FXUS61 KRNK 241940
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
240 PM 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 /THROUGH FRIDAY/...
VERY DRY AIRMASS OVER THE REGION AT THIS TIME...BUT SATELLITE PWAT
PRODUCT SHOWS DEEP MOISTURE LURKING TO OUR SOUTH. LOW LEVEL
SOUTHEAST FLOW STRENGTHENS RAPIDLY INTO TONIGHT...WITH TREMENDOUS
MOISTURE TRANSPORT INTO THE AREA BY MORNING. THINKING IS THAT
THERE WILL NOT BE MUCH CONVECTION CUTTING OFF MOISTURE
TRANSPORT...WITH THE UPPER LOW LIFTING UP THROUGH THE CENTRAL MISS
VALLEY...ANY CONVECTIVE LINE WILL BE MOVG SLOWLY EASTWARD. SHOULD
BE A GOOD PERIOD OF ISENTROPIC LIFT ACROSS THE AREA LATE TONIGHT
INTO FRIDAY. WITH A LOW LEVEL EAST WIND...AREAS ALONG THE BLUE
RIDGE...AND OTHER EASTERN SLOPES...WILL TEND TO STAY BELOW
FREEZING LONGER. WILL CONTINUE THE ICE STORM WARNINGS AS
ISSUED...AS THIS IS WHERE THE PRECIP MOVES IN THE SOONEST...AND
THERE WILL BE THE LONGEST PERIOD OF FREEZING RAIN. FURTHER
NORTH...WHERE WE HAD THE WATCH...HAVE DECIDED TO ISSUE FREEZING
RAIN ADVISORIES AT THIS TIME SINCE PRECIP STARTS LATER AND THE
PERIOD OF FREEZING RAIN IS SHORTER. STILL COULD SEE SOME ACCUMS
ALONG THE BLUE RIDGE PARKWAY FROM ROANOKE NORTHWARD CLOSE TO A
QUARTER INCH...BUT AMOUNTS ACROSS MOST OF THE AREA SHOULD BE LESS
THAN A QUARTER INCH. WILL ISSUE UPDATED WSW PRODUCTS SOON.
WIND ADVISORIES AND HIGH WIND WARNINGS LOOK GOOD WHERE THEY ARE.
MTN WAVE MAY BREAK THE STRONG 70 KT 850 MB JET TO THE SFC ON THE
NW SIDE OF THE HIGHER RIDGES WHERE WE HAVE THE HIGH WIND GOING.
TAZEWELL USUALLY GETS THE STRONGER WINDS...AND OTHER COUNTIES HAVE
A CHANCE.
FINALLY...THE THREAT OF FLOODING HAS LESSENED...AS THE
HEAVIER RAIN LOOKS TO BE NEAR THE BLUE RIDGE WHERE THERE IS STILL
A DEEPER SNOW COVER. THINKING IS THAT THE TEMPS WILL STAY COLD
ENOUGH THAT THE SNOW WILL ABSORB MUCH OF THE RAIN AND NOT MELT
MUCH...AND THERE WILL BE LESS RUNOFF THAN IF ON A WET GROUND.
HOWEVER...THIS PATTERN HAS THE POTENTIAL TO PRODUCE EVEN HEAVIER
RAIN...SO THE FLOOD THREAT WILL HAVE TO BE WATCHED.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/...
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. HOWEVER 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 /MONDAY THROUGH WEDNESDAY/...
AMPLIFIED TROUGH OVER THE EASTERN CONUS DELIVERING A DOSE OF FAIRLY
CHILLY AIR BY EARLY NEXT WEEK ON BOTH GFS/ECMWF...H85 TEMPS -8 TO
-12 EARLY MONDAY. TROUGH LIFTS OUT TO THE NORTHEAST SOME BY MID-WEEK
WITH MORE ZONAL FLOW AND MODERATING TEMPS BY WED. POTENTIAL FOR A
REINFORCING SHORT-WAVE AND COLDER BY LATER IN THE WEEK WITH GFS
SUGGESTING A WEAK COASTAL LOW BY FRIDAY WHICH WILL HAVE TO BE
WATCHED IN LIGHT OF THE TENDENCY THIS YEAR FOR SUCH SYSTEMS TO
STRENGTHEN AND AMPLIFY. H5 MEAN HEIGHT NEGATIVE ANOMALIES ON THE GFS
RANGE ANYWHERE FROM 100 TO 150DM THRU MUCH NEXT WEEK SO IT WILL BE
CHILLY WEEK REGARDLESS...ALTHOUGH THE MUCH COLDER CORE OF AIR
REMAINS UP OVER NEW ENGLAND PER THE EC MODEL WHICH IS THE PREFERRED
SOLUTION PER THE NCEP EPD DISCUSSION. AT THIS TIME WILL MAINTAIN LOW
POPS FOR MUCH OF THE WEEK...ALTHOUGH MTN SNOW SHOWERS POSSIBLE
MONDAY AS THE COLDER AIR SPILLS EASTWARD COULD PRODUCE SOME SNOW IN
FAVORED AREAS DEPENDING ON EXACT TRAJECTORIES. A SPRAWLING RIDGE OF
COLD SURFACE HIGH PRESSURE ACROSS THE CENTRAL US WILL BUILD EASTWARD
IN THE EARLY TO MID-WEEK PERIOD WITH THAT POTENTIAL SURFACE LOW
DEVELOPING OVER THE GULF COAST BY LATER IN THE WEEK...OBVIOUSLY MANY
OUTCOMES POSSIBLE WITH SOMETHING THAT FAR OUT...BUT RAISED POPS INTO
THE CHANCE CATEGORY BY NEXT THU/FRI.
&&
.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
VFR CONDS ALL SITES WILL LAST INTO EARLY EVENING.
HOWEVER...STRENGTHENING SE WINDS WILL BRING LLWS TO ALL BUT BLF BY
SHORTLY AFTER 00Z FRIDAY. CIGS WILL BE LOWERING OVERNIGHT...AND
PRECIP WILL DEVELOP BY AROUND 12Z MOST SITES. ALL SITES MAY SEE
FREEZING PRECIP AT THE BEGINNING...BUT BLF AND DAN WILL LIKELY
CHANGE OVER QUICKLY TO RAIN. ROA...LYH AND LWB WILL HAVE A
PROLONGED PERIOD OF FREEZING PRECIP. IN ADDITION... THE LLWS WILL
INCREASE AT ALL SITES BUT BLF...WHERE THE WINDS WILL LIKELY MIX TO
THE SFC. SFC WIND GUSTS AT BLF WILL BE AROUND 40 KNOTS...WITH A
CHANCE FOR SOME GUSTS TO AROUND 50 KNOTS IN THE MORNING HOURS. THE
LOW MVFR OR IFR CIGS SHOULD HOLD THRU THE 24 HOUR PERIOD...18Z
FRIDAY.
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 LATE SATURDAY AFTERNOON OR EVENING...AND LASTING INTO
MONDAY. HOWEVER...THERE WILL BE 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...FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST
FRIDAY FOR VAZ010-011-013-014-018-022-033-045>047.
WINTER STORM WATCH FRIDAY AFTERNOON FOR VAZ011-013-014-018>020-
022>024-033>035.
FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO 4 PM EST
FRIDAY FOR VAZ019-020-023-024-034-035.
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...FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST
FRIDAY FOR WVZ042>045.
WINTER STORM WATCH 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...JJ
NEAR TERM...JJ
SHORT TERM...REB
LONG TERM...PC
AVIATION...JH/JJ
