Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 260039 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 739 PM EST TUE NOV 25 2014 .SYNOPSIS... LOW PRESSURE WILL FORM IN THE GULF OF MEXICO THIS EVENING AND WILL CONTINUE TO DEEPEN AND TRACK NORTHEAST ALONG A FRONT...REACHING THE NORTH CAROLINA COAST BY WEDNESDAY MORNING...AND NOVA SCOTIA BY THURSDAY MORNING. A CLIPPER IN MONTANA WILL MOVE SOUTHEAST TONIGHT AND WEDNESDAY AND WILL CROSS THE MID ATLANTIC STATES ON WEDNESDAY NIGHT. HIGH PRESSURE WILL COVER THE REGION THURSDAY NIGHT AND FRIDAY. && .NEAR TERM /THROUGH WEDNESDAY/... AS OF 340 PM EST TUESDAY... CHANGES IN PARTS OF THE GUIDANCE WITH THE UPCOMING SNOW STORM. THE 09Z NSSL SREF AND 12Z NAM REMAINED SLIGHTLY COLDER WITH THE TEMPERATURE PROFILE THAN THE GFS WHICH STILL HAD SURFACE WET BULB TEMPERATURES JUST ABOVE FREEZING...FOR EXAMPLE AT ROANOKE AND BLACKSBURG. AT THIS TIME RANGE THE NAM/SREF AND OTHER SHORT RANGE/HIGH RESOLUTION GUIDANCE SHOULD HAVE A HANDLE ON THE SURFACE AND LOW LEVEL TEMPERATURES. WILL STAY WITH NON-DIURNAL HOURLY TEMPERATURES FOR TONIGHT AND WEDNESDAY BUT WILL HAVE COOLER VALUES THAN THE GFS. SNOWFALL AMOUNTS WILL BE HIGHLY INFLUENCED BY RATES SINCE BOUNDARY LAYER TEMPERATURE FROM THE SURFACE THOROUGH ABOUT 900 MB WILL BE ISOTHERMAL AND RIGHT AROUND FREEZING. FROM THE 09Z NSSL SREF AND 12Z BUFKIT SOUNDINGS...BEST VERTICAL LIFT LINES UP WITH HEIGHT OF BEST SNOW GROWTH TEMPERATURES AROUND 12Z/7AM WEDNESDAY MORNING. STRONGEST FRONTOGENESIS LINES UP ALONG THE BLUE RIDGE FROM 06Z/1AM THROUGH 18Z/1PM. SPC SREF SUGGESTED THERE IS A DECENT PROBABILITY OF RATES NEAR ONE INCH PER HOUR FROM 09Z/4AM THROUGH 15Z/10AM. THIS COINCIDES WITH LOW DEEPENING ALONG THE EAST COAST...ALTHOUGH MODELS HAVE THE LOW STARTING TO DEEPEN AT A FASTER RATE AS IT GETS NORTH OF VIRGINIA. THE BOTTOM LINE IS THAT AMOUNT OF LIFT SUPPORTS MUCH HIGHER LIQUID EQUIVALENT PRECIPITATION AND SNOWFALL RATES THAT WILL KEEP THE PRECIPITATION HEAVY ENOUGH TO STAY AS SNOW ALL THE WAY TO THE SURFACE. COMPLICATED PART IS THAT THE MOST INTENSE LIFT WILL BE IN VERY NARROW CORRIDORS AND FINE TUNING WHERE THESE BANDS WILL BE WAS CHALLENGING. IN GENERAL...AMOUNTS WILL BE HIGHLY VARIABLE. HIGHEST ELEVATIONS...INCLUDING ALONG THE BLUE RIDGE WILL HAVE THE BEST OPPORTUNITY FOR MORE SNOW ACCUMULATION. HAVE ADDED TO SNOW AMOUNTS ALONG AND WEST OF THE BLUE RIDGE AND EXPANDED THE ADVISORIES AND WARNINGS. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... AS OF 340 PM EST TUESDAY... CLIPPER CURRENTLY ENTERING MONTANA WILL BE IN THE TENNESSEE VALLEY BY WEDNESDAY NIGHT. MODELS WEAKEN THIS FEATURE AS IT CROSSES THE SOUTHERN APPALACHIANS BUT SOUTHERN BLUE RIDGE AND WESTERN MOUNTAINS WILL STILL HAVE ADDITIONAL LIGHT SNOW ACCUMULATIONS WITH THIS LOW. PRECIPITATION WILL EXTENDED WELL EAST OF THE BLUE RIDGE BUT ANY SNOWFALL AMOUNTS THAT FAR EAST WILL REMAIN LIGHT. WILL STAY JUST BELOW GUIDANCE FOR LOWS ON WEDNESDAY NIGHT SINCE THERE WILL BE NEW SNOW ON THE GROUND. BLEND OF MET/MAV GUIDANCE WAS REASONABLE FOR HIGHS ON THURSDAY AND LOWS ON THURSDAY NIGHT. UPSLOPE SNOW SHOWERS IN THE MOUNTAINS TAPER OFF THURSDAY NIGHT. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 145 PM EST TUESDAY... GUSTY NORTHWEST FLOW IN THE WAKE OF THE DEPARTING SYSTEM WILL CONTINUE THROUGH THE MORNING HOURS...BEFORE BACKING SOUTHWEST BY THE AFTERNOON. THE RESULT WILL BE SOME LINGERING ISOLATED UPSLOPE SNOW SHOWERS OR FLURRIES ACROSS THE MOUNTAINS DURING THE MORNING...WITH DECREASING CLOUD COVER AND THE ONSET OF SOME MODERATING TEMPERATURES BY THE AFTERNOON. DEPENDING UPON HOW MUCH SNOW ACTUALLY FALLS TONIGHT AND WEDNESDAY...THERE STILL MAY ENOUGH OF A SNOWPACK AROUND TO INFLUENCE BOTH THE FRIDAY HIGH AND THE FRIDAY NIGHT LOW. HAVE GONE WITH SLIGHTLY COOLER READINGS BOTH OF THESE TIME PERIODS WHERE WE CURRENT ANTICIPATE THE GREATEST SNOWFALL. BY LATE FRIDAY AFTERNOON AND INTO THE EVENING...THE CENTER OF SURFACE HIGH PRESSURE WILL MOVE ACROSS AND THEN EAST OF OF THE REGION. THIS WILL HELP SET THE STAGE FOR A SOUTHWEST FLOW...WARM AIR ADVECTION PATTERN TO TAKE US INTO AND THROUGH THE WEEKEND. CONCURRENTLY...A COLD FRONT WILL HEAD SOUTH...AND THEN STALL ALONG THE OHIO RIVER VALLEY. INCREASING MOISTURE WITHIN THE SOUTHWEST FLOW...AND THE PROXIMITY OF THE BAROCLINIC ZONE...WILL ALLOW FOR SMALL CHANCES OF LIGHT PRECIPITATION TO GRADUALLY WORK THEIR WAY INTO THE AREA FROM THE NORTHWEST SATURDAY NIGHT INTO SUNDAY. BY SUNDAY AFTERNOON...PRECIPITATION CHANCES WILL RANGE FROM ROUGHLY 20 TO 40 PERCENT ACROSS THE MOUNTAINS...WITH DRY WEATHER STILL EXPECTED EAST OF THE CREST OF THE BLUE RIDGE. THE BOUNDARY WILL START TO SAG SOUTH INTO THE REGION BY MONDAY...WITH PRECIPITATION CHANCES LIKEWISE SPREADING INTO MORE OF THE REGION. BY TUESDAY...GUIDANCE HAS NOTABLE DIFFERENCES AS TO THE PROGRESSION OF THE FRONT. WILL LEAN ON THE SIDE OF CONSENSUS WITH A SLIGHT CHANCE STILL OVER THE AREA. THE PRECIPITATION TYPE IS EXPECTED TO BE MAINLY RAIN. THE EXCEPTION MAY BE SOME PARTS OF THE FAR NORTHWEST AND NORTH PARTS OF THE FORECASTS AREA EARLY SATURDAY MORNING...AND THEN AGAIN LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING. THERE MAY BE SOME ISOLATED SPOTS THAT HAVE SURFACE TEMPERATURES BELOW FREEZING. WITH A STRONG WARM NOSE ALOFT...PRECIPITATION IS EXPECTED TO BE RAIN. A FEW ISOLATED SPOTS COULD SEE FREEZING RAIN FOR A SHORT DURATION. TEMPERATURES SHOULD GRADUALLY MODERATE THROUGH MONDAY WITH READINGS SOME 10 TO 15 DEGREES ABOVE NORMAL BY THAT TIME. TEMPERATURES WILL COOL TO NEAR NORMAL READINGS BEHIND THE FRONT ON TUESDAY. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 700 PM EST TUESDAY... DEVELOPING LOW PRESSURE OFF THE SE COAST TONIGHT WILL QUICKLY BRING DEEP MOISTURE BACK INTO THE REGION FROM THE SOUTH DURING THE OVERNIGHT WITH RAPID DETERIORATING FLIGHT CONDITIONS ANTICIPATED FROM SOUTH TO NORTH ACROSS THE MID ATLANTIC AFTER MIDNIGHT. THIS STORM SYSTEM WILL PRODUCE MAINLY RAIN EAST OF THE BLUE RIDGE...WITH SNOW ALONG AND WEST OF THE BLUE RIDGE. EVENING RNK SOUNDING PROFILE INDICATED ABOVE FREEZING TEMPERATURES THROUGH ABOUT 9KFT AGL. THIS LAYER IS EXPECTED TO COOL RAPIDLY WITH ONSET OF PRECIPITATION AFTER MIDNIGHT WITH THE FREEZING LEVEL DROPPING TO WITHIN 1-3KFT OF THE SURFACE BEFORE DAYBREAK WEDNESDAY. FOR THE MOUNTAIN TERMINALS WHICH INCLUDE KBLF/KLWB/KBCB ONSET OF PRECIPITATION IS EXPECTED BETWEEN MIDNIGHT AND 2AM. INITIAL P-TYPE WILL BE RAIN BUT THEN CHANGE TO SNOW BEFORE DAYBREAK AS THE FREEZING LEVEL DROPS TO WITHIN 1KFT OF THE SURFACE. SOME ACCUMULATIONS LIKELY AT THESE THREE AIRPORTS THROUGH MIDDAY WEDNESDAY...WITH PLOWABLE SNOW MOST LIKELY AT KBLF/KLWB...PERHAPS AT KBCB. BETWEEN 8AM AND NOON...SNOWFALL RATES OF AN INCH AN HOUR ARE POSSIBLE. FARTHER EAST...CLOSER TO THE BLUE RIDGE VCNTY OF KROA...RAIN IS ALSO EXPECTED AT THE ONSET...THEN MIXING WITH AND POSSIBLY CHANGING TO SNOW BEFORE ENDING. FREEZING LEVEL AT KROA IS EXPECTED TO DROP TO WITHIN 2KFT OF THE SURFACE...CERTAINLY ALLOWING FOR ACCUMULATING SNOW ON THE SURROUNDING RIDGES...BUT LESS CONFIDENT ON MUCH IN THE WAY OF ACCUMULATION AT THE AIRPORT DUE TO THE WARMER VALLEY TEMPERATURES. IN SPITE OF THE WARM GROUND TEMPERATURES...IT IS STILL POSSIBLE THAT DE-ICING PROCEDURES WILL BE NEEDED FOR A FEW HOURS AT KROA WED MORNING. SNOW MAY MIX WITH RAIN AT KLYH AS WELL...BUT FOR BOTH KLYH AND KDAN DO NOT EXPECT ANY IMPACT FROM SNOW ON RUNWAY SURFACES AT THIS TIME...WITH PRIMARILY RAIN OCCURRING AT BOTH KLYH AND KDAN...THE FREEZING LEVEL ONLY DROPPING TO WITHIN 3KFT OF THE SURFACE. DEVELOPMENT OF WIDESPREAD MVFR CONDITIONS IS ANTICIPATED AT ALL LOCATIONS BETWEEN MIDNIGHT AND 08Z WEDNESDAY...WITH AREAS OF IFR/LIFR IN SNOW FROM KBCB WEST FROM ABOUT 10Z/5AM - 16Z/NOON. THIS STORM SYSTEM IS EXPECTED TO MOVE RAPIDLY NORTHEAST IMPACTING NUMEROUS FLIGHT TERMINALS EAST OF THE APPALACHIAN MOUNTAINS AND ALONG THE NEW ENGLAND COAST. FOR THE LOCAL REGION...THIS STORM SYSTEM SHOULD EXIT THE AREA BY MID/LATE WEDNESDAY AFTERNOON 18-21Z...ONLY TO BE FOLLOWED BY A FAST MOVING CLIPPER TYPE AREA OF LOW PRESSURE...UPPER LEVEL DISTURBANCE...WEDNESDAY NIGHT INTO EARLY THURSDAY. THIS SECOND WEATHER FEATURE HAS THE POTENTIAL TO BRING WIDESPREAD SUB-VFR WEDNESDAY NIGHT WITH MVFR/IFR VSBY RESTRICTIONS IN LIGHT SNOW OVERNIGHT. LIGHT ACCUMULATIONS OF UP TO 2 INCHES ARE LIKELY AT KBLF/KLWB/KBCB...AND WITH A DUSTING TO AN INCH POSSIBLE FARTHER EAST BY THURSDAY MORNING. EXTENDED DISCUSSION... LOW CLOUDS AND SNOW SHOWERS/FLURRIES MAY PERSIST AT KBLF/KLWB INTO THURSDAY NIGHT WITH MVFR CIGS POSSIBLE. OTRW EXPECTING DOWNSLOPE DRYING TO BRING A RETURN TO VFR FROM THE BLUE RIDGE EAST AS HIGH PRESSURE STARTS TO BUILD IN AND DRIER AIR WINS OUT. THIS HIGH PRESSURE SYSTEM SHOULD BUILD ACROSS THE REGION AND TO THE EAST BY THE WEEKEND RESULTING IN MORE WIDESPREAD VFR TO END THE WEEK. BY LATE SUNDAY OR MONDAY...A WEAK FRONTAL BOUNDARY COULD SLIDE DOWN FROM THE NORTH BRINGING THE NEXT CHANCE FOR LIGHT PRECIP AND SUB-VFR CONDITIONS TO THE REGION...BUT ANY PRECIP LOOKS TO BE IN THE FORM OF RAIN. && .EQUIPMENT... AS OF 340 PM EST TUESDAY... THE VISIBILITY SENSOR AT KLYH...LYNCHBURG AIRPORT...HAS BEEN REPAIRED AND IS ONCE AGAIN OPERATIONAL. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...WINTER WEATHER ADVISORY UNTIL 4 PM EST WEDNESDAY FOR VAZ007- 009>018. WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST WEDNESDAY NIGHT FOR VAZ019. WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT EST WEDNESDAY NIGHT FOR VAZ020-024-035. WINTER STORM WARNING UNTIL 4 PM EST WEDNESDAY FOR VAZ015. WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT EST WEDNESDAY NIGHT FOR VAZ020. NC...WINTER WEATHER ADVISORY UNTIL 4 PM EST WEDNESDAY FOR NCZ001- 002-018. WINTER STORM WARNING UNTIL 4 PM EST WEDNESDAY FOR NCZ001-018. WV...WINTER WEATHER ADVISORY UNTIL 4 PM EST WEDNESDAY FOR WVZ042>044. WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST WEDNESDAY NIGHT FOR WVZ507. WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT EST WEDNESDAY NIGHT FOR WVZ508. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...AMS/NF LONG TERM...DS AVIATION...PM EQUIPMENT...AMS

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