Severe Thunderstorm Warning 45, NWS Greenville-Spartanburg, SC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
826 PM EDT FRI APR 10 2009

.SYNOPSIS...
STRONG LOW PRESSURE WILL PASS BY TO THE NORTH TONIGHT...DRAGGING A
COLD FRONT ACROSS THE REGION. HIGH PRESSURE WILL SLOWLY BUILD IN
FROM THE NORTHWEST SATURDAY THROUGH SUNDAY. ANOTHER LOW PRESSURE
SYSTEM WILL APPROACH FROM THE WEST BY MONDAY...BRINGING UNSETTLED
WEATHER TO THE REGION THROUGH THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH SATURDAY/...
EXPECT FRONT AND ASSOC STRONG CONVECTION TO MOVE THRU CWA BY
MIDNIGHT WITH LINGERING CONVECTION ENDING 06-09Z AS UPPER FORCING
CLEARS AREA. STILL EXPECT TEMPS TO BE WARM ENOUGH TO PRECLUDE SNOW
AT HIGHER ELEVS AS UPSLOPE SHOWERS LINGER INTO MIDDAY SAT. ADJUSTED
POPS AND HOURLY TEMP/DP/RH TO REFLECT LATEST TRENDS. NEW ZONE FCST
OUT SOON.

PREVIOUS DISCUSSION...AS THE DEEP UPPER LOW PRES CENTER MOVES EAST
THROUGH KY LATE THIS AFTERNOON THROUGH THIS EVENING...STRONG DPVA
AHEAD OF THIS FEATURE WILL LIFT ACROSS THE FORECAST AREA 21Z TO 00Z.
MEANWHILE...A 130 KT UPPER LEVEL JET STREAK WILL STRETCH ACROSS THE
DEEP SOUTH THIS EVENING...PRODUCING STRONG DIVERGENCE IN THE LEFT
EXIT REGION OVER THE WESTERN CAROLINAS. THIS WILL ALLOW CONVECTIVE
COVERAGE TO STEADILY INCREASE ACROSS THE AREA. THE MAIN UPPER
FORCING WILL MOVE ACROSS THE FORECAST AREA FROM THE WEST BETWEEN
ABOUT 8 PM AND 1 AM. LOW LEVEL FLOW SHOULD BEGIN TO BACK SHARPLY
TOWARD 21Z...STRONGLY ENHANCING LOW LEVEL HELICITY. A TONGUE OF
LOWER 60S DEWPOINTS COINCIDENT WITH THE BETTER SHEAR AXIS WILL
TRAVERSE THE SRN PART OF THE FORECAST AREA THIS EVENING TO GREATLY
ENHANCE THE ORGANIZED SEVERE TSTM THREAT. A WATCH IS LIKELY LATER
THIS AFTERNOON OR THIS EVENING.

850 MB FLOW WILL TURN QUICKLY WESTERLY OVERNIGHT FOLLOWING
FROPA...PRODUCING DOWNSLOPE DRYING EAST OF THE MTNS. NORTHWEST FLOW
SHOULD ALLOW UPSLOPE SHOWERS TO CONTINUE ALONG THE SPINE OF THE
SOUTHERN APPALACHIANS THROUGH SATURDAY MORNING...ALONG WITH WINDY
CONDITIONS IN THE COLD ADVECTION FLOW. PROFILES STAY WARM ENOUGH FOR
THE PTYPE TO REMAIN LIQUID. CONTINUED CLEARING THROUGHOUT IS
EXPECTED SAT AFTN. A STRONG GRADIENT IN MAX TEMPS WILL
DEVELOP...WITH HIGHS GENERALLY IN THE 50S IN THE MTNS AND LOW TO MID
70S IN THE SE PIEDMONT.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 205 PM FRIDAY...UPPER LEVEL RIDGE CONTINUES TO BUILD ACROSS
THE MIDWEST SAT NIGHT WHILE THE LAST LOBE OF S/W ENERGY CROSSES THE
CWFA TO THE EAST. THE GFS AND THE NAM BOTH AGREE ON THIS WAVE
LEAVING THE AREA BY 06Z THUS ENDING ANY REAL CHANCE OF PRECIP.
THE 12Z GFS DOES HANG ONTO H85 MOISTURE THROUGH THE DAY SUNDAY WHICH
DOESNT MAKE MUCH SENSE CONSIDERING ITS BRINGING IT ACROSS THE MTNS
IN DOWNSLOPE FLOW AND INTO AN INCREASING SUBSIDENCE INVERSION.
HOWEVER...THE 12Z GFS HAS COME IN DRIER THAN THE 00Z GFS WHICH
COMPARES MORE FAVORABLY WITH THE EVEN DRIER 12Z NAM. SO...WONT
EXPECT MUCH CLOUD COVER NOR ANY UPSLOPE PRECIP AS DEPICTED BY THE
GFS. THE MODELS DO AGREE ON DEVELOPING A FAIRLY STRONG INSITU WEDGE
LATE SUNDAY AND MAINTAINING IT THROUGH MON. THE GFS IS MORE BULLISH
WITH THE STRENGTH...BUT IN EITHER CASE THE EXPECTED WX SHOULD BE
SIMILAR. THIS SITUATION HAS LED TO PUSHING BACK CHC POPS SUN NIGHT
UNTIL AFTER 06Z MON FOR THE WRN THIRD OF THE CWFA. BASICALLY A DRY
WEDGE SETTING UP SUN...BECOMING A MOIST WEDGE SUN NIGHT THROUGH MON.

UPPER LEVEL SUPPORT WILL BE LOW WITH THE NEXT LOW PRESSURE SYSTEM
AND COLD FRONT. H5 PVU/S ARE LESS THAN 1 AND H3 DIV REMAINS NW OF THE
MTNS. ALSO...ANOTHER SIGN OF THE CLASSICAL GSP SLIT WILL BE
INCREASED INSTABILITY TO THE SOUTH AND WEST. BUFKIT SOUNDINGS FOR
KGSP INDICATE LI/S WILL REMAIN ABOVE 10 THROUGH MON AND THE NAM
KEEPS ALL THE CONVECTIVE PRECIP OVER AL AND SRN GA THROUGH 00Z TUE.
SO SUFFICE TO SAY...THE CHC THUNDER HAS BEEN REMOVED FROM THE GRIDS
MON. STILL EXPECT LIKELY POPS MON AFTERNOON AND EVENING AS WEDGE
CONTINUES TO HOLD AND PROVIDE VERY GOOD ISENTROPIC LIFT FOR
WIDESPREAD -RA. MIN TEMPS ARE EXPECTED TO BE RIGHT AROUND NORMAL
SUN...AND FEW ABOVE NORMAL MON AS OVC SKIES DEVELOP. HIGHS SHOULD
ALSO BE RIGHT AROUND NORMAL SUN...WITH GOOD INSOLATION OFFSETTING AN
INCREASING NE/LY FLOW AND WEAK CAA. HIGHS FOR MON WILL BE ABOUT 10
DEGREES BELOW NORMAL AS MOIST WEDGE SETS UP EARLY AND PERSISTS
THROUGHOUT THE DAY.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 240 PM FRIDAY...THE EXT RANGE BEGINS WITH STABLE WEDGE
REMAINING IN CONTROL...HOWEVER UPPER DYNAMICS WILL BE INCREASING
THROUGH MON NIGHT AND DURING THE DAY TUE. THE WEDGE SHOULD BREAKDOWN
BY 12Z AS THE COLD FRONT CROSSES THE REGION. STILL DONT SEE MUCH
UPPER SUPPORT WITH THIS FRONT. VORTICITY LOOKS TO REMAIN STREAMLINED
WITH UPPER LOW AND THE STRONGEST FORCING CROSSES THE LOWER OH
VALLEY. HARD TO JUDGE THE AMOUNT OF LLVL INSTABILITY DEVELOPING
TUE AS THE WEDGE BREAKS DOWN FROM THE SW. SOME EVIDENCE EXISTS FOR
TS POTENTIAL WITH LI/S DROPPING INTO THE LOWER SINGLE DIGITS AND
WEAK ELEVATED CAPE SHOWING UP ON THE SOUNDINGS. ALSO...BOTH THE GFS
AND THE ECMWF INDICATE ANOTHER POSSIBLE TRIPLE POINT LOW CROSSING
THE UPSTATE AND PIEDMONT BTW 18Z AND 00Z. FOR NOW...WILL KEEP ALL
THE PRECIP NON/CONVECTIVE AS TOO MUCH UNCERTAINTY EXISTS WITH THE
TIMING OF THE WEDGE BREAKDOWN AND INCREASING INSTABILITY POTENTIAL.
A PROGRESSIVE PATTERN IS EXPECTED THO...AND BY 06Z THE FRONT SHOULD
BE NEAR THE COAST.

ANOTHER WEAK WEDGE BUILDS IN THU AND REMAINS THROUGH FRI AHEAD OF
YET ANOTHER SYS PUSHING INTO THE DEEP SOUTH. THE 12Z GFS HAS SLOWED
DOWN AND IS MORE INLINE WITH THE 00Z ECMWF. THIS GIVE THE MED RANGE
FCST BETTER CONFIDENCE AS THE GFS WAS PRETTY MUCH THE ONLY MODEL
HANGING ONTO THE FASTER SOLN. SOLID CHC POPS STILL LOOK GOOD FOR FRI
LINGERING INTO SAT AS THE AXIS OF THE SFC TROF SHOWS GOOD CONTIGUITY
BTW THE OP MODELS. WONT EXPECT MUCH OF A WARM UP THROUGH THE
REMAINDER OF THE WEEK...HOWEVER TEMPS WILL BE RIGHT AROUND NORMAL.
THE LLVL WIND FIELD REALLY DOESNT GET A S/LY COMPONENT UNTIL LATE
FRI AHEAD OF THE NEXT FRONT...BEFORE THAT A WEAKENING WEDGE WIND
FIELD...NE/LY TO SE/LY IS EXPECTED. PLENTY OF SUNSHINE WED THROUGH
FRI WILL HELP MAX TEMPS REACH AROUND 70 F NON/MTNS...MID 60S
MTNS...IF NOT A FEW DEGREES ABOVE THU AND FRI.

&&

.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
LINE OF TSTMS MAIN THREAT WITH BACK EDGE OF STRONGEST CONVECTION
EXPECTED TO MOVE THRU GSP AROUND 02Z CLEARING KCLT AROUND 04Z. VRB
WINDS WITH G18KT DUE TO CONVECTION...STRONGER NEAR STORMS. DAMAGING
WIND AND HAIL PSBL ACROSS CWA...ISOLD TORNADOES SC-GA IN LESS STABLE
AIR. EXPECT SHOWERS TO LINGER UNTIL AFTER MIDNIGHT...BKN MVFR CIGS
INTO EARLY MRNG HOURS. WINDS SWING AROUND SW-NW BEHIND
FRONT...BECOMING NW AND GUSTY AFTER DAYBREAK.

OUTLOOK...DRY HIGH PRESSURE WILL BUILD INTO THE REGION SAT EVE
THRU SUN. THE NEXT STORM SYSTEM WILL BRING MOISTURE BACK INTO THE
AREA SUN NIGHT THRU TUE...WITH ASSOC RESTRICTIONS. IMPROVEMENT
EXPECTED MID WEEK.

&&

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

&&

SYNOPSIS...HG
NEAR TERM...HG/RB
SHORT TERM...SBK
LONG TERM...SBK
AVIATION...RB

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