FXUS61 KRNK 250117
AFDRNK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
817 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/...
18Z GFS/21Z LOCAL WRF HAVE A BETTER HANDLE ON PRECIP
ATTM...ALTHOUGH THE GFS IS TOO WARM IN THE BOUNDARY LAYER WITH NAM
DOING A BETTER JOB HERE. GIVEN THE LOCATION OF THE PRECIP ON
RADAR...DECIDED TO LIMIT ITS NWD ADVANCEMENT BY 3 HRS...AND
DELAYED THE HIGHER POPS UNTIL MIDNIGHT IN THE FAR SW...THEN MOVING
IT NEWD INTO THE REST OF THE AREA TOWARD 12Z. GIVEN THE CURRENT
DRY AIRMASS AS DEPICTED BY THE 00Z RNK SOUNDING...AND WET BULBS IN
THE MID TO UPPER 20S...ANY PRECIP PUSHING INTO THE NC PIEDMONT AND
SOUTHSIDE VA...WILL BE FZRA LATE TONIGHT. HAVE ADDED 3 MORE
COUNTIES TO THE FREEZING RAIN ADVISORY FOR LIGHT ICE ACCRETION.
THIS BEING PITTSYLVANIA AND HENRY COUNTY IN VA AND ROCKINGHAM
COUNTY IN NC. THIS AREA WILL BE IN THE ADVISORY FROM MIDNIGHT
TONIGHT UNTIL NOON FRIDAY. FURTHER EAST...THE PRECIP WILL BE VERY
LIGHT...AND BY THE TIME THE MAIN BATCH REACHES THIS AREA...SHOULD
BE WARMING UP IN THE MORNING TO AT OR ABOVE FREEZING. CANNOT RULE
OUT TRACE AMOUNTS OF GLAZE AS FAR EAST AS YANCEYVILLE TO
HALIFAX...BUT WILL LEAVE THEM OUT OF THE ADVISORY.
MOISTURE TRANSPORT STILL LOOKS STRONG INTO THE AREA AND WILL BE
WATCHING THE HEAVIER BATCH OF CONVECTION OVER THE GULF COASTAL
STATES AS IT PUSHES ENE THROUGH THE NIGHT...AND WHETHER IT IMPACTS
THIS MOISTURE TRANSPORT. NORMALLY IN THESE SLOW MOVING
SYSTEMS...AND MORE ATLANTIC INFLOW WE STILL TEND TO GET MORE
PRECIP THAN MODELS INDICATE. POTENTIAL FOR DAMAGING ICE ACCRETION
POSSIBLE ALONG THE BLUE RIDGE FROM DEEP GAP TO MABRY MILL. STILL
WILL BE CONSERVATIVE WITH TOTALS AROUND 1/4 INCH TO LESS THAN ONE
HALF INCH.
THE REST OF THE ADVISORIES/WARNING AREAS REMAIN UNCHANGED. THE
WINDS ARE GUSTING AT TIMES TO 40 MPH ACROSS THE MTNS OF FAR SW
VA...AND THE NAM/GFS SWINGS THE 8H JET IN AT 65+ KNOTS AT 06Z. SO
THE WIND WARNINGS/ADVISORIES ARE LOOKING GOOD.
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 /01Z 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 VAZ010-011-013-014-018-022-033-043>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...FREEZING RAIN ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST
FRIDAY FOR NCZ005.
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/WP
SHORT TERM...REB
LONG TERM...PC
AVIATION...JJ/WP
