701
FXUS62 KCHS 201120
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
720 AM EDT THU AUG 20 2026
WHAT HAS CHANGED
THE AVIATION SECTION WAS UPDATED FOR THE 12Z TAFS.
KEY MESSAGES
- 1) HEAT WILL REMAIN A CONCERN INTO LATE WEEK.
- 2) AFTERNOON AND EVENING THUNDERSTORM COVERAGE WILL REMAIN
ISOLATED THROUGH THURSDAY. AN INCREASE IN THUNDERSTORM
COVERAGE IS EXPECTED FRIDAY THROUGH THE WEEKEND.
DISCUSSION
KEY MESSAGE 1: HEAT WILL REMAIN A CONCERN INTO LATE WEEK.
FINALLY, AFTER BAKING ON THE SURFACE OF THE SUN FOR THE PAST
TWO WEEKS IT APPEARS OUR HEAT WAVE IS FINALLY COMING TO A CLOSE.
THE RIDGE THAT HAS PLAGUED US HAS WEAKENED AS UPPER TROUGHING
BEGINS TO TAKE CONTROL OVER THE EASTERN US. WE WILL STILL HAVE
ONE TO POSSIBLY TWO MORE DAYS OF HOT TEMPERATURES AS WE REMAIN
IN A RATHER NEBULOUS REGIME BEFORE THE UPPER TROUGH FULLY EJECTS
EASTWARD WITH THE ASSISTANCE OF SEVERAL EMBEDDED SHORTWAVE
TROUGHS. OVERALL, HEAT INDICES WILL BE SLIGHTLY LOWER TODAY AS
THE COMBINATION OF SOME DRIER AIR MIXING DEWPOINTS INTO THE 60S
INLAND AND THE POTENTIAL FOR AN EARLY START TO AFTERNOON
SHOWERS AND STORMS SHOULD HELP KEEP THINGS MORE MANAGEABLE IN
THE 105 TO 108 RANGE. THE ONLY REAL CONCERNS LOOK TO BE
PREDOMINATELY ALONG THE IMMEDIATE COASTLINE AND INTO THE TRI-
COUNTY AREA BEHIND THE AFTERNOON SEABREEZE. A FEW LOCATIONS
ALONG THE COAST COULD REACH HEAT INDICES AROUND 110-112 DEGREES
FOR A HOUR OR TWO THIS AFTERNOON AND AS A RESULT A HEAT
ADVISORY REMAINS IN EFFECT.
THE GRADUAL COOLING TREND WILL PERSIST INTO FRIDAY AS THE
INFLUENCES OF THE UPPER TROUGH TO OUR WEST SLOWLY BEGIN TO INCH
THEIR WAY EASTWARD INTO THE AREA. WHILE AIR TEMPERATURES WILL
LIKELY CLIMB BACK INTO THE LOW TO MID 90S, INCREASED CLOUD COVER
AND EARLY STORM INITIATION SHOULD HELP LIMIT AFTERNOON HEATING
ENOUGH TO KEEP MOST OF THE AREA BELOW ADVISORY CRITERIA. THE
MAIN AREAS WOULD BE ALONG THE IMMEDIATE COASTLINE WHERE ONCE
AGAIN THE OVERLAP OF NEAR 80S DEWPOINTS AND TEMPERATURES IN THE
90S COULD RESULT IN HEAT INDICES IN THE 108-110 RANGE BEHIND
THE SEABREEZE. HOWEVER, CONFIDENCE IN HOW LONG THESE HEAT
INDICES WILL LAST AND STORM COVERAGE ARE CURRENTLY LIMITING THE
NEED FOR ONE FINAL HEAT ADVISORY TOMORROW. WE WILL LIKELY
REVISIT THE NEED FOR AN ADVISORY WITH A LATER ISSUANCE AS THE
POTENTIAL OR LACK THERE OF BECOMES CLEARER.
BY THE WEEKEND, THE UPPER TROUGH WILL BE IN FULL CONTROL AS A
SURFACE FRONT MOVES INTO OUR AREA. AN INCREASE IN SHOWER AND
THUNDERSTORM ACTIVITY THIS WEEKEND LOOKS TO COOL US OFF ENOUGH
TO POSSIBLY GO WITHOUT ANY HEAT ADVISORIES/WARNINGS, THOUGH HIGH
TEMPERATURES LOOK TO STILL PEAK IN THE LOWER TO MID 90S.
KEY MESSAGE 2: ISOLATED TO SCATTERED THUNDERSTORMS THIS AFTERNOON
AND EVENING, MAINLY ACROSS THE CHARLESTON TRI-COUNTY. STRONGER AND
MORE WIDESPREAD THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL ARE
EXPECTED FRIDAY AND SATURDAY.
TODAY: MID-LEVEL RIDGING WILL PREVAIL, LEADING TO ANOTHER DAY OF
ABOVE NORMAL TEMPERATURES AND STIFLING HUMIDITY. THIS WILL YIELD
DECENT INSTABILITY, GENERALLY 2,000-3,000 J/KG OF SBCAPE, WITH
LOCALLY HIGHER AMOUNTS POSSIBLE. ADDITIONALLY, DCAPES WILL BE ABOVE
1,000 J/KG. ALL OF THIS COMBINED WITH LIFT FROM A COASTAL TROUGH AND
THE SEA BREEZE SHOULD GENERATE ISOLATED TO SCATTERED THUNDERSTORMS
THIS AFTERNOON AND EVENING. THE CAMS AND DETERMINISTIC MODELS
GENERALLY HAVE THE CONVECTION ACROSS THE CHARLESTON TRI-COUNTY, SO
THE FORECAST REFLECTS THIS WITH UP TO CHANCE POPS. THE CONVECTION IS
MOST LIKELY TO FORM ALONG THE SEA BREEZE AND THEN SHIFT INLAND,
DRIVEN BY OUTFLOW AND BOUNDARY INTERACTIONS. GIVEN THE CONDITIONS,
STRONG TO SEVERE THUNDERSTORMS ARE POSSIBLE WITH THE MAIN THREAT
BEING DAMAGING WINDS. HEAVY RAINFALL IS ALSO A CONCERN DUE TO THE
VERY WEAK STEERING WINDS AND ELEVATED PWATS, SO LOCALIZED FLOODING
IS POSSIBLE. ANY CONVECTION WILL DECREASE THIS EVENING.
FRIDAY AND SATURDAY: MID-LEVEL RIDING OVER OUR AREA WILL QUICKLY
DISSIPATE FRIDAY MORNING, BEING REPLACED BY TROUGHING OVER THE
EASTERN HALF OF THE U.S. THE TROUGH WILL STRENGTHEN/AMPLIFY DURING
THE WEEKEND. AT THE SAME TIME, THERE WILL BE A SERIES OF SHORTWAVES
ROUNDING THE BASE OF THE TROUGH AND MOVING OVER OUR REGION. AT THE
SURFACE, A SLOW MOVING FRONT WILL APPROACH FROM THE WEST AND
NORTHWEST ON FRIDAY, POSSIBLY TRANSITIONING INTO A STATIONARY FRONT
FRIDAY NIGHT, AND THEN MEANDERING JUST TO OUR WEST AND NORTHWEST
THROUGH THE WEEKEND. THERE WILL BE A DEEP PLUME OF MOISTURE JUST
AHEAD OF THE FRONT, WITH PWATS RISING ABOVE 2" FRIDAY AND THE FIRST
HALF OF SATURDAY, THEN REMAINING SOMEWHAT ELEVATED INTO SUNDAY.
THESE VALUES ARE NEAR THE 90% MARK FOR CHS PER SPC SOUNDING
CLIMATOLOGY. EVEN THOUGH TEMPERATURES WILL BE A FEW DEGREES "COOLER"
THAN THE PREVIOUS FEW DAYS, THEY'LL STILL BE WELL ABOVE NORMAL,
GENERATING A DECENT AMOUNT OF INSTABILITY AND DCAPE. ALL OF THE
MODELS ARE IN GENERALLY GOOD AGREEMENT INDICATING WIDESPREAD SHOWERS
AND THUNDERSTORMS STARTING ON FRIDAY AND OCCURRING AGAIN ON
SATURDAY. GIVEN THE CONDITIONS, STRONG TO SEVERE THUNDERSTORMS ARE
POSSIBLE WITH THE MAIN THREAT BEING DAMAGING WINDS. SPC HAS MOST OF
OUR AREA IN A MARGINAL RISK OF SEVERE THUNDERSTORMS ON FRIDAY, AND
WE WOULDN'T BE SURPRISED IF THIS IS REPEATED ON SATURDAY. HEAVY
RAINFALL WILL ALSO BE A CONCERN ON FRIDAY DUE TO THE VERY WEAK
STEERING WINDS AND ELEVATED PWATS, THEN AGAIN ON SATURDAY DUE TO
STORM MOTIONS MOVING ALONG THE FRONT. THE EXACT QPF AMOUNTS WILL BE
HIGHLY DEPENDENT ON WHERE THE THUNDERSTORMS FORM, HOW SLOW THEY
MOVE, AND IF THERE IS ANY BACKBUILDING, OR TRAINING. BUT BASED ON
SOME OF THE ENSEMBLES, THERE IS THE POTENTIAL FOR SEVERAL INCHES OF
RAINFALL TO FALL IN VERY LOCALIZED AREAS FRIDAY AND SATURDAY. WPC
HAS PORTIONS OF OUR AREA UNDER A MARGINAL RISK FOR EXCESSIVE
RAINFALL BOTH DAYS. FLASH FLOODING IS CERTAINLY POSSIBLE BOTH DAYS.
WHILE THERE SHOULD BE SOME LET UP IN THE CONVECTION DURING
FRIDAY/SATURDAY EVENING AND OVERNIGHT, IT MAY NOT COMPLETELY DRY
OUT, ESPECIALLY CLOSER TO THE COAST. IT'S NOT UNTIL SUNDAY THAT THE
CONVECTION TRENDS LOWER AS THE FRONT SLOWLY MOVES OFFSHORE.
AVIATION /12Z THURSDAY THROUGH MONDAY/
20/12Z TAFS: VFR CONDITIONS WILL PREVAIL THROUGHOUT THE
FORECAST WITH LIGHT SOUTHWESTERLY WINDS THIS MORNING BECOMING
SOUTHERLY DURING THE AFTERNOON AS THE SEABREEZE MOVES INLAND.
SCATTERED SHOWERS AND THUNDERSTORMS COULD DEVELOP BETWEEN 19Z
AND 22Z IN AND AROUND CHS POSSIBLY LEADING TO TEMPORARY
RESTRICTIONS IN VSBYS AND CEILINGS. STORMS SHOULD SUBSIDE BY THE
EARLY EVENING WITH VFR CONDITIONS PREVAILING OVERNIGHT. WINDS
WILL BE LIGHT OUT OF THE SOUTH-SOUTHWEST.
EXTENDED AVIATION OUTLOOK: A FRONT IN OUR VICINITY WILL BRING
SHOWERS AND THUNDERSTORMS FRIDAY INTO THE WEEKEND, LEADING TO
OCCASIONAL FLIGHT RESTRICTIONS.
MARINE
THERE ARE NO LARGE-SCALE MARINE CONCERNS. MORNINGS WILL GENERALLY
START OUT WITH SOUTH-SOUTHWESTERLY WINDS, INCREASING IN STRENGTH AS
THEY BECOME SOUTHEASTERLY IN THE AFTERNOON, AND BACK TO SOUTH-
SOUTHWESTERLY OVERNIGHT. SEAS MOSTLY IN THE 2-3 FT RANGE. THERE MAY
BE SOME ISOLATED SHOWERS/STORMS THAT MOVE OUT INTO THE WATERS TODAY
AND THURSDAY AFTERNOON, WITH COVERAGE INCREASING FRIDAY.
EXTENDED MARINE: A TYPICAL SUMMERTIME WIND PATTERN IS EXPECTED WITH
WINDS/SEAS THAT ARE BELOW SMALL CRAFT ADVISORY LEVELS. EACH DAY
THERE WILL BE SOME BACKING OF THE WINDS. THEY'LL BE THE STRONGEST
ALONG THE LAND/SEA INTERFACE DUE TO THE SEA BREEZE. EACH NIGHT WINDS
WILL VEER A BIT. SEAS WILL MAINLY BE IN THE 2-3 FT RANGE.
CLIMATE
RECORD HIGH TEMPERATURES:
AUGUST 20:
KCHS: 97/2005
KSAV: 102/1900
RECORD HIGH MINIMUM TEMPERATURES:
AUGUST 20:
KCHS: 78/2017
KCXM: 82/2017
AUGUST 21:
KCHS: 79/2010
KCXM: 82/2023
KSAV: 80/1902
AUGUST 22:
KCHS: 79/2023
AUGUST 24:
KCHS: 76/2010
KCXM: 80/1975
AUGUST 25:
KCHS: 77/1982
AUGUST 26:
KCHS: 78/1998
CHS WATCHES/WARNINGS/ADVISORIES
GA...HEAT ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT THIS EVENING
FOR GAZ217>219-239>241.
SC...HEAT ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT THIS EVENING
FOR SCZ045-148>152.
MARINE...NONE.
BLACK
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