Issued by NWS Blacksburg, VA
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KRNK 210846 CCA AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 342 AM EST SAT NOV 21 2009 .SYNOPSIS... HIGH PRESSURE WILL REMAIN IN THE AREA TODAY INTO EARLY TONIGHT. LOW PRESSURE DEVELOPING ACROSS THE GULF COAST STATES WILL IMPACT OUR WEATHER SUNDAY WHILE HIGH PRESSURE WEDGES DOWN FROM THE NORTHEAST. && .NEAR TERM /THROUGH TONIGHT/...-- Changed Discussion --THE 00Z MODELS HAVE CONTINUED TO TREND DRIER THIS RUN WITH THE SYSTEM COMING OUT OF THE GULF COASTAL REGION. THE 00Z GFS ATTM...IS DOING A BETTER JOB HANDLING THE CS POURING OVER THE REGION AHEAD OF THE NRN STREAM TROUGH ACROSS THE MIDWEST. THESE HIGH CLOUDS HAVE LIMITED FOG DEVELOPMENT...BUT STILL SHOULD SEE SOME THINNING ACROSS THE RIVER VALLEYS SO KEPT SOME PATCHY FOG IN THIS MORNING. FOR TODAY...THE MAIN FORECAST CHALLENGE WILL BE EXTENT OF CLOUDINESS AND EFFECT ON TEMPS. DURING THE LATE FALL MONTHS THE GFS SEEMS TO DO A BETTER JOB WITH HIGH CLOUDS IN TERMS OF ITS RH DEPICTION IN THE UPPER LVLS...AND THE AMOUNT OF OPAQUENESS IS SOMETIMES UNDERESTIMATED. FOR NOW...WITH THE NRN STREAM SHORTWAVE MOVING ACROSS THE OHIO VALLEY TODAY THINK THE HIGH CLOUDS WILL GET SHUNTED EAST...WITH SOME LOWER CLOUDS ARRIVING IN THE NWRN CWA...ALTHOUGH NOT IMPRESSED WITH THAT ATTM. WITH THIS IN MIND...HAVE RUN WITH A MIDDLE OF THE ROAD APPROACH FOR SKY COVER WITH 40-60 PERCENT COVERAGE. HIGHS AS SUCH WILL REMAIN CLOSE TO THE PREVIOUS FORECAST OF 50S IN THE MTNS TO LOWER 60S OUT EAST...CLOSE TO A MOS BLEND. TONIGHT...THE NRN STREAM SHORTWAVE SLIDES SLOWLY INTO THE MID ATLANTIC STATES WITH SHORTWAVE RIDGING OCCURRING OVER OUR CWA....WHILE THE TROUGH OVER TX SLIDES INTO THE GULF COAST STATES. HAVE BACKED OFF ON POPS THINKING THAT THE RAIN SHIELD STAYS SOUTH OF OUR CWA UNTIL AFTER 12Z SUNDAY. HOWEVER...KEPT THE CHANCE IN THERE FOR POTENTIAL OF NRN STREAM SHORTWAVE SLIDING FURTHER EAST. THE E-SE FLOW LATE TONIGHT MAY HELP SATURATE THE LOW LVLS OVER THE NC MTNS. ALL IN ALL...PRETTY DRY TONIGHT...WITH CLOUDS DECREASING IN THE NORTH BUT INCREASING AFTER MIDNIGHT OVER THE SOUTH. LOWS TONIGHT WILL REMAIN CLOSE TO MOS...DROPPED A COUPLE DEGREES FROM PREVIOUS FORECAST DUE TO SLOWER ARRIVAL OF CLOUDS AND SOME EVAP COOLING POTENTIAL WITH VIRGA IN THE SOUTH.-- End Changed Discussion --&& .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... MODELS CONTINUE TRENDING SLOWER...DRIER AND KEEPING HEAVIER RAIN SE OF THE CWA ON SUNDAY. BECAUSE OF THIS WAS FORCED TO REDUCE AND SLOW POPS...HOWEVER DID NOT GO AS LOW AS GUIDANCE SINCE MODELS MAY PROBABLY AGAIN CHANGE DRASTICALLY. ALTHOUGH LOW PRESSURE MOVES UP THE COAST ON MONDAY...AN UPPER LEVEL DISTURBANCE ENTERING FROM THE WEST IN ITS WAKE...MAY ALLOW ANOTHER RAIN SHIELD TO DEVELOP LATER MONDAY. TUESDAY SHOULD PROVIDE AM OPPORTUNITY TO DRY OUT WITH TEMPS CLOSE TO 60F AGAIN. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... ECMWF INDICATES UPPER LEVEL RIDGING APPROACHING THE AREA TUESDAY AFTERNOON INTO EARLY WEDNESDAY MORNING...WHILE THE SURFACE WEDGE HANGS ON THROUGH THE END OF THE WEEK. IT ALSO SUGGESTS A SURFACE AND UPPER LOW PRESSURE SYSTEM DEVELOPING OVER THE MIDWEST AND PUSHING TOWARD THE AREA BY MID TO LATE WEEK. HAVE AT LEAST CHANCE TO SLIGHT CHANCE OF POPS ACROSS THE COUNTY WARNING AREA THROUGH THE EXTENDED PERIOD. WITH THICKNESSES 1000-850MB AND 850-700MB THICKNESSES LOWERING BY MID WEEK...THERE COULD BE SOME LIGHT SNOW MIXED WITH RAIN IN THE HIGHER ELEVATIONS OF SOUTHEAST WEST VIRGINIA. IN THESE SAME AREAS MAINLY ALONG THE RIDGES...SURFACE LOW TEMPERATURES COULD ALSO REACH FREEZING OR A FEW DEGREES BELOW. GFS HAS BEEN HAVING A HARD TIME WITH RUN TO RUN CONSISTENCY IN THE EXTENDED. IT HAS BEEN FASTER AND MORE PROGRESSIVE WITH PUSHING THE SYSTEMS THROUGH THE FORECAST AREA. DUE TO THIS HAVE LEANED MORE TOWARD THE ECMWF AS IT SEEMS TO BE A BIT MORE CONSISTENT IN EACH RUN THE PAST FEW DAYS. && .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/... HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH THIS EVENING. KEPT THE LIFR FOG IN AT LWB AT THE 10Z TIME FRAME...BUT THE DENSER HIGH CLOUDS MAY KEEP THAT FROM HAPPENING. DAN WILL FLUCTUATE BETWEEN MVFR AND VFR VSBY THROUGH 12Z SO KEPT THEM PREDOMINANTLY MVFR AT 5SM. OTHERWISE VFR CONDITIONS AREA EXPECTED THROUGH SATURDAY NIGHT. THE NEXT THREAT OF WIDESPREAD IFR/MVFR CONDITIONS WILL BE ENCOUNTERED SUNDAY INTO MONDAY AS A SLOW MOVING AREA OF LOW PRESSURE MOVES NORTHEAST FROM THE GULF OF MEXICO. CLOUD BASES SATURDAY AND SATURDAY NIGHT SHOULD REMAIN ABOVE 10KFT. SUNDAY...CLOUD BASES WILL LOWER WITH CIGS FALLING BLO 3KFT SUNDAY AFTERNOON AND INTO SUNDAY NIGHT. A 12-24 HOUR PERIOD OF -RA OR DRIZZLE WILL ACCOMPANY THE IFR/MVFR CIGS...AND VSBYS MAY OBSCURE THE MTN RIDGES. TUESDAY WILL FEATURE IMPROVING CONDITIONS AS THE SFC LOW TRACKS NORTHEAST UP THE EASTERN SEABOARD WITH HIGH PRESSURE BUILDING OVER THE MID ATLANTIC FOR MID WEEK. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PM/WP NEAR TERM...WP SHORT TERM...KM LONG TERM...REB AVIATION...AMS/PM/WP
