FXUS61 KRNK 250003
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
703 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/...
COLD FRONT CONTINUES TO PUSH THROUGH FRIDAY NIGHT WITH A WEAK WAVE
DEVELOPING SOUTHEAST OF THE AREA. MAINTAINED CATEGORICAL POPS OUT EAST
THEN TAPERING OFF THE PRECIP FROM WEST TO EAST AS THE FRONT PUSHES
NORTHEAST. NAM INDICATES THE PRECIP DISSIPATING A BIT EARLIER THAN
THE GFS. LEANED TOWARD THE GFS SOLUTION AND HAVE DRY WEATHER
BEGINNING AT 12Z SATURDAY AS DRY AIR PUNCHES IN QUICKLY IN THE WAKE
OF THE FRONT.
COLD ADVECTION WILL FILTER INTO THE MOUNTAINS SATURDAY...AND FURTHER
EAST SATURDAY NIGHT INTO SUNDAY WITH 850MB TEMPERATURES AS LOW AS
-11 DEGREE C IN SOUTHEAST WEST VIRGINIA. SATURDAY MAX TEMPERATURES
WILL MODERATE INTO THE UPPER 30S TO LOWER 50S FROM NORTHWEST TO
SOUTHEAST RESPECTIVELY.
A SURFACE RIDGE TO THE SOUTHWEST NOSES INTO THE WESTERN PORTION OF
THE COUNTY WARNING AREA WHICH WILL INFLUENCE THE DRY WEATHER THROUGH
SUNDAY. WITH CLOUDS THINNING IN COMBINATION WITH THE DRY AIR AND
COLD ADVECTION...TEMPERATURES WILL DROP INTO THE UPPER TEENS IN THE
MOUNTAINS WITH THE PIEDMONT SEEING MID 20S FOR SUNDAY NIGHT.
THE NEXT DISTURBANCE WILL APPROACH THE AREA SUNDAY NIGHT WITH A
SOUTHWESTERLY FLOW INCREASING MOISTURE IN THE WESTERN ZONES. WINDS
WILL THEN VEER TOWARD A WEST TO NORTHWEST DIRECTION WHICH WILL
ENHANCE THE UPSLOPE COMPONENT. WITH TEMPERATURES BEING WELL BELOW
FREEZING...EXPECT SNOW SHOWERS ALONG AND WEST OF THE APPALACHIAN
MOUNTAINS.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
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 /00Z FRIDAY THROUGH TUESDAY/...
AVIATION CONDITIONS WILL DETERIORATE THROUGH THE NIGHT AS SLUG OF
MOISTURE STREAMS NORTH FROM THE GULF COAST STATES. LOOKING AT MVFR
TO IFR CONDITIONS ARRIVING IN THE DAN AREA BY 05Z...REACHING BLF
BY 08Z...THEN LWB-ROA-LYH IN THE 10-12Z TIME FRAME. TWO MAIN
AVIATION IMPACTS BESIDES THE LOW CLOUDS/VSBYS WILL BE FREEZING
PRECIPITATION AND LOW LVL WIND SHEAR. STRONG SOUTHEAST TO SOUTH
LLJ WILL INCREASE TO 50+ KNOTS OVERNIGHT INTO FRIDAY MORNING. THIS
IS GOING TO BRING LOW LVL WIND SHEAR AT ALL TAF SITES THRU THE
PERIOD...EXCEPT AFT 08Z FOR BLF AS WINDS MIX ON THE DOWNSLOPE SIDE
WITH GUSTS UP TO 40 KNOTS THERE FOR A PERIOD IN THE MORNING FRMO 08Z-16Z.
FREEZING RAIN WILL MOVE INTO DAN/LYH/ROA BY 10-12Z AND LWB AT 13Z.
MODELS HAVE TRENDED SLOWER. BLF WILL BE ON THE VERGE OF FZRA OR
RAIN LINE...AND FOR THE MOMENT THINK THEY WILL STAY WARMER THAN
AREAS SOUTHEAST OF THEM. BY MIDDAY TO EARLY AFTERNOON CHRISTMAS
DAY ALL TAF SITES SHOULD HAVE TRANSITIONED TO RAIN...BUT
CIGS/VSBYS WILL STAY IN THE MVFR TO IFR RANGE...OCCASIONALLY
DROPPING TO LIFR OVER THE BLUE RIDGE AND EAST.
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.
FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO 4 PM EST
FRIDAY FOR VAZ019-020-023-024-034-035.
HIGH WIND WARNING UNTIL 4 PM EST FRIDAY FOR VAZ007-009-010.
ICE STORM WARNING UNTIL NOON EST FRIDAY FOR VAZ012-015-016.
WIND ADVISORY UNTIL 4 PM EST FRIDAY FOR VAZ012-015.
ICE STORM WARNING UNTIL 4 PM EST FRIDAY FOR VAZ017-032.
NC...ICE STORM WARNING UNTIL NOON EST FRIDAY FOR NCZ001>003-018-019.
WIND ADVISORY UNTIL 4 PM EST FRIDAY FOR NCZ001-002-018.
FREEZING RAIN ADVISORY UNTIL NOON EST FRIDAY FOR NCZ004-020.
WV...FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST
FRIDAY FOR WVZ042>045.
HIGH WIND WARNING UNTIL 4 PM EST FRIDAY FOR WVZ042.
WIND ADVISORY UNTIL 4 PM EST FRIDAY FOR WVZ043-045.
&&
$$
SYNOPSIS...JJ
NEAR TERM...JJ
SHORT TERM...REB
LONG TERM...PC
AVIATION...JJ/WP
