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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KGSP 181806
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
206 PM EDT SAT MAY 18 2013

.SYNOPSIS...
-- Changed Discussion --
A WEAK UPPER LEVEL TROUGH WILL LINGER OVER THE REGION THROUGH
MONDAY...THEN LIFT NORTHEAST. THE FORECAST AREA WILL REMAIN IN A
MOIST AND RATHER UNSTABLE AIRMASS...BEFORE A COLD FRONT CROSSES EAST
LATE NEXT WEEK.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
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AS OF 200 PM...AREA OF SHOWERS HAS BEEN GRADUALLY ERODING OVER THE
PAST COUPLE OF HOURS ACROSS THE EASTERN HALF OF THE AREA...BUT
REMAINS VIGOROUS ENOUGH TO SUPPORT LIKELY POPS FOR AT LEAST A COUPLE
MORE HOURS. OTHERWISE...WIDESPREAD CLOUD COVER AND LINGERING EFFECTS
OF THE SHOWER BAND ARE RESULTING IN ONLY WEAK INSTABILITY ACROSS THE
AREA ATTM. THEREFORE...IT/S SOMEWHAT UNCLEAR AS TO HOW CONVECTIVE
TRENDS ARE GOING TO EVOLVE FOR THE DURATION OF THE AFTERNOON/
EVENING. NEVERTHELESS...SOME CLEARING IS OCCURRING ACROSS THE
WESTERN ZONES...AND WITHIN THIS VERY MOIST AIR MASS SUPPORTED BY
REMNANT UPPER LOW UPSTREAM OVER THE TENN VALLEY...IT/S NOT GOING TO
TAKE MUCH TO SEE NEW CONVECTION INITIATE. THEREFORE...WILL TREND
BACK TOWARD LIKELY POPS LATE THIS AFTERNOON INTO THE EVENING...ESP
ACROSS THE WESTERN MTNS. IN LIGHT OF THE WEAK INSTABILITY...SEVERE
STORMS APPEAR TO BE OF MINIMAL CONCERN...ALTHOUGH RAINFALL RATES
WILL NEED TO BE MONITORED CLOSELY.

THE LOW AND TROF SLIDE INTO THE PIEDMONT TONIGHT. THE SLY FLOW
SLIDES EASTWARD AS WELL. THIS WILL TAKE THE FOCUS OF THE CONVECTION
EAST AS WELL. BEST PRECIP CHC WILL BE OVER THE PIEDMONT DURING THE
NIGHT AND DIMINISH ELSEWHERE. EXPECT THE BEST QPF TO SLIDE EAST THRU
THE NITE AS WELL. WPC QPF FCST IS 1 INCH OR LESS TOTAL THRU THE END
OF THE NITE. THEREFORE...WHILE ISOLATED HEAVY RAINFALL IS
POSSIBLE...WIDESPREAD HEAVY RAINFALL IS NOT. ESPECIALLY AS IT LOOKS
LIKE THE MTNS WILL SEE THE HIGHEST RAINFALL DURING THE DAY AND THE
PIEDMONT DURING THE NITE. LOWS WILL BE 5 TO 10 DEGREES ABOVE NORMAL.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
AT 300 AM EST SATURDAY...ON SUNDAY MORNING...THE REMAINS OF AN UPPER
LOW WILL BE SOMEWHERE OVER THE CENTRAL APPALACHIANS. A WEAK TROUGH
ASSOCIATED WITH THIS SYSTEM WILL CROSS THE WESTERN CAROLINAS AND NE
GA SUNDAY AND SUNDAY NIGHT. UPPER LEVEL RIDGING MOVES SLOWLY EAST
OVER THE SOUTHERN AND CENTRAL APPALACHIANS ON MONDAY AND MONDAY
NIGHT IN THE WAKE OF THE UPPER TROUGH.

MOISTURE ASSOCIATED WITH THE TROUGH WILL SUPPORT WIDESPREAD
PRECIPITATION ON SUNDAY. INSTABILITY WILL BE LIMITED BY CLOUD
COVER...BUT SHOULD STILL BE SUFFICIENT FOR CONVECTION. MODEL
SOUNDINGS SHOW A VERY MOIST PROFILE...WITH LITTLE DRY AIR ALOFT AND
LIMITED DRY AIR BENEATH THE CLOUD LAYER FOR EVAPORATIVE COOLING OR
DOWNDRAFT PRODUCTION. STEERING FLOW WILL BE ENOUGH TO KEEP CELLS
MOVING SLOWLY TO THE NE. A LIGHT SOUTHERLY SURFACE FLOW WILL PROVIDE
UPSLOPE FLOW ENHANCEMENT OF PRECIPITATION...MAINLY ALONG THE SOUTH
FACING BLUE RIDGE ESCARPMENT. SOME INSTABILITY WILL PERSIST THROUGH
SUNDAY NIGHT AS THE UPPER TROUGH PASSES...WITH STEERING FLOW
GRADUALLY VEERING TO THE EAST.

ON MONDAY SOME DRY IS INTRODUCED AT MID LEVELS AS THE UPPER TROUGH
DEPARTS. CLOUDS HEIGHTS RISE...WITH MORE DRY AIR AT THE SURFACE.
INSTABILITY INCREASES...SUPPORTING MORE OF A CONVECTIVE MODE TO
PRECIPITATION...THOUGH WITH DECREASING COVERAGE. MOISTURE WILL BE
SLOW TO DEPART TO THE EAST ON MONDAY NIGHT...BUT THE BEST MOISTURE
WILL BE NEAR THE COAST.

MAXIMUM TEMPERATURES WILL BE NEAR NORMAL...WITH MINIMUM TEMPERATURES
A COUPLE OF CATEGORIES ABOVE NORMAL. PRECIPITATION TOTALS COULD
EXCEED ONE INCH ALONG THE SOUTH FACING BLUE RIDGE ESCARPMENT OF
SW NC...WITH MOST OF THAT FALLING ON SUNDAY AND SUNDAY NIGHT.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AT 300 AM EST SATURDAY...AN UPPER RIDGE WILL MOVE SLOWLY ACROSS THE
CAROLINAS AND GA ON TUESDAY AND WEDNESDAY...WHILE AN UPPER TROUGH
ASSOCIATED WITH ANOTHER CLOSED LOW IN THE PLAINS MOVES TO THE MS
RIVER VALLEY. THE TROUGH DEAMPLIFIES AS IT CROSSES THE OH AND TN
VALLEYS ON THURSDAY...AND REACHES THE CENTRAL AND SOUTHERN
APPALACHIANS ON FRIDAY.

A WARM AND MOIST AIR MASS REMAINS OVER THE SOUTHEAST FROM TUESDAY
THROUGH FRIDAY. DIURNALLY MODULATED CONVECTION IS EXPECTED ON
TUESDAY AND WEDNESDAY. ON WEDNESDAY NIGHT BOTH THE GFS AND ECMWF
SHOW A CONVERGENCE OF ATLANTIC MOISTURE WITH MOISTURE LEFT OVER FROM
A DYING COLD FRONT THAT ARRIVES FROM  THE WEST...JUST ABOUT OVER THE
SOUTHERN APPALACHIANS. THIS MOISTURE LINGER OVER OUR AREA INTO
THURSDAY...BEFORE STARTING TO MOVE OFF TO THE EAST ON FRIDAY. IF
THIS SCENARIO HOLD...PRECIPITATION WOULD BE MORE LIKELY TO PERSIST
OVERNIGHT...WITH GREATER COVERAGE AND ACCUMULATION. ON SATURDAY A
COLD CROSSES THE AREA FROM THE NORTH.

TEMPERATURES WILL BRIEFLY WARM ABOVE NORMAL AS THE UPPER RIDGE AXIS
ARRIVES...FALLING TO AROUND NORMAL AS HEIGHTS FALL WITH THE ADVANCE
OF THE UPPER TROUGH.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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AT KCLT/KHKY...THE BAND OF SHOWERS HAS BECOME MORE RAGGED/LESS
CONCENTRATED AS IT MOVES ACROSS THE NC FOOTHILLS AND PIEDMONT. WILL
CONTINUE TO INCLUDE A TEMPO FOR SHRA/MVFR CONDITIONS AT KCLT FOR THE
FIRST COUPLE OF HOURS OF THE PERIOD. IT IS SOMEWHAT UNCLEAR AS TO
HOW CONVECTIVE TRENDS WILL EVOLVE THIS AFTERNOON...AS THE SHOWERS
HAVE STABILIZED THE ATM ACROSS MUCH OF THE REGION. HOWEVER...SOME
CLEARING IS OCCURRING ACROSS NW SOUTH CAROLINA AND PORTIONS OF THE
NC MTNS. CONVECTION WILL LIKELY REIGNITE IN THESE AREAS DURING THE
AFTERNOON...AND POSSIBLY APPROACH KCLT BY EARLY EVENING. TEMPOS HAVE
THEREFORE BEEN INCLUDED FOR TSRA. OCCASIONAL SHOWERS AND POSSIBLE TS
WILL CONTINUE OFF AND ON THROUGH THE END OF THE PERIOD. WITH THE
VERY MOIST AIR MASS IN PLACE...DETERIORATING FLT CONDITIONS ARE
EXPECTED OVERNIGHT...WITH IFR CIGS EVENTUALLY BECMG LIKELY. GRADUAL
IMPROVEMENT IS EXPECTED BY THE END OF THE PERIOD.

ELSEWHERE...SHOWERS HAVE CLEARED THE TERMINALS LEAVING MVFR/VFR
CONDITIONS IN THEIR WAKE. (THE SMALL AREA OF IFR CIGS AT KGSP SHOULD
LIFT NO LATER THAN 19Z). CONVECTION IS EXPECTED TO REDEVELOP OVER
THE TENN VALLEY/SOUTHERN APPALACHIANS/UPPER SAVANNAH RIVER VALLEY
THIS AFTERNOON...AND VCTS/SHRA WILL BE CARRIED FROM LATE AFTERNOON
ON. OCCASIONAL SHOWERS AND POSSIBLE TS WILL CONTINUE OFF AND ON
THROUGH THE END OF THE PERIOD. WITH THE VERY MOIST AIR MASS IN
PLACE...DETERIORATING FLT CONDITIONS ARE EXPECTED OVERNIGHT...WITH
IFR CIGS EVENTUALLY BECMG LIKELY. GRADUAL IMPROVEMENT IS EXPECTED BY
THE END OF THE PERIOD.

OUTLOOK...SHOWERS AND THUNDERSTORMS...AND ASSOCIATED RESTRICTIONS...
WILL PERSIST THROUGH MONDAY. FAIR WEATHER MAY RETURN BY TUESDAY.

CONFIDENCE TABLE...

            18-24Z        00-06Z        06-12Z        12-18Z
KCLT       HIGH  98%     HIGH  98%     HIGH  97%     HIGH  93%
KGSP       HIGH 100%     HIGH  95%     HIGH  98%     HIGH  88%
KAVL       HIGH  81%     HIGH  95%     HIGH  89%     HIGH  90%
KHKY       HIGH 100%     HIGH  80%     HIGH  96%     HIGH  95%
KGMU       HIGH  91%     HIGH  95%     HIGH  96%     HIGH  83%
KAND       HIGH  96%     HIGH  88%     HIGH  92%     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
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&&

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

&&

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