Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 190400 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1100 PM EST THU DEC 18 2014 .SYNOPSIS... HIGH PRESSURE OVER THE UPPER MIDWEST WILL GRADUALLY BUILD EAST ACROSS THE AREA RESULTING IN OVERALL DRY WEATHER THROUGH FRIDAY EVENING. A WEAK AREA OF LOW PRESSURE WILL EVENTUALLY DEVELOP ALONG THE GULF COAST STATES FRIDAY NIGHT AND MOVE EAST-NORTHEAST OVER THE CAROLINAS ON SATURDAY. THIS SYSTEM WILL BRING A PERIOD OF LIGHT WINTRY PRECIPITATION SATURDAY MORNING...CHANGING TO RAIN OVER THE PIEDMONT IN THE AFTERNOON. && .NEAR TERM /THROUGH FRIDAY/... AS OF 1035 PM EST THURSDAY... UPDATED FORECAST TO LOWER THREAT OF PRECIP IN THE NW. STILL COULD SEE SOME FLURRIES ACROSS THE MTNS OF WRN GREENBRIER TOWARD DAWN. OTHERWISE...LOOKING AT SKIES TURNING LESS CLOUDY OUT EAST AS ONE SHORTWAVE EXITS EAST. ADJUSTED TEMPS ESPECIALLY IN THE FOOTHILLS AND ROANOKE AS THEY ARE RUNNING MILDER...BUT AS SKIES CLEAR AND WINDS FADE TEMPS WILL STILL FALL INTO THE LOWER 30S. STILL LOOKING AT MID TO UPPER 20S WEST. PREVIOUS VALID DISCUSSION... WAVE ALOFT PASSES EAST OVERNIGHT LEAVING WEAK SUBSIDENCE IN PLACE AS HIGH PRESSURE TO THE NW NOSES BACK IN LATE. FRIDAY LOOKS TO BE ON THE DRY SIDE AS HIGH PRESSURE STRETCHING FROM THE GREAT LAKES THROUGH THE OHIO RIVER VALLEY REMAINS THE MAIN FEATURE IN OUR WEATHER PATTERN. MOSTLY SUNNY SKIES AND LIGHT NORTHWESTERLY DOWNSLOPE WINDS WILL ALLOW AFTERNOON TEMPERATURES TO RANGE FROM THE MID 30S ALONG THE WESTERN RIDGES...TO AROUND 50 OVER THE SOUTHSIDE AND THE NORTH CAROLINA PIEDMONT. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... AS OF 250 PM EST THURSDAY... MODELS HAVE BEEN TRENDING QUITE A BIT WEAKER WITH THE SHORT WAVE COMING OUT OF ARIZONA AND REACHING THE MID ATLANTIC REGION ON SATURDAY. ISENTROPIC LIFT AND VORTICITY ADVECTION COME THROUGH ON SATURDAY AND WILL BE EAST OF THE FORECAST AREA ON SATURDAY NIGHT. MOST SIGNIFICANT CHANGE IN THE GUIDANCE IS WITH THE AMOUNT OF MOISTURE. 12Z GUIDANCE NOW KEEPS BULK OF THE DEEPER MOISTURE SOUTH OF THE FORECAST AREA...ESPECIALLY THE 12Z NAM. WILL FOLLOW THIS TREND AND LOWER PROBABILITY OF PRECIPITATION IN ALL BUT THE SOUTHERN THIRD OF THE COUNTY WARNING AREA. WILL ALSO CUT BACK ON AMOUNT OF PRECIPITATION. SURFACE HIGH PRESSURE OVER THE UPPER MISSISSIPPI VALLEY WILL GRADUALLY MOVE EAST AND WILL BE OVER THE OHIO VALLEY ON SATURDAY. THE HIGH CONTINUES SLOW PROGRESS TO THE EAST SATURDAY NIGHT AND BY LATE SUNDAY THE RIDGE AXIS WILL BE OFFSHORE. THIS WILL BEGIN TO BRING SURFACE AND LOW LEVEL WINDS AROUND TO THE SOUTH LATE IN THE DAY. SURFACE REFLECTION OF THE SHORT WAVE ON SATURDAY WILL BE AN INVERTED TROF OVER THE SOUTHERN APPALACHIANS. EXPECT CLOUDS AND PRECIPITATION WILL KEEP MAXIMUM TEMPERATURES ON SATURDAY COOLER THAN GUIDANCE. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... AS OF 230 PM EST THURSDAY... A VERY ACTIVE WEATHER PATTERN EXPECTED DURING THE MEDIUM RANGE WITH ENOUGH MODEL DIFFERENCES TO MAKE THE DETAILS OF THE SENSIBLE WEATHER A GOOD CHALLENGE. AN AREA OF LOW PRESSURE SYSTEM WILL DEVELOP ALONG THE GULF COAST SUNDAY NIGHT...PUSH MOISTURE NORTHWARD AND INTRODUCING ANOTHER CHANCE OF RAIN...AND POTENTIALLY FREEZING PRECIPITATION TO THE MOUNTAINS. UTILIZED THE TOPDOWN APPROACH LEANING TOWARDS GFS FOR TEMPERATURE PROFILES. HELD LOW TEMPERATURES A FEW DEGREES BELOW MOS WITH CLOUDS AND PRECIPITATION. IN GENERAL...SUNDAY NIGHT LOWS WILL RANGE FROM THE UPPER 20S IN THE MOUNTAINS TO THE LOWER 30S IN THE PIEDMONT. FOR MONDAY...A WAVE OF LOW PRESSURE ALONG THE FRONTAL BOUNDARY WILL BE LOCATED ALONG THE NORTH CAROLINA COAST WITH AXIS OF MOISTURE/PRECIPITATION MOVING NORTH ASSOCIATED WITH INCREASING WARM ADVECTION AHEAD OF THE DEVELOPING LONGWAVE TROUGH TO THE WEST. HOW MUCH THE LOW CENTER DEEPENS...ITS ASSOCIATED PRECIPITATION AND PTYPE REMAINS PROBLEMATIC FOR OUR REGION. EACH MODEL HAS A DIFFERENT TAKE ON THE MAGNITUDE OF THE WARM NOSE OVER OUR REGION. WILL MAINTAIN THE RAIN VERSUS FREEZING RAIN FORECAST DURING MUCH OF MONDAY MORNING. THERMAL PROFILES SUGGEST SOME POTENTIAL FOR LIGHT FREEZING RAIN OR SLEET ACROSS THE VIRGINIA HIGHLANDS AND SOUTHERN SHENANDOAH VALLEY. FELT THAT THERE WAS ENOUGH SUPPORT TO RAISE POPS FROM SLIGHT INTO THE CHANCE LEVEL MONDAY. KEPT HIGHS MONDAY COOLER THAN GUIDANCE WITH READINGS FROM THE MID 30S IN THE WEST TO THE MID 40S IN THE EAST. BY MONDAY NIGHT...LOW PRESSURE MOVES INTO THE MIDWEST WITH TRAILING FRONTAL BOUNDARY SOUTH INTO THE MISSISSIPPI VALLEY. A DEEP LONGITUDINAL TROUGH DEVELOPS SOUTH TO THE GULF OF MEXICO BY TUESDAY AFTERNOON WITH INCREASING SOUTHERLY LOW LEVEL FLOW ACROSS OUR REGION...ACCOMPANIED BY INCREASING MOISTURE ADVECTION. USING SUPERBLEND FOR LOW TEMPERATURES MONDAY NIGHT PRODUCED READINGS GENERALLY IN THE UPPER 20S AND LOWER 30S. TEMPERATURES WILL TREND MILDER FOR HIGHS TUESDAY FROM THE MID 40S TO THE LOWER 50S. BY TUESDAY NIGHT INTO WEDNESDAY...BOTH GFS AND ECWMF DEEPEN THE UPPER LOW AND ASSOCIATED TROUGH AND NEGATIVELY TILT THE FEATURE SO THAT THE TROUGH AXIS SHIFTS TO OFF THE NORTH CAROLINA COAST...COINCIDENT TO THE POSITION OF THE ASSOCIATED SURFACE OCCLUDED FRONT...WITH THE TRIPLE POINT PASSING SOMEWHERE NEAR OR JUST SOUTH OF OUR REGION. AT THIS TIME...SPC DOES NOT HAVE ANY THUNDERSTORMS IN ITS DAY 4-8 CONVECTIVE OUTLOOK. IT LOOKS LIKE...THERE IS THE POTENTIAL FOR OUR REGION TO HAVE ACTIVE WEATHER LATE TUESDAY NIGHT INTO WEDNESDAY WITH PLENTY OF SHOWERS...PERHAPS VERY GUSTY WINDS AND A FEW THUNDERSTORMS. COLD AIR PUSHES INTO THE REGION TUESDAY NIGHT INTO WEDNESDAY MORNING...ALLOWING FOR SOME RAIN AND SNOW SHOWERS. IF ENOUGH COLD AIR ARRIVES QUICKLY...THERE COULD BE SOME ACCUMULATING SNOW IN THE WESTERN MOUNTAINS. KEPT THE HIGHEST POPS OF RAIN AND SNOW SHOWERS IN THE WEST AS THE LOW CENTER MARCHES NORTHEAST PUSHES A COLD FRONT TO THE COAST. IN THE WAKE OF THE COLD FRONT A COOLING TRENDS WILL CONTINUE WEDNESDAY INTO THURSDAY...WITH WEST TO NORTHWEST FLOW ALOFT. UPPER FLOW SHIFTS TO THE SOUTHWEST AS TROF CURVES OUT IN THE CENTRAL US WITH SFC INFLECTION OF LOW PRESSURE DEVELOPS OVER THE TENNESSEE VALLEY BY FRIDAY MORNING. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/... AS OF 1045 PM EST THURSDAY... NOT MUCH CHANGE TO THE AVIATION FORECAST...THOUGH CONFIDENCE IS LESS THAT BLF WILL DROP BELOW 1KFT PER UPSTREAM OBS. STILL WILL HAVE A TEMPO GROUP TOWARD 12Z FOR BLF DROPPING TO 9H FEET FOR A COUPLE HOURS. OTHERWISE BECOMING MVFR AT BLF/LWB OVERNIGHT THEN BACK TO VFR BY MIDDAY FRIDAY...WHILE REST OF THE TAF SITES STAY VFR. COULD SEE SOME SCT SUB 3KFT CLOUDS ACROSS BCB BUT CONFIDENCE HIGH THAT THREAT OF BKN IS NOT GOING TO HAPPEN. CLOUDS AHEAD OF THE NEXT SYSTEM WILL BE INCREASING OVERNIGHT FRIDAY SO EXPECT MAINLY CIRROSTRATUS IN THE LATE EVENING ACROSS THE REGION. EXTENDED DISCUSSION... THE SAT SYSTEM NOW HAS TRENDED WEAKER AND WILL SHIFT MOST OF THE PRECIP ACROSS THE CAROLINAS...THOUGH STILL WILL SEE SOME WINTRY MIX BUMP UP INTO THE SE WV/SW VA CORRIDOR INTO THE NC MTNS...THOUGH TRENDS ARE SHOWING LESS. EXPECT SUB VFR THOUGH AT TIMES SATURDAY INTO SAT NIGHT. ON THE HEELS OF THIS SYSTEM WILL BE ANOTHER SYSTEM TO POTENTIALLY IMPACT MAINLY THE EASTERN PORTION OF THE REGION SUNDAY NIGHT INTO MONDAY...WITH YET ANOTHER SYSTEM SLATED FOR LATE TUESDAY INTO WEDNESDAY. THESE SYSTEMS ARE EXPECTED TO BRING A PERIOD MAINLY RAIN BUT COULD BE SOME WINTRY WX AS WELL ESPECIALLY IN THE MOUNTAINS. EXPECT POTENTIAL LOW LEVEL WIND SHEAR AS WELL AND POOR FLYING WEATHER MONDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RCS NEAR TERM...RCS/WP SHORT TERM...AMS LONG TERM...KK AVIATION...JH/RCS/WP

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