481  
FXUS62 KGSP 180743  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
343 AM EDT MON JUN 18 2018  
   
SYNOPSIS
 
 
HOT HIGH PRESSURE WILL BUILD ATOP THE REGION THROUGH THE MIDDLE OF  
THE WEEK. SCATTERED AFTERNOON AND EVENING THUNDERSTORMS ARE EXPECTED  
EACH DAY, FOCUSING OVER THE MOUNTAINS. MOISTURE WILL INCREASE TOWARD  
THE END OF THE WEEK AS A WEAK FRONTAL BOUNDARY SAGS SOUTH INTO THE  
AREA.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
THE UPPER RIDGE AXIS WILL BECOME MORE OR LESS CENTERED OVER THE  
FORECAST AREA TODAY, WITH RESULTANT INCREASING THICKNESS VALUES  
CONTRIBUTING TO A CONTINUED WARMING TREND. MAX TEMPS THIS AFTERNOON  
ARE EXPECTED TO AVERAGE A COUPLE OF DEGREES WARMER THAN ON SUNDAY IN  
MOST AREAS, WITH MID-90S EXPECTED TO BE COMMON ACROSS THE PIEDMONT,  
PARTICULARLY THE I-77 CORRIDOR. DEWPOINTS HAVE BEEN CONSISTENTLY  
MIXING OUT A BIT OVER THE PAST SEVERAL AFTERNOON, AND SEE NO  
EVIDENCE THAT WOULD LEAD ME TO BELIEVE THIS WON'T HAPPEN AGAIN  
TODAY. THEREFORE, WHILE HEAT INDICES IN THE 100-102-ISH RANGE APPEAR  
LIKELY ACROSS OUR SOUTHERN AND EASTERN PIEDMONT AREAS, OCCURRENCE OF  
HEAT ADVISORY CRITERIA OF >= 105 SHOULD BE ISOLATED AT BEST.  
 
DESPITE THE NEGATIVE INFLUENCE OF THE UPPER RIDGE (POOR MID-LEVEL  
LAPSE RATES/OVERALL SUPPRESSED ENVIRONMENT), FORECAST SOUNDINGS  
DEPICT MODERATE/SEASONAL LEVELS OF INSTABILITY ACROSS THE AREA THIS  
AFTERNOON, ALTHOUGH LOCALIZED CAPE MINIMA WILL PROBABLY DEVELOP IN  
AREAS THAT SEE SFC DEWPOINTS MIX OUT STRONGLY. SHORT TERM AND  
CONVECTION-ALLOWING MODELS SUGGEST INITIATION OF DEEP CONVECTION IN  
AREAS OF DIFFERENTIAL HEATING THIS PM, AND 40-50 POPS ARE ADVERTISED  
ALONG THE RIDGE TOPS. MEANWHILE, STEERING FLOW WITHIN THE AXIS OF  
THE UPPER RIDGE WILL BE EXTREMELY WEAK, IN FACT CLOSE TO 0 ACCORDING  
TO MEAN LCL-TO-EL WINDS FROM FORECAST SOUNDINGS. INDIVIDUAL CELLS  
WILL THEREFORE MAKE LITTLE HEADWAY INTO THE VALLEYS OR THE  
FOOTHILLS, ALTHOUGH 20-30 POPS ARE NEVERTHELESS WARRANTED IN THESE  
AREAS FOR POTENTIAL INITIATION ALONG OUTFLOW BOUNDARIES. MEANWHILE,  
SEE LITTLE JUSTIFICATION FOR A MENTIONABLE POP ACROSS MUCH OF THE  
PIEDMONT, ALTHOUGH AN ISOLATED CELL OR TWO WILL BE POSSIBLE ACROSS  
EXTREME SOUTHEAST AREAS IN ASSOCIATION WITH SURFACE LEE/THERMAL  
SURFACE. MIN TEMPS TONIGHT WILL BE 5-10 DEGREES ABOVE CLIMO.  
 

 
   
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
 
 
AS OF 300 AM MONDAY: THE LARGE UPPER RIDGE WILL BEGIN TO WEAKEN  
TUESDAY AND ESPECIALLY WEDNESDAY, AS A TROUGH CARVES OUT OVER THE  
GREAT LAKES TO NEW ENGLAND. THIS WILL BRING THE MEAN FLOW OUT OF THE  
WEST/NORTHWEST, ALBEIT STILL PRETTY WEAK. AT THE SURFACE, HIGH  
PRESSURE WILL BE SHUNTED SOUTH SLIGHTLY, ALLOWING FOR A MORE  
PRONOUNCED LEE/PIEDMONT TROUGH BOTH DAYS. SO EXPECT SLIGHTLY GREATER  
COVERAGE OF DIURNAL CONVECTION EAST OF THE MOUNTAINS THAN LAST  
COUPLE DAYS. SEVERE THREAT WILL REMAIN MARGINAL, WITH A HANDFUL OF  
PULSE SEVERE STORMS POSSIBLE BOTH DAYS. THE HEAT IS STILL A CONCERN.  
THE LATEST FORECAST CHANGED LITTLE IN TERMS OF AFTN/MAX HEAT INDEX  
VALUES. MUCH OF THE PIEDMONT ALONG AND SOUTHEAST OF I-85 WILL LIKELY  
SEE HEAT INDEX VALUES IN THE 100-104 RANGE, BOTH AFTERNOONS;  
ALTHOUGH, A FEW LOCATIONS COULD FLIRT WITH 105 OR GREATER. THE MAIN  
LIMITING FACTOR IS MIXING SHOULD BRING AFTN DEW POINTS DOWN INTO THE  
UPPER 60S TO LOWER 70S. AND COMBINED WITH FORECAST HIGHS IN THE  
93-97 DEG RANGE, HEAT INDEX DOESN'T QUITE REACH ADVISORY CRITERIA.  
WILL CONTINUE TO MENTION EXCESSIVE HEAT POSSIBLE IN THE HWO.  
 

 
   
LONG TERM /THURSDAY THROUGH SUNDAY/
 
 
AS OF 315 AM MONDAY: GUIDANCE COMING INTO A LITTLE BETTER AGREEMENT  
ON THE HANDLING OF A CLOSED LOW OVER THE ROCKIES, THAT WILL DRIFT  
OUT ACROSS THE PLAINS AT THE START OF THE MEDIUM RANGE, GRADUALLY  
OPENING UP AND LIFTING NE INTO THE NORTHERN STREAM FLOW. THIS WILL  
BRING THE UPPER FLOW OUT OF THE SW WITH SOME DIFFLUENCE ATOP THE CWA  
FOR FRIDAY. AT THE SFC, A FRONT WILL SAG SOUTH AND STALL ACROSS THE  
OHIO VALLEY TO THE CAROLINAS THURSDAY, THEN START TO LIFT BACK NORTH  
AS A WARM FRONT FRIDAY. THIS SHOULD POOL SOME MOISTURE ACROSS THE  
REGION AND RESULT IN FAIRLY DECENT CONVECTIVE COVERAGE BOTH DAYS.  
POPS RAMP UP TO CHC TO LIKELY, HIGHEST ON FRIDAY. SEVERE THREAT MAY  
BE A LITTLE HIGHER, AS WELL, AS 0-6 KM BULK SHEAR INCREASES TO 20-30  
KTS. CAPE WILL LIKELY BE IN THE 1500-2500 J/KG RANGE. AS THE TROUGH  
LIFTS NORTH OF THE AREA, A WEAK FRONT WILL PUSH THRU THE AREA ON  
SATURDAY, RESULTING IN CONTINUED SOLID CHC POPS. AN UPPER RIDGE  
BEGINS TO RE-BUILD OVER THE AREA SUNDAY, BRINGING POPS BACK DOWN  
CLOSER TO CLIMO. AS FOR TEMPS, THURSDAY STILL LOOKS ANOTHER HOT,  
HUMID DAY, WITH HEAT INDEX VALUES AGAIN IN THE TRIPLE DIGITS ACROSS  
THE PIEDMONT. THEN THE HEAT BREAKS SOMEWHAT DUE TO MORE CONVECTION  
FRIDAY AND SATURDAY. TEMPS START TO BUMP BACK UP INTO THE MID 90S ON  
SUNDAY.  
 

 
   
AVIATION /08Z MONDAY THROUGH FRIDAY/
 
 
AT KCLT AND ELSEWHERE: VFR CONDITIONS ARE EXPECTED TO PERSIST AT  
MOST TERMINALS THROUGH THE PERIOD. THE MOST LIKELY EXCEPTION IT AT  
KAVL. THE LATEST DERIVED SATELLITE IMAGERY DEPICTS GRADUALLY  
EXPANDING FOG AND/OR LOW STRATUS JUST UP-VALLEY FROM KAVL, AS WELL  
AS IN MOST OF THE OTHER MAJOR MOUNTAIN VALLEYS. THAT BEING THE CASE,  
FELT THAT A TEMPO FOR 2SM/SCT002 WAS IN ORDER FROM 10-12Z. CANNOT AT  
ALL RULE OUT WORSE CONDITIONS, BUT ALSO CAN'T RULE OUT THAT THE FOG  
AND STRATUS WILL STAY AWAY FROM THE IMMEDIATE KAVL AREA. OTHERWISE,  
A TEMPO FOR 4SM/BR HAS BEEN INCLUDED AT KHKY. CONVECTION WILL  
DEVELOP ACROSS THE MTNS AGAIN THIS AFTERNOON/EVENING, BUT VERY WEAK  
STEERING FLOW IS EXPECTED TO KEEP THE BULK OF THE ACTIVITY OVER THE  
HIGH TERRAIN. THEREFORE, PROB30S FOR TSRA ARE LIMITED TO KAVL ATTM.  
WINDS SHOULD GENERALLY FAVOR LIGHT SW THROUGH THE PERIOD.  
 
OUTLOOK: TYPICAL SUMMERTIME PATTERN WILL CONTINUE THROUGH AT LEAST  
MID-WEEK, WITH DIURNALLY-DRIVEN SHOWERS AND THUNDERSTORMS FAVORING  
THE HIGH TERRAIN, AND SOME MORNING FOG POSSIBLE IN THE MOUNTAIN  
VALLEYS AND OVER LAKES EACH DAY. CHANCES FOR PRECIP LOOK GREATER  
LATE IN THE WEEK AS UPPER RIDGE BEGINS TO BREAK DOWN.  
 
CONFIDENCE TABLE...  
 
07-13Z 13-19Z 19-01Z 01-06Z  
KCLT HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KGSP HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KAVL MED 75% HIGH 100% HIGH 100% HIGH 100%  
KHKY HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KGMU HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
KAND HIGH 100% HIGH 100% HIGH 100% HIGH 100%  
 
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:  
 
WWW.WEATHER.GOV/GSP/AVIATION  
 

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

 
 

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