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[Printable]
904
FXUS61 KRNK 252053
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
353 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 /21Z TUESDAY THROUGH SUNDAY/...
AS OF 110 PM EST TUESDAY...

COLD FRONT HAS EXITED THE FCST AREA INTO THE CENTRAL PIEDMONT OF
VA AND NC...WITH W TO NW WINDS MAINLY UNDER 10KTS EXCEPT FOR ALONG
RIDGES. HIGH CLOUDS WILL CONTINUE CLEARING IN THE WEST THROUGH THE
AFTERNOON..BUT WILL INCREASE AGAIN BY LATE AFTERNOON AND EARLY
EVENING...LOWERING EVERYWHERE THROUGH THE EVENING IN ADVANCE OF
NEXT SYSTEM MOVING IN FROM THE SOUTHWEST...WHICH WILL HAVE A
SIGNIFICANT IMPACT ON MOST AIRPORTS.

DEVELOPING LOW PRESSURE OFF THE SE COAST LATE TONIGHT WILL QUICKLY
BRING DEEP MOISTURE BACK INTO THE REGION FROM THE SOUTH THIS
EVENING WITH PRECIP OVERSPREADING THE AREA OVERNIGHT. MOST OF THIS
WILL TAKE THE FORM OF RAIN TO START WITH AROUND 04/05Z THEN A
CHANGE TO SNOW AT KBLF/KLWB/KBCB WITHIN A COUPLE HOURS OF ONSET.
SOME ACCUMULATIONS CERTAINLY POSSIBLE AT THESE THREE AIRPORTS
THROUGH MIDDAY WEDNESDAY...WITH PLOWABLE SNOW MOST LIKELY AT
KBLF/KLWB...PERHAPS AT KBCB AS WELL. SNOW AMOUNTS REMAIN VERY
TRICKY AND WILL VARY SIGNIFICANTLY ACROSS THE MOUNTAINS. FARTHER
EAST...SOME MIX WITH SNOW AT KROA BEFORE LIKELY CHANGEOVER TO ALL
SNOW AFTER DAYBREAK...BUT THIS LESS CERTAIN THAN AT THE HIGHER
ELEVATIONS. VERY UNCLEAR HOW MUCH MAY ACCUMULATE AT KROA...BUT
MOST LIKELY LESS THAN AN INCH. IT IS 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. THIS SYSTEM SHOULD BRING WIDESPREAD MVFR TO ALL LOCATIONS
BETWEEN MIDNIGHT AND 08Z WEDNESDAY...WITH AREAS OF IFR/LIFR IN
SNOW FROM KBCB WEST DURING THE EARLY MORNING HOURS.

THIS STORM SYSTEM SHOULD EXIT TO THE NE BY WEDNESDAY AFTERNOON ONLY
TO BE FOLLOWED BY A FAST MOVING CLIPPER TYPE AREA OF LOW PRESSURE
WEDNESDAY NIGHT INTO EARLY THURSDAY. THIS FEATURE AGAIN 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 FROM 9 PM THIS EVENING TO 4 PM EST
     WEDNESDAY FOR VAZ007-009>018.
     WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO MIDNIGHT EST
     WEDNESDAY NIGHT FOR VAZ019.
     WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO MIDNIGHT EST
     WEDNESDAY NIGHT FOR VAZ020-024-035.
     WINTER STORM WARNING FROM 9 PM THIS EVENING TO 4 PM EST
     WEDNESDAY FOR VAZ015.
     WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO MIDNIGHT EST
     WEDNESDAY NIGHT FOR VAZ020.
NC...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 4 PM EST
     WEDNESDAY FOR NCZ001-002-018.
     WINTER STORM WARNING FROM 9 PM THIS EVENING TO 4 PM EST
     WEDNESDAY FOR NCZ001-018.
WV...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 4 PM EST
     WEDNESDAY FOR WVZ042>044.
     WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 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...JH/KK/SK
EQUIPMENT...AMS




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