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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