSE RATES OF 6.0-6.5 C/KM...MODERATE INSTABILITY...AND 0-6 KM SHEAR OF 20-30 KT WOULD SUPPORT A POTENTIAL FOR MARGINALLY SEVERE HAIL AND/OR ISOLD DOWNBURSTS IN ASSOCIATION WITH ANY VIGOROUS UPDRAFTS /DEEP CONVECTION/ THAT DEVELOPS ALONG AND AHEAD OF THE FRONT LATE THIS AFTERNOON AND EVENING FROM THE OH VALLEY EAST INTO THE APPALACHIANS. -VINCENT TONIGHT...STILL WILL SEE SOME CONVECTION AROUND BUT DISSIPATING OUT EAST AFTER MIDNIGHT. FRONTAL BOUNDARY WILL MAKE ITS WAY TOWARD THE WV/KY LINE BY THU MORNING...AND MODELS AGREE THAT PRECIP WILL BE IN THE SE WV/FAR SW VA CORRIDOR BY LATE TONIGHT SO HAVE KEPT LIKELY POPS HERE FADING TO SLIGHT CHANCE EAST OF THE BLUE RIDGE. MORE CLOUD COVER AND HIGH DEWPOINTS WILL KEEP LOWS ELEVATED IN THE MID 60S TO LOWER 70S. -WP && .SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/... AS OF 345 AM EDT WEDNESDAY... WILL START THURSDAY OFF WITH THE COLD FRONT MAKING ITS WAY ACROSS WEST VIRGINIA TOWARD OUR AREA. WITH THE FRONT IN SUCH CLOSE PROXIMITY...WILL ALREADY HAVE SPOTTY SHOWERS AND A FEW THUNDERSTORMS PASSING MAINLY ACROSS THE MOUNTAINS BY SUNRISE...WITH COVERAGE INCREASING THROUGH LATE MORNING AS THE FRONT ENTERS OUR AREA AND DAYTIME HEATING INCREASES. WHILE MUCH OF OUR AREA WILL EXPERIENCE RAINFALL DURING THE MORNING AND AFTERNOON...BELIEVE INSTABILITY WILL BE MORE MUTED COMPARED TO WEDNESDAY DUE IN PART TO THE INCREASED CLOUD COVER. AS SUCH...MOST OF THE THUNDERSTORM ACTIVITY THAT DEVELOPS ACROSS THE MOUNTAINS WILL BE WEAK...ALTHOUGH CANNOT RULE OUT A FEW STRONG STORMS ACROSS THE SOUTHSIDE DURING THE AFTERNOON/ EVENING WHERE HEATING AND INSTABILITY WILL BE STRONGEST. AFTERNOON HIGHS WILL RANGE FROM THE MID 70S ACROSS THE MOUNTAINS TO THE MID 80S ACROSS THE SOUTHSIDE. THE COLD FRONT IS EXPECTED TO SHIFT SOUTH OF OUR AREA THURSDAY NIGHT BEFORE STALLING ACROSS THE CAROLINAS FRIDAY MORNING. REGARDLESS... HIGH PRESSURE BUILDING IN BEHIND THE FRONT IS NOT VERY STRONG...AND WITH MID TO UPPER 60 DEGREE DEWPOINTS LINGERING ACROSS THE SOUTHSIDE...MAY STILL SEE A FEW SHOWERS AND ISOLATED THUNDERSTORMS DEVELOP WITH AFTERNOON HEATING. OTHERWISE...INCREASED SUNSHINE WILL HELP AFTERNOON HIGHS REACH NEAR NORMAL FOR LATE JULY...WITH TEMPERATURES RANGING FROM THE UPPER 70S WEST TO THE UPPER 80S EAST. WIND FLOW ALOFT WILL SHIFT NORTHWESTERLY FRIDAY AS AN UPPER LEVEL TROUGH PASSES EAST ACROSS THE GREAT LAKES...WHILE A LARGE DOME OF HIGH PRESSURE REMAINS SITUATED OVER THE SOUTHWEST U.S. THIS WILL OPEN THE DOOR FOR UPPER LEVEL DISTURBANCES TO ENTER THE AREA FROM THE MIDWEST FOR THE WEEKEND. THE NAM/ECMWF/CANADIAN MODELS ALL ARE PICKING UP ON ONE DISTURBANCE APPROACHING BY SUNRISE SATURDAY...MOST LIKELY TRIGGERING A BAND OF STORMS THAT WILL BE SIGNIFICANTLY WEAKENED AS IT ENTERS OUR SOUTHEAST WEST VIRGINIA/MOUNTAIN EMPIRE COUNTIES. STILL NOT ENTIRELY CONFIDENT IN THIS SCENARIO PLAYING OUT AT THIS POINT...SO WILL STICK WITH A SLIGHT CHANCE OF SHOWERS AND STORMS FOR SATURDAY MORNING. MORE DISTURBANCES ARE SLATED TO ARRIVE ON SATURDAY AND SATURDAY NIGHT...ALTHOUGH TIMING OF THESE DISTURBANCES THIS FAR IN ADVANCE IS ALWAYS DIFFICULT. && .LONG TERM /SUNDAY THROUGH TUESDAY/... AS OF 400 PM EDT TUESDAY... INTO EARLY NEXT WEEK...THE AREA REMAINS VULNERABLE TO NW FLOW DISTURBANCES TRACKING AROUND THE LARGE WESTERN/CENTRAL CONUS UPPER RIDGE. A PARTICULARLY STRONG DISTURBANCE...NOTED BY ALL THE MODELS...PROMISES TO AMPLIFY THE EASTERN LONG WAVE TROUGH...A FEATURE THAT SHOULD KEEP CONDITIONS UNSETTLED WITH NEAR TO SLIGHTLY BELOW NORMAL TEMPERATURES WHILE THE EXTREME HEAT REMAINS WELL TO OUR WEST AND WELL AWAY FROM OUR PART OF THE COUNTRY. THE BEST CHANCE FOR SHOWERS/STORMS LOOKS TO BE SUNDAY AS THE SURFACE FRONT ASSOCIATED WITH THE STRONG DISTURBANCE CROSSES THE FORECAST AREA FROM THE NORTHWEST. POTENTIAL EXISTS FOR STORMS TO BE ORGANIZED WITH UPSTREAM MCS IMPACTING THE FORECAST AREA. GENERALLY FOLLOWED HPC GUIDANCE THROUGH THE PERIOD. TRENDED POPS UP FOR SUNDAYS FROPA...THEN DOWN FOR A DAY OR TWO AFTER SUNDAYS FRONTAL PASSAGE. TENDENCY FOR FRONTAL PASSAGES IS TO BRING SOME DOWNTIME AS WITH RESPECT TO POPS BEFORE MOISTURE AND INSTABILITY CAN RETURN. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... AS OF 725 AM EDT WEDNESDAY... FOG BECAME DENSE AT LWB/BCB WITH MVFR AT DAN/LYH. FOG WILL DISSIPATE BY 13Z...WITH VFR EXPECTED MUCH OF THE DAY. HIGH-RES MODELS ARE FAVORING CONVECTION OVER THE BLUE RIDGE AND ALLEGHANY HIGHLANDS BY 18Z...SO HAVE VCTS AT ROA/BCB/BLF/LWB...PER HRRR. THE CONVECTION WILL WANE LATE AFTERNOON/EARLY EVENING BEFORE FRONTAL PRECIP ARRIVES AFTER MIDNIGHT IN THE BLF/LWB CORRIDOR. AMENDMENTS MAY BE NEEDED FOR TSRA TODAY IF TERMINALS ARE THREATENED. OTHERWISE...COVERAGE DOES NOT DICTATE HAVING PREDOMINANT TSRA IN THE TAFS. EXTENDED AVIATION DISCUSSION... NEXT NORTHERN STREAM UPPER TROUGH AND ITS ASSOCIATED COLD FRONT WILL APPROACH WORK THROUGH THE REGION ON THURSDAY. THIS WILL BRING THE BEST CHANCES OF MORE WIDESPREAD SHOWERS TO THE MOUNTAINS AND PERHAPS SOME DEEPER CONVECTION EAST OF THE BLUE RIDGE PENDING TIMING OF THE BOUNDARY THURSDAY AFTERNOON. AIRMASS WILL DRY OUT BEHIND THE FRONT GOING INTO FRIDAY- SATURDAY. OVERALL EXPECT SUB VFR AT TIMES THURSDAY WITH SHRA/TSRA AND MAYBE SOME FOG THU NIGHT...FOLLOWED BY VFR FRI- SAT OUTSIDE OF ANY VALLEY FOG AT KLWB/KBCB EACH MORNING. && .EQUIPMENT... AS OF 405 AM EDT WEDNESDAY... KFCX RADAR IS DOWN. TECHNICIANS WILL AGAIN BE WORKING ON THE RADAR TODAY.. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT/WP SHORT TERM...NF LONG TERM...PM AVIATION...PH/WP EQUIPMENT...PH/WP

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