Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 260552 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 152 AM EDT SAT JUL 26 2014 .SYNOPSIS... WEAK HIGH PRESSURE WILL REMAIN OVER THE AREA TONIGHT BEFORE SLIDING OFFSHORE THE SOUTHEAST COAST ON SATURDAY. A STRONG COLD FRONT WILL APPROACH FROM THE NORTHWEST SUNDAY AND PASS ACROSS THE REGION SUNDAY NIGHT INTO MONDAY. COOL HIGH PRESSURE SETTLES IN BEHIND THE FRONT LATER MONDAY RESULTING IN COOLER AND DRIER WEATHER INTO THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THROUGH TODAY/... AS OF 100 AM EDT SATURDAY... ANOTHER UPDATE TO ACCOUNT FOR SHRA OVER THE FOOTHILLS OF THE BLUE RIDGE IN VA/NC. 0Z LOCAL WRF SHOWED THIS WELL AND DEVELOPS SHOWERS FURTHER NORTH AND EAST ACROSS THE FOOTHILLS THRU THE MORNING. INCREASING THETA-E IN THE LOW LVLS AND CONVERGENCE LEADING TO THIS. SLOW MOVERS WILL POSE SOME HEAVY RAIN ISSUES FOR SOME. OTHERWISE...NO OTHER MAJOR CHANGES TO THE OTHER FORECAST PARAMETERS EXCEPT ADJUSTING SKY COVER TO MATCH LATEST SAT/MODEL TRENDS THROUGH 12Z. PREVIOUS VALID DISCUSSION... PATCHY FOG POSSIBLE IN SOME OF THE WETTER LOCATIONS BUT NOT EXPECTING WIDESPREAD EARLY MORNING FOG WITH SOME MID-LEVEL CLOUDS POSSIBLY INHIBITING FORMATION. THE HIGH QUICKLY SHIFTS EAST ON SATURDAY WITH A WARM FRONT SURGING NORTH OF THE AREA AND A BROAD WEST TO SOUTHWEST FLOW DEVELOPING AT LOW TO MID-LEVELS ALONG WITH INCREASING HUMIDITY. DEWPOINTS WILL RISE INTO L/M 60S BY AFTERNOON ACROSS MUCH OF THE AREA AND TEMPS ALSO WARM BY ABOUT 5F OR SO FROM TODAYS HIGHS...RANGING FROM NEAR 80 NW TO NEAR 90 SE. SUPPORT FOR AFTERNOON CONVECTION APPEARS WEAK AS FAIRLY STRONG CAP EXPECTED TO BE IN PLACE BETWEEN 850-800 MB AND NO TRIGGER ACROSS THE REGION...KEPT POPS OUT THROUGH THE PERIOD. && .SHORT TERM /TONIGHT THROUGH MONDAY/... AS OF 215 PM EDT FRIDAY... WEAK RIDGING WILL CONTINUE TO BREAK DOWN SATURDAY NIGHT IN ADVANCE OF HEIGHT FALLS TO THE NW IN ASSOCIATION WITH THE DEVELOPING UPSTREAM TROUGH AND COLD FRONT. MOISTURE APPEARS LACKING SATURDAY EVENING EXCEPT ACROSS THE FAR NORTH WITH ANY UPSTREAM SHRA/TSRA LIKELY NOT MAKING A RUN AT THE FAR NW UNTIL LATE AT NIGHT. THUS REMOVED POPS SATURDAY EVENING AND THEN KEPT A SHARP GRADIENT TO LIKELY POPS EXTREME NW AS A PROBABLE COMPLEX OF STORMS MOVES IN FROM THE OHIO RIVER. WITH GUIDANCE SHOWING THE BEST JET ALOFT AND THETA-E STILL WELL WEST DID SLOW DOWN ARRIVAL OF POPS UNTIL AROUND DAYBREAK ALTHOUGH MAY BE MORE LIKE A SURGING OUTFLOW OF WIND GIVEN TIMING PER LACK OF FORECAST INSTABILITY. MAIN CONCERN REMAINS ON SUNDAY WITH THIS AFOREMENTIONED MCS POTENTIAL EARLY AND THEN ADDED DEVELOPMENT OF AT LEAST STORM CLUSTERS ESPCLY NORTH AND WEST UNDER A PASSING STRONG WAVE TO THE NORTH. HOWEVER MODELS REMAIN RELUCTANT TO BRING ORGANIZED CONVECTION OVER THE WESTERN MOUNTAINS AND INTO DEEP WESTERLY FLOW WELL AHEAD OF THE COLD FRONT TO THE NW. BEST INSTABILITY ALSO STAYS OFF TO THE NORTH/WEST AND THEN DEVELOPS TO THE SW WHERE MAY SEE THE INITIAL MCS MOVE TOWARD...OR ANOTHER DEVELOP SUNDAY AFTERNOON/EVENING BEHIND THE INITIAL IMPULSE PER LATEST 12Z ECMWF. DOES APPEAR GIVEN THE STRONG FLOW ALOFT THAT SOME OF THE CONVECTION COULD MOVE FASTER THAN EXPECTED INTO THE WEST SUNDAY MORNING AND THEN REDEVELOP WITH HEATING UNDER THE PASSING TAIL OF THE VERY STRONG MID LEVEL JET JUST NORTH SUNDAY AFTERNOON. SINCE THINK GUIDANCE TOO DRY...STAYED WITH LIKELY/CAT POPS NW THIRD SUNDAY AND INCLUDED CHANCE COVERAGE ELSW WITH INCLUSION OF GUSTY WINDS NW. TEMPS WILL SURGE SUNDAY PROVIDED CAN BURN OFF EARLY DEBRIS CLOUDS WITH HIGHS LIKELY LOW/MID 90S EAST AND 80S WEST AS DEEP WEST/SW FLOW PUNCHES 85H TEMPS TO AROUND +25C. UNCERTAINTY CONTINUES SUNDAY NIGHT INTO MONDAY WITH LATEST MODEL TRENDS TO LINGER CONVECTION WESTERN SLOPES SUNDAY EVENING BEFORE JUMPING TO THE EASTERN LEE TROUGH OVERNIGHT BEFORE COVERAGE FADES. ONCE THIS HAPPENS THE ACTUAL FRONT MAY BLEND INTO THE LEE TROUGH...AND CAUSE A SURGE IN DRIER AIR ALOFT ON MORE OF A NW TRAJECTORY...IN TURN LIMITING POPS TO MORE OF THE FAR WEST AND SE INTO MONDAY AFTERNOON. SINCE THIS SCENARIO SIMILAR TO THE LATEST ECMWF...ADJUSTED POPS DOWN SOME ON MONDAY WITH A SPLIT IN COVERAGE ALONG THE BLUE RIDGE WHERE COULD GO MOSTLY DRY AFTER SUNDAY NIGHT. ENOUGH COOL ADVECTION TO KEEP HIGHS IN THE 70S WEST OF THE BLUE RIDGE MONDAY WITH STILL 80S TO NEAR 90 EAST. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... AS OF 1245 PM EDT FRIDAY... COLD FRONT ALONG THE LEADING EDGE OF THE LARGE 5H TROUGH FOR LATE JULY WILL BE WELL TO THE EAST BY MONDAY NIGHT ALLOWING STRONG COOL ADVECTION TO CONTINUE AS HIGH PRESSURE BUILDS IN FROM THE NW. MAY SEE SOME UPSLOPE SHOWERS PERSIST MONDAY EVENING AT THE ONSET OF THE BETTER COOLING ALOFT AND NW FLOW SO WILL KEEP SOME LOW POPS FAR WEST EARLY. OTRW SHOULD BE DRYING OUT WITH A SIGNIFICANT COOL SHOT THAT WILL PERSIST FOR MUCH OF THE WEEK. MODELS DO BRING A COUPLE RE-ENFORCING SHORTWAVES AROUND THE UPPER TROUGH LATE IN THE PERIOD WITH THESE PIVOTING THROUGH THE REGION THURSDAY INTO FRIDAY. HOWEVER MOISTURE LIMITED UNDER THE CONTINUED WEAK RIDGING WITH POPS MAINLY DRIVEN BY COLD AIR ALOFT AND WEAK LOCAL CONVERGENCE MAINLY MOUNTAINS. THUS INCLUDING SOME SLIGHT POPS LATER THURSDAY AND A BIT MORE CHANCE COVERAGE FRIDAY WITH A SECOND STRONGER MID LEVEL WAVE THAT LOOKS TO SHARPEN UP THE TROUGH A LITTLE MORE. BELOW NORMAL TEMPS THE MAIN ASPECT OF NEXT WEEK WITH HIGHS LIKELY A GOOD 5-10 DEGREES BELOW AVERAGE MUCH OF THE PERIOD AND LOWS DIPPING INTO THE 40S AND 50S. COLDEST MORNINGS LOOK TO BE WEDNESDAY AND THURSDAY WHEN THE SURFACE RIDGE WILL BE NEARBY AND 85H TEMPS REMAIN AROUND +10C OVER THE WEST. THIS COULD PRODUCE SOME RECORD LOWS WITH COOP MOS DATA GIVING DEEP VALLEY READINGS WELL DOWN INTO THE 40S. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... AS OF 130 AM EDT SATURDAY... MAINLY VFR CONDITIONS PREVAILING ACROSS THE REGION...WITH SUB VFR AND SHOWERS BETWEEN HLX AND MTV AND MWK. FOLLOWED THE 00Z LOCAL WRF HAS IT HANDLED THINGS PRETTY WELL PER LATEST RADAR/OBS. THE SHOWERS NORTH OF MWK ARE PROGGED TO STAY IN THE FOOTHILLS OF VA INTO 08Z WITH MORE SHRA DEVELOPMENT FURTHER NORTH EAST OF ROA AND NEAR LYH. ADDED VCSH AT LYH BY 10Z. THINK THE MVFR CIGS WILL GET INTO ROA/LYH AFTER 08Z. FOG IS ALSO POSSIBLE AT LYH. FURTHER SOUTH IN DAN LOOKING AT VFR CIGS DROPPING TO IFR AT TIMES WITH FOG. IN THE MTNS...WATCHING FOR POTENTIAL FOG FORMATION ESPECIALLY LWB/BCB. HOWEVER...SOME MID/HIGH CLOUDS ARE MOVING ACROSS WHICH COULD INHIBIT HOW LOW VSBYS GO. CONFIDENCE IS MODERATE TO HAVE IFR TEMPO AT LWB/BLF AND BCB IN THE 08-12Z TIME FRAME. ANY LOWER CLOUDS AND FOG SCATTERS OUT BY LATE MORNING THOUGH SOME VFR CIG ARE EXPECTED AT TIMES IN ROA/BCB/DAN...AROUND 5-8KFT. NEXT ISSUE FOR SUB VFR WILL BE WITH UPSTREAM SYSTEM AND POSSIBLE TSRA ARRIVING BY MID AFTERNOON SUNDAY. MODELS FAVORING BLF/LWB MORE FOR STORMS ARRIVING BY 18Z SUNDAY...WITH POTENTIAL STRONG WINDS AND SUB VFR CIGS/VSBYS WITH HEAVY RAIN. SOME CONVECTION ALSO POSSIBLE TO THE EAST BUT MAINLY EAST OF A LYH/DAN LINE BY 00Z MONDAY. A STRONG FRONT IS GOING TO ARRIVE BY MONDAY MORNING. MODELS STILL FAVORING THE WRN CWA BLF/LWB WITH SHRA/TSRA INTO SUNDAY NIGHT AND EARLY MONDAY WITH LITTLE DOWNSTREAM OVER THE REST OF THE CWA. SOME GUSTY WINDS BEHIND THE FRONT MONDAY WITH DRIER AIR PUSHING IN FOR TUE-WED...AND MAINLY VFR. CANNOT RULE OUT LATE NIGHT FOG BCB/LWB BUT LOW LVLS MAY STAY DRY ENOUGH FOR LESS FOG COVERAGE. && .CLIMATE... RAINFALL YESTERDAY (7/24) AT LYNCHBURG AIRPORT OF 3.88 INCHES WAS 2ND HIGHEST ON RECORD AFTER JULY 24 1916 WHEN 4.03 INCHES FELL. IT WAS ALSO THE 2ND HIGHEST FOR ANY JULY DAY. WILL ISSUE PNS (WBCPNSRNK) WITH A FEW MORE DETAILS ON THIS UNUSUAL EVENT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/WP NEAR TERM...PC/RAB/WP SHORT TERM...JH LONG TERM...JH AVIATION...PC/RCS/WP CLIMATE...PC

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