Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 242046 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 346 PM EST WED DEC 24 2014 .SYNOPSIS... A NARROW WEDGE OF HIGH PRESSURE REMAINED IN PLACE ALONG AND EAST OF THE APPALACHIANS THIS AFTERNOON. A STRONG COLD FRONT WILL MOVE THROUGH THIS EVENING AND BRING COLDER TEMPERATURES...MORE RAIN AND SOME GUSTY WINDS AS IT PASSES. HIGH PRESSURE WILL THEN BUILD OVER THE EASTERN UNITED STATES INTO THE WEEKEND WITH GENERALLY FAIR WEATHER EXPECTED INTO SATURDAY. && .NEAR TERM /THROUGH THURSDAY/... AS OF 340 PM EST WEDNESDAY... AT 3 PM...THE WEDGE OF COOL SHALLOW AIR REMAINED ALONG AND EAST OF THE BLUE RIDGE. THIS MORNING...A SHORT WAVE PASSED OVER THIS WEDGE AND BROUGHT A FAIR AMOUNT OF RAIN (0.50 TO 1.50 INCHES) TO THE REGION. THIS WAVE HAS PASSED WITH ONLY LIGHT RAIN/DRIZZLE LEFT IN ITS WAKE. GRAY CLOUDY CONDITIONS WILL PERSIST INTO THIS EVENING WHILE A LULL IN THE RAIN WILL LAST FOR A FEW HOURS BEFORE A COLD FRONT AND ASSOCIATED SHOWERS ENTER THE WEST LATE THIS AFTERNOON...EXITING THE PIEDMONT LATE THIS EVENING. THE WEDGE HAS LEFT MOST OF THE AREA IN A STABLE ENVIRONMENT BUT CAN NOT RULE OUT A RUMBLE OF THUNDER FROM ELEVATED CONVECTION AS THE COLD FRONT PASSES THIS EVENING. SHOWERS WITH THE FRONT MAY HAVE SOME GUSTY WINDS WITH THEM...BUT IT WILL BE THE SHARP PRESSURE RISES BEHIND THE FRONT THAT WILL BRING A FEW HOURS OF BREEZY AND GUSTY CONDITIONS TO THE REGION. THE STRONGER LONGER LASTING BREEZY AND GUSTY WINDS WILL OCCUR EARLY CHRISTMAS MORNING WITH A TIGHT PRESSURE GRADIENT...MODEST COLD AIR ADVECTION AND A 50 KT LOW LEVEL JET. HIGH PRESSURE BUILDS IN QUICKLY THURSDAY AFTERNOON TO SHUT DOWN THE WINDS. AS THE WEDGE ERODES...TEMPERATURES ARE WARMING INTO THE MID TO UPPER 50S. AREA ALONG AND EAST OF THE BLUE RIDGE...PARTICULARLY IN THE FOOTHILLS AND PIEDMONT COUNTIES...MAY NOT SEE HIGH TEMPERATURES TODAY UNTIL THIS EVENING (5P-7P). ONCE THE FRONT MOVES EAST...TEMPERATURES WILL SLOWLY DROP INTO THE 30S AND 40S. AS THE UPPER LEVEL TROUGH PASSES OVERHEAD FRIDAY MORNING...A FEW SHOWERS ARE POSSIBLE. TEMPERATURES AND BOUNDARY LAYER ARE TO WARM FOR SNOW EXCEPT FOR HIGHER ELEVATIONS AND WESTERN SLOPES. AFTER A BREEZY COOL MORNING...AFTERNOON HIGHS WILL WARM INTO THE 40S WEST TO 50S EAST. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... AS OF 250 PM EST WEDNESDAY... TRANQUIL AND MILD CONDITIONS ARE IN STORE FOR THE INITIAL POST- CHRISTMAS PERIOD OVER THE CENTRAL/SOUTHERN APPALACHIAN REGION. A SURFACE AND UPPER RIDGE OF HIGH PRESSURE CENTERED OVER THE SOUTHEASTERN U.S. WILL DOMINATE THE PATTERN IN OUR REGION FOR SEVERAL DAYS AS UPPER TROUGHING AND STORMINESS IS CONFINED TO THE WESTERN CONUS. VERY MILD TEMPS ON FRIDAY WITH WIDESPREAD 50S LIKELY FOR HIGHS UNDER A PLEASANT LATE DECEMBER SUN. WINTER WEATHER LOVERS PREPARE TO BE LESS THAN PLEASED. THE HIGH WILL SHIFT OFF THE EAST COAST BY LATE SATURDAY AS HEIGHT FALLS AND A COLD FRONT OVER THE MID-MISSISSIPPI VALLEY SLOWLY PUSH EAST. SKIES WILL BE CLEAR FRIDAY NIGHT AND MOST OF SATURDAY WITH TEMPERATURES AGAIN RUNNING 10-15F ABOVE LATE DECEMBER NORMALS...LOWS IN LOW TO MID-30S AND HIGHS LOW 50S TO NEAR 60. HIGH CLOUDS WILL INCREASE LATE SATURDAY AHEAD OF THE FRONT WITH ANOTHER MILD NIGHT IN STORE AS TEMPS LIKELY TO REMAIN ABOVE FREEZING IN NEARLY ALL AREAS. POPS SLOWLY INCREASE AS WELL TO CHC BY EARLY SUNDAY IN THE FAR WEST WITH RAIN AS THE P-TYPE IN ALL BUT VERY COLDEST LOCATIONS. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 300 PM EST WEDNESDAY... LATE WEEKEND INTO MID NEXT WEEK LOOKS TO BE POTENTIALLY UNSETTLED WITH LARGE SCALE TROUGH OVER THE WESTERN TWO THIRDS OF THE COUNTRY KICKING SEVERAL SHORT WAVES OUT INTO SOUTHERN APPALACHIAN REGION. MODELS OFFER SIGNIFICANT DIFFERENCES IN THE STRENGTH AND TIMING OF THESE WAVES...AND AMOUNT OF GULF MOISTURE THEY ARE ABLE TO TAP. ALSO RUN-TO-RUN INCONSISTENCIES ARE MAKING THIS OVERALL A RATHER LOW CONFIDENCE FORECAST. AM CONCERNED THAT THE ECMWF IN PARTICULAR HAS HAD A TENDENCY TO DIG THE SHORT WAVES A LITTLE TOO MUCH AND THEN ULTIMATELY DRIVE A DEEPENING SFC WAVE TOO FAR NORTH UP THE APPALACHIANS OR TO THE WEST OF US. THE FLATTER MORE PROGRESSIVE GFS HAS BEEN BETTER AS OF LATE. LATEST 12Z ECMWF HAS TRENDED TOWARD THE MORE SUBDUED GFS FOR THE FIRST SYSTEM HEADED UP OUR WAY SUNDAY INTO MONDAY...WHILE CANADIAN NOW HAS A MUCH STRONGER SYSTEM TRACKING JUST TO OUR SOUTH ON MONDAY AND MONDAY NIGHT. WILL LEAN MORE TOWARD THE WEAKER/FLATTER IDEA ADVERTISED IN THE LATEST GFS AND NOW ECMWF...AT LEAST THROUGH TUES. ECWMF IS A LITTLE STRONGER WITH ANOTHER WAVE ON WEDNESDAY...WHILE GFS IS FASTER...COLDER...AND GENERALLY KEEPS IT SOUTH OF US. WHILE CONFIDENCE IN THE TIMING AND STRENGTH OF THESE SYSTEMS IS QUITE LOW RIGHT NOW...THERE IS MORE CLARITY THAT THIS WILL AT THE VERY LEAST BE A CLOUDY PERIOD...AND THAT LOW LEVEL TEMPS AND THICKNESSES WILL GENERALLY BE WARM ENOUGH NOT TO HAVE ANY REAL PRECIP TYPE CONCERNS...WITH THE POSSIBLE EXCEPT OF HIGHEST RIDGES ACROSS THE FAR NORTH SUNDAY AND MONDAY...WITH ANY SYSTEM ON WEDNESDAY THERE COULD BE ENOUGH DAMMING SETTING UP THAT OVERRUNNING COULD BE SOME SORT OF WINTRY MIX...BUT NOT EVEN SURE WE WILL HAVE PRECIP ON WED. ECMWF WOULD SUGGEST FREEZING RAIN. A LITTLE MORE CONFIDENCE AT THE BEGINNING OF THIS PERIOD...SO HAVE SOME LIKELY AND HIGH CHC POPS IN FOR SUNDAY...BUT ALL RAIN...AND MOST LIKELY LIGHT. AS WE GET INTO THE WEEK...THE LARGE SFC HIGH NOSES IN MORE AND MORE AND EACH DAY LOOKS A LITTLE COOLER THAN THE PREVIOUS ONE WHICH IS REFLECTED IN THE TEMPERATURE FORECAST. WHILE I HAVE LOWERING POPS EACH DAY...LARGELY DUE TO INCREASING UNCERTAINTY...AM KEEPING A LOW CHC TO SLIGHT CHC IN THROUGH THE PERIOD WITH MORE INDICATION OF SOME WINTRY PRECIP AS WE GET INTO TUES NIGHT AND WED. OVERALL...FORECAST REALLY REFLECTS A VERY BROAD BRUSH RATHER THAN GOING EXACTLY WITH ANY ONE SOLUTION...AND EXPECT THERE WILL BE QUITE A FEW CHANGES TO THE EARLY WEEK FORECAST AS WE GET INTO THE WEEKEND. NOT MUCH CHANCE FOR A MAJOR STORM DURING THIS PERIOD...AND AFTER SUNDAY ITS POSSIBLE THAT DRY BUT COOL HIGH PRESSURE MANAGES TO DOMINATE...BUT BEST GUESS FOR NOW IS SOMETHING IN BETWEEN. AS ALWAYS...STAY TUNED! && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... AS OF 1215 PM EST WEDNESDAY... SEQUENCE OF EVENTS DURING THIS TAF FORECAST PERIOD WILL EVOLVE SOMETHING LIKE THIS...WEDGE IN PLACE INTO MID AFTERNOON WITH IFR TO LIFR CEILINGS...LOW LEVEL WIND SHEAR ABOVE THE SHALLOW LAYER OF COOLER AIR...AND WIDESPREAD LIGHT TO MODERATE RAIN. THEN THE DRY SLOT COMES THROUGH THE AREA...POTENTIALLY LIFTING CEILINGS BRIEFLY TO VFR...ESPECIALLY AT KLWB AND KBLF. NEXT THE COLD FRONT WITH A LINE OF SHOWERS AND GUSTY WIND COMES THROUGH LATE THIS AFTERNOON AND EVENING. ISOLATED THUNDERSTORMS ARE POSSIBLE AT KBLF/KLWB AND KDAN. BEHIND THE FRONT PRECIPITATION ENDS...CEILINGS IMPROVE TO VFR EAST OF THE BLUE RIDGE AND WILL REMAIN MVFR IN THE MOUNTAINS. WINDS WILL BE GUSTY OUT OF THE WEST...WITH GUSTS UP TO 30 KNOTS LIKELY. TIMING IS THE MOST QUESTIONABLE PART OF THE FORECAST. MODELS STILL SHOWED DIFFERENCES IN WHEN THE WEDGE BREAKS TODAY AND WHEN THE COLD FRONT PASSES THROUGH. TAFS REFLECT THE MOST LIKELY TIMING OF THESE EVENTS WITH MEDIUM CONFIDENCE. EXTENDED DISCUSSION... THURSDAY...MVFR CEILINGS AND UPSLOPE RAIN/SNOW SHOWERS SHOULD PERSIST IN THE MOUNTAINS...WITH VFR CONDITIONS IN THE PIEDMONT. THURSDAY NIGHT AND FRIDAY HIGH PRESSURE SHOULD BUILD OVER THE SOUTHEAST...WHICH WILL PROVIDE VFR WEATHER WITH LIGHTER WINDS. ANOTHER COLD FRONT WITH ASSOCIATED LOW PRESSURE WILL APPROACH THE REGION SATURDAY AND BE OVER OR JUST WEST OF THE AREA SUNDAY. GIVEN THE SLOWER TRENDS...APPEARS WEATHER MAY STAY VFR FOR SATURDAY WITH SUB-VFR CONDITIONS RETURNING WITH CLOUDS/PRECIP ON SUNDAY FOR NOW. && .HYDROLOGY... AS OF 335 PM EST WEDNESDAY... WITH THE BULK OF THE RAINFALL HAVING SHIFTED NORTHEAST THIS AFTERNOON STORM TOTAL RAINFALL FROM THE RAIN GAGE NETWORK THROUGH 18Z HAS RANGED GENERALLY FROM 0.50 TO 1.50 INCHES WITH THE HIGHEST AMOUNTS OVER NW NORTH CAROLINA IN PARTS OF THE UPPER NEW AND TENNESSEE BASINS RIVER BASIN AND ACROSS THE UPPER DAN BASIN. RIVERS HAVE SEEN ONLY MINOR RISES OF A FEW FEET AND DO NOT EXPECT ANY GAGED LOCATIONS TO EVEN REACH ACTION STAGE. IN FACT LONGER- TERM PRECIPITATION DEFICITS EXTANT OVER PARTS OF THE PIEDMONT WILL REMAIN AFTER THIS EVENT. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RCS NEAR TERM...RCS SHORT TERM...PC LONG TERM...SK AVIATION...RCS HYDROLOGY...PC

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