FXUS62 KGSP 240549
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1249 AM EST THU DEC 24 2009

.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH THURSDAY...BEFORE 
A STRONG COLD FRONT PUSHES ACROSS THE REGION ON CHRISTMAS DAY. DRY 
HIGH PRESSURE WILL THEN RETURN DURING THE WEEKEND AND REMAIN THROUGH 
THE EARLY PART OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TODAY/...
SOUTHWEST MID LEVEL FLOW WILL CONTINUE TO STREAM THICK CLOUDS ACROSS 
THE CWA TONIGHT. BASED ON THE SATELLITE TRENDS AND LATEST GUIDANCE I 
WILL INCREASE SKY COVER TO MENTION MOSTLY CLOUDY SKY COVER. INCREASE 
SKY COVER AND BROAD WAA WILL RESULT IN LOW TEMPERATURES AROUND 
NORMAL...MILD COMPARED TO RECENT NIGHTS. LOW NAM CONDENSATION 
PRESSURE DEFICITS WITHIN A ACTIVE MELTING AREA MAY YIELD PATCHY FOG 
ACROSS THE I-40 CORRIDOR LATE TONIGHT.

AS THE SYSTEM CONTINUES TO APPROACH THU...LOW LVL MOISTURE WILL 
SURGE N FROM THE GULF...AND FROM THE ATLANTIC...AND BEGIN TO 
SATURATE THE LOWER LEVELS OF THE ATMOSPHERE. ISENTROPIC LIFT AND 
UPSLOPE FLOW BEGIN TO INCREASE AS WELL...WHILE DRYER AIR CONTINUES 
TO GET PULLED DOWN FROM THE NE. MODELS ARE NOT IN GOOD AGREEMENT 
TIMING THE ONSET OF PRECIP WITH THE GFS FASTER THAN THE NAM AND 
ECMWF. IN THIS CASE WE USED A MODEL BLEND WHICH KEEPS THE AREA DRY 
THRU THE MRNG HOURS...THEN BEGINS TO BRING CHC POPS IN FROM THE SW 
BY MID-LATE AFTN. CONSIDERING THE TIME OF DAY...KEPT THE PRECIP AS 
ALL RAIN ATTM...EVEN WHERE THERE IS A SLIGHT CHC OF PRECIP UP INTO 
THE NC N MTNS AND PART OF THE NC FOOTHILLS. ESP SINCE HIGH TEMPS ARE 
EXPECTED TO REACH THE L-M40S...WITH A FEW U40S TO NEAR 50 ACROSS THE 
S ZONES.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
AS OF 245 PM WEDNESDAY...STRENGTHENING WAA PATTERN REMAINS ON TRACK 
TO OVERSPREAD THE REGION THURSDAY NIGHT ACCOMPANIED BY PROGRESSIVELY 
DEEPER FORCING AND MOISTURE. WILL PLAN ON CONTINUING TO RAMP UP TO 
100 POP CWFAWIDE AS THE NIGHT WEARS ON. THERE EXISTS SUBTLE 
DIFFERENCES BETWEEN 12 UTC MODEL QPF...WITH THE 15 UTC SREF A 
GOOD COMPROMISE...PROGGING AN AXIS OF HEAVY PCPN UP THE FTHLS.
SFC HIPRES REMAINS PROGGED TO ORIENT ITSELF INTO A FAVORABLE 
POSITION TO DRIVE AND MAINTAIN SUB 32 DEG F WETBULB TEMPERATURES
SWWD ALONG THE NC ESCARPMENT AS PCPN BECOMES HEAVIER AND WIDESPREAD 
OVERNIGHT. 

CONSEQUENTLY...WILL ADVERTISE EXPANDING FREEZING RAIN 
AREA...EVENTUALLY MAKING IN TO THE UPPER FRENCH BROAD VALLEY AND
PERHAPS EAST ALONG I-40. NAM BUFKIT SNDGS ADVERTISE DEVELOPING 
COLD NOSE AT KTNB...LEADING TO A POSSIBILITY OF SOME SLEET AS WELL. 
SREF PLUME P-TYPE DIAGRAMS HAVE BEEN CONSISTENT THE PAST SVRL RUNS 
IN FCSTG MEAN VALUES OF ICE ACCRETION IN THE ADVISORY LVL AT BOTH 
ASHEVILLE AND HICKORY AND WARNING LVLS AT BOONE. 

BASED ON THIS...WILL HOIST WINTER STORM WATCH FOR THE NORTHERN NC 
MTNS/FTHLS FOR A DAMAGING ICE ACCUMULATION THURSDAY NIGHT INTO 
FRIDAY MORNING. THERE WILL LIKELY BE A TIER OF WINTER WX ADVISORIES 
BOUNDING THIS AREA...WHICH LATER SHIFTS MAY ISSUE AS WE GET CLOSER 
TO THE EVENT.

60 KT SSE LLVL JET IS ALSO PROGGED TO TRANSLATE ACRS THE MTNS
THURSDAY NIGHT INTO FRIDAY MORNING...LEADING TO THE POTENTIAL
FOR STRONG WIND GUSTS ACRS HIGHER ELEVATIONS...PERHAPS TOPPLING
SOME TREES WITHIN THE WET SOILS. 

DEEPER LIFT/MOISTURE DEPARTS BY FRIDAY AFTERNOON AND WIDESPREAD 
MORNING PCPN WILL DWINDLE AS THE DAY WEARS ON. IMPINGING WEDGE FRONT 
FROM THE SE LATE THU/EARLY FRIDAY ALONG WITH POSSIBLE TRIPLE POINT 
LOW...DOES RAISE A SLIGHT EYEBROW TO DEEP CONVECTIVE CHANCES...BUT 
WITH THE NAM/S FCST OF POSITIVE VALUES OF 0-3 KM MUCAPE CLOSER TO
THE COAST...WITH KEEP ALL RAINFALL STRATIFORM. 

LOCALLY AS MUCH AS 2 INCHES OF LIQUID EQIV PCPN IS PSBL...LEADING TO
RUNOFF CONCERNS...ESPECIALLY WHERE SNOWMELT WILL AID IN FLOWS.
AT THIS POINT...GIVEN DIFFERENCES IN THE PLACEMENT OF HEAVIEST
QPF AXIS AMONG THE MODELS...AND HEAVY RAIN POTENTIAL HOLDING
OFF TO LATER THIRD PERIOD...WILL CONTINUE TO JUST ADDRESS THREAT IN 
HWO. EVEN THOUGH BROAD CYCLONIC FLOW WILL LINGER ACRS THE EASTERN 
CONUS FOR SATURDAY...DEEP DRYING OVERSPREADING THE REGION FRIDAY
NIGHT AND LINGERING INTO SATURDAY TO PROVIDE GENERALLY FAIR AND
SEASONABLE CONDITIONS.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM WEDNESDAY...THE MEDIUM RANGE LOOKS QUIET COMPARED TO 
WHAT IT HAS BEEN LATELY. WHILE THERE IS SOME SIGNIFICANT DIFFERENCES 
AS TO HOW THE GFS AND ECMWF ARE HANDLING THE DEEP UPPER LOW OVER THE 
MIDWEST BEGINNING SATURDAY NIGHT...IN THE END IT DOES NOT HAVE TOO 
MUCH IMPACT ON OUR WEATHER. EVEN IF THE MORE SRN TRACK OF THE UPPER 
LOW SHOWN BY THE ECMWF COMES TO PASS...THE FLOW AT 850MB IS STILL 
TOO WESTERLY TO GENERATE MUCH IN THE WAY OF UPSLOPE SNOW SHOWER 
ACTIVITY...THAT IS UNTIL SUNDAY NIGHT AND MONDAY MORNING. THIS IS 
GENERALLY ACCEPTED AND A SLIGHT CHANCE POP ALONG THE TN BORDER IS 
APPROPRIATE FOR THIS FAR OUT IN THE FUTURE. THE MOISTURE SHOULD PULL 
OUT ON MONDAY WITH HIGH PRESSURE BUILDING IN FROM THE WEST FOR THE 
EARLY PART OF NEXT WEEK. TEMPS WERE NUDGED TOWARD A BLEND OF THE 
MOSGUIDE AND HPCGUIDE. 

BOTH MODELS SHOW THE DEVELOPMENT OF A SRN STREAM LOW PRESSURE SYSTEM 
DURING THE MIDDLE PART OF NEXT WEEK...WITH THE GFS ABOUT 24 HOURS 
FASTER BUT WEAKER THAN THE ECMWF. CONFIDENCE COULD NOT BE MUCH LOWER 
THAN IT IS. WENT WITH HPC PRECIP CHANCES...WHICH ARE DOWN IN THE 
SLIGHT CHANCE RANGE. PARTIAL THICKNESSES SUGGEST IT WILL BE A 
RAIN/SNOW DEAL SO THAT IS WHAT WAS PUT IN THE GRIDS...BUT NOT TOO 
MUCH STOCK SHOULD BE PUT ON THIS EVENT JUST YET BECAUSE A LOT WILL 
CHANGE BETWEEN NOW AND THEN.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...THIS TAF PERIOD WILL FEATURE BRIEF PERIODS 
OF MVFR FOG AT KAVL AND KHKY THIS MORNING...STRENGTHENING NE 
WINDS...AND LOWERING CIG HEIGHTS. LATEST NAM AND GFS MOISTURE FIELDS 
SHOW A DIFFERENCE IN THE TIMING OF LOWERING CIGS WITH THE GFS BEING 
THE FASTER AND MORE PESSIMISTIC SOLUTION. I HAVE GENERALLY TAKEN A 
COMPROMISE BETWEEN THE TWO AND HAVE STARTED TO ADVERTISE LOWERING 
CIGS SOONER THAN THE PREVIOUS FORECAST...PER SREF PROBS. BOTH THE 
NAM AND THE GFS SHOW LOW LEVEL SOUTHEASTERLY FLOW STRENGTHENING 
DURING THE AFTERNOON AS LOW LEVEL MOISTURE SPREADS ACROSS THE FA. AS 
SUCH...I INTRODUCE AN MVFR CIG AT KAND BY 20Z AND SPREAD THAT 
NORTHEASTWARD THROUGH 00Z AT KHKY. THEN LATER IN THE PERIOD I SHOW 
VCSH ACROSS THE WEST AFTER 00Z WITH A LOWERING MVFR CIG. KAND DOES 
FEATURE AN IFR CIG WITH -RA AFTER 03Z AS THE PRECIP COVERAGE SHOULD 
REALLY BEGIN TO INCREASE NEAR THE END OF THE TAF PERIOD.

OUTLOOK...A BRIEF PERIOD OF WINTRY WEATHER WILL BE POSSIBLE THURSDAY 
NIGHT INTO CHRISTMAS BETWEEN KAVL AND KHKY...MAINLY AT THE ONSET OF 
PRECIP. WIDESPREAD MVFR/IFR RESTRICTIONS CAN BE EXPECTED ON FRIDAY 
AS A COLD FRONT CROSSES THE AREA. CONDITIONS SHOULD IMPROVE FRIDAY 
NIGHT THROUGH SAT AS DRY AIR COMES IN FROM THE W.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...WIND ADVISORY FROM 6 PM THIS EVENING TO NOON EST FRIDAY FOR 
     GAZ010-017.
NC...WINTER STORM WATCH FROM THIS EVENING THROUGH FRIDAY MORNING 
     FOR NCZ033-049-050-501>506.
     WIND ADVISORY FROM 6 PM THIS EVENING TO NOON EST FRIDAY FOR 
     NCZ051-058-062.
SC...NONE.

&&

$$
SYNOPSIS...SBK
NEAR TERM...NED/RB
SHORT TERM...CSH
LONG TERM...PM
AVIATION...BSH