Flash Flood Warning 21, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
751 AM EDT FRI JUN 5 2009

.SYNOPSIS...
A BROAD AREA OF LOW PRESSURE WILL REMAIN ACROSS THE DEEP SOUTH
THROUGH TONIGHT. THE LOW WILL WEAKEN AND SHIFT FARTHER SOUTHEAST OF
THE REGION SATURDAY. WEAK HIGH PRESSURE MOVES OVER THE AREA
SATURDAY...AND GRADUALLY SHIFTS SOUTHEAST OF THE AREA FOR THE FIRST
HALF OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
WE CONTINUE TO TRACK A SMALL SURFACE LOW ON THE KGSP RADAR THAT IS
ON COURSE TO MOVE NORTHEAST ACROSS THE EASTERN PIEDMONT OF SOUTH
CAROLINA THROUGH THE PREDAWN HOURS...THEN ACROSS METRO CHARLOTTE
AFTER SUNRISE...AND EVENTUALLY THE NC PIEDMONT DURING THE MIDDLE
PART OF THE MORNING. FORCING AHEAD OF THE LOW AND ASSOCIATED WITH
THE LOW COMBINED WITH THE DEEP MOISTURE SIGNAL A VERY HIGH
LIKELIHOOD OF SHOWERS THIS MORNING SO THE AREA IN THE PATH OF THE
LOW GETS A CATEGORICAL POP. PRECIP HAS ALREADY BEGUN TO TAPER OFF
ACROSS FAR WESTERN NC AND NE GEORGIA...SO A LOWER POP IS CARRIED IN
THOSE PLACES. THE LOW SHOULD DEPART BY MID MORNING LEAVING BEHIND
THE DEEP MOISTURE. MORE SHOWERS COULD FORM AT ANY TIME AS ANOTHER
WEAK SHORT WAVE LIFTS NE...SO THE POP WILL BE KEPT LIKELY INTO THE
AFTERNOON ALONG THE SOUTHEAST FRINGE AWAY FROM THE DEVELOPING
DOWNSLOPE IN THE WAKE OF THE LOW. A CHANCE SHOULD SUFFICE ELSEWHERE.
HAVE BUMPED MAX TEMPS UP A DEGREE OR SO OVER THE SOUTHEAST BECAUSE
OF THE POSSIBILITY OF A BIT MORE SUN THIS AFTERNOON.

AS THE CONVECTION HAS EVOLVED IN THE PAST SEVERAL HOURS...RAINFALL
RATES HAVE TAPERED OFF...BUT RIGHT AROUND THE CORE OF THE SMALL LOW
THERE REMAINS SOME POTENTIAL FOR FLOODING. GIVEN THE SOAKING RAIN
THAT FELL ACROSS THE CHARLOTTE METRO AREA ON THURSDAY...THINK IT
BEST TO EXTEND THE FLASH FLOOD WATCH ACROSS MECKLENBURG COUNTY. FOR
THAT MATTER...THE COURSE OF LEAST REGRET IS TO EXTEND THE WATCH FOR
ALL ZONES AHEAD OF THE LOW...UNTIL THE DANGER IS PAST AROUND NOON.

HIGH PRESSURE SHOULD START TO BUILD IN TONIGHT WITH DRIER AIR COMING
IN FROM THE NW. CONTINUED THE FORECAST TREND OF TAPERING OFF THE POP
FROM THE NW. A BLEND OF THE MAV AND MOSGUIDE LOOKS REASONABLE FOR
LOW TEMPS.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 215 AM FRIDAY...WEAK LOW PRES INVOF SOUTHERN GA WILL BE IN
POSITION SUCH THAT THE CWFA WILL BE UNDER A NARROW BUT STRONG AREA
OF SUBSIDENCE ON SATURDAY. MODEL FCST SNDGS IN AGREEMENT ON
DEPICTION OF AN INVERSION IN THE 800-700 MB LYR. LGT LLVL FLOW WITH
AN ELY COMPONENT WILL BE MOIST...SO EXPECT A BE DECENT CU FIELD TO
DEVELOP WITH DAYTIME HEATING. I KEPT A SLGT CHC POP AS A HEDGE
CLOSER TO THE AFOREMENTIONED LOW ALONG SRN FRINGE OF AREA. TEMPS
WILL BE NORMAL (UPR 70S TO ARND 80 MTNS AND LWR 80S PIEDMONT FOR
HIGHS AND 50S MTNS TO MID 60S PIEDMONT FOR LOWS).

THE LOW MEANDERS AND REMAINS WEAK INVOF OF THE FL PENINSULA...WITH
SOME MOISTURE RETURNING TO OUR AREA FROM THE SOUTHEAST. FCST SNDGS
SHOW MUCH WEAKER INVERSION...WITH WEAK FLOW THRU THE MID LVLS. SO I
EXPECT MTN-TOP CONVECTION SUNDAY AFTN. WITH A MOIST BL...THINK SVR
THREAT WILL BE LOW AND MAINLY LIMITED TO LARGE HAIL. ALSO...OUTFLOW-
INITIATION OUTSIDE OF MTNS/FOOTHILLS LOOKS TO BE MINIMAL. SO CHC POP
MTNS AND SLGT CHC ELSEWHERE LOOKS GOOD. TEMPS WILL BE AT OR A
CATEGORY ABOVE SATURDAY/S READINGS.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 230 AM FRIDAY...UPR RIDGE AXIS IS PROGGED TO BE DIRECTLY OVER
THE CWFA MONDAY...WITH SCATTERED PULSE CONVECTION EXPECTED AGAIN.
MODELS SHOW DECENT CAPE AND THINK COVERAGE SHUD BE A LTL HIGHER THAN
SUNDAY. FCST THICKNESSES ARE RATHER WARM...SO ABV NORMAL TEMPS
EXPECTED MONDAY (LWR-MID 80S MTNS AND UPR 80S TO NEAR 90 PIEDMONT).

THE RIDGE MOVES EAST OF THE AREA FOR TUESDAY...AND IS REPLACED BY A
WEAK TROF OVR THE EASTERN CONUS FOR WEDNESDAY AND THURSDAY. NEAR
NORMAL TEMPS EXPECTED...WITH INCREASING CHANCES OF MAINLY DIURNAL
CONVECTION THRU WEDNESDAY. THE AXIS OF THE TROF PUSHES JUST E OF THE
AREA FOR THURSDAY...SO SLIGHTLY LOWER POP IN THE FCST. THE 00Z/05
GFS IS A LITTLE SLOWER ON PROGATING THE TROF THAN THE 12Z/04 ECMWF.
I AM AWAITING NEW ECMWF GUIDANCE...BUT DO NOT SEE ANY REASON TO MAKE
CHANGES BEYOND DAY 5 (TUES) ATTM.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
INTERESTING SITUATION OVER THE NEXT SEVERAL HOURS THROUGH LATE
MORNING AS RADAR CLEARLY SHOWS A SWIRL ASSOCIATED WITH A
WEAK SURFACE LOW OF TROPICAL ORIGIN...PROGRESSING SLOWLY TO THE
NORTHEAST ACROSS THE EASTERN PIEDMONT OF SC. THIS FEATURE...WHICH IS
NOT REALLY HANDLED BY THE MODEL GUIDANCE...IS ON A NORTHEAST COURSE
MOVING ABOUT 20 KT THAT WILL TAKE IT RIGHT OVER THE CLT METRO AREA
THROUGH 14Z. WARM ADVECTION UPGLIDE AHEAD OF THE WEAK LOW WILL
CAUSE SHOWERS TO CONTINUE DEVELOPING IN ADVANCE OF THE FEATURE...
WHILE STEADIER RAIN AFFECTS LOCATIONS TO THE NORTH AND NORTHWEST OF
THE TRACK SUCH AS KHKY. WINDS AROUND THE CENTER ARE RELATIVELY
LIGHT. HOWEVER...AS THE LOW MOVES PAST KCLT...WE SHOULD EXPECT A
SOUTHEAST WIND AHEAD OF IT THEN SHIFTING AROUND TO SOUTHWEST AS THE
CENTER PASSES JUST WEST OF THE AIRFIELD...THEN NORTHWEST OR NORTH
BEHIND IT. ALL THIS WOULD HAPPEN THROUGH 15Z. VISIBILITY WILL ALSO
RANGE FROM P6 AHEAD OF THE LOW...TO MVFR WHERE STEADIER PRECIP
CONTINUES TO FALL...ALONG WITH SOME POCKETS OF IFR IN HEAVIER RAIN.

OTHERWISE...MAINLY IFR CEILING WILL PREVAIL WITH OCCASIONAL MVFR OR
EVEN VFR WHERE PRECIP CLEARS OUT BRIEFLY AHEAD OF THE LOW OVER THE
FOOTHILLS AND PIEDMONT OF NC. IN THE WAKE OF THE LOW...DEVELOPING
DOWNSLOPE IS TAKING CARE OF THE LOW CLOUDS LEAVING MAINLY VFR.

THE LOW SHOULD MOVE AWAY THIS MORNING BUT MOISTURE WILL REMAIN
FAIRLY DEEP...SO ANOTHER ROUND OF SHOWERS IS LIKELY TODAY. THIS WILL
BE HANDLED WITH A VCSH UNTIL SOME BETTER IDEA OF TIMING IS POSSIBLE.
CEILINGS SHOULD IMPROVE TO MVFR BY MID MORNING AND THEN LOW CLOUDS
WILL BREAK UP IN THE EARLY AFTERNOON AS LOW LEVEL DOWNSLOPE FLOW
KICKS IN. LATE TONIGHT...LOW CLOUDS TRAPPED UNDER AN INVERSION MAY
BRING MVFR CEILINGS BACK ACROSS THE AIRFIELDS.

OUTLOOK...DRIER CONDITIONS EXPECTED SATURDAY THRU TUESDAY. MORNING
FOG/STRATUS IS POSSIBLE EACH DAY WHICH COULD BRING VISIBILITY DOWN
TO MVFR. EXPECT ISOLATED-SCATTERED AFTERNOON CONVECTION EACH DAY.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...FLASH FLOOD WATCH UNTIL NOON EDT TODAY FOR NCZ035>037-056-057-
     068>072-082.
SC...FLASH FLOOD WATCH UNTIL NOON EDT TODAY FOR SCZ008-009-013-014.

&&

SYNOPSIS...ARK
NEAR TERM...PM
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...PM

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