Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000
FXUS61 KRNK 142110
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
410 PM EST SUN DEC 14 2014

.SYNOPSIS...
HIGH PRESSURE WILL GRADUALLY BUILD EAST ACROSS THE AREA INTO
MONDAY BEFORE SLIDING OFFSHORE MONDAY NIGHT. THIS FEATURE WILL
PRODUCE PRIMARILY FAIR WEATHER. HOWEVER LOW LEVEL MOISTURE
TRAPPED ON THE WEST SIDE OF THE APPALACHIAN MOUNTAINS WILL KEEP
LOW CLOUDS AND FOG MAINLY WEST OF THE APPALACHIAN DIVIDE THROUGH
MONDAY MORNING. A COLD FRONT WILL CROSS THE AREA TUESDAY WITH AN
OPPORTUNITY FOR SHOWERS.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 245 PM EST SUNDAY...

SURFACE HIGH PRESSURE AND UPPER LEVEL RIDGE WILL SLIDE EAST OF
THE OHIO-TENNESSEE VALLEYS TONIGHT. THE COMBINATION OF THESE TWO
SYSTEMS WILL ALLOW FOR GOOD RADIATIONAL COOLING CONDITIONS
OVERNIGHT...ESPECIALLY EAST OF THE BLUE RIDGE. MOISTURE TRAPPED
UNDER A STRONG SUBSIDENCE INVERSION WILL ALSO GLIDE OVER THE
MOUNTAINS. WITHIN THIS THICK DECK OF CLOUDS (2500-3500
FEET)...TEMPERATURES WILL DROP BELOW FREEZING COATING ELEVATED
SURFACES WITH A THIN LAYER OF ICE. SINCE CONFIDENCE AND AREAL
COVERAGE IS LOW FOR FREEZING FOG OR RIMING ICE...WE WILL NOT ISSUE
ANY HEADLINES WITH THE AFTERNOON PACKAGE...BUT WILL HIGHLIGHT IN
HAZARDOUS WEATHER OUTLOOK (HWO).

THROUGH THE DAY MONDAY...SURFACE HIGH AND UPPER LEVEL RIDGE AXIS
SHIFTS EAST TO THE COAST. LOW LEVEL CLOUDS MAY HANG ON THROUGH THE
MORNING AND LIFT/SCOUR AS SOUTHERLY FLOW RETURNS TO THE REGION.
THE CENTER OF THE SURFACE RIDGE TO THE WEST HAS BEEN COLD WITH
EXTENSIVE LOW CLOUDS. AS THIS CHILLY HIGH TRACKS OVER THE FORECAST
AREA TOMORROW MORNING...TEMPERATURES WILL BE SLOW TO RISE. ONCE
THIS SYSTEM MOVES EAST...TEMPERATURES WILL WARM ABOVE NORMAL WITH
WIDESPREAD 50S ACROSS THE AREA TO LOWER 60S ALONG AND SOUTH OF THE
VA/NC BORDER.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
AS OF 230 PM EST SUNDAY...

STRONG RIDGING BOTH SURFACE/ALOFT FINALLY PUSHES OFFSHORE MONDAY
NIGHT IN ADVANCE OF THE NEXT FAST MOVING UPSTREAM 5H UPPER LOW AND
ITS ASSOCIATED COLD FRONT THAT WILL APPROACH THE APPALACHIANS BY
EARLY TUE. DECENT SW FLOW AHEAD OF THE BOUNDARY SHOULD CONTINUE
THE WARM ADVECTION PATTERN ESPCLY ALOFT WITH CLOUDS QUICKLY
INCREASING FROM THE WEST DURING THE EVENING...FOLLOWED BY A PRE-
FRONTAL AXIS OF SHOWERS THAT SHOULD ACCELERATE INTO THE MOUNTAINS
BY DAYBREAK TUE. SOMEWHAT FASTER TIMING AS SUGGESTED OFF THE GFS
AND 12Z ECMWF COULD POSE A BRIEF ISOLATED MOUNTAIN VALLEY FREEZING
RAIN ISSUE...BUT APPEARS TEMPS WILL REBOUND JUST ENOUGH AFTER
EARLY COOLING TO PRECLUDE MENTION FOR NOW.

BEST DYNAMICS HEAD WELL TO THE NORTH TUESDAY AS THE SURFACE FRONT
PUSHES ACROSS THE REGION PRECEDED BY A JET DRIVEN BAND OF SHOWERS
THAT WILL RACE EAST THROUGH THE PIEDMONT BY MID AFTERNOON AS DRY
SLOTTING KICKS IN. APPEARS BEST COVERAGE OVER THE NW TUE MORNING
WHERE CLOSER TO THE UPPER SUPPORT AND WITHIN A BROAD UPPER
DIFFLUENT ZONE. THUS GOING WITH A PERIOD OF LIKELY POPS WEST-NORTH
EARLY ON...TAPERING TO CHANCE COVERAGE ELSW...AND MOSTLY SLIGHT
POPS FAR SOUTH/SE PER LESS MOISTURE. ELEVATED INSTABILITY A BIT
STRONGER FAR NW BUT GIVEN MORNING TIMING AND WEAK LAPSES WONT
INCLUDE...ALTHOUGH A FEW FAST MOVING HEAVIER SHOWERS POSSIBLE
ACROSS THE NORTH GIVEN THE 40-50+ KT MID LEVEL JET. HIGH TEMPS
MOSTLY 50S BUT LIKELY LATER IN THE DAY WEST WHEN SOME BREAKS OCCUR
BEHIND THE EXITING PRECIP/FRONT.

SECONDARY 85H FRONT CROSSES TUESDAY NIGHT WITH A PERIOD OF GUSTY
NW WINDS AND BRIEF/LIGHT UPSLOPE INDUCED RAIN/SNOW SHOWERS WESTERN
SLOPES INTO WED AFTERNOON. HOWEVER MOISTURE LOOKS RATHER SHALLOW
SO ONLY EXPECTING SOME LIGHT SNOWFALL AT BEST FAR NW WHERE WILL
KEEP HIGH CHANCES TUESDAY NIGHT...THEN FADING TO MORE ISOLATED
NATURE DURING WED. OTRW CLEARING AND BREEZY ELSW WITH HIGHS 40S
WEST TO MID 50S EAST AS BEST COLD ADVECTION PASSES NORTH UNDER THE
FAST BUT FLAT ZONAL UPPER FLOW. WEAK HIGH PRESSURE BUILDS IN WED
NIGHT BUT MAY QUICKLY BE UNDERCUT BY SHEARED HIGH/MID CLOUDS
ALREADY ZIPPING IN FROM THE WEST LATE. THIS ASSOCIATED WITH YET
ANOTHER FAINT SOUTHERN STREAM SHORTWAVE THAT WILL RACE EAST INTO
RESIDUAL DRY AIR WITHIN THE 5H CONFLUENT FLOW. THIS COULD LIMIT
TEMP FALLS LATE SO BLENDED TOWARD THE WARMER SIDE OF MOS WITH
25-30 MOUNTAINS AND MAINLY LOW 30S EAST. OTRW BECOMING PC AND
WITHOUT POPS WED NIGHT FOR NOW.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
AS OF 330 PM EST SUNDAY...

A WEAK UPPER LEVEL DISTURBANCE MAY BRING A FEW LIGHT RAIN SHOWERS TO
OUR AREA ON THURSDAY...HOWEVER HIGH PRESSURE BUILDING IN FROM THE
NORTHERN PLAINS WILL BE THE MAIN FEATURE OF OUR WEATHER PATTERN. THE
DOWNSLOPE WESTERLY WIND FLOW AND RAYS OF SUNSHINE THAT MANAGE TO
FIND BREAKS IN THE CLOUD COVER WILL HELP AFTERNOON HIGHS RANGE FROM
THE UPPER 30S ACROSS THE MOUNTAINS...TO THE LOW 50S ACROSS THE
SOUTHSIDE. OVERNIGHT LOWS WILL BE IN THE UPPER 20S AND LOW 30S.

ON FRIDAY...THE HIGH OVER THE PLAINS WILL SHIFT EAST ACROSS THE
GREAT LAKES...WITH A FINGER OF THE HIGH BEGINNING TO BUILD
SOUTHWARD ACROSS THE MID ATLANTIC TO WEDGE AGAINST THE EASTERN
FACE OF THE APPALACHIANS. AS THE HIGH BUILDS IN...WE WILL NOTICE
WINDS BECOMING INCREASINGLY NORTHEASTERLY...DRAWING COOLER AIR
INTO THE AREA. MEANWHILE...AND DEEP UPPER LEVEL TROUGH WILL
ADVANCE EAST FROM THE ROCKIES TO FORM A SURFACE LOW OVER SOUTHERN
TEXAS. THE SURFACE LOW WILL MOVE EAST NORTHEAST THROUGH THE
DAY...RESULTING IN INCREASING HIGH CLOUDS FOR THE EAST COAST
REGION.

THE APPROACH OF THIS LOW PRESSURE SYSTEM SETS THE STAGE FOR OUR
FIRST REAL WINTER STORM OF THE SEASON...ALTHOUGH IT REMAINS
UNCLEAR AS TO HOW THE STORM WILL AFFECT OUR AREA AS THE WEATHER
FORECAST MODELS ARE STILL TRYING TO GET A HANDLE ON HOW THIS STORM
WILL DEVELOP AND THE TRACK IT WILL TAKE. THE GFS AND ECMWF
FORECAST MODELS DEVELOP THE STORM DIFFERENTLY AND TAKE IT ON
DIFFERENT TRACKS PAST OUR AREA. FOR NOW...AM STICKING CLOSER TO
THE ECMWF SOLUTION... WHICH TAKES THE MAIN LOW FROM CENTRAL
ALABAMA FRIDAY NIGHT ACROSS THE CENTRAL CAROLINAS ON SATURDAY AND
OVER THE DELMARVA SATURDAY NIGHT. THE GFS SOLUTION IS MORE
COMPLEX...WITH ONE LOW PASSING WEST OF THE APPALACHIANS...AND
ANOTHER ONE THEN DEVELOPING ALONG THE COAST AND TAKING OVER AS THE
MAIN SYSTEM. THIS FAR OUT IN TIME... WOULD NOT BE AT ALL SURPRISED
TO SEE EITHER SOLUTION CHANGE. MORE CLARITY WILL
ARISE...HOPEFULLY...DURING THE EARLY HALF OF THIS WEEK.

IN LEANING TOWARD THE ECMWF SOLUTION...EXPECT POTENTIALLY HEAVY
SNOW FOR THE MOUNTAINS...WITH SLEET AND FREEZING RAIN DEVELOPING
ACROSS THE FOOTHILLS AND PORTIONS OF THE PIEDMONT...AND POSSIBLY
WARM ENOUGH TEMPERATURES ACROSS THE SOUTHSIDE TO MAINTAIN MAINLY
RAIN. MOUNTAIN SNOW APPEARS REASONABLE AT THIS POINT...BUT HAVE NO
CONFIDENCE IN PRECIPITATION TYPE RIGHT NOW FURTHER EAST. THE BRUNT
OF THE SYSTEM IN EXPECTED TO PASS US BY LATE SATURDAY
EVENING...WITH WINDS SHIFTING NORTHWESTERLY...TRANSITIONING
PRECIPITATION TO UPSLOPE SNOW SHOWERS ACROSS THE WESTERN RIDGES.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
AS OF 1220 PM EST SUNDAY...

SFC HIGH PRESSURE ANCHORED ON THE WEST SIDE OF THE APPALACHIANS
IS RESULTING IN A STRONG SUBSIDENCE INVERSION AT ABOUT 1KFT AGL.
THIS WARM LAYER IS CAPPING A VERY COOL SURFACE LAYER AND IS
RESULTING IN A LARGE AREA OF LOW LEVEL CLOUDINESS OVER THE OH/TN
VALLEYS. THIS MOISTURE EXTENDS AS FAR EAST AS THE WV/VA
APPALACHIAN DIVIDE. BLUEFIELD AND POINTS NORTH AND WEST ARE
EXPERIENCING IFR CONDITIONS...WHICH WILL LIKELY CONTINUE INTO
MONDAY MORNING. THIS PERSISTENT LOW CLOUDS/FOG WILL RESULT IN RIME
ICE WHICH WILL COAT ELEVATED SURFACES IN THE VICINITY OF KBLF/KLWB
IF TEMPERATURES DROP AGAIN BELOW FREEZING. THESE FREEZING
CONDITIONS MAY NOT RETURN UNTIL TONIGHT.

ON THE EAST SIDE OF THE APPALACHIANS IT IS A DIFFERENT WORLD WITH
DOWNSLOPE FLOW RESULTING IN DRY NEAR CLOUD FREE CONDITIONS...VFR
FROM THE BLUE RIDGE KROA/KLYH/KDAN TO THE SOUTHEAST ATLANTIC
COAST. MODEL FORECAST KEEP OUR EASTERN TERMINALS VFR THROUGH THE
TAF PERIOD...AND MODERATE TO HIGHLY CONFIDENCE THIS WILL BE THE
CASE. THE ONLY EXCEPTION MAY BE TERMINALS RIGHT AGAINST THE BLUE
RIDGE WHERE SOME OF THE LOW LEVEL MOISTURE MAY BLEED OVER THE
HIGHER MOUNTAINS TO THE WEST AND RESULT IN MVFR AT KBCB AND
POSSIBLY KROA.

WINDS TODAY WILL BE SIMILAR TO YESTERDAY...SUSTAINED 6-12 KTS
FROM THE WEST WITH GUSTS NEAR 20 KTS. WITH THE CENTER OF THE HIGH
PASSING OVERHEAD TONIGHT...WINDS SHOULD DIMINISH AT
SUNSET...BECOME LIGHT AND VARIABLE DURING THE OVERNIGHT.

EXTENDED DISCUSSION...

NEXT OPPORTUNITY FOR LOW CIGS/VSBYS WILL BE ASSOCIATED WITH A
FRONTAL PASSAGE TUESDAY. MVFR CONDITIONS ARE POSSIBLE TUESDAY
ASSOCIATED WITH RAIN SHOWERS. LOW PRESSURE WILL BE MOVING ACROSS
THE GREAT LAKES ON TUESDAY...ITS ASSOCIATED COLD FRONT CROSSING
THE APPALACHIANS. HIGH PRESSURE BUILDS IN BEHIND THE FRONT
BRINGING A RETURN TO VFR FOR ALL AREAS WEDNESDAY INTO THURSDAY.

&&

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

&&

$$
SYNOPSIS...RCS
NEAR TERM...RCS
SHORT TERM...JH
LONG TERM...NF
AVIATION...RCS



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