Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 201102
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
602 AM EST SAT DEC 20 2014

.SYNOPSIS...
WEAK LOW PRESSURE ACROSS THE SOUTHEAST STATES WILL PASS EAST AND
OFFSHORE THIS AFTERNOON KEEPING MOST SIGNIFICANT PRECIPITATION TO
THE SOUTH OF THE REGION. HIGH PRESSURE WILL SPILL BACK SOUTH INTO
THE AREA TONIGHT THROUGH SUNDAY NIGHT AHEAD OF ANOTHER LOW
PRESSURE SYSTEM THAT WILL SLIDE UP THE COAST ON MONDAY. A STRONG
COLD FRONT APPROACHES FROM THE WEST TUESDAY INTO TUESDAY NIGHT
BEFORE PASSING THROUGH THE REGION ON WEDNESDAY.
&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 222 AM EST SATURDAY...

LIGHT PRECIP EVENT TO UNFOLD THIS MORNING STILL LOOKS ON TRACK AS
SURFACE LOW PRESSURE PASSES WELL TO THE SOUTH AND EAST OF THE
REGION THROUGH THIS EVENING. THIS SHOULD KEEP THE MAJORITY OF THE
BETTER LIFT AND DEEP MOISTURE OFF TO THE SE WITH ANY PRECIP OVER THE
REGION PRIMARILY DRIVEN VIA WEAK UPPER DIFFLUENCE BETWEEN MID LEVEL
WAVES. ONE SUCH SHORTWAVE BEING WITH THE LEAD SOUTHERNMOST IMPULSE
LOOKS TO SLIDE ACROSS NW N CAROLINA THIS MORNING AND COINCIDE WITH WEAK
SE FLOW UNDER THE LEFT FRONT OF THE PASSING SPEED MAX ALOFT. THIS
SHOULD HELP DEVELOP AN AXIS OF LIGHT SNOW FROM THE NC MOUNTAINS ALONG
THE I-77 CORRIDOR EARLY ON WITH SOME OF THIS SPREADING EAST BUT IN A
DIMINISHING STATE GIVEN DAMPENING SUPPORT AND RESIDUAL DRY AIR.

WITH THE LATEST MODELS ESPCLY SREF PRINTING OUT QPF OF AROUND A
TENTH OF AN INCH OR SO...BUMPED UP POPS TO HIGHER CHANCE SW AND
KEPT EXTENSION OF THE GOING CHANCE POPS ESPCLY SOUTH OF HIGHWAY
460 THIS MORNING. THIS MAY BRING A HALF/ONE INCH OF SNOW AT
ELEVATION FROM I-77 AND POINTS WEST EARLY ON BUT WITHOUT ANY
HEADLINES AS COULD EASILY END UP BEING SNOW SHOWERS/FLURRIES AT
WORSE PER LATEST RADAR TRENDS. ELSW EXPECT LITTLE OR NO
ACCUMULATION GIVEN THE VERY LIGHT PRECIP TYPE SCENARIO IF AT ALL
AS SEEN OFF THE LATEST HRRR. HIGH TEMPS REMAIN TRICKY AFTER SUCH A
COLD START WITH POTENTIAL TO SEE SOME BREAKS DEVELOP BLUE RIDGE
AND ACROSS THE NORTH/WEST LATER ON. THUS TRENDED VALUES UP A
DEGREE OR TWO NORTH WHILE DECREASING A CAT OR SO ESPCLY SE WHERE
SOMEWHAT DEEPER MOISTURE WILL BE LAST TO EXIT.

WEAK RIDGING TO THE NW DIPS BACK INTO THE AREA BEHIND THE DEPARTING
WAVE OVERNIGHT ALLOWING DRYING ALOFT TO TAKE SHAPE UNDER WEAK
SUBSIDENCE. HOWEVER JUST HOW MUCH LOW LEVEL MOISTURE REMAINS TRAPPED IN
QUESTION AND PARTLY DEPENDENT ON THE DEGREE OF MOISTENING TODAY WITH
THE CURRENT EVENT. GFS REMAINS RATHER DRY WITH WEAK NW FLOW THROUGH THE
COLUMN...WHILE THE NAM WETTER UNDER A LIGHT LOW LEVEL EAST/SE
COMPONENT THAT KEEPS QUITE A BIT OF BOUNDARY LAYER MOISTURE ACROSS THE
REGION. THIS COULD POSE A FREEZING DRIZZLE ISSUE ESPCLY BLUE RIDGE WITH
LOTS OF FREEZING FOG/LOW CLOUDS AROUND BUT QUITE IFFY. THUS WILL
GO WITH MORE CLOUDS AND SOME FREEZING FOG OVERNIGHT WHILE LEAVING
OUT ANY -FZDZ MENTION FOR NOW DESPITE DECENT DEPTH TO MOISTURE
UNDER THE INVERSION OFF THE NAM. LOW TEMPS ALSO REFLECT MOISTURE
DIFFERENCES WITH THE MAV MOS WELL INTO THE 20S MOST SPOTS WHILE
THE MET MOS A GOOD 5-10 DEGREES WARMER DUE TO CLOUDS. FOR
NOW...TWEAKED DOWN IN THE VALLEYS AND BLUE RIDGE WHILE LEAVING
THINGS A BIT WARMER WEST-SW WHERE LEFTOVER CLOUDS MORE OF A GOOD
BET IN THE WAKE OF TODAYS POSSIBLE PRECIP.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
AS OF 430 AM EST SATURDAY...

WILL START SUNDAY OFF WITH LOW PRESSURE DEVELOPING ALONG THE
SOUTHEAST COAST. HIGH PRESSURE OVER EASTERN CANADA WILL CONTINUE TO
BUILD SOUTHWARD ACROSS NEW ENGLAND AND THE MID ATLANTIC...BECOMING
INCREASINGLY WEDGED AGAINST THE EASTERN FACE OF THE APPALACHIANS.
WILL SEE WINDS SHIFT MORE EAST NORTHEASTERLY BY EVENING...WITH THE
UPSLOPE FLOW ALONG THE BLUE RIDGE SUPPORTING POCKETS OF LIGHT RAIN
OR DRIZZLE...MAINLY OVER THE NORTH CAROLINA HIGHLANDS BY SUNSET.

THE LOW WILL PASS ALONG THE CAROLINA COAST SUNDAY NIGHT...RESULTING
IN INCREASING PRECIPITATION CHANCES APPROACHING DAWN ON MONDAY. AS
TEMPERATURES COOL THROUGH THE NIGHT...EXPECT TO SEE LIGHT RAIN/
DRIZZLE CHANGE OVER TO A MIXTURE OF RAIN AND FREEZING DRIZZLE OR
SLEET ACROSS THE AREA...WITH MORE MIXED PRECIPITATION NORTH OF
HIGHWAY 460. FORECAST SOUNDINGS INDICATE THAT MOISTURE REMAINS
SHALLOW HOWEVER...SO EXPECT VERY LITTLE ICE ACCUMULATION...IF ANY.
20/00Z MODELS HAVE TRENDED SLIGHTLY WEAKER WITH THIS LOW...WITH SOME
MODELS INDICATING MOISTURE HAVING A HARD TIME MAKING IT INTO
SOUTHEAST WEST VIRGINIA/FAR WESTERN VIRGINIA...REMAINING MORE
CONFINED TO THE PIEDMONT AND BLUE RIDGE. PRECIPITATION AMOUNTS ARE
ALSO LOWER...GENERALLY A FEW HUNDREDTHS OF AN INCH ACROSS THE
WESTERN RIDGES...TO A TENTH OR TWO ACROSS THE PIEDMONT.

MODEST DAYTIME WARMING ON MONDAY WILL CAUSE ANY MIXED PRECIPITATION
TO CHANGE OVER TO LIQUID MOST AREAS...ALTHOUGH A FEW POCKETS OF
SLEET OR LIGHT FREEZING RAIN MAY LINGER IN THE COLDER AIR ALONG AND
NORTH OF THE INTERSTATE 64 CORRIDOR THROUGH THE DAY. THE BRUNT OF
THE ENERGY WILL PASS EAST DURING EARLY AFTERNOON...LEAVING ONLY
SPOTTY PRECIPITATION THROUGH THE REMAINDER OF THE DAY.

BEGINNING MONDAY NIGHT...WILL SEE A GRADUAL WARMING TREND TAKE SHAPE
AS A DEEP LOW PRESSURE SYSTEM DEVELOPS OVER THE SOUTHERN PLAINS. THE
HIGH PRESSURE WEDGE WILL REMAIN IN PLACE THROUGH THE NIGHT...HOWEVER
TEMPERATURES ARE EXPECTED TO REMAIN WARM ENOUGH MOST LOCATIONS FOR
PRECIPITATION TO REMAIN LIQUID.

LOW PRESSURE WILL PUSH NORTH TOWARD THE GREAT LAKES TUESDAY AND
TUESDAY NIGHT...RESULTING IN INCREASING RAIN CHANCES DURING THE
PERIOD. PRECIPITABLE WATER VALUES WILL INCREASE SIGNIFICANTLY...
ESPECIALLY TUESDAY NIGHT...RISING TO THE 1.1 TO 1.4 INCH RANGE...
WHICH IS SIGNIFICANTLY HIGHER THAN NORMAL FOR LATE DECEMBER. AS
SUCH...HAVE WENT WILL HIGHER PRECIPITATION CHANCES FOR TUESDAY
NIGHT...WITH A COLD FRONT APPROACHING FROM THE WEST. MAY ALSO SEE
GUSTY WINDS TUESDAY NIGHT ACROSS THE MOUNTAINS AS A 50KT TO 60KT LOW
LEVEL JET ENTERS THE AREA.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 400 AM EST SATURDAY...

MODEL CONSENSUS OF GFS AND ECMWF IS THAT A SYNOPTIC UPPER TROUGH
OVER THE MISSISSIPPI VALLEY WILL EJECT A NEGATIVELY TILTED
THROUGH THE SOUTHEAST U. S. EARLY WEDNESDAY. WITH THE POSITION OF
THE ASSOCIATED SURFACE OCCLUDED FRONT AND THE TRIPLE POINT PASSING
SOMEWHERE NEAR OR JUST SOUTH OF OUR REGION...THERE IS THE
POTENTIAL FOR OUR REGION TO HAVE ACTIVE WEATHER WEDNESDAY WITH
PLENTY OF SHOWERS...PERHAPS VERY GUSTY WINDS AND A FEW
THUNDERSTORMS. LOOKS LIKE THE AXIS OF BETTER INSTABILITY MAY BE A
LITTLE FURTHER SOUTH ON THE 12Z MODEL RUN.

A COLD FRONT WILL MOVE EAST ACROSS OUR REGION WEDNESDAY INTO
WEDNESDAY NIGHT. HIGHS ON WEDNESDAY WILL WARM INTO THE LOWER 40S
IN THE WEST TO THE LOWER 50S IN THE EAST. RAIN AND SNOW SHOWERS
WILL CHANGEOVER TO SNOW SHOWERS AND SNOW FLURRIES IN THE WEST
WEDNESDAY NIGHT. LOW TEMPERATURES WEDNESDAY NIGHT WILL DROP INTO
THE MID 20S IN THE MOUNTAINS TO THE LOWER 30S IN THE PIEDMONT.
WEST TO NORTHWEST UPPER FLOW WILL CONTINUE INTO THURSDAY WITH
HIGHS FROM THE UPPER 20S IN THE MOUNTAINS TO AROUND 50 IN
PIEDMONT. WINDS WILL BE QUITE STRONG ON THURSDAY AS A 50 TO 55
KNOT 850MB JET PIVOTS ACROSS THE REGION. THE UPPER FLOW SHIFTS TO
THE SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS TROF CURVES OUT IN THE
CENTRAL US WITH SFC INFLECTION OF LOW PRESSURE DEVELOPING OVER THE
TENNESSEE VALLEY BY FRIDAY MORNING. MOISTURE SLOWLY RETURN FRIDAY
NIGHT INTO SATURDAY AS THE HIGH CENTER SLIDE OFF THE COAST.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
AS OF 545 AM EST SATURDAY...

AXIS OF LIGHT SNOW NOW MOVING ACROSS THE FAR WEST/SW AND LIKELY TO
IMPACT KBLF SHORTLY WITH A BRIEF PERIOD OF MVFR CIGS/VSBYS. OTRW
LOOKING AT LOWERING CIGS THIS MORNING FROM WEST TO EAST WITH MVFR
CIGS POSSIBLY SPREADING AS FAR EAST AS KBCB/KROA...AND NORTH AS
KLWB WHERE STILL MAINTAINING VFR VSBYS IN -SN THROUGH LATE
MORNING FOR NOW. THINKING EASTERN SITES SHOULD STAY VFR WITH ONLY
SOME SPOTTY -RA/-SN ARRIVING BY MID MORNING IF THE PRECIP HOLDS
TOGETHER.

THIS SYSTEM MOVES OUT FAIRLY QUICKLY WITH MOST PRECIPITATION
ENDING BY 19-20Z/2-3PM IF NOT SOONER. HOWEVER...A SHALLOW LAYER OF
MOISTURE BANKING UP AGAINST THE WESTERN SLOPES WILL KEEP
CLOUDS...LOWERING TO MVFR LEVELS AT KBLF THIS AFTERNOON. MAY SEE
CIGS ACTUALLY RISE A BIT BEHIND THE DEPARTING SPOTTY PRECIP ELSW BEFORE
SHALLOW MOISTURE BECOMES MORE WIDESPREAD THIS EVENING ESPCLY WHERE
ANY EARLIER SNOW/RAIN OCCURRED. THIS MAY LEAD TO LOW CLOUDS WITH
EVEN IFR CONDITIONS IN SPOTS GIVEN WESTERLY FLOW AROUND KBLF
OVERNIGHT...AND MVFR TO IFR ALONG THE BLUE RIDGE LATE. SOME
PATCHY DRIZZLE/LIGHT SNOW IS ALSO POSSIBLE THIS EVENING THEN
PERHAPS MORE WIDESPREAD ALONG THE BLUE RIDGE INCLUDING PATCHY
DENSE FOG AFTER MIDNIGHT. THIS HOWEVER REMAINS LOW CONFIDENCE
GIVEN DIFFERING MODEL SOLUTIONS BUT DID INCLUDE SOME LOWER
CIGS/VSBYS AT MOST SPOTS WITH POSSIBLE IFR IN STRATUS/FOG.

EXTENDED DISCUSSION...

ONCE THIS FEATURE EXITS WILL SEE THE NEXT WAVE ALONG THE COAST
BRING ANOTHER ROUND OF SUB-VFR CONDITIONS FOR LATER SUNDAY NIGHT
INTO MONDAY. RAIN WILL BE THE PRIMARY PRECIPITATION TYPE WITH
THE POTENTIAL FOR POCKETS OF FREEZING RAIN LATE SUNDAY NIGHT INTO
MONDAY MORNING ACROSS COLDER NORTHERN PORTIONS OF FORECAST AREA WHICH
MIGHT IMPACT LWB IF TEMPERATURES ARE COLD ENOUGH.

RAIN WILL IMPACT AREAS ALONG AND EAST OF THE BLUE RIDGE...WITH
YET ANOTHER SYSTEM SLATED FOR LATE TUESDAY INTO WEDNESDAY AHEAD OF
A STRONG COLD FRONT. THESE SYSTEMS ARE EXPECTED TO BRING A PERIOD
MAINLY RAIN BUT COULD BE SOME WINTRY WX AS WELL ESPECIALLY IN THE
MOUNTAINS WITH THE SUNDAY NIGHT/MONDAY EVENT. EXPECT POTENTIAL LOW
LEVEL WIND SHEAR AS WELL AND POOR FLYING WEATHER FOR EARLY NEXT
WEEK. RAIN AND SNOW SHOWERS WILL CONTINUE INTO WEDNESDAY. GUSTY
NORTHWEST WINDS ARE POSSIBLE WEDNESDAY INTO THURSDAY. MOUNTAIN
SNOW SHOWERS AND SNOW FLURRIES EXPECTED WEDNESDAY NIGHT INTO
CHRISTMAS.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...NONE.
NC...NONE.
WV...NONE.

&&

$$
SYNOPSIS...JH
NEAR TERM...JH
SHORT TERM...AMS/NF
LONG TERM...KK
AVIATION...JH/PH/WP



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