878  
FXUS62 KGSP 231102  
AFDGSP  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC  
702 AM EDT SUN APR 23 2017  
   
SYNOPSIS
 
 
COOL AND MOIST HIGH PRESSURE WILL REMAIN OVER THE AREA THROUGH  
MONDAY. MEANWHILE, A DEEP AND VIGOROUS LOW PRESSURE SYSTEM MOVES  
ACROSS GEORGIA TO THE CAROLINA COAST CREATING A LENGTHY PERIOD OF  
MODERATE TO HEAVY RAINFALL THAT PERSISTS THROUGH MONDAY. DRY HIGH  
PRESSURE RETURNS BY WEDNESDAY. TEMPERATURES WARM THROUGH NEXT  
WEEKEND WITH A SMALL CHANCE OF AFTERNOON MOUNTAIN THUNDERSTORMS.  
 

 
   
NEAR TERM /THROUGH TONIGHT/
 
 
AS OF 700 AM EDT: SHOWERS ARE BLOSSOMING ACROSS THE CWFA, AS  
ISENTROPIC LIFT AND MOISTURE DEEPENS ATOP A STRENGTHENING WEDGE. NO  
SIGNIFICANT CHANGES WERE NEEDED WITH THIS UPDATE.  
 
AS OF 330 AM EDT: AN UPPER CLOSED LOW WILL CONTINUE TO SLOWLY DRIFT  
SE FROM THE MID-SOUTH TO NEAR COLUMBUS, GA BY 12Z MONDAY. THIS SLOW  
DRIFT WILL PLACE THE CWFA WITHIN A REGION OF VERY STRONG DEEP-LAYER  
Q-VECTOR CONVERGENCE, ESPECIALLY TONIGHT. AT THE SURFACE, AN AREA OF  
LOW PRESSURE WILL STALL OVER NORTHERN GA, WHILE A BACKDOOR COLD  
FRONT CLEARS OUR AREA TO THE SOUTH KEEPING A HYBRID WEDGE LOCKED IN  
ACROSS THE ENTIRE CWFA. PERSISTENT LOW LEVEL UPGLIDE ATOP THE WEDGE  
SHOULD BRING ROUNDS OF SHOWERS THRU THE DAY. THE CAMS SEEM TO AGREE  
ON PERHAPS A COUPLE "ROUNDS" OF CATEGORICAL POPS, ONE THIS MORNING,  
THEN ANOTHER THIS EVENING. TOTAL QPF AMOUNTS TODAY THRU TONIGHT WILL  
RANGE FROM GENERALLY 1.5 TO 3", HIGHEST ACROSS THE SELY UPSLOPE  
AREAS OF THE BLUE RIDGE AND ADJACENT FOOTHILLS. SO THE FLOOD WATCH  
LOOKS GOOD FOR THE NC ZONES. AS FOR SEVERE POTENTIAL, IT REALLY DOES  
LOOK LIKE THE WEDGE FRONT WILL MAKE LITTLE PROGRESS NORTH AS THE LOW  
IS SLOW TO APPROACH FROM THE WEST, AND ONGOING RAIN KEEPS IT  
REINFORCED. I KEEP A MENTION OF SLIGHT CHC TO CHC FOR THUNDER ACROSS  
THE I-85 CORRIDOR AND SOUTH/EAST, DUE TO POTENTIAL ELEVATED  
CONVECTION. THERE IS STILL A MARGINAL RISK IN THE DAY ONE CONVECTIVE  
OUTLOOK FOR POSSIBLE HAIL AND WIND, BUT THE CAMS KEEP THE STRONGEST  
CONVECTION SOUTH AND EAST OF THE CWFA. TEMPS WILL BE NEARLY STEADY  
ACROSS MOST OF THE AREA, UNLESS THE WEDGE FRONT DOES NUDGE BACK INTO  
THE SOUTHERN TIER OF COUNTIES, WHERE TEMPS MAY BUMP BACK UP INTO THE  
UPPER 60S TO LOWER 70S. LOWS TONIGHT DROP SLIGHTLY INTO THE 40S IN  
THE MOUNTAINS AND LOWER TO MID 50S ELSEWHERE.  
 

 
   
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
 
 
AS OF 355 AM SUNDAY: THE HEAVY RAIN POTENTIAL CONTINUES MONDAY AS  
OUR AREA WILL STILL BE IN THE SOUTHERLY DIFFLUENT FLOW/DEFORMATION  
ZONE AROUND THE UPPER LOW MOVING EAST FROM WEST CENTRAL GA TO THE  
SC/GA COAST. UPPER DIVERGENCE FOLLOWS A SIMILAR PATTERN. STRONG LOW  
LEVEL EASTERLY FLOW REMAINS OVER THE AREA AS THE LOW LEVEL LOW  
PRESSURE AREAS FOLLOW A SIMILAR PATTERN AS WELL. IN FACT, THE LOW  
LEVEL EASTERLY FLOW IS UP TO 3 STANDARD DEVIATIONS ABOVE NORMAL.  
THIS WILL CREATE STRONG ISENTROPIC LIFT OVER THE COLD DOME FROM THE  
DAMMING THAT REMAINS IN PLACE. THE MOIST AIR MASS REMAINS IN PLACE  
AS WELL WITH PW VALUES 1 TO 2 SD ABOVE NORMAL. THE HEAVIEST RAIN  
WILL LIKELY FALL ACROSS THE NC FOOTHILLS AND PIEDMONT, BUT COULD  
SHIFT SOUTH INTO THE EASTERN UPSTATE. AN ADDITIONAL 1 TO 2 INCHES OF  
RAIN COULD FALL IN THESE AREAS. THEREFORE, HAVE ADDED UNION COUNTY  
NC TO THE FLOOD WATCH TO COVER THE POTENTIAL. MODERATE TO HEAVY RAIN  
COULD LINGER MONDAY EVENING, BUT PRECIP TAPERS OFF FROM SW TO NE  
OVERNIGHT. HIGHS WILL INCREASE A LITTLE BUT REMAIN AROUND 10 DEGREES  
BELOW NORMAL. LOWS WILL BE UP TO 5 DEGREES ABOVE NORMAL.  
 
PRECIP CONTINUES TAPERING OFF FROM SW TO NE TUESDAY ENDING DURING  
THE AFTERNOON. WITH PRECIP ENDING AND SUNSHINE GRADUALLY RETURNING,  
HIGHS WILL BE NEAR NORMAL. DRY FORECAST CONTINUES TUESDAY NIGHT WITH  
LOWS AROUND 5 DEGREES ABOVE NORMAL.  
 

 
   
LONG TERM /WEDNESDAY THROUGH SATURDAY/
 
 
AS OF 330 AM SUNDAY: SHORT WAVE RIDGE OVER THE AREA WEDNESDAY MOVES  
EAST AS A SERIES OF SHORT WAVES MOVE BY TO OUR NORTH AND WEST  
THURSDAY AND FRIDAY. A STRONGER RIDGE DEVELOPS OVER THE SE CONUS  
SATURDAY. DRY REMAINS OVER THE AREA WEDNESDAY WITH TEMPS ABOVE  
NORMAL. MOISTURE RETURNS AHEAD OF A WEAK COLD FRONT THURSDAY AND  
FRIDAY. THIS WILL LEAD TO DIURNAL CONVECTION EACH DAY FAVORING THE  
MOUNTAINS. TEMPS REMAIN ABOVE NORMAL. SOUTHERLY FLOW AROUND THE  
RIDGE SURFACE AND ALOFT WILL KEEP SOME MOISTURE ACROSS THE MOUNTAINS  
WITH DIURNAL CONVECTION ONCE AGAIN. TEMPS REMAIN ABOVE NORMAL AS  
WELL.  
 

 
   
AVIATION /11Z SUNDAY THROUGH THURSDAY/
 
 
AT KCLT AND ELSEWHERE: AS EXPECTED, IFR CIGS HAVE FINALLY FILLED IN  
ACROSS ALL THE TAF SITES (EXCEPT BARELY MVFR AT KAVL), AS SHOWERS  
CONTINUE TO DEVELOP ATOP A BUILDING COLD AIR DAMMING WEDGE. GUIDANCE  
IS STILL ON TRACK FOR A PERIOD OF HEAVIER RAIN/GREATER COVERAGE THIS  
MORNING, THEN PERHAPS A RELATIVE LULL THIS AFTERNOON. THEN ANOTHER  
ROUND OF RAIN TONIGHT. STILL MAY SEE SOME ELEVATED THUNDER ACROSS  
THE UPSTATE AND AT KCLT LATE THIS AFTERNOON THRU THE EVENING. FOR  
NOW, ONLY WILL MENTION A PROB30 AT KCLT WHERE CHANCE IS GREATEST FOR  
EMBEDDED THUNDER WITH THE SECOND ROUND OF RAIN. IFR CIGS WILL LIKELY  
LOWER TO LIFR ACROSS THE PIEDMONT SITES TONIGHT, AS THE COLD DOME OF  
THE WEDGE STARTS TO SHRINK WITH A PASSING AREA OF LOW PRESSURE TO  
THE SOUTH. SHOWERS WILL START TO TAPER OFF IN THE WEST TOWARD THE  
END OF THE TAF PERIOD.  
 
OUTLOOK: AN AREA OF LOW PRESSURE WILL CROSS THE SOUTHERN CWFA THRU  
MONDAY WHILE STRONG SFC RIDGING BUILDS IN FROM THE NORTH. WIDESPREAD  
LOW CLOUDS AND PRECIPITATION ARE EXPECTED TO PERSIST THRU THIS TIME.  
CONDITIONS SHOULD GRADUALLY IMPROVE TUESDAY THRU WEDNESDAY MORNING  
AS DRY AIR WORKS IN BEHIND THE DEPARTING LOW.  
 
CONFIDENCE TABLE...  
 
11-17Z 17-23Z 23-05Z 05-06Z  
KCLT HIGH 100% LOW 50% MED 78% MED 60%  
KGSP HIGH 87% LOW 50% MED 78% HIGH 87%  
KAVL HIGH 87% MED 78% MED 78% HIGH 87%  
KHKY HIGH 81% HIGH 83% HIGH 83% MED 69%  
KGMU HIGH 81% LOW 44% MED 78% HIGH 87%  
KAND HIGH 87% MED 61% HIGH 100% HIGH 87%  
 
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...FLOOD WATCH THROUGH MONDAY EVENING FOR NCZ033-035>037-048>053-  
056>059-062>065-068>072-082-501>510.  
SC...NONE.  
 

 
 

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