Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 170455 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1155 PM EST TUE DEC 16 2014 .SYNOPSIS... A COLD FRONT WILL MOVE EAST INTO THE ATLANTIC OCEAN TONIGHT. HIGH PRESSURE IS EXPECTED TO RETURN FOR WEDNESDAY ASSOCIATED WITH DRY WEATHER FOR MID WEEK. UNSETTLED WEATHER WILL RETURN FOR THE WEEKEND AS AN AREA OF LOW PRESSURE MOVES ACROSS THE SOUTHEAST STATES...REACHING INTO THE MID ATLANTIC REGION SATURDAY. && .NEAR TERM /THROUGH WEDNESDAY/... AS OF 935 PM EST TUESDAY... RADAR VERY QUIET BUT TO BE EXPECTED AS MOISTURE IN THE LOW LEVELS ACROSS THE MOUNTAINS IS OVERSHOT BY THE RADAR BEAM. NONETHELESS...AS SHORTWAVE PIVOTS ACROSS THE AREA OVERNIGHT THE NW FLOW IS GOING TO GENERATE ISOLATED/SCATTERED RAIN/SNOW SHOWERS. AS THE NIGHT WEARS ON THE MOISTURE BECOMES SHALLOW SO THAT DZ/FZDZ WILL OCCUR. GIVEN THE LACK OF COVERAGE OF BELOW FREEZING TEMPS...OPTED TO JUST ISSUE A SPECIAL WX STATEMENT FOR THE NC MTNS/GRAYSON HIGHLANDS AND WRN GREENBRIER TO ACCOUNT FOR ANY LIGHT ICING/RIME ICING LATE TONIGHT. THE FOG OUT EAST TO ERODE AS DRIER AIR WORKS IN AND WINDS PICK UP SLIGHTLY. ALREADY HAVE SEEN LYH GO FROM 1/4SM FG TO 10SM IN LESS THAN 1 HOUR. STILL EXPECT LOWS FROM THE LOWER 30S ACROSS THE WRN SLOPES TO UPPER 30S...NEAR 40 EAST. PREVIOUS VALID DISCUSSION... FOR EAST SIDE OF THE MOUNTAINS...STRONG DOWNSLOPE FLOW WILL MAINTAIN CLEAR TO PARTLY CLOUDY SKIES OVERNIGHT. WEST TO NORTHWEST WINDS OF 30-35 KTS ARE PROGGED AT 85H...SO SURFACE WINDS WILL BECOME GUSTY...ESPECIALLY ALONG THE RIDGE CRESTS AND JUST LEE OF THE BLUE RIDGE. LOW TEMPERATURES OVERNIGHT WILL RANGE FROM THE UPPER 20S IN ELEVATIONS ABOVE 3500 FT TO THE MID AND UPPER 30S IN THE PIEDMONT. UPPER TROF SHIFTS OFFSHORE WEDNESDAY AS WE TRANSITION TO A MORE ZONAL UPPER FLOW BY WEDNESDAY NIGHT. BLUSTERY NORTHWEST WINDS WILL CONTINUE INTO WEDNESDAY. DOWNSLOPING DRYING EXPECTED FOR THE EAST. WHILE IN THE WEST...UPSLOPE FLOW WILL RESULT IN A VERY SHALLOW MOIST LAYER LOCKED IN UNDER THE SUBSIDENCE INVERSION. WILL CONTINUE CLOUDS AND THE UPSLOPE LIGHT RA/FZRA THROUGH THE MORNING HOURS...THEN PRECIPITATION ENDS WHILE CLOUDS LINGER. HIGH TEMPERATURES WEDNESDAY WILL RANGE FROM THE MID 30S IN THE NORTHWEST MOUNTAINS TO THE MID 50S IN THE SOUTHEAST. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... AS OF 305 PM EST TUESDAY... PATTERN IS PROGRESSIVE AND ZONAL THROUGH FRIDAY. MODELS BRING A SHORT WAVE FROM THE MISSISSIPPI VALLEY THROUGH THE MID ATLANTIC REGION THURSDAY AND THURSDAY NIGHT. MODELS NOT SHOWING MUCH CONSENSUS WITH THE LOCATION OF ANY PRECIPITATION ON THURSDAY. WHATEVER PRECIPITATION DOES FALL WILL BE LIGHT. SURFACE HIGH PRESSURE WILL EXTEND FROM THE UPPER MISSISSIPPI VALLEY TO THE TENNESSEE VALLEY THROUGH FRIDAY. THE RIDGE MOVES FAR ENOUGH EAST BY THE END OF THE DAY FRIDAY FOR SURFACE AND LOW LEVEL WINDS TO COME AROUND TO THE EAST. NO CHANGE IN AIR MASS THROUGH THE PERIOD BUT WITH CLOUDS ON THURSDAY WILL KEEP MAXIMUM TEMPERATURES NEAR COOLER MET GUIDANCE. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... AS OF 230 PM EST TUESDAY... FRIDAY NIGHT...A SURFACE NOSE OF HIGH PRESSURE WILL BE ACROSS THE REGION...ALTHOUGH NOT WITH THE BEST ORIENTATION FOR OPTIMAL WEDGE CONDITIONS. DESPITE THIS...WE STILL ANTICIPATE A MIX OF TEMPERATURES A FEW DEGREES EITHER SIDE OF FREEZING AT THE ONSET OF THE EVENT...AND THROUGH THE SATURDAY NIGHT TIME PERIOD. AT 85H...SOUTHERLY WINDS WILL TRANSPORT MOISTURE INTO THE REGION IN ASSOCIATION WITH AN AREA OF LOW PRESSURE MOVING THROUGH THE GULF COAST STATES. GUIDANCE HAS SLOWED BY AN AVERAGE OF 6 HOURS ON THE ARRIVAL OF PRECIPITATION INTO THE AREA. HAVE ADJUSTED ACCORDINGLY WITH THE FORECAST. MODEL GUIDANCE IS SHOWING ENOUGH OF A RUN TO RUN DIFFERENCE WITH EACH OTHER...AND WITH ITS OWN EARLIER RUNS FOR THERE STILL TO BE NOTABLE UNCERTAINTY AS TO THE LOW LEVEL THERMAL PROFILE AT THE ONSET...AND DURING THE COURSE OF THE PRECIPITATION EVENT THIS LOW WILL BRING TO OUR REGION THROUGH SATURDAY NIGHT. BY SUNDAY...THERE IS BETTER AGREEMENT WITH THE MODELS THAT THE AREA WILL BE ON THE BACKSIDE OF THE SYSTEM WITH ENOUGH COLD AIR ACROSS THE REGION WITH A STIFF NORTHWEST WIND TRAJECTORY FOR UPSLOPE SNOW SHOWERS IN THE WEST TO CONCLUDE THE EVENT. THE BEST CONSENSUS OF THE MODELS SUGGEST SOME TYPE OF WINTRY MIX WHERE THE SURFACE AND BOUNDARY LEVEL TEMPERATURES ARE COLD ENOUGH LATE FRIDAY NIGHT...THROUGH SATURDAY NIGHT. MOST OF THIS WINTRY MIX LOOKS TO BE CONFINED TO THE MOUNTAINS. ANY MIX ACROSS THE PIEDMONT WILL BE LIMITED BY MILDER SURFACE AND BOUNDARY LEVEL TEMPERATURES THERE...WITH THE BEST POTENTIAL FOR A MIX TO BE ALONG AND NORTH OF THE ROANOKE RIVER VALLEY. SOUTHSIDE VIRGINIA...SOUTH INTO PARTS OF NORTH CENTRAL NORTH CAROLINA AT THIS POINT LOOK TO BE PRIMARILY RAIN. GIVEN THESE VARIOUS UNCERTAINTIES AND LOCAL POLICY...THE FORECAST FRIDAY NIGHT THROUGH SATURDAY SATURDAY NIGHT WILL BE A RAIN VERSUS SNOW FORECAST...WITH THE FLEXIBILITY OF SOME AREAS WITH RAIN AND SNOW SIMULTANEOUSLY. WHILE OUR FINAL WEATHER PICTURE MAY DEPICT A GREATER RANGE OF WINTRY PRECIPITATION TYPES...RAIN VERSUS SNOW IS A CONSERVATIVE APPROACH TO TAKE AT THIS POINT. IN A COUPLE OF DAYS...OUR CONFIDENCE MAY HAVE INCREASED ENOUGH TO ALLOW FOR A GREATER MIX OF PRECIPITATION TYPES IN THE FORECAST DURING THIS PERIOD OF THE FORECAST. AS MENTION EARLIER...BY THE TIME WE GET TO SUNDAY...MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT THAT THE SYSTEM WILL BE LIFTING OUT OF THE REGION...AND SUB FREEZING AIR WILL HAVE WRAPPED IN BEHIND THE SYSTEM AT THE LOWER LEVELS. ANY LINGERING PRECIPITATION HAS A GREATER CHANCE TO BE SNOW OR RAIN WITHOUT THE PRESENCE OF A WARM NOSE ALOFT. BY SUNDAY AFTERNOON INTO SUNDAY NIGHT...LINGERING UPSLOPE SNOW SHOWERS ACROSS THE PREFERRED AREA OF SOUTHEAST WEST VIRGINIA AND NEIGHBORING PARTS OF SOUTHWEST VIRGINIA WILL GRADUALLY ERODE AS DRIER AIR WORKS ITS WAY INTO THE REGION AND THE LOW LEVEL FLOW GRADUALLY BACKS WEST TO SOUTHWEST. MONDAY INTO MONDAY NIGHT...HIGH PRESSURE BUILDS INTO THE THE REGION WITH LIGHT WINDS...LIMITED CLOUD COVER AND NO PRECIPITATION EXPECTED. TUESDAY WILL BE ANOTHER DAY WITH CONSIDERABLE UNCERTAINTY. THE GFS IS QUICK TO BRING THE COLD FRONT TOWARDS THE REGION IN ASSOCIATION WITH AN UPPER TROUGH PUSHING THROUGH THE GREAT LAKE REGION. THIS SYSTEM IS KEPT DISTINCT FROM A DISTURBANCE OFF THE COAST OF THE CAROLINAS THAT HAS LITTLE OR NO INTERACTION WITH THE GREAT LAKES TROUGH THROUGH AT LEAST THE END OF OUR FORECAST PERIOD. FOLLOWING THIS SOLUTION YIELD LIMITED COVERAGE OF RAIN OR SNOW REACHING THE WESTERN PARTS OF THE AREA THROUGH THE END OF THE DAY TUESDAY. THE ECMWF SOLUTION ALSO HAS THE TWO SYSTEMS DISTINCT THROUGH TUESDAY...BUT FOR A DIFFERENT REASON. THIS SOLUTIONS IS FARTHER WEST WITH THE COASTAL SYSTEM...AND WRAPS MOISTURE...AND A WARM NOSE...INTO OUR AREA DURING THE COURSE OF THE DAY TUESDAY. THE GREAT LAKES SYSTEM IS NOT AS PROGRESSIVE...AND HAS THE TIME TO ELONGATE MORE SOUTH INTO THE MISSISSIPPI RIVER VALLEY. IF THE ECMWF IS ON TRACK...THE AREA WILL HAVE A GENEROUS COVERAGE OF A WINTRY MIX MOVING INTO THE REGION FROM SOUTHEAST TO NORTHWEST ON TUESDAY. OUR FORECAST AT THIS POINT WILL RESEMBLE MORE THAT OF THE GFS. TEMPERATURES DURING THE FORECAST PERIOD WILL BE TRICKY. WHILE WE ARE EXPECTING A GENERAL TREND TOWARDS MILDER TEMPERATURES EACH DAY PAST TUESDAY...HOW MUCH...AND WHERE ANY SUBSTANTIAL ACCUMULATIONS OF SNOW ARE DEPOSITED WILL PLAY A FACTOR IN BOTH THE HIGHS AND THE LOWS. AT THIS POINT...AM LEANING ON THE LOW SIDE OF GUIDANCE...WITH SOME ALLOTMENT TOWARDS EVEN MORE COOLER WHERE...AT LEAST NOW...THE BEST CHANCE OF SNOW IS EXPECTED. AT THIS POINT...WILL NOT TOUCH THE FOG POTENTIAL ONCE WE START TO GET INTO THE RETURN FLOW SIDE OF THE SURFACE HIGH. ALTHOUGH...AS MILDER AIR STARTS ADVECTING ACROSS ANY REMAINING SNOWPACK...THE DEW POINT OF THAT AIR WILL LIKELY BE MILDER THAN THE TEMPERATURE OF THE SNOW IT WILL BE MOVING ACROSS. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 1125 PM EST TUESDAY... FRONT HAS PUSHED EAST...AND NOT EXPECTING ANY SUB VFR EAST OF THE MOUNTAINS. HOWEVER...THE BLF/LWB/BCB TO HAVE MVFR OR WORSE THROUGH THE MORNING. THINK BCB WILL BE GOING TO VFR CIGS AT 13-14Z...THEN SCATTERING OUT IN THE AFTERNOON. CIGS TO STAY AROUND IN BLF/LWB BUT RISE TO MVFR AFTER 15Z...MAY SEE SCATTERED CLOUDS IN THE AFTERNOON BUT 00Z NAM/CMC STILL HANG ONTO THE LOWER CIGS INTO THURSDAY MORNING. ATTM...WILL LEAVE IT SCATTERED FROM LATE AFTERNOON-06Z THU. NOT EXPECTING MUCH IF ANY PRECIP AT BLF/LWB. WINDS WILL BE GUSTY AT TIME FROM THE WNW AT ROA/BLF AND BCB...THEN WINDS WILL DIMINISH BY LATE AFTERNOON WEDNESDAY. EXTENDED DISCUSSION... THURSDAY AND FRIDAY LOOK RELATIVELY BENIGN...THOUGH LOWER CIGS WILL LINGER IN THE WEST THU. THE FRI NIGHT-SAT SYSTEM NOW HAS TRENDED WEAKER BUT WILL STILL NEED TO BE WATCHED AS IT LOOKS TO STILL BRING A PERIOD OF SUB VFR WINTRY WEATHER ESPECIALLY FROM THE BLUE RIDGE WEST SAT. AVIATION INTERESTS WILL NEED TO MONITOR THIS SITUATION AS LATER FORECASTS BECOME AVAILABLE. THIS WILL LIKELY HAVE AN IMPACT ON AIR TRAVEL OVER THE WEEKEND...FROM THE SOUTHERN APPALACHIANS AND CAROLINAS NORTH TO THE MID ATLANTIC.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PM NEAR TERM...KK/WP SHORT TERM...AMS LONG TERM...DS AVIATION...DS/KK/WP

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