Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 162334 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 634 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 305 PM EST TUESDAY... THE COLD FRONT WILL MOVE EAST AND OFF THE ATLANTIC COAST TONIGHT WHILE THE PARENT AREA OF LOW PRESSURE MOVES NORTHEAST THROUGH THE GREAT LAKES AND INTO QUEBEC CANADA. MAIN BATCH OF PREFRONTAL RAIN ALONG THE COAST HEADING OUT TO SEA. A STRONG MID LEVEL DISTURBANCE LOCATED IN OHIO WILL TRAVEL EAST JUST TO OUR NORTH THIS EVENING INTO TONIGHT. WRAP AROUND MOISTURE FROM THE UPPER LOW ACROSS THE GREAT LAKES WILL BRING A SHALLOW LAYER OF MOISTURE BACK INTO THE MOUNTAINS WITH AN OPPORTUNITY FOR SOME LIGHT SHOWERS/FLURRIES OR FREEZING DRIZZLE DURING THE OVERNIGHT ALONG THE WESTERN SLOPES. WPC HAS PAINTED JUST A SMALL AREA OF FREEZING DRIZZLE POSSIBLE ACROSS WESTERN GREENBRIER COUNTY TONIGHT INTO EARLY WEDNESDAY. BECAUSE AREAL COVERAGE IS SMALL AND QPF LIGHT WITH LIMITED COLD AIR...IN COORDINATION WITH LWX AND RLX WILL HOLD OFF ON ANY ADVISORY AT THIS TIME. FOR EAST SIDE OF THE MOUNTAINS...STRONG DOWNSLOPE FLOW WILL MAINTAIN CLEAR TO PARTLY CLOUDY SKIES. 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 ENLONGATE 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 /00Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 625 PM EST TUESDAY... SURFACE COLD FRONT CONTINUES TO PUSH EAST THROUGH THE REGION THIS EVENING. WHILE THE IMPACT OF THE WIND SHIFT HAS TAKEN PLACE ALOFT IN AREAS EAST OF THE CREST OF THE BLUE RIDGE...IT HAS NOT WORKED ITS WAY TO THE SURFACE IN ALL LOCATIONS YET. WE EXPECTED NORTHWEST WINDS TO PREVAIL AT ALL LOCATIONS OVERNIGHT. IN THE EAST...THIS WILL HELP ERODE THE LINGERING IFR/MVFR CLOUD COVER ALONG AND EAST OF A KLYH-KDAN LINE AS THE NIGHT PROGRESSES. GUSTY CONDITIONS AND SCATTERED LIGHT RAIN SHOWERS OR SPRINKLES ARE POSSIBLE THIS EVENING ACROSS THE MOUNTAINS ALONG WITH A CONTINUATION OF IFR/MVFR CLOUD COVER. LOCALIZED IFR CONDITIONS ARE POSSIBLE TONIGHT ALONG THE WESTERN SLOPES VCNTY OF KBLF AND JUST WEST OF KLWB WITH THE POTENTIAL FOR LIGHT FREEZING DRIZZLE AND FOG. DURING THE DAY WEDNESDAY...EXPECT A GRADUAL IMPROVEMENT TO VFR CONDITIONS ACROSS THE MOUNTAINS WITH CLOUD COVER ERODING FROM EAST TO WEST. WINDS WILL REMAIN GUSTY...IF NOT GUST A LITTLE STRONGER NEAR 25KTS IN SOME LOCATIONS FROM THE LATE MORNING THROUGH THE MID AFTERNOON. WINDS WILL START TO WEAKEN IN THE LATE AFTERNOON...BUT STILL PREVAIL IN THE 8 TO 10 KT RANGE. EXTENDED DISCUSSION... THURSDAY AND FRIDAY LOOK RELATIVELY BENIGN. THERE IS THE POTENTIAL FOR A PERIOD OF MVFR THURSDAY ASSOCIATED WITH AN UPPER LEVEL DISTURBANCE WHICH IS FORECAST TO PASS JUST SOUTH OF THE REGION VCNTY OF THE VA/NC BORDER. POTENTIAL EXISTS FOR A WINTER STORM TO IMPACT THE REGION THIS WEEKEND...FLIGHT CONDITIONS DETERIORATING ACROSS THE AREA LATE FRIDAY NIGHT INTO SATURDAY. LOW PRESSURE IS EXPECTED TO FORM OVER TEXAS FRIDAY...THEN TRACK NORTHEAST TO NEAR THE MID ATLANTIC COAST BY LATE SATURDAY. THIS TRACK WILL PLACE OUR FORECAST AREA ON THE COLD SIDE OF THE SYSTEM PROVIDING AN OPPORTUNITY FOR ACCUMULATING SNOW OR A WINTRY MIX. 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 SHORT TERM...AMS LONG TERM...DS AVIATION...DS/KK/PM

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