FXUS61 KRNK 241117
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
617 AM EST THU DEC 24 2009
.SYNOPSIS...
HIGH PRESSURE WELL TO THE NORTH OF THE AREA WILL DRIFT SLOWLY
EAST AND CONTINUE TO WEDGE SOUTH ALONG THE BLUE RIDGE TODAY
AND TONIGHT. STRONG LOW PRESSURE WILL PASS WELL TO THE WEST
LATE TONIGHT AND FRIDAY...PUSHING A COLD FRONT EAST ACROSS THE
REGION FRIDAY NIGHT. WEAK HIGH PRESSURE WILL BUILD IN BEHIND THE
FRONT ON SATURDAY BRINGING DRIER WEATHER.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
TODAY WILL BE CHARACTERIZED BY PROGRESSIVELY INCREASING SOUTHERLY
FLOW ALOFT IN ADVANCE OF A STRONG MID MISSISSIPPI LOW PRESSURE
SYSTEM. THE AREA WILL BE ON THE BACK SIDE OF A DEPARTING UPPER
RIDGE...SO EXPECTING MUCH OF THE AREA TO REMAIN ON THE DRY AND MILD
SIDE THROUGHOUT THE DAY. THERE WILL BE A SLIGHT CHANCE OF SOME LIGHT
RAIN ACROSS THE MOUNTAINS AND FOOTHILLS OF NORTH CAROLINA VERY LATE
IN THE DAY AS INCREASING UPSLOPE FLOW AND MOISTURE LEVELS MAY ALLOW
FOR SOME VERY LIGHT PRECIPITATION TO BE GENERATED. GUIDANCE HAS BEEN
RUNNING TOO LOW ON DAYTIME HIGHS...AND EXPECT THIS TO BE THE CASE AS
WELL TODAY WITH THE INCREASING SOUTHERLY FLOW.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
COMPLEX FRONTAL SYSTEM WILL BEGIN TO TILT TOWARD THE AREA FROM THE
SW OVERNIGHT BEFORE LIFTING NE ACROSS THE REGION BY LATE
CHRISTMAS DAY. INCREASING SE FLOW SHOULD AID IN MOISTENING THE
COLUMN OVER THE SW THIS EVENING AHEAD OF THE MAIN ARC OF
ISENTROPIC LIFT SCHEDULED TO ARRIVE BY FRIDAY MORNING. HOWEVER
MODEL CONSENSUS CONTINUES TO SLOW DOWN MUCH OF THE SIG PRECIP
UNTIL AFTER MIDNIGHT OVER THE FAR SW WITH ONLY LIGHT AMOUNTS INTO
THE NEW AND ROA RIVER VALLEYS BY FRIDAY MORNING. THIS PRESENTS A
DILEMMA WITH THE WATCH/WARNING SCENARIO ESPCLY SINCE THE BETTER
SLUG OF LIFT ALONG THE SOUTHERN BLUE RIDGE WONT OCCUR UNTIL FRIDAY
MORNING WHEN TEMPS ARE STARTING TO WARM SOME. ALSO SOUNDING
PROFILES ARE A BIT WARMER GIVEN THE SLOWING AS DEWPOINTS LOOK TO
RISE MORE BEFORE GOOD EVAPORATION CAN TAKE PLACE IN THE HEAVIER
PRECIP. HOWVER GIVEN THE LINGERING SNOW PACK UNDER STUBBORN LOW
LEVEL EASTERLY FLOW...APPEARS THE EASTERN SLOPES OF THE BLUE
RIDGE STILL IN FOR A DECENT ICING EVENT SO PLANNING TO UPGRADE
PART OF THE GOING WATCH TO A ICE STORM WARNING SW ZONES TONIGHT
INTO FRIDAY MORNING. WILL LIKELY BUFFER WITH ADVISORIES JUST OFF
THE FOOTHILLS IN NW NC BUT CONFIDENCE FOR SIG ICING OUTSIDE THE
BLUE RIDGE A BIT LOWER ATTM. FARTHER NORTH...SINCE BETTER FZRA
LIKELY WONT REACH UNTIL EARLY FRIDAY DECIDED TO LEAVE THE WATCH IN
PLACE FOR LATE TONIGHT RATHER THAN UPGRADE TO MAINLY A 3RD PERIOD
WARNING. ALSO A BIT CONCERNED THAT CONVECTION TO THE SE MAY TEND
TO ROB SOME OF THE INFLOW WITH SE FLOW ALSO LEAVING THE BETTER QPF
FROM ROA NE ALONG THE EASTERN SLOPES DURING FRIDAY WHEN TEMPS MAY
JUST BUMP ABOVE FREEZING. LATEST RH TRANSPORT PROGS SHOW THIS WELL
WITH MOST OF THE REAL DEEP MOISTURE STAYING ACROSS THE FAR SOUTH
AND EAST ON FRIDAY. OTRW SLOWED DOWN POPS SOME TONIGHT FROM SW TO
NE AND THEN LEFT CAT POPS ON CHRISTMAS. LOOKS LIKE MAIN FLOOD
POTENTIAL NOW WILL BE OVER THE SOUTH AND PERHAPS EAST DURING
FRIDAY IF PROGGED QPF DOESNT GET CUT OFF THE SOUTH MORE THAN
EXPECTED. SINCE LATER 3RD PERIOD AND IFFY WILL JUST KEEP MENTION
IN THE HWO AND FOREGO A FLOOD WATCH ATTM. MADE SOME SMALL UPWARD
ADJUSTS TO TEMPS OVER THE WEST TONIGHT AND LEFT HIGHS BELOW GOING
MOS ON FRIDAY.
GUIDANCE REMAINS VERY STRONG WITH LOW LEVEL SE WINDS INTO THE
WESTERN ZONES STARTING LATER THIS EVENING AND PERSISTING INTO FRIDAY
AS THE UPPER LOW WINDS UP TO THE NW. BUFKIT PROFILES SUGGEST SOME OF
50-60 KT SPEEDS MIXING DOWN INTO MERCER/TAZEWELL CTYS AND POSSIBLY
CLIPPING THE HIGHER RIDGES FARTHER SOUTH ESPCLY MIDDAY FRIDAY WHEN
THE WEDGE WILL BE WEAKENING A BIT. JUST HOW DEEP THE INVERSION GETS
WILL BE CRITICAL TO GETTING STRONGER WINDS INTO LOWER ELEVATIONS OF
THE MOUNTAIN EMPIRE/NW NC AS 85H JET STRONGER THAN MOST SEEN OF
LATE. THEREFORE WILL UPGRADE THE WATCH TO A WARNING AND EXTEND
WIND ADVISORIES INTO NW NC AND NORTH ACROSS THE WESTERN SLOPES OF
SUMMERS/GREENBRIER CTYS TNGT/FRIDAY.
DRY SLOT IS NOW A BIT FASTER TO KICK OUT DEEP MOISTURE FRIDAY NIGHT
WITH THE SECONDARY WEAK WAVE OFF TO THE EAST DURING THE EVENING.
SINCE TIMING HAS BEEN INCONSISTENT WITH THIS ONLY SPED UP POP
EXODUS BY A FEW HOURS WHICH STILL DRIES OUT MOST OF THE SW HALF
AFTER MIDNIGHT IF NOT SOONER. TEMPS IN THE DEEPER VALLEYS OF THE
NW MAY STILL BE COLD ENOUGH FOR PATCHY FREEZING PRECIP BUT
SHOULDNT BE WIDESPREAD ENOUGH FOR PROBLEMS. SATURDAY REMAINS THE
TRANSITION DAY BETWEEN THE EXITING FRONT AND THE COLD ADVECTION
AHEAD OF THE 5H LOW TO THE NW. LOOKS LIKE ENOUGH WEAK RIDGING IN
FROM THE SW TO PERHAPS HOLD THE 85H BOUNDARY BACK ALONG THE
MOUNTAINS UNTIL LATE. IF CAN MIX OUT THE LOW LEVELS THEN A DECENT
SHOT AT SEEING IMPROVING CONDITIONS WITH MORE SUN AND MILDER TEMPS
ALL EXCEPT THE FAR NW. THUS BUMPED UP HIGHS SOME ON SATURDAY BUT
COULD GO HIGHER IF TRENDS CONTINUE.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
WEAKENING VORTEX OVER UPPER MS VALLEY SUNDAY LIFTS NORTHEAST INTO
NEW ENGLAND MONDAY...WHICH WILL KEEP UPSLOPE SNOW GOING INTO MONDAY
AND MONDAY NIGHT. REINFORCING SURGE OF COLD AIR ARRIVES MONDAY WHICH
WILL ENHANCE UPSLOPE SNOW. AS A RESULT...EXPANDED CHANCE POPS EVEN
INTO THE NW NORTH CAROLINA MTNS. A QUICK LOOK AT THE 12Z ECMWF
BRINGS 40+ KT 850MB WINDS INTO THE REGION MONDAY AND MONDAY
NIGHT...SO INCREASED WIND SPEEDS DURING THIS TIME.
HEIGHTS RISE ON TUESDAY IN ADVANCE OF THE NEXT SOUTHERN PLAINS STORM
SYSTEM...KEEPING DRY CONDITIONS DRY. HOWEVER...WEAK SHORTWAVES IN
SOUTHWEST FLOW IN ADVANCE OF THE SYSTEM ALONG WITH WAA...MAY BRING
PRECIP BACK INTO THE REGION LATE WEDNESDAY OR WEDNESDAY
NIGHT...WITH A BETTER CHANCE BEYOND THE LONG TERM. GFS AND ECMWF
DISAGREE ON THE AMPLITUDE OF THE UPPER AIR PATTERN...WITH THE GFS
KEEPING THE FLOW MORE ZONAL ALLOWING COLDER AIR TO REMAIN IN
PLACE...WHILE THE 12Z ECMWF BUILDS A RIDGE IN ADVANCE OF THE LATE
WEEK SYSTEM RESULTING IN WARMER TEMPERATURES. THEREFORE...KEPT
PRECIP GRIDS AS RAIN AND/OR SNOW. ENSEMBLES SUGGEST A SOLUTION
BETWEEN GFS/ECMWF.
TEMPERATURES WILL BE BELOW AVERAGE THROUGH MONDAY UNDER THE
INFLUENCE OF THE NEW ENGLAND UPPER VORTEX...BUT MODERATING TUESDAY
AND WEDNESDAY. DOWNSLOPING WINDS WILL HELP MITIGATE THE COLD AIR
ADVECTION EAST OF THE BLUE RIDGE.
&&
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
OUTSIDE OF PATCHY FREEZING FOG AT KLWB EARLY THIS MORNING EXPECTING
VFR CONDITIONS TO PREVAIL TODAY WITH DRY AIR KEEPING CIGS ABOVE
10K FEET UNTIL THIS EVENING. WINDS ARE GOING TO PICK UP OVER SE
WV LATE THIS PERIOD OUT OF THE EAST TO SOUTHEAST WITH GUSTS TO 20
KNOTS EXPECTED BY 00Z FRI IN KBLF AND PERHAPS AS HIGH AS 40 KNOTS
LATER TONIGHT.
BEYOND THIS PERIOD...THE APPROACHING STORM SYSTEM WILL
LIKELY BRING ANOTHER LENGTHY PERIOD OF WIDESPREAD IFR TO LIFR
WEATHER LATE TONIGHT THROUGH CHRISTMAS DAY...WITH FREEZING RAIN
AND/OR RAIN THE MOST PROBABLE PRECIPITATION THREAT. VERY STRONG
SOUTHEAST WINDS ARE POSSIBLE FRIDAY/CHRISTMAS DAY AT BLUEFIELD.
GUSTS MAY REACH 50 KNOTS AROUND 12Z ON FRIDAY. LOW LVL WIND SHEAR
MAY ALSO BECOME PROMINENT EVERYWHERE LATER TONIGHT INTO CHRISTMAS.
THE ARRIVAL OF STRONG COLD WESTERLY WINDS ON THE BACKSIDE OF THIS
SYSTEM SHOULD ALLOW FOR RETURN TO VFR WEATHER EAST OF THE BLUE
RIDGE SATURDAY INTO MONDAY...BUT WITH TYPICAL MVFR TO LOCALIZED
IFR RESTRICTIONS CONTINUING IN THE UPSLOPE AREAS WEST OF THE BLUE
RIDGE (KBLF/KLWB) DUE TO STRATOCUMULUS AND SCATTERED SNOW SHOWERS.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
FOR VAZ011-013-014-018>020-022>024-033>035.
HIGH WIND WARNING FROM 6 PM THIS EVENING TO 4 PM EST FRIDAY
FOR VAZ007-009-010.
ICE STORM WARNING FROM 9 PM THIS EVENING TO NOON EST FRIDAY
FOR VAZ012-015-016.
WIND ADVISORY FROM 6 PM THIS EVENING TO 4 PM EST FRIDAY FOR
VAZ012-015.
ICE STORM WARNING FROM 9 PM THIS EVENING TO 4 PM EST FRIDAY
FOR VAZ017-032.
NC...ICE STORM WARNING FROM 9 PM THIS EVENING TO NOON EST FRIDAY
FOR NCZ001>003-018-019.
WIND ADVISORY FROM 6 PM THIS EVENING TO 4 PM EST FRIDAY FOR
NCZ001-002-018.
FREEZING RAIN ADVISORY FROM 9 PM THIS EVENING TO NOON EST
FRIDAY FOR NCZ004-020.
WV...WINTER STORM WATCH FROM LATE TONIGHT THROUGH FRIDAY AFTERNOON
FOR WVZ044-045.
HIGH WIND WARNING FROM 6 PM THIS EVENING TO 4 PM EST FRIDAY
FOR WVZ042.
WIND ADVISORY FROM 6 PM THIS EVENING TO 4 PM EST FRIDAY FOR
WVZ043-045.
&&
$$
SYNOPSIS...JH/JJ
NEAR TERM...DS
SHORT TERM...JH
LONG TERM...PH
AVIATION...AMS/DS/JH/WP
