Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 261912 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 312 PM EDT SAT JUL 26 2014 .SYNOPSIS... A WEAK WARM FRONT LIFTS NORTHEAST ACROSS THE AREA TONIGHT IN ADVANCE OF A STRONG UPPER DISTURBANCE APPROACHING FROM THE WEST LATE. THUNDERSTORMS WILL DEVELOP WITH THIS FEATURE ALONG THE FRONTAL BOUNDARY ACROSS THE MIDWEST THIS EVENING AND SPREAD EAST TOWARD OUR AREA BY EARLY SUNDAY. A STRONG COLD FRONT SHOULD MOVE ACROSS THE REGION LATER SUNDAY NIGHT INTO MONDAY...WITH COOLER WEATHER INTO THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH SUNDAY NIGHT/... AS OF 210 PM EDT SATURDAY... THINGS REMAIN QUIET THIS AFTERNOON IN THE WAKE OF THE MID LEVEL WAVE PASSING TO THE NE AND UNDER WEAK SURFACE RIDGING ACROSS THE MOUNTAINS. COULD STILL POP AN ISOLATED SHRA FAR SE GIVEN CLOSE PROXIMITY TO THE LOW LEVEL THETA-E RIDGING AND WARM FRONT...OTRW EXPECTING A TRANQUIL EVENING TO INIT AS THE WARM FRONT EDGES NE INTO THE CWA. MAIN CONCERN THEN SWINGS INTO THE LATE NIGHT HOURS AS MID LEVEL ENERGY NOW OVER IA/MO STARTS TO SWING EAST UNDER THE APPROACHING 5H TROF WELL TO THE NW. MODELS TEND TO AMPLIFY THE SOUTHERN SHORTWAVE THIS EVENING AS IT CROSSES VERY HIGH INSTABILITY OVER THE MIDWEST WITH AN EVOLVING MCS JETTING EAST LATER ON. THIS FEATURE LOOKS ON TRACK TO APPROACH THE NW SLOPES ALONG THE RETREATING WARM FRONT BY DAYBREAK AIDED BY A VERY STRONG WESTERLY JET ALOFT. FORWARD MOMENTUM EAST OF THE INDUCED COLD POOL ALOFT THE KEY TO GETTING THIS SYSTEM IN FASTER WITH AN ENHANCED SEVERE THREAT THE SOONER IT ARRIVES SINCE LIKELY TO WEAKEN UPON CROSSING THE RIDGES AROUND 12Z. THEREFORE KEPT HIGH POPS IN SIMILAR TO EARLIER WITH LOW LIKELYS FAR NW AND CHANCE COVERAGE OUT TO NEAR THE BLUE RIDGE LATE. LOW TEMPS LOOK QUITE WARM/MUGGY WITH SOME SPOTS STAYING IN THE 66-73 RANGE PER RISING DEWPOINTS AND CLOUDS/MIXING LATE. BIGGEST UNCERTAINTY REMAINS IN THE SUNDAY-SUNDAY EVENING PERIOD IN REGARDS TO THE EVOLUTION OF THE INITIAL MCS AND LATER DEVELOPMENT OF PERHAPS ANOTHER SYSTEM JUST TO OUR SW BEFORE MORE CONVECTION ARRIVES WITH THE ACTUAL COLD FRONT SUNDAY EVENING. GUIDANCE SPREAD REMAINS QUITE LARGE WITH SOLUTIONS VARYING FROM PUNCHING A WEAKENING SYSTEM ACROSS NORTH OF HIGHWAY 460 SUNDAY MORNING PER GFS/NCEP WRF...TO KEEPING THE CORE TO THE NW SIMILAR TO THE NAM/CMC...TO RIDING THE FEATURE SOUTH DOWN THE WESTERN SLOPES LIKE THE ECMWF TO WHERE BETTER INSTABILITY WILL RESIDE. FOR NOW WILL LEAN MORE TOWARD THE GFS GIVEN FAST MOVEMENT/BACKING FLOW AND BRING ACTIVITY FARTHER EAST ACROSS THE NORTH SOONER ALONG THE RESIDUAL WARM FRONT...FOLLOWED BY A LULL CENTRAL/EASTERN SECTIONS IN THE AFTERNOON AS A STRONG MID LEVEL DRY PUNCH ON DEEP WESTERLY FLOW ARRIVES IN ITS WAKE. HOWEVER LIKELY TO SEE ANOTHER MCS TAKE SHAPE OVER THE FAR SW AND WESTERN SECTIONS INTO WEST VA ON THE TAIL OF THE RESIDUAL EARLIER OUTFLOW SO SOMETHING TO WATCH. DEGREE OF DEBRIS CLOUDS AND MIXING TO DETERMINE IF ADDED CLUSTERS OF STORMS REDEVELOP NORTH HALF DURING THE LULL SUNDAY AFTERNOON...AND PERHAPS FARTHER SOUTH INTO SOUTHSIDE VA/NW NC WHERE MAY GET MISSED BY MUCH OF THE ACTIVITY OUTSIDE THE MOUNTAINS INTO SUNDAY NIGHT. USED A BLEND OF HIGHS RANGING FROM THE COOLER MET MOS NW UNDER THE CLOUDS/PRECIP TO THE VERY WARM MAV VALUES SOUTH WHERE LIKELY MORE SUNSHINE AIDED COMPRESSIONAL WARMING LIKELY TO PUSH THE MID 90S. THUS WILL GO WITH A PERIOD OF CAT/LIKELY POPS INCLUDING GUSTY WINDS/HEAVY RAIN MENTION NW INTO EARLY AFTERNOON SUNDAY...AND ALONG THE WESTERN SLOPES INTO SW VA THROUGH LATE IN THE DAY. HOWEVER WILL HOLD OFF ON A FLOOD WATCH AT THIS POINT GIVEN QPF UNCERTAINTY AND DRY ANTECEDENT CONDITIONS. ELSW...GOING WITH MORE CHANCE NATURE POPS FOR NOW AND CAN BUMP UP LATER IF THINGS TREND FARTHER SOUTH THAN EXPECTED. ACTUAL COLD FRONT ALONG WITH BETTER DYNAMICS AND COLDER AIR ALOFT ARRIVE SUNDAY NIGHT WITH PERHAPS ANOTHER BAND OF CONVECTION ATTEMPTING TO CROSS THE WESTERN SLOPES. THUS KEPT LIKELY POPS SUNDAY EVENING FAR WEST AND CHANCE BLUE RIDGE BUT ONLY SLIGHT COVERAGE EAST PER CONTINUED DOWNSLOPE. WINDS WILL TURN GUSTY FROM THE NW LATE SUNDAY NIGHT AS THE 85H FRONT CROSSES AND THE JET MIXES DOWN UNDER THE INCREASING COOL ADVECTION. MAV/MET MOS SIMILAR AND FOLLOWED FOR LOWS WHICH WILL STILL BE QUITE MILD...MOSTLY 60S SUNDAY NIGHT UNDER MIXING. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 200 PM EDT SATURDAY... SHORT TERM PERIOD WILL BE CHARACTERIZED BY UPPER TROFFING AND COLD ADVECTION AS SURFACE HIGH PRESSURE BUILDS SLOWLY SOUTHEAST FROM OUT OF THE UPPER MIDWEST. UPSLOPING CLOUDS ALONG THE WESTERN FLANKS OF THE APPALACHIANS WILL BE COMMON...ALONG WITH THE THREAT FOR DIURNALLY DRIVEN SHOWERS...AND POSSIBLY AN ISOLATED LATE AFTERNOON/EVENING THUNDERSHOWER DUE TO COOLER AIR ALOFT CLOSER TO TROF AXIS...AND INFLUENCE OF WEAK FORCING PROVIDED BY SERIES OF WEAK SHORT WAVE TROFS EMBEDDED IN UPPER FLOW TO IMPACT AREA BOTH MONDAY AND ON TUESDAY. TEMPERATURES IN THE MOUNTAINS WILL BE UNSEASONABLY COOL...WITH DAYTIME HIGHS NOT LIKELY TO CLIMB OUT OF THE 60S ON EITHER MONDAY OR TUESDAY ACROSS THE HIGHEST TERRAIN WHERE UPSLOPING CLOUDS WILL BE MAXIMIZED. EAST OF THE BLUE RIDGE...INFLUENCE OF COLD ADVECTION WILL BE OFFSET SOMEWHAT BY DOWNSLOPING/COMPRESSIONAL WARMING AND BETTER INSOLATION TO SUPPORT HIGHS REACHING INTO THE 80S...YET STILL A BIT LOWER THAN CLIMATOLOGICAL AVERAGES. NIGHTTIME LOWS WILL BE LARGELY GOVERNED BY EXTENT OF MIXING AND CLOUD COVER. HIGHER ELEVATIONS WHERE/IF CLOUDS CAN CLEAR...AND ESPECIALLY THE MOUNTAIN VALLEYS WHERE BOUNDARY LAYER DECOUPLING WILL MORE READILY OCCUR SHOULD EXPERIENCE READINGS DOWN INTO THE 40S...PERHAPS WELL DOWN INTO THE 40S...ESPECIALLY LATE TUESDAY NIGHT AS SURFACE RIDGE PRESSES CLOSER INTO THE AREA AND AS GRADIENT WINDS RELAX. READINGS EAST OF THE BLUE RIDGE WILL BE A BIT MILDER...MAINLY 50S...YET STILL 8-10F BELOW CLIMATOLOGICAL AVERAGES. && .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 /19Z SATURDAY THROUGH THURSDAY/... 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 SHORT TERM...WERT LONG TERM...CF AVIATION...JH/WP

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