059
FXUS62 KCHS 011022
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
622 AM EDT SAT AUG 1 2026
WHAT HAS CHANGED
THE AVIATION SECTION WAS UPDATED FOR THE 12Z TAF CYCLE.
KEY MESSAGES
- 1) THERE IS RISK FOR LOCALLY HEAVY RAINFALL AND ISOLATED FLASH
FLOODING ACROSS SOUTHEAST GEORGIA INTO THE WESTERN SOUTH
CAROLINA LOWCOUNTRY THIS AFTERNOON AND EVENING. A FEW STRONG
TO MARGINALLY SEVERE THUNDERSTORMS ARE POSSIBLE.
- 2) SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL BRING
THE POTENTIAL FOR HEAVY RAINFALL, LOCALIZED FLOODING, AND/OR
GUSTY WINDS SUNDAY THROUGH EARLY NEXT WEEK.
DISCUSSION
KEY MESSAGE 1: THERE IS RISK FOR LOCALLY HEAVY RAINFALL AND
ISOLATED FLASH FLOODING ACROSS SOUTHEAST GEORGIA INTO THE
WESTERN SOUTH CAROLINA LOWCOUNTRY THIS AFTERNOON AND EVENING. A
FEW STRONG TO MARGINALLY SEVERE THUNDERSTORMS ARE POSSIBLE.
THE UPPER FLOW WILL BECOME INCREASINGLY CYCLONIC THROUGH THE DAY
AS A POWERFUL UPPER LOW DIGGING ACROSS MID-MISSISSIPPI VALLEY
PROPAGATES INTO THE WESTERN OHIO VALLEY BY TONIGHT. AT THE
SURFACE, A WEAK WARM FRONT EXTENDING ACROSS PARTS OF THE
LOWCOUNTRY INTO THE MIDLANDS WILL MEANDER NORTH THROUGH THE DAY
PLACING ALL OF SOUTHEAST SOUTH CAROLINA AND SOUTHEAST GEORGIA
SOLIDLY WITHIN THE WARM SECTOR OF THE MATURING CYCLONE ASSOCIATED
WITH THE UPPER LOW. A FEW MORNING SHOWERS COULD BRUSH PARTS OF
THE LOWER SOUTH CAROLINA COAST THROUGH DAYBREAK, BUT THE BETTER
CHANCES OR SHOWERS/TSTMS WILL HOLD OFF UNTIL LATER THIS
AFTERNOON AND EVENING AS THE SEA BREEZE MOVES INLAND AND POTENT
SHORTWAVE ENERGY APPROACHES FROM THE NORTHWEST. FORCING WITH
THIS FEATURE COUPLED WITH MODEST INSTABILITY WILL SUPPORT
SCATTERED TO NUMEROUS SHOWERS/TSTMS BY MID-LATE AFTERNOON WITH
ACTIVITY LIKELY CONCENTRATING ACROSS MUCH OF SOUTHEAST GEORGIA
INTO THE FAR WESTERN SOUTH CAROLINA LOWCOUNTRY BY EARLY
EVENING.
PWATS ARE FORECAST TO SURGE TO 2.35-2.50" WHICH WILL BE NEAR
DAILY MAXIMUMS FOR 1 AUGUST PER SPC SOUNDING CLIMATOLOGY. WHILE
850-200 HPA FLOW WILL REMAIN OUT OF THE SOUTHWEST AT AROUND 10
KT SUGGESTS STORM MOTIONS SHOULD REMAIN SOMEWHAT PROGRESSIVE,
MESOSCALE BOUNDARY COLLISIONS WILL LIKELY AUGMENT THE STEERING
ENVIRONMENT SOMEWHAT WITH THE POTENTIAL FOR TRAINING AND/OR
BACK-BUILDING INCREASING WITH TIME AS CAPE PROFILES ELONGATE AND
NARROW (A CLASSIC HEAVY RAIN SIGNATURE). GIVEN THE NEAR RECORD
NET MOISTURE VALUES, IMPRESSIVE HOURLY RAINFALL RATES WILL
LIKELY OCCUR WITH THE 01/00Z HREF AND REFS BOTH SUGGESTING
LOCALIZED AMOUNTS IN EXCESS OF 3-4"/3-HR ARE POSSIBLE
(NEIGHBORHOOD PROBABILITIES FOR >3" RUNNING 30-50%), MAINLY
ACROSS INTERIOR PORTIONS OF SOUTHEAST GEORGIA INTO ALLENDALE AND
HAMPTON COUNTIES IN SOUTHEAST SOUTH CAROLINA. THIS COULD LEAD
TO POCKETS OF FLASH FLOODING EVEN WITH FAIRLY HIGH 1-HR AND
3-HR FLASH FLOOD GUIDANCE VALUES IN PLACE. THE NEED FOR A FLOOD
WATCH FOR THE ABOVE MENTIONED AREAS WAS CONSIDERED, BUT THE
DECISION WAS MADE TO HOLD OFF GIVEN THE DEGREE OF FLASH FLOODING
SHOULD REMAIN FAIRLY ISOLATED AND LIKELY LIMITED TO THE BASE-
LEVEL CATEGORY. COORDINATED WITH WPC TO INTRODUCE A SLIGHT RISK
ACROSS THE FAR INTERIOR AREAS THROUGH TONIGHT FOR THE DAY 1 WFO
EXCESSIVE RAINFALL GUIDANCE. RIGHT NOW, THE CORRIDOR OF HEAVIEST
RAINS LOOK TO REMAIN WEST OF BOTH THE CHARLESTON AND SAVANNAH
METRO AREAS. IN ADDITION TO THE RISK FOR HEAVY RAINFALL AND
ISOLATED FLASH FLOODING, A STRONG TO MARGINALLY SEVERE TSTM
COULD OCCUR JUST ABOUT ANYWHERE THIS AFTERNOON AND EVENING WHERE
UPDRAFTS CAN BECOME ENHANCED, MOST LIKELY NEAR MESOSCALE
BOUNDARY COLLISIONS.
CONVECTION SHOULD WANE DURING THE EVENING HOURS, BUT THERE ARE
SIGNALS THAT A SECONDARY WAVE COULD SPREAD NORTH THROUGH THE
REGION EARLY SUNDAY MORNING AND MORE SHORTWAVE ENERGY APPROACHES
AND INTERACTS WITH A CONTINUED VERY MOIST AND UNSTABLE ATMOSPHERE.
KEY MESSAGE 2: SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS
WILL BRING THE POTENTIAL FOR HEAVY RAINFALL, LOCALIZED FLOODING,
AND/OR GUSTY WINDS SUNDAY THROUGH EARLY NEXT WEEK.
AS A MID-LEVEL TROUGH SETTLES OVER THE EASTERN CONUS SUNDAY, A
COLD FRONT WILL INCH TOWARD THE FORECAST AREA SUNDAY INTO MONDAY
BEFORE STALLING. THIS PATTERN, COMBINED WITH A VERY MOIST
AIRMASS, WILL SUPPORT SCATTERED TO NUMEROUS SHOWERS AND
THUNDERSTORMS EACH DAY THROUGH EARLY NEXT WEEK. FORECAST
SOUNDINGS INDICATE PWAT VALUES INCREASING TO AROUND 2.2 INCHES
BY SUNDAY MORNING AND REMAINING BETWEEN 2.2 AND 2.4 INCHES
THROUGH MONDAY AND POSSIBLY TUESDAY. THESE CONDITIONS WILL FAVOR
EFFICIENT RAINFALL PRODUCTION AND HIGH RAINFALL RATES,
INCREASING THE POTENTIAL FOR LOCALIZED FLOODING. WHILE MOST
FLOODING IMPACTS SHOULD REMAIN MINOR, REPEATED HEAVY DOWNPOURS
OR TRAINING CONVECTION OVER URBAN AREAS SUCH AS THE CHARLESTON
AND SAVANNAH METRO AREAS COULD WARRANT FLOOD ADVISORIES OR FLASH
FLOOD WARNINGS.
WITH REGARDS TO THE SEVERE POTENTIAL, THE PRIMARY LIMITING
FACTOR WILL BE MODEST INSTABILITY, WITH FORECAST SOUNDINGS
SUGGESTING SBCAPE PEAKING NEAR 1500 J/KG AS WIDESPREAD CLOUD
COVER LIMITS DIURNAL HEATING. DESPITE THIS, THE COMBINATION OF
DEEP MOISTURE AND FORCING ALOFT AS LOBES OF VORTICITY ROTATE
AROUND THE UPPER TROUGH, SHOULD SUPPORT AT LEAST SCATTERED
THUNDERSTORMS, WITH THE STRONGEST CELLS CAPABLE OF PRODUCING
ISOLATED DAMAGING WIND GUSTS. SUNDAY APPEARS TO HAVE THE
GREATEST THREAT FOR ISOLATED STRONG TO SEVERE STORMS DUE TO THE
PROXIMITY OF THE APPROACHING FRONT PROVIDING AN ADDITIONAL
SOURCE OF FORCING, BUT ALSO INCREASING SHEAR VALUES TO AROUND 15
KT. THIS COULD COULD ALLOW SOME STORMS TO BECOME SOMEWHAT
ORGANIZED, ESPECIALLY INLAND.
AVIATION /10Z SATURDAY THROUGH WEDNESDAY/
01/12Z TAF DISCUSSION:
KCHS/KJZI: VFR SHOULD PREVAIL FOR MUCH OF THE 12Z TAF PERIOD,
TRENDING TO MVFR PRIOR TO DAYBREAK SUNDAY THE RISK FOR
SHOWERS/TSTMS SHOULD GENERALLY REMAIN WEST OF BOTH TERMINALS
THIS AFTERNOON/EVENING, BUT COULD GET CLOSE ENOUGH TO JUSTIFY A
PROB30 AT KCHS FROM ROUGHLY 19-21Z UNTIL THE SEA BREEZE CAN PUSH
FARTHER TO THE WEST. A SECONDARY AROUND OF SHOWERS/TSTMS WILL
MOVE IN FROM THE SOUTH PRIOR TO DAYBREAK SUNDAY, WHICH COULD
PRODUCE MVFR CONDITIONS. A PROB30 GROUP WAS INTRODUCED 09-12Z AT
BOTH KCHS AND KJZI TO ADDRESS POSSIBILITY.
KSAV: VFR THIS MORNING WITH AN INCREASING RISK FOR TSTM IMPACTS
BY MID-AFTERNOON. A TEMPO GROUP FOR MVFR CONDITIONS IN TSRA
WERE INTRODUCED 21-00Z. CONDITIONS COULD CERTAINLY END UP LOWER
TO IFR OR EVEN LIFR LEVELS AT TIMES, BUT PINNING THAT DOWN THIS
FAR OUT IS NEARLY IMPOSSIBLE. CONDITIONS WERE LIMITED TO MVFR
FOR NOW. IN ADDITION, GUSTY WINDS COULD ACCOMPANY THE TSTMS, BUT
TO WHAT DEGREE IS UNCERTAIN. FURTHER REFINEMENTS WILL MOSTLY
CERTAINLY BE MADE AS THE DAY PROGRESS AND SHORT TERM TRENDS
BECOME MORE APPARENT. A SECONDARY AROUND OF SHOWERS/TSTMS WILL
MOVE IN FROM THE SOUTH PRIOR TO DAYBREAK SUNDAY, WHICH COULD
PRODUCE MVFR CONDITIONS. A PROB30 GROUP WAS INTRODUCED 09-12Z AT
BOTH KCHS AND KJZI TO ADDRESS POSSIBILITY.
EXTENDED AVIATION OUTLOOK: PERIODIC FLIGHT RESTRICTIONS ARE
EXPECTED IN SHOWERS AND THUNDERSTORMS THROUGH EARLY NEXT WEEK.
LOCALLY HEAVY RAINFALL MAY PRODUCE BRIEF IFR OR LOWER VISIBILITY
RESTRICTIONS.
MARINE
THROUGH TONIGHT: THERE ARE NO CONCERNS. SOUTH TO SOUTHEAST WINDS
THIS MORNING WILL PERSIST TODAY, THEN BECOME MORE SOUTH TO
SOUTHWEST TONIGHT. WINDS WILL REMAIN 15 KT OR LESS TODAY, THEN
INCREASE TO 15 KT TO 15-20 KT TONIGHT AS NOCTURNAL SURGING TAKES
HOLD. SEAS 1-3 FT TODAY WILL BUILD TO 2-4 FT TONIGHT.
SUNDAY THROUGH THURSDAY: THE PRESSURE GRADIENT WILL STRENGTHEN
SUNDAY AS BROAD LOW PRESSURE DEVELOPS INLAND WITH AN APPROACHING
FRONT AND HIGH PRESSURE REMAINING IN THE ATLANTIC. SOUTHWESTERLY
WINDS WILL INCREASE DURING THE AFTERNOON, WITH FREQUENT GUSTS
BETWEEN 25 AND 30 KT EXPECTED ACROSS THE LOCAL WATERS. IN
ADDITION, WAVE HEIGHTS ARE FORECAST TO INCREASE TO 4 TO 7 FEET
SUNDAY EVENING. SMALL CRAFT ADVISORIES HAVE BEEN ISSUED FOR THE
NEARSHORE MARINE ZONES OUT TO 20 NM AND THE OUTER GEORGIA WATERS
FROM 20-60 NM, AS WELL AS THE CHARLESTON HARBOR. CONDITIONS
SHOULD GRADUALLY IMPROVE MONDAY NIGHT, WITH BENIGN WIND AND SEA
CONDITIONS EXPECTED FOR TUESDAY THROUGH THE REST OF THE PERIOD.
RIP CURRENTS: GUSTY SOUTHWEST WINDS COMBINED WITH A 7 TO 8
SECOND SWELL WILL SUPPORT AN ELEVATED RIP CURRENT RISK ON
SUNDAY. A MODERATE RISK OF RIP CURRENTS HAS BEEN POSTED FOR THE
SOUTH CAROLINA BEACHES, AND A SIMILAR RISK MAY EVENTUALLY BE
NEEDED ALONG THE SOUTHEAST GEORGIA COAST.
CLIMATE
RECORD HIGH MINIMUM TEMPERATURES:
AUGUST 1:
KCHS: 81/1999
KCXM: 86/1999
KSAV: 79/2020
AUGUST 2:
KCHS: 79/2022
KCXM: 84/1999
KSAV: 80/1886
AUGUST 5:
KCHS: 79/1980
KCXM: 82/1991
KSAV: 80/1883
AUGUST 6:
KCHS: 79/1991
KCXM: 82/2006
KSAV: 80/1899
AUGUST 7:
KCHS: 79/2007
KCXM: 83/2007
KSAV: 80/1879
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM NOON SUNDAY TO 2 AM EDT MONDAY FOR
AMZ340.
SMALL CRAFT ADVISORY FROM NOON SUNDAY TO 2 AM EDT TUESDAY FOR
AMZ360-362.
SMALL CRAFT ADVISORY FROM NOON SUNDAY TO 8 AM EDT MONDAY FOR
AMZ364.
SMALL CRAFT ADVISORY FROM NOON SUNDAY TO NOON EDT MONDAY FOR
AMZ384.
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