985
FXUS62 KGSP 191834
AFDGSP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
234 PM EDT SAT SEP 19 2026
WHAT HAS CHANGED
ADJUSTMENTS WERE MADE TO PRECIP CHANCES EARLY IN THE WEEK AND
TEMPERATURES DURING THE SECOND HALF OF THE UPCOMING WEEK.
KEY MESSAGES
1. THUNDERSTORMS ARE POSSIBLE EACH AFTERNOON AND EVENING THROUGH
MONDAY, WITH A FEW OF THEM SEVERE TODAY AND MONDAY. DAMAGING WIND
GUSTS AND EXCESSIVE RAIN ARE THE MAIN THREATS.
2. A PATTERN CHANGE DURING THE MIDDLE PART OF THE UPCOMING WEEK
IS EXPECTED TO BRING IN COOLER TEMPS RIGHT ON SCHEDULE FOR THE
START OF AUTUMN.
DISCUSSION
KEY MESSAGE 1: THUNDERSTORMS ARE POSSIBLE EACH AFTERNOON AND EVENING
THROUGH MONDAY, WITH A FEW OF THEM SEVERE TODAY AND MONDAY. DAMAGING
WIND GUSTS AND EXCESSIVE RAIN ARE THE MAIN THREATS.
OUR WEATHER REMAINS A BIT UNSETTLED OVER THE NEXT FEW DAYS AS WE
ARE UNDER WHAT AMOUNTS TO AN ATMOSPHERIC COL REGION IN-BETWEEN
THE OLD UPPER ANTICYCLONE OVER THE SOUTHERN PLAINS, THE ATLANTIC
SUBTROPICAL RIDGE, A WEAK MID/UPPER LOW OVER THE FL PENINSULA AND
EASTERN GULF, AND THE NORTHERN STREAM. WITHIN THIS REGIME, A OLD
QUASI-STATIONARY BOUNDARY ACROSS THE MIDDLE OF THE FORECAST AREA
TODAY SHOULD WASH OUT OVER THE NEXT 24 HOURS. THAT WILL LEAVE US
WITH AMPLE DEEP MOISTURE ACROSS THE REGION THAT WILL FUEL INCREASING
MAINLY DIURNAL SHOWER AND THUNDERSTORM CHANCES THAT EXPAND FROM
THE MOUNTAINS TO THE WHOLE FORECAST AREA THROUGH TUESDAY. WE WILL
LACK MID/UPPER FORCING THE NEXT TWO DAYS BUT WILL MAKE UP FOR THAT
WITH A LIGHT EASTERLY FLOW AND THERMODYNAMICS.
THE MAIN CONCERN FOR THE NEXT FEW DAYS WILL BE A FEW SEVERE
THUNDERSTORMS WITH DAMAGING WIND GUSTS AND EXCESSIVE RAIN, MAINLY
IN THE LATE AFTERNOON AND EVENING. NOTE THAT SPC HAS INCLUDED MOSTLY
THE MOUNTAINOUS PARTS OF THE FORECAST AREA IN A MARGINAL RISK TODAY
AND MONDAY. THIS SEEMS REASONABLE WITH THE EXPECTATION OF 2000-3000
J/KG OF SFC-BASED CAPE EACH AFTERNOON AND WATER-LOADED DOWNDRAFTS
FALLING THROUGH SUFFICIENT DCAPE TO ALLOW FOR STRONG OUTFLOWS. THIS
AFTERNOON MIGHT BE THE POOREST OF THE THREE DAYS AS WE APPEAR TO BE
IN A DCAPE MINIMUM FOR THE MOST PART, BUT WE HAVE THE BENEFIT OF
THE OLD BOUNDARY DRAPED ACROSS THE REGION. GUIDANCE SUGGESTS THAT
BUOYANCY WILL IMPROVE A BIT EACH DAY, SO OUR CHANCES FOR SEVERE
MIGHT ALSO IMPROVE SLIGHTLY. BY MONDAY AND TUESDAY, THE RISK FOR
EXCESSIVE RAIN ALSO TICKS UPWARD AS WARM CLOUD DEPTH INCREASES AND
STORM MOTIONS ARE MORE SLUGGISH. NOTE THAT WPC HAS THE REGION IN
THE MARGINAL RISK FOR EXCESSIVE RAINFALL FOR MONDAY INTO TUESDAY.
AS FOR TEMPERATURES, THEY WILL REMAIN ABOVE NORMAL THROUGH MONDAY,
BUT THEN DROP DOWN CLOSE TO NORMAL FOR TUESDAY ASSUMING INCREASED
CLOUD COVER AND RAIN COVERAGE KEEPS THEM IN CHECK.
KEY MESSAGE 2: A PATTERN CHANGE DURING THE MIDDLE PART OF THE UPCOMING
WEEK IS EXPECTED TO BRING IN COOLER TEMPS RIGHT ON SCHEDULE FOR
THE START OF AUTUMN.
AS WE GET INTO THE FIRST PART OF THE UPCOMING WEEK, THE NORTHERN
STREAM BECOMES MORE BLOCKY OVER THE NORTHERN PLAINS/GREAT
LAKES/MIDWEST, WITH A MID/UPPER LOW CONSOLIDATING OVER THE MIDWEST
TUESDAY INTO WEDNESDAY. THIS UPPER LOW COMBINED WITH CYCLOGENESIS
OFF THE MID-ATLANTIC COAST WOULD BRING A BACK DOOR COLD FRONT DOWN
TUESDAY AND ESTABLISH A COLD AIR DAMMING WEDGE BY WEDNESDAY THAT
WOULD PERSIST INTO THURSDAY AT LEAST. THE COOL NORTHEASTERLY FLOW
AND LIGHT PRECIP POTENTIAL WILL HELP TO DROP TEMPS DOWN TO ABOUT
TEN DEGREES BELOW NORMAL FOR THE END OF THE WEEK. CONFIDENCE IN
THE DETAILS IS NOT GREAT, BUT IT LOOKS LIKE A NOTICEABLE CHANGE OF
SEASONS AT ANY RATE. THE UPPER LOW MAY ULTIMATELY SWING THROUGH
TO OUR NORTH THURSDAY OR FRIDAY, AFTER WHICH WE COME MORE UNDER
THE INFLUENCE OF THE DRIER RIDGE TO OUR WEST, BUT TEMPS WOULD STAY
BELOW NORMAL THROUGH THE END OF THE PERIOD.
AVIATION /18Z SATURDAY THROUGH THURSDAY/
AT KCLT AND ELSEWHERE: SATELLITE IMAGERY SHOWS A WELL-DEVELOPED
STRATOCU FIELD ACROSS THE REGION WITH CLOUD BASES HOVERING BETWEEN
025 AND 035, WHICH MEANS THAT A TEMPORARY MVFR CEILING RESTRICTION
WILL BE POSSIBLE AT MOST TERMINALS FOR THE NEXT FEW HOURS. BY 20-22Z
THE BOUNDARY LAYER DEEPENS AND RAISES THE CEILINGS TO VFR IF THEY
EXIST. MEANWHILE, SHOWERS AND THUNDERSTORMS ARE DEVELOPING OVER THE
SOUTHERN MOUNTAINS OF NC AS SHOWN BY THE HRRR, WHICH PUTS KAND AT
THE GREATEST CHANCE FOR A STORM THROUGH EARLY EVENING. THEY GET A
TEMPO AS DOES KAVL FOR LATER DEVELOPMENT OVER THE MTNS, BUT THE
OTHER SITES WARRANT ONLY A PROB30 UNTIL A CLEARER INDICATION OF
STORM DEVELOPMENT IS SEEN. WIND SHOULD STAY MAINLY NE. THINK THE
RECENT ESE FLOW AT KCLT IS A TEMPORARY FLUCTUATION AND THE DIRECTION
WILL COME BACK AROUND TO N OF E. TONIGHT, THE NORTHEASTERLY FLOW
AT LOW LEVELS IS EXPECTED TO HELP A LOW CLOUD CEILING DEVELOP
DURING THE EARLY MORNING HOURS, FALLING DOWN THROUGH MVFR TO IFR,
ESPECIALLY CLOSE TO THE ESCARPMENT. MOUNTAIN/VALLEY FOG AND STRATUS
SHOULD RESULT IN LIFR OR VLIFR. ALL OF THIS SHOULD MIX OUT BY 13Z
OR SO. WE SHOULD THEN DO IT ALL AGAIN IN THE AFTERNOON UNDER A
SIMILAR SETUP.
OUTLOOK: SHOWER AND THUNDERSTORM CHANCES CONTINUE EACH AFTERNOON
THROUGH TUESDAY. MOUNTAIN VALLEY FOG AND LOW STRATUS POSSIBLE
EACH MORNING.
GSP WATCHES/WARNINGS/ADVISORIES
GA...NONE.
NC...NONE.
SC...NONE.
PM
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