Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 252334 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 734 PM EDT FRI JUL 25 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 SATURDAY/... AS OF 730 PM EDT FRIDAY... ISOLATED -SHRA POPPED ALONG THE EAST FACING SLOPES OF THE BLUE RIDGE FROM WATAUGA NORTHEASTWARD TO FLOYD. DEWPOINT DISCONTINUITY AND DIFFERENTIAL HEATING ALONG WITH CONTINUED CYCLONIC FLOW ALOFT ENOUGH TO SUPPORT SUCH. SINCE THIS ACTIVITY IS THRIVING ALMOST ENTIRELY ON DAYTIME HEATING AND THERE IS LITTLE AMBIENT INSTABILITY...EXPECT THIS ACTIVITY TO DISSIPATE QUICKLY WITHIN AN HOUR OF SUNSET. OTHERWISE...WILL MAINTAIN NON-MENTIONABLE POPS ELSEWHERE AND ACROSS THE ENTIRE CWA AFT 03Z. ONLY MINOR CHANGES TO TEMPS/DEWPOINTS TO BRING INTO LINE WITH CURRENT OBSERVATIONS. AS OF 330 PM EDT FRIDAY... TRANQUIL AND DRY CONDITIONS EXPECTED THE NEXT 24 HOURS AS HIGH PRESSURE REMAINS IN CONTROL OVERNIGHT AND INTO SATURDAY. OVERNIGHT TEMPS WILL BE CLOSE TO LATE JULY NORMALS WITH UPPER 50S FAR NW TO MID-60S SE AND GENERALLY CLEAR SKIES. 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 /SATURDAY NIGHT 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 /00Z SATURDAY THROUGH WEDNESDAY/... AS OF 730 PM EDT FRIDAY... MAINLY VFR CONDITIONS PREVAILING ACROSS THE REGION THIS EVENING WITH SCATTERED TO BROKEN FAIR WEATHER CUMULUS CLOUDS...GENERALLY 3 TO 6KFT. SOME INSTABILITY UPSLOPE MVFR CLOUDS AND LIGHT SHOWERS ARE OVER THE NORTH CAROLINA HIGH COUNTY BUT WILL FADE THROUGH THE EVENING WITH LOSE OF HEATING. LINGERING MOISTURE WILL LIKELY GET TRAPPED UNDER A SUBSIDENCE INVERSION OVERNIGHT WITH CEILINGS IN THE 2-4KFT RANGE FOR AREAS ALONG AND EAST OF THE BLUE RIDGE. DOWNSLOPE EASTERLY FLOW WILL KEEP WESTERN SLOPES CLEAR MOST OF THE NIGHT...WITH IFR FOG POSSIBLE BY SUNRISE...LIFR IN MOUNTAIN VALLEYS. EXTENDED AVIATION DISCUSSION... EXPECT MAINLY VFR THROUGH SUNDAY EXCEPT FOR OVERNIGHT FOG IN THE VLYS OF LWB/BCB. ANOTHER FRONT IS GOING TO ARRIVE BY MONDAY. BEFORE THIS SEVERAL DISTURBANCES IN NW FLOW ALOFT MAY BRING SHRA/TSRA TO THE BLF/LWB CORRIDOR. SATURDAY IS LESS LIKELY AS MODELS FAVOR A NWD TREND IN CONVECTION TOWARD PA/NRN VA. SUNDAY COULD BE MORE FAVORABLE...BUT STILL LOOKS LIKE A NWD TRACK. WILL HAVE TO WATCH HOW THIS DEVELOPS...BUT POTENTIAL FOR SUB VFR SHRA/TSRA IN THE MTNS IS POSSIBLE LATE THIS WEEKEND. BETTER THREAT WILL BE WITH THE FRONT MONDAY WITH UPPER TROUGH MOVING ACROSS BY TUESDAY DRYING THINGS OUT. && .HYDROLOGY... AS OF 330 PM EDT THURSDAY... RAINFALL YESTERDAY FELL MAINLY EAST OF THE INCREASINGLY DRY AREAS OF THE NEW RIVER VALLEY INTO THE UPPER JAMES BASINS. U.S. DROUGHT MONITOR ISSUED YESTERDAY AND VALID AS OF 12Z TUESDAY JULY 22 SHOWED EXPANSION OF THE EXISTING ABNORMALLY DRY CONDITIONS INTO MOST OF OUR SE WV COUNTIES AND FAR WESTERN VA...MAINLY THE UPPER JAMES RIVER BASIN. 30-DAY RAINFALL DEFICITS IN MUCH OF THIS AREA ARE RUNNING 2 TO 3 INCHES OR ONLY 25 TO 50 PERCENT OF NORMAL AND 60-DAY RAINFALL NUMBERS NOT MUCH BETTER. JULY IS CLIMATOLOGICALLY THE WETTEST MONTH IN OUR CWA WITH AN AVERAGE RANGING FROM 4 TO 5 INCHES. && .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 SHORT TERM...JH LONG TERM...JH AVIATION...PC/RCS HYDROLOGY...PC CLIMATE...PC

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