FXUS62 KGSP 221132
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
632 AM EST TUE DEC 22 2009
.SYNOPSIS...
HIGH PRESSURE WILL REMAIN OVER THE AREA THROUGH WEDNESDAY. STRONG
LOW PRESSURE WILL MOVE FROM THE PLAINS TO THE GREAT LAKES LATER IN
THE WEEK...PUSHING A COLD FRONT THROUGH THE WESTERN CAROLINAS AND
NORTHEAST GEORGIA ON FRIDAY. DRY HIGH PRESSURE WILL THEN RETURN OVER
THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
QUASI-ZONAL FLOW ALOFT AND SFC HIGH PRES ACRS THE AREA TODAY...WILL
RESULT IN SUNNY/MSUNNY SKIES AND WARMER TEMPS. I DID UNDERCUT MOS
CONSENSUS ON MAX TEMPS ACRS MUCH OF THE NC MTNS BY ABOUT 4 F...AS
THERE IS STILL PLENTY OF SNOW TO MELT TODAY. NEAR NORMAL TEMPS
ELSEWHERE (UPR 40S NW PIEDMONT TO MID 50S ACRS SRN UPSTATE AND NE
GA).
TONIGHT...MODEL T-SECTIONS INDICATE SOME INCREASING UPR LVL MOISTURE
INDICATIVE OF INCREASING CIRRUS. LOOKING AT IR SATL UPSTREAM...THIS
SEEMS REASONABLE. OTHERWISE...A QUIET NIGHT WITH TEMPS ABOUT THE
SAME AS TUESDAY MORNING (20S MOST PLACES TO LWR 30S IN THE THERMAL
BELT).
&&
.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 300 AM TUE...A DEEP LOW PRES SYSTEM WILL EMERGE INTO THE
PLAINS STATES ON WED. A RIDGE WILL DEVELOP ACROSS THE SE IN
RESPONSE. ONLY THE OPERATIONAL NAM TRIES TO SNEAK A LITTLE MOISTURE
BACK INTO THE MOUNTAINS ON WED AHEAD OF THE STORM SYSTEM...BUT THIS
SHOULD BE HELD AT BAY BY THE FIRM RIDGING WITH ONLY SOME THICKENING
HIGH CLOUDS TO BE ADVERTISED.
THE LOW PRES SYSTEM WILL THEN BE REINFORCED BY ENERGY DIVING SWD
FROM ALBERTA ON THU...FORMING INTO A DEEP CENTRAL CONUS VORTEX BY
FRI. MEANWHILE...SFC HIGH PRES WILL BUILD FROM THE GREAT LAKES INTO
NEW ENGLAND AND SET UP A COLD AIR DAMMING CONFIGURATION E OF THE
APPALACHIANS. THE MODELS HAVE CONTINUED TO SLOW THE ADVANCE OF
DEEPER MOISTURE AHEAD OF THE LOW PRESSURE...SO TEMPS WILL BE WARMED
VERY SLIGHTLY FOR THU GIVEN THE SLOWER ONSET OF PRECIPITATION. THE
LATER ONSET SHOULD ALSO KEEP ANY FREEZING OR FROZEN PRECIP CHANCES
EARLY THU LIMITED TO THE SLIGHT CHANCE RANGE.
RETURNING GULF MOISTURE WILL THEN SET UP ACROSS THE FORECAST AREA
THU NIGHT. THE BEST FORCING WILL BE ALONG AND AHEAD OF AN
APPROACHING OCCLUDING FRONT LATER THU NIGHT INTO FRI MORNING. 850 MB
WINDS SHOULD EASILY TOP 50 KT IN THE PEAK WARM ADVECTION FLOW LATE
THU NIGHT...SO MTN WINDS COULD APPROACH ADVISORY LEVELS IN THE
HIGHER TERRAIN. THE SFC COLD NOSE MAY GET REINFORCED BY THE CAD AT
THIS TIME...SO LIGHT ICE ACCUMS FROM FREEZING RAIN WILL POSSIBLE
NEAR THE BLUE RIDGE TOWARD DAYBREAK. ALSO...POSSIBLE EROSION OF THE
CAD ACROSS THE EXTREME SRN PIEDMONT COULD LEAD TO SHALLOW CONVECTION
FRI MORNING. THIS WILL HAVE TO BE MONITORED CLOSELY GIVEN THE
TREMENDOUS SFC TO 4 KM SHEAR...750 TO 1000 M2/S2...THAT WILL BE IN
PLACE.
THE LATER ONSET AND RAPID SPEED OF THE SYSTEM COULD HELP TO LIMIT
HYDROLOGY PROBLEMS. SNOW MELT HAS CAUSED STREAM AND RIVER LEVELS TO
REMAIN FAIRLY STEADY THE PAST FEW DAYS...SO TRIBUTARIES ARE SOMEWHAT
PRIMED FOR RAPID RISES. HOWEVER...QPF SHOULD BE LIMITED TO BETWEEN 1
AND 1.5 INCHES IN MOST LOCATIONS. A DRY SLOT SHOULD WORK IN QUITE
RAPIDLY FROM THE SW FRIDAY AFTERNOON TO SHUT PRECIPITATION OFF.
&&
.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
AS OF 315 AM TUESDAY...DESPITE THE RECENT FRONTAL PASSAGE...WARMING IS
INDICATED ON SATURDAY AS CLEARING DEVELOPS...WESTERLY 850 MB WINDS
DOWNSLOPE INTO THE PIEDMONT...AND THE BETTER COLD ADVECTION DOES NOT
DEVELOP UNTIL LATE DAY.
FAIRLY ABUNDANT NORTHWEST FLOW MOISTURE WILL THEN RETURN TO THE
WESTERN NC MTNS SAT NIGHT THROUGH SUNDAY. TEMPERATURES SHOULD BE
PLENTY COLD FOR MTN SNOW...BUT UPSLOPE WINDS APPEAR TO BE NO BETTER
THAN 20 TO 25 KT AT 850 MB DURING THE PEAK COLD ADVECTION...AND
DIRECTIONS ARE MORE WESTERLY THAN NW. STILL...SOME LIGHT
ACCUMULATIONS APPEAR POSSIBLE IN THE UPSLOPE PREFERRED AREAS SAT
NIGHT INTO SUNDAY. A DRIER NORTHWEST FLOW WILL THEN DEVELOP THROUGH
MONDAY. TEMPERATURES WILL RECOVER A LITTLE...BUT REMAIN SLIGHTLY
BELOW NORMAL.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AT KCLT...VFR CONDITIONS XPCTD THRU THE PERIOD...WITH JUST SOME
FEW-SCT CIRRUS STREAMING OVERHEAD. LGT NELY WND EARLY...THEN
BECOMING SLY BY ARND MIDDAY.
AT KAVL...FREEZING FOG IS BEING REPORTED...BUT SHOULD QUICKLY
LIFT/SCATTER OUT AFTER SUNRISE. FREEZING FOG WILL BE POSSIBLE AGAIN
TONIGHT. OTHERWISE...JUST PERIODS OF CIRRUS STREAMING BY AND LGT
WND...BECOMING SELY.
ELSEWHERE...VFR WITH FEW-SCT CIRRUS AND CALM OR LGT N/NELY WND...
BECOMING SLY BY EARLY AFTN. GUIDANCE IS FCSTING FOG AT KHKY TOMORROW
MORNING. FOR NOW...I HAVE ADDED AN MVFR VSBY AFTER 8Z TO SHOW THE
TREND.
OUTLOOK...VFR TUE NIGHT-WED EXCEPT FOR BRIEF MRNG FOG. A STRONG
STORM SYSTEM WILL APPROACH FROM THE W THU...PRODUCING WIDESPREAD
MVFR/IFR RESTRICTIONS AND PSBL WINTRY WEATHER. CONDITIONS SHOULD
IMPROVE FRI-FRI NIGHT AS DRY AIR WORKS IN FROM THE W.
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.
&&
$$
SYNOPSIS...HG
NEAR TERM...ARK
SHORT TERM...HG
LONG TERM...HG
AVIATION...ARK
