849
FXUS62 KCAE 291729
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
129 PM EDT SAT AUG 29 2026
WHAT HAS CHANGED
INCREASED CONFIDENCE IN ANOMALOUSLY STRONG UPPER RIDGE AND HOT
AND HUMID CONDITIONS RETURNING NEXT WEEK. AVIATION DISCUSSION
UPDATED FOR 18Z TAF ISSUANCE.
KEY MESSAGES
- 1. DIURNAL THUNDERSTORMS EXPECTED THROUGH THIS WEEKEND WITH
THE MAIN THREAT OF LOCALLY HEAVY RAINFALL.
- 2. WELL ABOVE NORMAL TEMPERATURES WITH DANGEROUS HEAT INDEX
VALUES POSSIBLE NEXT WEEK.
DISCUSSION
KEY MESSAGE 1: DIURNAL THUNDERSTORMS EXPECTED THROUGH THIS
WEEKEND WITH THE MAIN THREAT OF LOCALLY HEAVY RAINFALL.
A LINGERING OUTFLOW BOUNDARY WAS A FOCUS OF EARLIER SHOWERS AND
LIKELY WILL BE AGAIN A FOCUS FOR DIURNALLY INDUCED CONVECTION
THIS AFTERNOON AND EVENING. MESOANALYSIS REVEALS A STRONG
GRADIENT IN PWATS FROM AROUND 1.6 INCHES IN THE PIEDMONT TO
AROUND 2.1 INCHES IN THE COASTAL PLAIN. EXPECT SCATTERED
CONVECTION TO DEVELOP WITH CONTINUED DAYTIME HEATING IN A
MODERATELY UNSTABLE ENVIRONMENT BUT WEAK SHEAR. CONVECTION
LIKELY TO FAVOR THE EASTERN MIDLANDS AND COASTAL PLAIN WHERE
DEEPER MOISTURE EXISTS AND AIDED BY CONVERGENCE ALONG THE SEA
BREEZE. DCAPE VALUES ARE POOR AS ARE LAPSE RATES SO NOT
EXPECTING MUCH OF A SEVERE THREAT, BUT WITH ELEVATED PWATS AND
WEAK STORM MOTION, HEAVY RAIN REMAINS THE PRIMARY THREAT WITH
HIGH RAIN RATES POSSIBLE. WPC CONTINUES TO OUTLOOK THE AREA IN A
MARGINAL RISK OF EXCESSIVE RAINFALL. LITTLE CHANGE SUNDAY IN
THE OVERALL PATTERN, ALTHOUGH THE UPPER TROUGH AXIS WILL BE
WEAKENING AS THE UPPER RIDGE TO THE WEST BEGINS TO EXPAND
EASTWARD. ISOLATED DIURNAL CONVECTION REMAINS POSSIBLE GIVEN
ABUNDANT ATMOSPHERIC MOISTURE IN PLACE.
KEY MESSAGE 2: WELL ABOVE NORMAL TEMPERATURES EXPECTED WITH
DANGEROUS HEAT INDEX VALUES POSSIBLE NEXT WEEK.
INCREASING CONFIDENCE IN A HOT AND HUMID START TO THE MONTH OF
SEPTEMBER. ENSEMBLES ARE IN GOOD AGREEMENT SHOWING AN ANOMALOUS
UPPER RIDGE GRADUALLY MIGRATING EASTWARD FROM THE MS VALLEY
EARLY IN THE WEEK TO THE APPALACHIANS AND CAROLINAS BY MID-LATE
WEEK. ESAT VALUES OF 500MB HEIGHTS ARE ABOVE THE 97TH PERCENTILE
MONDAY AND ABOVE THE 99TH PERCENTILE THROUGH MID WEEK AND
REMAINING ABOVE THE 90TH PERCENTILE THROUGH THE END OF THE WEEK.
THE STRONG UPPER RIDGING WILL CREATE STRONG SUBSIDENCE OVER THE
REGION WHICH SHOULD REALLY LIMIT CONVECTION MUCH OF THE WEEK.
THE RESULT SHOULD BE WELL ABOVE NORMAL TEMPERATURES AND THIS IS
SUPPORTED BY ENSEMBLE FORECAST TEMPERATURES AT 700/850/1000MB AT
OR ABOVE THE 99TH PERCENTILE WITH EC EFI VALUES FOR BOTH MAX
AND MIN TEMPERATURES IN THE 0.7-0.8 RANGE WITH NON-ZERO SHIFT OF
TAILS. HIGHS EXPECTED TO BE IN THE MID TO UPPER 90S WITH LOWS
IN THE LOWER TO MID 70S WITH LITTLE SPREAD AMONG THE NBM IQR.
THE COMBINATION OF ABOVE NORMAL TEMPERATURES AND INCREASED LOW
LEVEL MOISTURE WILL YIELD HIGH PROBABILITIES OF HEAT INDICES IN
THE 100-105 RANGE AND POSSIBLY HIGHER.
AVIATION /18Z SATURDAY THROUGH THURSDAY/
CONVECTION IS POSSIBLE THIS AFTERNOON AND EVENING, WITH
RESTRICTIONS EXPECTED TO RETURN AGAIN TONIGHT.
A MIX OF SUN AND CLOUDS IS PRESENT AT ALL TAF SITES EARLY THIS
AFTERNOON, WITH SOME CUMULUS BEGINNING TO BUBBLE UP JUST WEST OF
THE SITES. THE SETUP IS VERY SIMILAR TO YESTERDAY, WITH HIGHER
MOISTURE CLOSER TO THE COASTAL PLAIN BUT MORE SUNSHINE WEST OF
AGS/CAE/AIK. SO WE PLAY THE WAITING GAME AND HEDGE TOWARDS THE
POSSIBILITY FOR THUNDERSTORMS THIS AFTERNOON. SURFACE DEWPOINTS
ARE INTO THE 70S, SO IT SHOULDN'T BE DIFFICULT TO GET
THUNDERSTORMS TO DEVELOP THIS AFTERNOON. AS A RESULT, HAVE OPTED
FOR A PROB30 AT ALL SITES TO ACCOUNT FOR THIS POSSIBILITY.
HEADING INTO TONIGHT, GUIDANCE IS UNIFORMLY SHOWING THE
REDEVELOPMENT OF IFR RESTRICTIONS. WINDS IN LOWER 1KFT OF THE
ATMOSPHERE LOOK LIGHT AND WE'LL HAVE PLENTY OF LOW-LEVEL
MOISTURE. IFR CIGS LOOK LIKELY AS TEMPERATURES COOL OVERNIGHT,
WITH VISIBILITY RESTRICTIONS POSSIBLE EVERYWHERE AS WELL.
FAVORING STRATUS MORE AT THIS POINT BUT IT COULD BE MORE FOG
THAN STRATUS. REGARDLESS, THE RESTRICTIONS SHOULD DEVELOP
EVERYWHERE BETWEEN 06Z AND 09Z, LASTING THROUGH MID TO LATE
MORNING SUNDAY.
EXTENDED AVIATION OUTLOOK...MORNING CEILINGS AND VISIBILITY
RESTRICTIONS POSSIBLE INTO SUNDAY, ALONG WITH AFTERNOON
RESTRICTIONS FROM SHOWERS AND THUNDERSTORMS. DRIER CONDITIONS
EXPECTED EARLY NEXT WEEK.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
DISCUSSION...23
AVIATION...PL
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