000
FXUS62 KGSP 191804
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
204 PM EDT SUN MAY 19 2013

.SYNOPSIS...
A WEAK UPPER LEVEL TROUGH WILL SWING EAST OVER THE REGION THROUGH
MONDAY. THE FORECAST AREA WILL REMAIN IN A MOIST AND RATHER UNSTABLE
AIRMASS...BEFORE A COLD FRONT CROSSES THROUGH LATE IN THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 155 PM...CONVECTIVE COVERAGE CONTINUES TO INCREASE AS EXPECTED
ACROSS THE NC PIEDMONT THIS AFTERNOON WITHIN LOW LEVEL CONFLUENCE
AXIS ACTING UPON A MODERATELY UNSTABLE/VERY MOIST AIR MASS. LOCALLY
HEAVY/PERHAPS EXCESSIVE RAINFALL WILL BE THE PRIMARY THREAT...BUT
SOME PULSE SEVERE STORMS CANNOT BE RULED OUT. FARTHER WEST...
EXPANSIVE CIRRUS SHIELD ASSOCIATED WITH TENN VALLEY CONVECTION...AS
WELL AS OUTFLOW FROM THIS MORNING/S CONVECTION HAS LARGELY
STABILIZED THE ATM ACROSS THE UPPER SAVANNAH RIVER VALLEY.
MEANWHILE...TENN VALLEY CONVECTION HAS MOSTLY BEEN STRUGGLING TO
MAKE ITS WAY INTO THE SOUTHERN APPALACHIANS. HOWEVER...SCATTERED
CONVECTION HAS BEGUN INITIATING OVER THE HIGHER TERRAIN...LIKELY
ASSISTED BY OUTFLOW BOUNDARIES AS WELL AS DIFFERENTIAL HEATING
ACROSS THE EDGE OF THE CIRRUS SHIELD. WILL CONTINUE TO FEATURE
LIKELY/CAT POPS THROUGH THIS EVENING ACROSS WESTERN AREAS.

AS OF 1040 AM...LARGE COMPLEX OF SHOWERS THAT DEVELOPED ALONG A
SPEED CONVERGENCE AXIS ASSOCIATED WITH W/SW LLJ CONTINUES TO
DISSIPATE OVER OUR SOUTHERN ZONES LATE THIS MORNING. MEANWHILE...THE
FOCUS FOR HEAVY RAINFALL IN THE NEAR TERM HAS SHIFTED WELL WEST OF
THE GSP CWFA...ACROSS NW/CTRL GEORGIA...AT THE LEADING EDGE OF THE
MORE ROBUST INSTABILITY. THE AFTERNOON CONVECTIVE PICTURE FOR OUR
CWFA IS NOMINALLY CLEARER THAN IT WAS YESTERDAY. WITH ONLY A FEW
PATCHY AREAS OF SHOWERS AROUND THIS MORNING...FAIRLY RAPID CLEARING
OF THE OVERCAST IS OCCURRING...ESP ACROSS THE NC MTNS. THIS SHOULD
ALLOW FOR MODERATE LEVELS OF INSTABILITY TO DEVELOP THIS
AFTERNOON...ALLOWING FOR GREATER COVERAGE OF SHOWERS AND STORMS
THAT WAS SEEN SATURDAY AFTERNOON. IT IS SOMEWHAT DIFFICULT TO
PINPOINT ANY PARTICULAR AREAS FOR HIGHER POPS...BUT SHORT TERM
MODELS DO INDICATE AN AREA OF LOW LEVEL CONVERGENCE/CONFLUENCE
SETTING UP OVER THE EASTERN ZONES THIS AFTERNOON...AND WE WILL FOCUS
80 POPS ACROSS THIS AREA. ONCE AGAIN...AN ISOLATED SEVERE STORM
CANNOT BE RULED OUT...BUT HEAVY/LOCALLY EXCESSIVE RAINFALL WILL
CONTINUE TO BE THE PRIMARY THREAT. CURRENT INDICATIONS ARE THE MOST
LIKELY AREA FOR HEAVY RAINFALL WILL BE ACROSS THE EASTERN ZONES...
WHERE LOW LEVEL CONFLUENCE COULD AID AND ABET TRAINING OF CELLS...
AND SLIGHTLY ENHANCED LOW LEVEL SHEAR COULD ALSO PROMOTE SOME DEGREE
OF MESOSCALE ORGANIZATION. HOWEVER...CONSIDERING THE UNCERTAINTY IN
THIS EVOLUTION...AS WELL AS THE FACT THAT FFG/S ARE VERY HIGH IN
THOSE AREAS...DON/T THINK I CAN JUSTIFY ISSUANCE OF A WATCH IN THIS
OR ANY OTHER AREA DURING THE AFTERNOON.

EXPECT CONVECTION TO DIMINISH OVERNIGHT AS THE FORCING MOVES EAST OF
THE AREA. HOWEVER...THE FLOOD AND SVR THREAT WILL INTO THE EVENING.
LOWS WILL BE 5 TO 10 DEGREES ABOVE NORMAL.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AT 300 AM EST SUNDAY...ON MONDAY THE UPPER TROUGH AXIS WILL MOVE
SLOWLY OVER THE INTERSTATE 77 CORRIDOR. THE GFS BRINGS THIS
WEAKENING UPPER FEATURE EAST OF OUR AREA ON MONDAY NIGHT AS AN UPPER
RIDGE ARRIVES...WHILE THE NAM LEAVES IT ALMOST STATIONARY. ON
TUESDAY THE GFS RIDGE AXIS REACHES THE SPINE OF THE APPALACHIANS.

ON MONDAY AS THE UPPER TROUGH AXIS MOVES EAST...DRIER AIR ALOFT WILL
MOVE IN FROM THE EAST...INSTABILITY AND SHEAR INCREASE...SUPPORTING
MORE OF A CONVECTIVE MODE...EVEN AS COVERAGE GRADUALLY DECREASES.
SHEAR WILL DECREASE ON MONDAY NIGHT. TUESDAY FEATURES LESS SHEAR...
BUT EVEN GREATER INSTABILITY...AND MORE DRY ARI ALOFT AND BENEATH
THE CLOUD LAYER...SUPPORTING EVAPORATIVE COOLING AND DOWNDRAFT
PRODUCTION. INSTABILITY IS SLOW TO WANE ON TUESDAY NIGHT.
TEMPERATURES WILL TREND UPWARD FROM MONDAY TO TUESDAY...REACHING
ABOVE NORMAL VALUES...AS HEIGHTS RISE ALOFT.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AT 300 AM EST SUNDAY...AN UPPER RIDGE AXIS WILL CROSS THE EASTERN
SEABOARD ON WEDNESDAY...WHILE AND UPPER TROUGH CROSSES THE MS RIVER
VALLEY. THE TROUGH CROSSES THE OH AND TN VALLEYS ON THURSDAY...AND
CROSSES THE CENTRAL AND SOUTHERN APPALACHIANS ON FRIDAY. ON SATURDAY
THE ECMWF MOVES ITS TROUGH AXIS SLOWLY OFF THE COAST...WHILE THE GFS
TROUGH AXIS REMAINS ALONG THE EAST COAST.

THE CAROLINAS AND GA REMAIN IN A WARM AND MOIST AIR MASS ON
WEDNESDAY AND THURSDAY. BOTH THE ECMWF AND GFS SHOW ATLANTIC
MOISTURE MOVING INTO THE SOUTHERN APPALACHIANS IN AN EASTERLY
UPSLOPE COMPONENT WEDNESDAY...AND MOISTURE ASSOCIATED WITH A FORMER
COLD FRONT CONVERGING WITH THE ATLANTIC MOISTURE ON WEDNESDAY NIGHT.
THE MODELS ALSO SHOW A WEAK SURFACE LOW MOVING UP THE FLORIDA
PENINSULA...FEEDING MORE ATLANTIC MOISTURE INTO THE GA AND CAROLINA
COASTS. THE MODELS DIFFER ON WHETHER THE REMAINS OF THE OLD FRONT
WILL SWEEP EAST OF OUR AREA ON THU. THE ECMWF SUPPORTS DOES SO...
MOVING MOISTURE OUT OF OUR AREA...WHILE THE GFS KEEPS MOISTURE OVER
OUR AREA UNTIL THE SURFACE LOW MOVES OFF TO THE NE ON FRI. A COLD
FRONT WILL APPROACH FROM THE NW ON THURSDAY NIGHT...CROSSING OUR
AREA ON FRIDAY. SATURDAY WILL FEATURE COOL AND DRY HIGH PRESSURE
BUILDING IN FROM THE NORTH. TEMPERATURES WILL COOL FROM SLIGHTLY
ABOVE NORMAL ON WEDNESDAY TO AROUND NORMAL LATER IN THE WEEK AS
HEIGHTS FALL ALOFT.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
AT KCLT...CONVECTION IS EXPANDING IN COVERAGE AND INTENSITY ACROSS
THE PIEDMONT THIS AFTERNOON IN A MODERATELY UNSTABLE AIR MASS. HAVE
BEGUN THE FORECAST WITH A VCSH...BUT INTRODUCED TEMPOS FOR TSRA FROM
19Z THRU 00Z. GUSTY WINDS AND IFR VISBY WILL LIKELY ACCOMPANY TS
THAT MAKE A DIRECT HIT ON THE AIRFIELD...BUT AM UNCERTAIN OF THIS
ATTM. CONVECTION SHOULD GRADUALLY TAPER OFF THIS EVENING...BUT
LOWERING CIGS/POSSIBLY REDUCED VISBY WILL MAKE FOR ADVERSE AVIATION
WEATHER LATE TONIGHT INTO EARLY MONDAY.

ELSEWHERE...CONVECTION WILL BE A LITTLE SLOWER TO DEVELOP AS THE
ATMOSPHERE IS A LITTLE MORE STABLE WEST OF THE NC PIEDMONT.
NEVERTHELESS...CONVECTION MOVING SOUTHEAST OUT OF EAST TENN MAY
RESULT IN NEW CONVECTION DEVELOPING ACROSS WESTERN NC AND UPSTATE SC
BY LATE AFTERNOON/EARLY EVENING. CONVECTION SHOULD GRADUALLY TAPER
OFF THIS EVENING...BUT LOWERING CIGS/POSSIBLY REDUCED VISBY WILL
MAKE FOR ADVERSE AVIATION WEATHER LATE TONIGHT INTO EARLY MONDAY.

OUTLOOK...SCATTERED SHOWERS AND THUNDERSTORMS...AND ASSOCIATED
RESTRICTIONS...ARE EXPECTED TO CONTINUE DURING THE WEEK...BUT SHOULD
BECOME MORE FOCUSED DURING THE AFTERNOON AND EVENING.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       MED   64%     MED   77%     HIGH  87%     HIGH  80%
KGSP       HIGH  89%     MED   75%     MED   72%     MED   75%
KAVL       HIGH  89%     MED   72%     MED   68%     MED   79%
KHKY       HIGH  86%     HIGH  81%     HIGH  98%     MED   73%
KGMU       HIGH  86%     MED   70%     LOW   58%     MED   70%
KAND       HIGH  94%     MED   76%     MED   73%     MED   77%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE
HOURLY EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE
FORECASTS ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

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

&&

$$
SYNOPSIS...SBK
NEAR TERM...JDL/RWH
SHORT TERM...JAT
LONG TERM...JAT
AVIATION...JDL