FXUS62 KGSP 260811
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
311 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/...
DENSE FOG IS EXPECTED TO LINGER EAST OF THE MOUNTAINS IN NC THROUGH
SUNRISE...BUT INCREASING WESTERLY WINDS WILL ERODE FOG FROM THE WEST
IN GA AND SC...AND THE DENSE FOG ADVISORY WILL BE ADJUSTED
ACCORDINGLY. THE BLACK ICE ADVISORY WILL BE CANCELLED IN THE NC
FOOTHILLS...WHERE STRATUS AND ELEVATED DEW POINTS HAVE KEPT
TEMPERATURES IN THE UPPER 30S.
AN UPPER LOW WILL PERSIST IN THE MIDWEST THROUGH TONIGHT. A
SHORTWAVE ROUNDING THIS LOW WILL CROSS THE SOUTHERN APPALACHIANS
LATE TONIGHT. HIGH PRESSURE WILL CROSS THE GULF STATES TODAY AND
TONIGHT...WITH SCATTERED HIGH CLOUD MOVING ACROSS OUR AREA. BY LATE
TONIGHT THE LEADING EDGE OF LOW LEVEL MOISTURE ASSOCIATED WITH THE
SHORTWAVE WILL REACH THE NC MOUNTAINS BORDERING TN...BUT WITHOUT
ENOUGH OF AN UPSLOPE COMPONENT TO INTRODUCE ANY MORE THAN CLOUDS TO
IMMEDIATE BORDER. TEMPERATURES WILL BE A CATEGORY OR TWO ABOVE
NORMAL TODAY AND TONIGHT IN A WEAK DOWNSLOPE COMPONENT.
&&
.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 /08Z SATURDAY THROUGH WEDNESDAY/...
AT KCLT...LIFR WITH TEMPORARY VLIFR IN FOG AND STRATUS SHOULD
PERSIST IN CALM WINDS UNTIL SUNRISE...WHEN QUICK IMPROVEMENT TO VFR
WILL OCCUR. LIGHT NORTHWEST WIND AFTER DAWN WILL BACK TO THE
SOUTHWEST IN THE AFTERNOON. MODEL TIME HEIGHTS SUGGEST THAT
SCATTERED CIRRUS WILL ARRIVE AFTER DAYBREAK...AND PERSIST THROUGH
SATURDAY EVENING.
ELSEWHERE...LIFR CONDITIONS WILL TEMPORARILY LOWER TO VLIFR IN FOG
AND STRATUS WITH LIGHT WINDS EARLY OVERNIGHT...BUT AS WINDS INCREASE
FORM THE WEST...IMPROVEMENT WILL OCCUR BEFORE DAWN. FORECAST
MINIMUM TEMPERATURES SUPPORT FREEZING FOG BY DAWN AT THOSE SITES
STILL RESTRICTED...MOST NOTABLE KHKY...BUT OBSERVED DEW POINTS
SUGGEST THAT MINIMUM TEMPERATURES MAY HAVE TROUBLE GETTING TO
FREEZING. RAPID IMPROVEMENT TO VFR WILL TAKE PLACE AFTER DAWN AT
SITES WHERE THE WIND DID NOT COME UP EARLIER. LIGHT WEST OR
NORTHWEST WINDS WILL BACK TO THE SOUTHWEST IN THE AFTERNOON...
EXCEPT AT KAVL WHERE A LIGHT NORTH WIND WILL PERSIST UNTIL IT
BECOMES VARIABLE AT SUNSET. SCATTERED CIRRUS WILL ARRIVE AFTER
DAYBREAK AND PERSIST THROUGH SATURDAY EVENING ACCORDING TO MODEL
TIME HEIGHTS.
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...WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR NCZ033-
048>053-058-059-062>065-501-503-505-507-509.
DENSE FOG ADVISORY UNTIL 7 AM EST THIS MORNING FOR NCZ035>037-
056-057-068>072-082-502-504-506-508-510.
SC...NONE.
&&
$$
SYNOPSIS...BSH
NEAR TERM...JAT
SHORT TERM...RWH
LONG TERM...BSH
AVIATION...JAT
