-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 192132
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
532 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 MONDAY/...
-- Changed Discussion --
AS OF 515 PM...SO FAR THE CONVECTIVE CIRRUS SHIELD...WHICH
ENCOMPASSES 75% OF THE CWFA...IS LIMITING CONVECTIVE INITIATION FOR
THE MOST PART. THE NRN NC MTNS ARE BEING WORKED OVER...WHILE
CONVECTION SEEMS TO BE LOSING SOME STEAM ALONG A CONFLUENCE AXIS
ALONG I-77 CORRIDOR. THE 21Z LAPS CAPE STILL SHOWS 1500-2000 J/KG TO
THE WEST OF THE AXIS...FROM CALDWELL COUNTY SOUTH THRU THE ERN
UPSTATE. SURE ENUF...CELLS HAVE BEEN BACK-BUILDING INTO THIS ZONE.
THE 18Z NAM LINES UP WELL WITH HAVING THE BEST CONVECTIVE COVERAGE
IN THIS ZONE AS WELL...WITH AN MCV CROSSING THE AREA...I THINK
CONVECTION WILL CONTINUE IN THESE AREAS. OUTSIDE OF THIS...THERE IS
NOT MUCH INSTBY...SO HAVE CUT BACK POPS FOR THIS EVENING...GENERALLY
ALONG AND WEST OF I-26. THE MAIN THREAT STILL APPEARS TO BE
LOCALIZED HEAVY/EXCESSIVE RAINFALL. A NON-ZERO SEVERE HAIL/WIND
THREAT STILL EXISTS AS WELL.

PREVIOUS DISCUSSION...
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. 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...AS IT IS BEING FUELED BY THE VERY UNSTABLE
AIR TO ITS WEST/SOUTHWEST. 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. LOCALLY HEAVY/PERHAPS EXCESSIVE
RAINFALL WILL BE THE PRIMARY THREAT...BUT SOME PULSE SEVERE STORMS
CANNOT BE RULED OUT. THE PRIMARY THREAT AREA FOR HEAVY RAIN MAY
PROVE TO BE THE I-77 CORRIDOR...AS PERSISTENT CONFLUENT ZONE COULD
SUPPORT REPEATED DEVELOPMENT/TRAINING OF CELLS.

AS THE WEAKENING UPPER TROUGH AXIS CONTINUES TO SLOWLY PUSH EAST
ACROSS THE AREA THIS EVENING...DRIER MID-LEVEL AIR WILL BEGIN TO
ADVECT INTO WESTERN ZONES...WHICH SHOULD ALLOW THE FOCUS FOR
CONVECTION TO SHIFT TO EASTERN AREAS. AN OVERALL DOWNWARD TREND IN
COVERAGE IS EXPECTED OVERNIGHT...ESPECIALLY ACROSS THE EASTERN
ZONES.

FOR MONDAY...DRIER AIR SHOULD SPELL MORE CLEARING/BETTER INSOLATION
AND THEREFORE IMPROVED INSTABILITY BY AFTERNOON...ESP ACROSS THE
WEST. AS A RESULT...CONVECTION SHOULD FIRE ACROSS THE HIGHER TERRAIN
DURING THE AFTERNOON. ALTHOUGH COVERAGE SHOULD BE LESS THAN TODAY...
IMPROVED INSTABILITY SHOULD LEAD TO MORE VIGOROUS UPDRAFTS...AND A
GREATER THREAT FOR ISOLATED PULSE SEVERE STORMS. TEMPS WILL BE ABOVE
NORMAL THROUGH THE PERIOD.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
SFC/UPPER RIDGE REMAINS FIXED OVER THE WRN CAROLINAS AND NE GEORGIA
MON NIGHT AND TUESDAY KEEPING THE REGION DEVOID OF ANY SIGNIFICANT
FORCING...WITH WEAK WINDS THROUGHOUT THE COLUMN. THOUGH THE THERMAL
GRADIENT IS QUITE WEAK IN THE LOW-MID LEVELS THERE IS SOME SLIGHT WAA
MON NIGHT...WHICH ALONG WITH SUBSIDENCE UNDER THE RIDGE LOOKS TO
PRODUCE ENOUGH CAPPING TO PRECLUDE ANY OVERNIGHT CONVECTION.
SOUNDINGS DO REMAIN SOMEWHAT FAVORABLE INTO MON EVENING MAINLY IN THE
ERN ZONES...BUT ALL ACTIVITY SHOULD DIMINISH BY MIDNIGHT OR SO.
SKIES SHOULD CLEAR ENOUGH TO ALLOW FOR QUICK HEATING ON TUE AND
BREAKOUT OF CONVECTION. FLOW WILL BE VERY WEAK THROUGH MOST OF THE
CLOUD LAYER AND STORMS WILL BE SLOW MOVING...AND SFC TEMPS SHOULD
SUPPORT SBCAPE OF 1500-2000 J/KG PER BOTH NAM AND GFS PROG SOUNDINGS.
HEAVY RAIN POSSIBLY CAUSING LOCALIZED FLOODING WILL BE A CONCERN...AS
WILL PULSE SEVERE STORM MODES PRIMARILY PRODUCING HAIL DUE TO THE
INSTABILITY. SOUNDINGS ARE ONLY MODESTLY DRY...BUT DCAPE OF 200-700 J
INDICATIVE OF SOME DAMAGING WIND RISK. ACTIVITY SHOULD HAVE
DIFFICULTY ORGANIZING ENOUGH TO PERSIST PAST SUNSET SO POPS AGAIN
DIMINISH TUE NIGHT. HIGHS TUESDAY WILL BE QUITE WARM WITH WEAK SLY
FLOW AT THE SFC AND INITIALLY MOSTLY SUNNY SKIES ALLOWING TEMPS TO
RISE A FEW DEGREES ABOVE NORMAL...INTO THE MID TO UPPER 80S ACROSS
MUCH OF THE AREA.

CONVECTIVE CIRRUS DEBRIS MAY REMAIN OVER MUCH OF THE AREA
OVERNIGHT...WITH INCREASING UPPER MOISTURE AHEAD OF CENTRAL US TROUGH
INTRODUCING MORE HIGH CLOUD COVER TOWARD DAYBREAK AND CONTINUING INTO
WED. THIS SHOULD LIMIT HEATING AND INSTABILITY MAKING TUE OF MORE
INTEREST FOR SIGNIFICANT STORMS...WITH THE ADDITIONAL MID-UPPER
MOISTURE ARRIVING AHEAD OF THE INCOMING TROUGH ALSO MAKING SEVERE
LESS LIKELY. THE TROUGH WORKS INTO THE WEST BY AFTN PERHAPS PROVIDING
SOME ADDITIONAL LIFT. WITH INSTABILITY ALREADY PRESENT THERE HAVE
INCLUDED LIKELY POPS NEAR THE TENN BORDER AND CHC ELSEWHERE...WITH
THE LKLYS WANING WITH THE INSTABILITY TOWARD SUNSET. TEMPS WILL BE A
BIT COOLER WED WITH HIGH CLOUDINESS AND SLIGHTLY LOWER THICKNESSES
HAVING AN IMPACT.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF MIDDAY SUNDAY...GFS/EC HAVE COME INTO BETTER AGREEMENT
REGARDING MID TO LATE WEEK PATTERN. MIDWEST CYCLONE SHIFTS INTO THE
NE CONUS...DRAGGING A COLD FRONT ACROSS THE OH/TN VALLEYS WHICH
WEAKLY PUSHES ACROSS OUR CWFA FRIDAY. ERN TROUGH DEVELOPS AS THE
FRONT PUSHES SOUTH. GFS HAS COME MORE IN LINE WITH THE EC SOLUTION
WHICH WAS ALSO SHOWN ON PREVIOUS RUNS...AND GFS ENSEMBLE MEMBERS ARE
SPREAD SOMEWHAT EVENLY AROUND THE GFS/EC CONSENSUS. MOST OF THE UPPER
ENERGY ASSOCIATED WITH THE MIDWEST SYSTEM REMAINS WELL TO OUR NORTH
THOUGH SOME TRAILING VORT MOVES ACROSS WED NIGHT/THU CONCURRENT WITH
SOME VERY WEAK LLVL WAA.  THIS MAY ALLOW SOME ELEVATED CONVECTION WED
NIGHT...IN FACT THAT IS PROBABLY THE BEST CASE FOR POPS DURING THE
EVENT WITH RELATIVELY DRY COLUMNS SHOWN ON PROG SOUNDINGS. FAIRLY
STEADY POPS CONTINUE UNTIL FROPA FRIDAY. LARGELY DRY FCST FRI NIGHT.

OVER THE WEEKEND POSITION OF SFC HIGH AND UPPER TROUGH ARE INDICATIVE
OF CAD...ESPECIALLY ON THE GFS WHICH ALSO DEVELOPS A WEAK SUBTROPICAL
SYSTEM OFF THE SE COAST ENHANCING THE LLVL ELY FLOW IN THE WEDGE. CAD
LOOKS TO BE LOW IMPACT BEING ACCOMPANIED BY LITTLE MOISTURE.
RESULTING TEMPS ARE NEAR TO JUST BELOW NORMAL FOR THE WEEKEND. SOME
DIURNAL CONVECTION POSSIBLE ON SATURDAY WITH SLIGHTLY UNSTABLE
PROFILES SEEN MAINLY IN THE MTNS...BUT BY SAT NIGHT SUBSIDENCE
INVERSION WILL INHIBIT FURTHER CONVECTION...LEAVING DRY AND MCLR
CONDITIONS FOR SUN.

&&

.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
-- Changed Discussion --
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...

            21-03Z        03-09Z        09-15Z        15-21Z
KCLT       MED   77%     HIGH  95%     MED   75%     HIGH  90%
KGSP       HIGH  86%     MED   79%     HIGH  81%     MED   76%
KAVL       HIGH  80%     MED   79%     MED   68%     HIGH 100%
KHKY       HIGH  84%     HIGH 100%     HIGH  91%     MED   66%
KGMU       HIGH  81%     MED   66%     MED   75%     MED   73%
KAND       HIGH  91%     MED   67%     MED   75%     HIGH  83%

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
-- End Changed Discussion --

&&

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

&&

$$
SYNOPSIS...SBK
NEAR TERM...ARK/JDL
SHORT TERM...WIMBERLEY
LONG TERM...WIMBERLEY
AVIATION...JDL