FXUS62 KGSP 261834
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
134 PM EST SAT DEC 26 2009
.SYNOPSIS...
A LARGE LOW PRESSURE SYSTEM SITTING OVER THE UPPER MIDWEST WILL
SLOWLY LIFT NORTHWARD THROUGH THE WEEKEND ALLOWING HIGH PRESSURE TO
BUILD INTO THE SOUTHEAST. HIGH PRESSURE WILL THEN BE THE DOMINANT
WEATHER FEATURE ACROSS THE EASTERN HALF OF THE COUNTRY THROUGH MID
WEEK.
&&
.NEAR TERM /THROUGH SUNDAY/...
STILL EXPECTING PLUME OF CONSIDERABLE HIGH CLOUDS TO TRANSLATE
DOWNSTREAM OF THE CWFA THIS EVENING...SETTING US UP FOR A CLEAR
AND SEASONABLY CHILLY NIGHT. LLVL RIDGING ATOP THE REGION SUNDAY
MORNING WILL GIVE WAY TO A PERIOD OF WEAK RETURN FLOW. MODEL
CROSSSECTIONS DEPICT SOME DEGREE OF LOW TO MID LVL CLOUD DEVELOPMENT
WITHIN THIS AFOREMENTIONED NEUTRAL TO WEAK UPGLIDE FLOW AS THE
DAY WEARS ON. A MOS BLEND STILL LOOKS GOOD FOR NEAR TO SLIGHTLY
ABOVE NORMAL MAXES.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
AS OF 250 AM SAT...AN INTENSE UPPER LOW WILL FINALLY GET PICKED UP
BY THE WESTERLIES SUNDAY...THEN OPENING UP AND REACHING MAINE BY THE
END OF THE DAY MONDAY. AS THE LOW MOVES EAST...A STRONG SHORT WAVE
DROPS ACROSS THE AREA IN THE DEEP NW FLOW LATE SUNDAY NIGHT AND
EARLY MONDAY. RIDGE AXIS MOVES INTO THE AREA TUESDAY. AT THE
SFC...RIDGING OVER THE AREA MOVES EASTWARD SUNDAY AS SLOWLY
INCREASING NWLY LOW LEVEL FLOW DEVELOPS AS SFC LOW MOVES EASTWARD
NEAR THE GREAT LAKES. ANY GULF LOW DEVELOPMENT WILL REMAIN WELL TO
OUR SOUTH. THEREFORE...THE MAIN WEATHER FEATURE WILL BE THE
DEVELOPING NW FLOW SNOW SHOWERS OVER THE NC MTNS. WITH THE STRONG
SHORTWAVE AND CYCLONIC MID LEVEL FLOW...DECENT NWLY LOW LEVEL
FLOW...STRONG CAA AND COPIOUS LOW LEVEL MOISTURE. THE BEST CHANCE
FOR ACCUMULATING SNOW WILL BE SUNDAY NIGHT AND MONDAY MORNING. LOOKS
LIKE A GENERAL 1 TO 2 INCHES FROM AVERY TO MADISON AND HIGHER
ELEVATIONS OF HAYWOOD AND SWAIN. LESS THAN AN INCH ELSEWHERE ACROSS
THE REST OF THE MTNS AND NRN BLUE RIDGE. DRY FCST FOR THE REST OF
THE PERIODS ACROSS THE MTNS AND ALL TIMES ELSEWHERE. TEMPS A LITTLE
ABOVE NORMAL SUNDAY...FALL WELL BELOW NORMAL FOR MONDAY AND MONDAY
NIGHT...THEN BACK TO JUST BELOW NORMAL FOR TUESDAY.
&&
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
AS OF 300 AM SATURDAY...NO CHANGES WERE MADE TO THE GOING MEDIUM
RANGE FORECAST. 00Z MODEL GUIDANCE HAS COME IN AND TIMING
DIFFERENCES HAVE INCREASED FURTHER...SUPPORTING A VERY LOW
CONFIDENCE FORECAST. THE GFS AND THE ECMWF ACTUALLY START OFF AT
00Z WEDNESDAY VERY SIMILAR WITH A LOW PRESSURE SYSTEM BEGINNING TO
FORM OVER THE NW GULF. FROM THERE THE SOLUTIONS QUICKLY DIVERGE WITH
THE GFS BECOMING 24 TO 36 HOURS FASTER THEN THE ECMWF IN THE
THURSDAY/FRIDAY TIME FRAME. DESPITE THE ENORMOUS TIMING DIFFERENCES
THE TWO DO HAVE A SIMILAR LOW TRACK...TAKING THE SYSTEM ACROSS THE
NORTHERN GULF AND EVENTUALLY HUGGING THE SE COASTLINE. IN
FACT...THIS LOW TRACK LOOKS EERILY SIMILAR TO THE 18-19 DECEMBER
SYSTEM. IN ADDITION TO THE TRACK OF THE SYSTEM...THE MODELS DEPICT
A SIMILAR THERMAL STRUCTURE AS LOW LEVEL THICKNESSES ARE QUITE WARM
AND WOULD ONLY SUPPORT RAIN. WILL ALLOW THE DAY SHIFT TO REEVALUATE
THIS FORECAST PERIOD WITH HPC GUIDANCE AND THE 12Z MODEL SUITE.
&&
.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
AT KCLT AND ELSEWHERE...HIGH CLOUD SHIELD WILL DIMINISH THIS EVENING
WITH CLEAR SKIES TONIGHT INTO SUNDAY MORNING. LIGHT WINDS ARE
EXPECTED ACRS THE REGION.
OUTLOOK...VFR CONDITIONS EXPECTED SUNDAY THRU THURSDAY. MOISTURE
AHEAD OF A WEAK COLD FRONT WILL RETURN TO THE AREA ON WEDNESDAY.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...CSH
SHORT TERM...RWH
LONG TERM...BSH
AVIATION...CSH
