FXUS62 KGSP 092358
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
658 PM EST WED DEC 9 2009
.SYNOPSIS...
AN AREA OF HIGH PRESSURE WILL BUILD INTO THE FORECAST AREA FROM THE
WEST ON THURSDAY AS A COLD FRONT CONTINUES TO PUSH OFF THE EAST
COAST. MOISTURE WILL BEGIN TO INCREASE FROM THE SOUTH ON SATURDAY AS
AN AREA OF LOW PRESSURE DEVELOPS ALONG THE SOUTHEAST COASTLINE. THIS
LOW WILL PULL AWAY FROM THE COAST ON SUNDAY WITH WEAK HIGH PRESSURE
MOVING IN BEHIND IT FOR MONDAY.
&&
.NEAR TERM /THROUGH THURSDAY/...
LATEST METARS AND LAPS SNDGS INDICATE THAT MIXING IS BEGINNING TO
WANE WITH LOSS OF DAYTIME HEATING. OVERALL...WIND GUSTS HAVE BEEN
DECREASING EARLY THIS EVENING. SO WILL ALLOW HIGH WIND WARNING TO
EXPIRE AT 7 PM.
LATER THIS EVENING AND OVERNIGHT...MODELS INDICATE THAT A SURGE OF
CAA WILL OCCUR ACRS THE NC MTNS...AS FLOW VEERS A LTL MORE
WEST-NORTHWESTERLY AND REMAINS IN THE 35-50 KT RANGE. THE NAM AND
GFS BUFKIT SNDGS AT KTNB SHOW A LOW BUT STRONG INVERSION AT 850
MB...WITH A SCARY 50-60 KTS OF WIND AT THE BASE. AT KAVL...THE WINDS
ARE ONLY 30-40 KTS AT THIS LEVEL. WITH SUCH A LOW INVERSION...SOME
OF THE HIGH VALLEYS MAY EXPERIENCE SOME CHANNELED WINDS THAT COULD
BE STRONG ENUF TO TOPPLE MORE TREES. A WIND ADVISORY SEEMS PRUDENT
FOR THE NORTHERN MTNS. FROM THE FRENCH BROAD VALLEY AND
SOUTH/WEST...I WILL HOIST A LAKE WIND ADVISORY FOR THE SAME TIME
FRAME. ALL PRODUCTS SHOULD BE OUT SHORTLY.
PREVIOUS DISCUSSION...
TEMPERATURES ACROSS THE CWA HAS SURGED INTO THE LOW TO MID 60S THIS
AFTERNOON. THE COMBINATION OF THE MILD LLVL TEMPERATURE AND CAA
ALOFT HAS RESULTED IN A DEEP MIX LAYER ACROSS THE FORECAST AREA.
LATEST OBSERVATIONS INDICATE FREQUENT GUSTS IN THE 30-35 KTS RANGE.
PEAK GUSTS COULD ACTUALLY OCCUR BETWEEN 20Z-22Z AS THE HIGHEST H7
WINDS SWEEP ACROSS THE FORECAST AREA. WINDS GUSTS SHOULD DECREASE
AROUND SUNSET AND END BY 7 PM...EXCEPT FOR THE MTNS. LATEST POWER
OUTAGE MAPS FROM UTILITY COMPANIES WEB PAGES INDICATE AN INCREASING
TREND IN OUTAGES. IN ADDITION...SEVERAL REPORTS OF TREES ON ROADWAYS
HAVE BEEN POSTED ON THE SCHP WEB PAGE. IT APPEARS THAT THE GUSTY
WINDS AND SATURATED SOIL IS RESULTING IN SIGNIFICANT TREE AND POWER
LINE DAMAGE. I WILL KEEP THE HIGH WIND WARNING IN PLACE THROUGH 7
PM. AFTER 7 PM...IT APPEARS THAT GUSTY CONDITIONS WILL CONTINUE
ACROSS THE HIGH TERRAIN. THE EVENING SHIFT WILL DETERMINE IF THE
SPEEDS OVERNIGHT WILL WARRANT A ADVISORY OR POSSIBLE EXTENSION OF
THE HWW.
OTHERWISE...SKY COVER WILL REMAIN CLEAR ACROSS THE REGION THIS
EVENING...THEN INCREASING CIRRUS OVERNIGHT. ONGOING CAA WILL RESULT
IN MIN TEMPERATURES FALLING 2-4 DEGREES BELOW NORMAL. CAA WILL
CONTINUE ACROSS THE REGION DURING THE DAY ON THURSDAY. HIGH
TEMPERATURES WILL LIKELY REACH WITHIN A DEGREE OR TWO OF NORMAL.
HOWEVER...DEWPOINTS WILL MIX INTO THE LOW TEENS...YIELDING
WIDESPREAD RH VALUES IN THE 20S EAST OF THE MTNS.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH SUNDAY/...
AS OF 245 PM WEDNESDAY...NOT MUCH CHANGE IN THINKING FOR THE FIRST
PART OF THE SHORT RANGE. STILL EXPECTING MODIFIED ARCTIC HIGH TO
BUILD OVER THE REGION THURSDAY NIGHT AND FRIDAY. WE WILL REMAIN
SOUTH OF THE JET AXIS SO PATCHES OF MID/HIGH CLOUDS WILL PASS
OVERHEAD...BUT IT SHOULD REMAIN DRY. THIS BASICALLY LEAVES US WITH A
TEMP FORECAST...SO HAVE NUDGED HIGHS AND LOWS TOWARD A GUIDANCE
BLEND.
THE TREND OF THE GUIDANCE CONTINUES IN THE DIRECTION OF DELAYING THE
APPROACH OF THE NEXT STORM SYSTEM AND THE ONSET OF PRECIP. TIMING
WILL NO DOUBT REMAIN A PROBLEM WITH THE LACK OF STRONG SHORTWAVE AND
THE NEARLY ZONAL FLOW ALOFT. HOWEVER...AT THIS TIME ALL THE MODEL
GUIDANCE KEEPS THE PRECIP OFF TO THE SW THROUGH DAYBREAK ON
SATURDAY...SO HAVE CUT THE POP ALTOGETHER FRIDAY NIGHT.
CONSEQUENTLY...THE MIN TEMP WAS CUT BY A FEW DEGREES. UPPER
DIVERGENCE IN THE RIGHT ENTRANCE REGION OF THE JET AND SOME
ISENTROPIC UPGLIDE SHOULD BE ABLE TO GENERATE SOME LIGHT PRECIP FROM
SW TO NE THROUGH THE DAY ON SATURDAY. KEPT POP VERY MUCH IN LINE
WITH THE OLD SREF. THE COLD START WILL PRESENT SOME PRECIP TYPE
PROBLEMS OVER THE SOUTH ASSUMING PRECIP CAN REACH THE GROUND BEFORE
IT WARMS UP. PARTIAL THICKNESSES AND PRECIP TYPE NOMOGRAM SHOW THAT
THERE IS SOME POTENTIAL FOR LIGHT FREEZING RAIN OR SLEET BEFORE NOON
ACROSS THE AREA S OF AVL/GSP/CLT. THIS WOULD ONLY BE A NUISANCE
EVENT IN ANY CASE BECAUSE THE SURFACE HIGH OVER THE MID ATLANTIC IS
NOT IN A FAVORABLE LOCATION TO MAINTAIN ANY COLD AIR NEAR THE
SURFACE...SO PRECIP TYPE CHANGES TO ALL RAIN IN THE AFTERNOON. TEMPS
WILL REMAIN COLD WITH AN IN-SITU WEDGE EAST OF THE MTNS.
THE MAIN SURFACE LOW PASSES BY TO THE SOUTHEAST OFF THE COAST
SATURDAY NIGHT. THE GUIDANCE POP IN THE LIKELY RANGE WAS ACCEPTED.
THERE COULD BE SOME PRECIP TYPE PROBLEMS OVER THE HIGH ELEVATIONS OF
THE NRN MOUNTAINS LATE AT NIGHT. THE LOW MOVES AWAY ON SUNDAY AND WE
SHOULD BEGIN TO DOWNSLOPE AWAY THE PRECIP IN THE AFTERNOON IF THE
GFS IS CORRECT. UNFORTUNATELY...THE ECMWF IS ABOUT TWELVE HOURS
BEHIND THE GFS...SO THE BEST COURSE OF ACTION IS TO KEEP A CHANCE
POP ALL DAY. THE PRECIP TYPE SHOULD BE MOSTLY RAIN...WITH SOME MIX
AT ELEVATIONS ABOVE ABOUT 3000 FEET SUNDAY MORNING.
&&
.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM WEDNESDAY...HEIGHTS WILL RISE ACROSS THE FORECAST AREA
ON MONDAY...RESULTING IN A BRIEF PRECIPITATION LULL BETWEEN SYSTEMS.
A SRN STREAM SHORTWAVE WILL THEN MOVE THROUGH THE MS RIVER VALLEY ON
TUESDAY...WITH A 120 KT UPPER JET AHEAD OF THIS FEATURE BRINGING
STRONG UPPER DIVERGENCE BACK TO THE AREA. MOISTURE WILL ALSO RETURN
FROM THE WEST MON NIGHT INTO TUE. LOW LEVEL THICKNESSES AND MODEL
PROFILES APPEAR TOO WARM NOW FOR MUCH IF ANY MIXED PTYPE AT THE
BEGINNING OF THE EVENT MON NIGHT. WILL JUST FEATURE A BRIEF
RAIN/SNOW MIX ACROSS THE HIGHER RIDGE TOPS IN THE NC MTNS LATE
MONDAY NIGHT BEFORE THE AREA WARMS TO ALL RAIN.
THE BEST FORCING AND DEEPEST MOISTURE SHOULD CROSS THE REGION JUST
AHEAD OF THE COLD FRONT EARLY TUESDAY...WITH BETTER INSTABILITY
INDICATED ACROSS THE EXTREME SOUTHERN PIEDMONT TUE MORNING. WILL
ADVERTISE VERY SOLID CHANCE POPS ACROSS THE AREA TUE...WITH AN
ELBERTON TO LAURENS SCHC THUNDER MENTION. THE SEVERE POTENTIAL WILL
HAVE TO BE MONITORED IN THIS AREA ONCE AGAIN WITH STRONG SHEAR
ACCOMPANYING THE WAVE.
NW FLOW MOISTURE ON THE BACK SIDE OF THIS SYSTEM DOES NOT LOOK AS
COLD OR MOIST AS PREVIOUSLY. WILL JUST CARRY NRN AND WRN MTN LIGHT
SNOW SHOWER CHANCES TUE NIGHT...WITH NO ACCUM. STRONG AND COOL HIGH
PRES WILL THEN BUILD IN FROM THE NW ON WEDNESDAY.
&&
.AVIATION /00Z THURSDAY THROUGH MONDAY/...
AT KCLT AND ELSEWHERE...WESTERLY TO WEST-NORTHWESTERLY WINDS SHOULD
CONTINUE TO SUBSIDE THIS EVENING AS MIXING DEPTH DECREASES. THE ONE
EXCEPTION IS KAVL...WHERE A SURGE OF COLD ADVECTION WITH
WEST-NORTHWESTERLY 30-40 KT FLOW COULD RESULT IN GUSTY NWLY WINDS
THRU THE OVERNIGHT. OTHERWISE...WINDS SHOULD BE GENERALLY UNDER 10
KTS BY AROUND 06Z. WINDS WILL INCREASE OUT OF THE WEST OR
WEST-NORTHWEST AGAIN THU AFTN...BUT SHUD BE MUCH LIGHTER THAN WHAT
OCCURRED ON WED. THERE WILL BE NO CIG/VSBY RESTRICTIONS...JUST SCT
TO BKN HIGH CLOUDS THRU DAYBREAK THURSDAY.
OUTLOOK...VFR EXPECTED FRIDAY. A GULF COAST STORM SYSTEM COULD
SPREAD LIGHT MIXED PRECIP INTO THE REGION SATURDAY EVENING AND
NIGHT.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR GAZ010-017-
018-026-028-029.
NC...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR NCZ033-
035>037-048>053-056>059-062>065-068>072-082-501>510.
WIND ADVISORY UNTIL 4 AM EST THURSDAY FOR NCZ033-049-050-501-
503-505.
LAKE WIND ADVISORY UNTIL 4 AM EST THURSDAY FOR NCZ048-051>053-
058-059-062>065-507-509.
SC...HIGH WIND WARNING UNTIL 7 PM EST THIS EVENING FOR SCZ001>014-
019.
&&
$$
SYNOPSIS...BSH
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...HG
AVIATION...ARK
