Severe Thunderstorm Warning 392, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
247 PM EDT MON SEP 28 2009

.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA BY THIS EVENING...AND MOVE OFF THE
CAROLINA AND GEORGIA COAST TONIGHT. COOLER AND DRIER AIR WILL
BLANKET THE AREA AS HIGH PRESSURE BUILDS SOUTHEAST ACROSS THE
REGION. THE AIRMASS WILL REMAIN IN PLACE MOST THE WEEK BEFORE
ANOTHER COLD FRONT APPROACHES BY THE WEEKEND.

&&

.NEAR TERM /THROUGH TUESDAY/...
AT 1830Z...SFC OBS...SATELLITE...AND RADAR DATA INDICATED THAT THE
COLD FRONT ALONG THE TN BORDER COUNTIES OF NORTH CAROLINA. LATEST
LAPS CAPE ANALYSIS SHOWS CAPE VALUES AHEAD OF THE FRONT RANGED FROM
800-1400 J/KG. HOWEVER...A SIGNIFICANT INVERSION AROUND H7 AND DRY
LLVL AIR SHOULD KEEP MEASURABLE CIN VALUES ACROSS THE PRE FRONTAL
AREAS. I WILL FORECAST COVERAGE LESS THAN 20 PERCENT FOR THE REST OF
THE FIRST PERIOD. ACTIVE LLVL MIXING WILL KEEP GUSTS INTO THE L20
KTS THROUGH EARLY THIS EVENING. AFTER 23Z...SPEEDS SHOULD FALL INTO
THE 7-10 KTS RANGE.

THE COLD FRONT SHOULD PUSH EAST OF THE CWA BY MID EVENING. CAA
BEHIND THE FRONT WILL CONTINUE THROUGH SUNRISE TUESDAY. USING THE
PREFERRED MET MOS AND NAM12...MIN TEMPERATURES SHOULD TO THE MID 40S
WITHIN THE MTN VALLEYS AND L50S EAST. A FEW MTN PEAKS COULD SEE
VALUES FALL INTO THE U30S. SKY COVER SHOULD BECOME MOSTLY CLEAR WITH
A WNW WIND BETWEEN 6-8 KTS.

ON TUESDAY...LLVL THICKNESS AND H85 TEMPS WILL REMAIN VERY COOL.
HOWEVER...WEAK DOWNSLOPE FLOW AND STRONG INSOLATION WILL ALLOW A
WIDE DIURNAL SWING IN TEMPERATURES. USING A BLEND OF MET MOS AND
NAM12 SFC TEMPS...I WILL FORECAST HIGH TEMPERATURES WELL BELOW
NORMAL. HIGH TEMPERATURES SHOULD RANGE FROM THE L60S ACROSS THE MTNS
AND L70S EAST.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
AS OF 135 PM MONDAY...THE SHORT RANGE STILL LOOKS LIKE A SHORT
STRETCH OF DRY AND SEASONALLY COOL EARLY FALL WEATHER. THE MODELS
AGREE WITH A SLOWLY EVOLVING PATTERN WITH A DEEP UPPER TROF ON THE
EAST COAST AND A RIDGE OVER THE PLAINS. WITH THE AXIS OF THE TROF
ALREADY TO OUR EAST AND THE AXIS OF THE UPPER RIDGE REMAINING TO OUR
WEST THROUGH THURSDAY...THAT KEEPS THE WESTERN CAROLINAS UNDER A NW
FLOW ALOFT AND HIGH PRESSURE AT THE SURFACE. EXPECT SKY TO BE MOSTLY
CLEAR THROUGH THE PERIOD. TEMPS WERE NUDGED TOWARD A GUIDANCE BLEND.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
AS OF 215 PM MONDAY...THE LATEST GUIDANCE CONTINUES TO FOCUS ON THE
FRIDAY NIGHT OR SATURDAY TIME FRAME FOR MOVING A COLD FRONT ACROSS
THE FORECAST AREA. THE UPPER RIDGE AXIS SHOULD MOVE OVERHEAD SOME
TIME EARLY IN THE DAY FRIDAY WHICH SHOULD ALLOW MOISTURE TO RETURN.
THERE IS SOME BRIEF TAP FROM THE GULF ACCORDING TO THE MODELS...
WHICH MAY BE A RECENT TREND. THE MOSGUIDE AND HPC NUMBERS SHOW A
CHANCE OF PRECIP ACROSS THE ENTIRE FORECAST AREA FRIDAY NIGHT AND
SATURDAY MORNING. A RIBBON OF DEEPER MOISTURE SHOULD MOVE THROUGH
AHEAD OF THE FRONT ALONG WITH SOME UPPER DIVERGENCE. HAVE FOLLOWED
THIS TREND AND EXPANDED CHANCE POP AREA...BUT KEPT LOWER POP OVER
THE EAST AFTER COLLABORATION WITH NEIGHBORS. THIS SYSTEM SHOULD EXIT
TO THE EAST BY LATE SATURDAY.

AFTER THE FRONT MOVES THROUGH...THE UPPER LOW IS FORECAST TO LIFT NE
ACROSS THE GREAT LAKES AND INTO WRN ONTARIO...WHICH RESULTS IN A
NEARLY ZONAL FLOW ACROSS THE WESTERN CAROLINAS FROM SUNDAY ONWARD.
THIS WILL SUPPORT HIGH PRESSURE AT THE SURFACE AND DRY SEASONAL
WEATHER FOR THE FIRST PART OF NEXT WEEK.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
AT KCLT...VISIBILITY AND CEILING WILL REMAIN VFR THROUGH THE TAF
PERIOD. THE DEPTH OF THE MIXING LAYER WILL QUICKLY DECREASE AROUND
SUNSET...REDUCING THE POTENTIAL FOR SIGNIFICANT GUSTS. UNTIL
23Z...SOUTHWEST WINDS WILL CONTINUE TO GUSTS TO THE LOW 20 KTS. THIS
EVENING...A WEST CROSS WIND AROUND 6-10 KTS MAY REMAIN ACROSS THE
TERMINAL. WINDS SHOULD VEER TO NORTHWEST AROUND MIDNIGHT...SPEEDS
FORECAST TO RANGE FROM 4-8 KTS. AFTER SUNRISE...NORTHWEST WINDS ARE
FORECAST TO STRENGTHEN TO 8-10 KTS.

ELSEWHERE...VISIBILITIES AND CEILINGS WILL REMAIN VFR THROUGH THE TAF
PERIOD. GUSTY SOUTHWEST WINDS WILL CONTINUE ACROSS THE WESTERN
CAROLINAS THROUGH SUNSET. KAVL WILL SEE WINDS FAVOR A NORTHWEST
DIRECTION THE REST OF THIS AFTERNOON AND OVERNIGHT. WIND DIRECTIONS
ARE FORECAST TO REMAIN WNW...NW AT KAVL...AFTER SUNRISE TUESDAY.
SPEEDS WILL RANGE NEAR 10KTS...WITH MARGINAL GUSTS AT KAVL BY MID
MORNING.

OUTLOOK...A CONTINENTAL AIR MASS WILL REMAIN OVER THE REGION THROUGH
THE REST OF THE WORK WEEK. CONDITIONS ARE FORECAST TO REMAIN VFR.
HOWEVER...THE MTN VALLEYS COULD SEE A FEW PERIODS OF SHALLOW FOG
DURING THE PRE DAWN HOURS.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

SYNOPSIS...TJB
NEAR TERM...NED
SHORT TERM...PM
LONG TERM...PM
AVIATION...NED

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