Issued by NWS Blacksburg, VA
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-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KRNK 250435 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1135 PM EST TUE NOV 24 2009 .SYNOPSIS... WEAK HIGH PRESSURE WILL REMAIN ACROSS THE REGION TONIGHT. A STRONG COLD FRONT WILL SWING THROUGH THE AREA LATE THURSDAY BRINGING MUCH COLDER AIR ALONG WITH MOUNTAIN SNOW SHOWERS INTO FRIDAY NIGHT. HIGH PRESSURE WILL BUILD EAST ACROSS THE SOUTHEAST STATES DURING THE WEEKEND ALLOWING FOR A GRADUAL MODERATION IN TEMPERATURES THROUGH SUNDAY. && .NEAR TERM /THROUGH WEDNESDAY/... SATELLITE PICTURES STILL SHOWING A FEW BREAKS IN THE CLOUD COVER...MAINLY IN THE SOUTHWEST AND EASTERN COUNTY WARNING AREA. BAND OF CLOUDS COMING OUT OF THE OHIO VALLEY WILL FILL IN THE CLOUD COVER OVER THE MOUNTAINS OVERNIGHT. BY WEDNESDAY MORNING THE NEXT BAND OF CLOUDS...ASSOCIATED WITH THE SHORT WAVE CENTERED IN EASTERN IOWA...WILL REACH OUR WESTERN COUNTIES. THERE MAY BE A FEW SHOWERS WITH THIS FEATURE BUT MOISTURE IS VERY SHALLOW. HAVE KEPT PATCHY FOG AND DRIZZLE IN OVERNIGHT UNDER THE SURFACE HIGH OVER THE NORTHEAST COUNTIES. TRIMMED BACK THE CHANCE OF SHOWERS WITH THE IOWA SHORT WAVE ON WEDNESDAY. HIGH CLOUDS COMING INTO THE CAROLINAS WILL SPREAD OVER CENTRAL AND SOUTHERN VIRGINA BY MORNING. THIS MAY SLOW THE CLEARING ON WEDNESDAY BUT SINCE THESE CLOUDS ARE EXPECTED TO BE GONE BY AFTERNOON AND WINDS COME AROUND TO THE SOUTHWEST AT THE SURFACE...ALL LOCATIONS SHOULD BECOME CLEAR TO PARTLY CLOUDY BY THE END OF THE DAY. RAISED MINIMUM TEMPERATURES SLIGHTLY FOR TONIGHT. NO CHANGES NEEDED FOR HIGHS ON WEDNESDAY. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/... WEAK SURFACE HIGH PRESSURE WILL SLIDE ACROSS THE REGION WED NIGHT IN BETWEEN LOW PRESSURE OFF THE CAROLINAS AND THE NEXT VIGOROUS UPSTREAM S/W TROF. WITH VERY LIGHT FLOW THE NAM AGAIN REDEVELOPS LOW CLOUDS OVERNIGHT ESPCLY IN THE EAST WHILE OTHER GUIDANCE SHOWING LESS UNDER WEAK SW FLOW. SINCE LOW CLOUDS STILL POSSIBLE GIVEN LINGERING LOW LEVEL RH...WILL TREND THE EAST TOWARD PC OTRW MOSTLY CLEAR WITH LOWS MAINLY IN THE 30S. STRONG 5H TROF PIVOTS EAST T-GIVING DAY SWINGING AN INITIAL SURFACE COLD FRONT ACROSS THE APPALACHIANS BY EVENING FOLLOWED BY THE ACTUAL STRONGER 85H FRONT OVERNIGHT. MOISTURE AGAIN LOOKS QUITE LIMITED AHEAD OF THE FRONT WITH MOST LIFT TO THE NW AND OVERALL WESTERLY LOW LEVEL FLOW ACROSS THE CWA. HOWEVER PRE-FRONTAL RH SHOULD ACT TO INCREASE CLOUDS IN THE AFTERNOON WITH A CHANCE OF SHOWERS MAINLY WEST OF THE NEW RIVER VALLEY LATE IN THE DAY...OTRW DRY ELSW. HIGHS SHOULD RECOVER TO AROUND 60 EAST...WITH LOW/MID 50S ELSW EXCEPT ALONG THE WESTERN SLOPES WHERE EARLIER CLOUDS WILL HOLD READINGS IN THE UPPER 40S. COLD ADVECTION ARRIVES THU NIGHT AND LINGERS INTO FRIDAY ON GUSTY NW WINDS AROUND THE UPPER SYSTEM IN WAKE OF THE SURFACE COLD FRONT. COULD BE A NARROW BAND OF RAIN SHOWERS ACROSS THE FAR WEST ALONG THE FRONT...OTRW UPSLOPE POST FRONTAL FLOW KICKS IN GEAR OVERNIGHT WITH PROFILES SHOWING THE COLUMN COLD ENOUGH FOR SNOW FROM LATE EVENING ON OVER THE MOUNTAINS. LOOKS LIKE BEST RH AND NW TRAJECTORY COINCIDE WITH THE COLDEST 85H TEMPS FROM AROUND 06Z THRU 18Z FRIDAY. HOWEVER RATHER WARM GROUND TEMPS AND TENDENCY FOR THINGS TO MIX WITH RAIN DURING THE DAY MAY LIMIT SNOW ACCUMULATIONS TO THE OVERNIGHT PERIOD...EXCEPT ABOVE 3000 FEET FRIDAY GIVEN THE QUITE COLD FORECAST SOUNDINGS ACROSS THE RIDGES. PROGRESSIVE NATURE OF THE SYSTEM MAY ALSO TEND TO LIMIT AMOUNTS ESPCLY IF THE DEEPER RH SHIFTS A BIT FARTHER NORTH SO SOMETHING TO WATCH. OTRW WILL KEEP LIKELY/CAT POPS IN THE FAVORED UPSLOPE AREAS...WITH CHANCE POPS OUT TO THE BLUE RIDGE...BUT LITTLE OUT EAST WHERE DOWNSLOPE DRYING APPEARS QUITE STRONG. GIVEN POTENTIAL FOR ACCUMULATING SNOWFALL AROUND THE HOLIDAY WILL INCLUDE A SNOWFALL MENTION IN THE HWO ACROSS THE HIGHER ELEVATIONS OF THE FAR NW FOR NOW. WINDS WILL ALSO BE A FACTOR THU NIGHT AS THE FRONT AND COLD ADVECTION ARRIVE AND THEN FRIDAY WITH MIXING AND A STRONGER 85H JET ALOFT. SINCE SUBSIDENCE NOT ALL THAT GREAT AND THE INVERSION DOESNT LOWER MUCH THU NIGHT ONLY PUSHING GUSTS TO NEAR ADVISORY LEVELS NW NC MOUNTAINS WHERE WILL INCLUDE WINDS IN THE HWO AS WELL. WIDE RANGE OF HIGHS FRIDAY FROM THE LOW 50S SE TO ONLY THE MID/UPPER 30S NW AND LOW/MID 40S ALONG THE BLUE RIDGE. UPSLOPE MOISTURE SLOWLY FADES FRIDAY NIGHT AS THE COLD POOL EXITS AND NW FLOW WEAKENS. HOWEVER LOOKS LIKE ENOUGH OF A FETCH TO HELP WRING OUT ANY RESIDUAL RH TO PRODUCE -SHSN INTO LATE FRI NIGHT MAINLY SE WVA UPSLOPE AREAS. OTRW BECOMING PC TO MOSTLY CLEAR ELSW WITH GRADUALLY DIMINISHING WINDS...BUT COLD WITH LOWS 25-33. && .LONG TERM /SATURDAY THROUGH TUESDAY/... ON SATURDAY...ENOUGH DRIER AIR WILL HAVE MADE IT INTO THE REGION TO PRECLUDE ANY ADDITIONAL UPSLOPE RAIN/SNOW SHOWERS IN THE WEST AND ALSO LIMITED CLOUD COVER. ALSO...THE PRESSURE GRADIENT WILL BE WEAKENING THROUGH THE DAY AS THE CENTER OF HIGH PRESSURE DRAWS CLOSER. INCREASING HEIGHTS AND 850 MB TEMP WILL YIELD A MILDER DAY WITH EXPECTED HIGH TEMPERATURES SOME 5 DEGREES WARMER THAN THOSE EXPECTED ON FRIDAY. THE TREND FOR DRY AND MILDER WEATHER WILL CONTINUE THROUGH SUNDAY AS THE RIDGE BUILDS OVER OUR REGION. HOWEVER...THE DRY WEATHER WILL BE SHORT LIVED. OUR EYES TURN WEST AN APPROACHING TROUGH IN THE CENTRAL U.S. THERE IS VAST DIFFERENCES IN THE MODEL GUIDANCE OF THE TIMING AND SUBSEQUENT WEATHER AND TEMPERATURES FOR OUR AREA MONDAY THROUGH TUESDAY. THE 12Z GFS IS VERY FAST WITH THE SYSTEM WITH A COLD FRONTAL PASSAGE MONDAY NIGHT. THE 00Z ECMWF SOLUTION HAS THE TROUGH DEEPENING MORE AND BREAKING OFF TO FORM A CLOSED LOW IN THE CENTRAL U.S. WITH ASSOCIATED WARM FRONTAL PRECIPITATION STARTING TO APPROACH WESTERN PORTIONS OF OUR AREA MONDAY NIGHT...WITH A MUCH WARMER SOLUTION ON TUESDAY STILL IN THE WARM SECTOR AS COMPARED TO THE GFS COLDER POST COLD FRONT SOLUTION. THE HPC SOLUTION IS A SLIGHTLY FASTER SOLUTION TO THE SLOWER ECMWF GUIDANCE. HAVE FOLLOWED CLOSELY WITH HPC GUIDANCE FOR THIS PERIOD. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...-- Changed Discussion --VFR TO MVFR CLOUDS GENERALLY BETWEEN 1500-3500 FEET WERE COVERING MUCH OF THE FORECAST AREA AT 04Z. CEILINGS WILL LOWER THROUGH 09Z. DAN AND LYH ARE THE MOST LIKELY AT LYH AND DAN. DEW POINT DEPRESSIONS STILL NEED TO LOWER SOME FOR FOG FORMATION SO HAVE CUT BACK ON THE FORECAST OF LOWER VISIBILITIES. BY WEDNESDAY MORNING SURFACE AND LOW LEVEL WINDS WILL BE OUT OF THE SOUTHWEST. WITH SUCH SHALLOW LOW LEVEL MOISTURE AS SEEN ON THE 00Z SOUNDINGS AT RNK AND GSO...THIS WILL HELP SCATTER OUT THE CLOUDS BY AFTERNOON. CONDITIONS WILL STAY VFR FOR THE THE REST OF THE DAY. ARRIVAL OF ANOTHER...STRONGER COLD FRONT THURSDAY AND THURSDAY NIGHT WILL LIKELY BRING A RETURN TO MVFR TO IFR CONDITIONS IN UPSLOPE AREAS WEST OF THE BLUE RIDGE ALONG WITH COLDER AIR AND MOUNTAIN RAIN OR SNOW SHOWERS. DOWNSLOPE WINDS EAST OF THE BLUE RIDGE WILL KEEP THOSE AREAS MAINLY VFR RANGE INTO SUNDAY.-- End Changed Discussion --&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH NEAR TERM...AMS/KK SHORT TERM...JH LONG TERM...DS AVIATION...AMS/KK
