FXUS62 KGSP 261428
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
928 AM EST SAT DEC 26 2009
.SYNOPSIS...
AN AREA OF WEAK HIGH PRESSURE WILL REMAIN OVER THE SOUTHEAST THROUGH
SUNDAY MORNING AS A LARGE LOW PRESSURE SYSTEM SITS OVER THE UPPER
MIDWEST. THIS LOW WILL WEAKEN AND LIFT NORTHWARD THROUGH EARLY
MONDAY AS HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST. HIGH
PRESSURE WILL THEN BE THE DOMINANT WEATHER FEATURE ACROSS THE
EASTERN HALF OF THE COUNTRY THROUGH MID WEEK.
&&
.NEAR TERM /THROUGH TONIGHT/...
SUNSHINE WILL BE FILTERED BY SOME HIGH CLOUDINESS TODAY WITH MAX
TEMPS NEAR CLIMO IN THE MTNS TO AS MUCH AS 5 DEG F ABOVE NORMAL
IN THE PIEDMONT. WEAK SFC RIDGING TO BUILD IN...DIMINISHING
LOCALIZED MTN WIND GUSTS AND KEEPING WINDS ON THE LIGHT SIDE
ELSEWHERE. HI LVL RH DIMINISHES THIS EVENING AND SKIES TO
BECOME CLEAR. 12 UTC NAM CROSSSECTIONS DIMINISH LLVL RETURN
FLOW MOISTURE AHEAD OF SHEARING S/WV WEST OF THE MTNS DURING THE
OVERNIGHT HOURS.
&&
.SHORT TERM /SUNDAY 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 /15Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...IFR VISIBILITY IN FOG AND A LIFR CEILING IN STRATUS SHOULD
ERODE BY MID MORNING... YIELDING VFR FOR THE REST OF THE FORECAST.
LIGHT NORTHWEST WINDS WILL BACK TO THE SOUTHWEST BY AFTERNOON.
SCATTERED CIRRUS WILL CROSS THE AREA THIS AFTERNOON AND EVENING.
AT KAVL...A GUSTY NORTH WIND WILL DIMINISH DURING THE DAY. SCATTERED
CIRRUS WILL MOVE OVER THE AIRFIELD THIS AFTERNOON AND EVENING.
ELSEWHERE...LIFR FOG AND STRATUS...TEMPORARILY VLIFR...WILL PERSIST
FOR A COUPLE OF HOURS THIS MORNING...BEFORE BURNING OFF. VFR WILL
FOLLOW FOR THE REST OF THE FORECAST. LIGHT WEST NORTHWEST WINDS WILL
BACK TO THE SOUTHWEST THIS AFTERNOON. SCATTERED CIRRUS WILL CROSS
THE AREA FROM THE WEST THIS AFTERNOON AND EVENING.
OUTLOOK...VFR CONDITIONS EXPECTED SATURDAY THRU WEDNESDAY. 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/JAT
SHORT TERM...RWH
LONG TERM...BSH
AVIATION...JAT
