019
FXUS62 KCAE 211059
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
659 AM EDT FRI AUG 21 2026
WHAT HAS CHANGED
THUNDERSTORMS WILL DEVELOP THIS AFTERNOON AND COULD PRODUCE
DAMAGING WINDS AND LOCALIZED FLASH FLOODING.
KEY MESSAGES
- 1. SEVERE WEATHER AND FLASH FLOODING POSSIBLE TODAY.
DISCUSSION
KEY MESSAGE 1: SEVERE WEATHER AND FLASH FLOODING POSSIBLE
TODAY.
EARLY THIS MORNING, A CLUSTER OF THUNDERSTORMS ARE MOVING
THROUGH NORTHERN GA. ACTIVITY CONTINUES TO DIMINISH BUT THE
OUTFLOW BOUNDARY WILL PUSH INTO THE FORECAST AREA LATER THIS
MORNING. THE BOUNDARY WILL LIKELY SERVE AS ONE OF THE TRIGGERS
FOR CONVECTION THIS AFTERNOON.
WATER VAPOR IMAGERY THIS MORNING SHOWS THE AXIS OF THE UPPER
TROUGH HAS PUSHED EAST INTO THE TN RIVER VALLEY. THIS WILL
PROMOTE MOISTURE ADVECTION INTO THE REGION AND WEAK SURFACE LOW
PRESSURE DEVELOPMENT OVER THE FORECAST AREA TODAY. A SURFACE
BOUNDARY SITUATED IN NC THIS MORNING MAY WORK INTO THE NORTHERN
FA TODAY SERVING AS A TRIGGER FOR CONVECTION IN ADDITION TO THE
CONVECTIVE OUTFLOW FROM STORMS TO OUR WEST OVERNIGHT.
MOISTURE ADVECTION AND DAYTIME HEATING WILL ALLOW FOR MLCAPE
VALUES GENERALLY BETWEEN 1500 TO 2500 J/KG WITH POCKETS OF
GREATER INSTABILITY POSSIBLE. STEEP LOW LEVEL LAPSE RATES,
WEAK DIVERGENCE ALOFT, AND PWAT VALUES AROUND 2 INCHES
INCREASES THE RISK FOR THUNDERSTORMS TO PRODUCE WET MICROBURSTS
TODAY. DAMAGING WINDS AND HEAVY RAIN ARE THE PRIMARY THREATS BUT
WE CANNOT RULE OUT LARGE HAIL WITH DECENT CAPE IN THE HAIL
GROWTH ZONE ON FORECAST SOUNDINGS. THOUGH THE LOCATION OF
CONVECTIVE INITIATION DIFFERS BETWEEN THE CAMS THERE IS A
CONSISTENT TIMING FOR CONVECTION TO BEGIN AROUND 17Z OR 18Z AND
CONTINUE INTO THE EVENING.
DEEP LAYER SHEAR IS LACKING FOR THE EVENT WHICH POINTS MORE TO A
HEAVY RAIN AND DOWNBURST WIND THREAT. REFS AND HREF PMM RAINFALL
AMOUNTS GENERALLY SHOW AREAS OF 2 IN AMOUNTS THROUGH MUCH OF THE
FA BUT IN THE PEE DEE AND ALONG THE NC/SC BORDER THERE ARE
POCKETS OF 4 IN OR HIGHER AMOUNTS. THIS POINTS TO THE
POSSIBILITY OF TRAINING CELLS CLOSER TO THE W-E ORIENTED SURFACE
BOUNDARY TO OUR NORTH. THIS WILL BE THE AREA OF GREATEST CONCERN
FOR FLASH FLOODING TODAY BUT ANY URBAN AREAS OR TYPICALLY
FLOOD-PRONE LOCATIONS ARE ALSO CONCERNS.
SATURDAY, THE AXIS OF THE TROUGH WILL BE FURTHER EAST SO DRIER
AIR WILL BEGIN TO IMPINGE ON THE WESTERN FA. HOWEVER DEEPER
MOISTURE AND MODERATE CONDITIONAL INSTABILITY ALONG THE COAST
COULD LEAD TO ANOTHER DAMAGING WIND THREAT DURING THE AFTERNOON
CLOSER TO THE I-95 CORRIDOR. BEYOND THAT, A MORE SEASONAL
PATTERN EMERGES WITH TEMPERATURES CLOSER TO NORMAL AND DIURNAL,
ISOLATED TO SCATTERED THUNDERSTORMS.
AVIATION /12Z FRIDAY THROUGH TUESDAY/
VFR CONDITIONS EXPECTED THROUGH THIS MORNING, WITH RESTRICTIONS
EXPECTED IN CONVECTION THIS AFTERNOON AND EVENING.
QUIET WEATHER IS IN PLACE ACROSS THE AREA CURRENTLY. THERE HAVE
BEEN SOME PERSISTENT SHOWERS AND STORMS ACROSS THE UPSTATE AND
SOUTHERN NC OVER THE LAST SEVERAL HOURS BUT WE HAVE REMAINED
QUIET. MOISTURE IS FORECAST TO RETURN IN A HURRY AHEAD OF AN
APPROACHING SURFACE LOW AND SURFACE TROUGH THIS MORNING.
SOUTHERLY AND SOUTHEASTERLY FLOW WILL CONTINUE TO PUSH HIGHER PW
AIR IN PLACE AS A SURFACE LOW DEVELOPS OVERHEAD. CONVECTION IS
EXPECTED TO BEGIN EARLY AGAIN - LIKELY BETWEEN 15Z AND 17Z.
FORECAST SOUNDINGS ARE QUITE IMPRESSIVE FOR THIS SETUP, WITH
PLENTY OF MOISTURE AND INSTABILITY TO YIELD WIDESPREAD, STRONG
THUNDERSTORMS THROUGHOUT THIS AFTERNOON. GIVEN ROBUST FORCING
(ESP FOR AUGUST), PLENTIFUL MOISTURE, AND STRONG INSTABILITY IN
PLACE, FEEL COMFORTABLE TARGETING THE 17Z-21Z TIMEFRAME FOR A
TEMPO FOR TSRA, LOWERED VISIBILITIES, AND STRONG WIND GUSTS.
THIS MAY NEED TO BE ADJUSTED IF CONVECTION BEGINS EARLIER BUT
THIS SEEMS LIKE A GOOD STARTING POINT FOR THE TEMPO GROUP.
EXPECTING THE CONVECTION TO LIKELY WIND DOWN IN THE 21Z TO 00Z
TIMEFRAME, WITH RAIN SHOWERS EXPECTED TO PERSIST INTO THE
EVENING HOURS. CLOUDS WILL BE COPIOUS DURING THIS TIME, AND AS
THE AFORMENTIONED SURFACE LOW AND SURFACE BOUNDARY MOVE TO OUR
SOUTH/EAST BY TONIGHT, GUIDANCE IS HINTING AT SOME MVFR OR IFR
CIGS DEVELOPING. THIS IS PRETTY UNCERTAIN RIGHT NOW BUT IF
RAINFALL IS WIDESPREAD AND PERSISTENT ENOUGH, IT WON'T BE TOUGH
TO GET SOME CEILING RESTRICTIONS. HAVE TRENDED TOWARDS THIS
BEGINNING IN THE 03Z GROUP.
EXTENDED AVIATION OUTLOOK...THUNDERSTORM CHANCES REMAIN INTO
THE WEEKEND, WITH SCATTERED TO WIDESPREAD CONVECTION EXPECTED.
CAE WATCHES/WARNINGS/ADVISORIES
SC...NONE.
GA...NONE.
DISCUSSION...CJR
AVIATION...PL
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