Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
020 FXUS62 KCHS 202324 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 724 PM EDT Thu Aug 20 2026 .WHAT HAS CHANGED... All Key Messages and sections were updated. && .KEY MESSAGES... - 1) Heat remains a concern into Friday. - 2) Increased risk for showers and thunderstorms into the weekend. && .DISCUSSION... KEY MESSAGE 1: Heat remains a concern into Friday. Friday: Mid-level troughing will dominate the east coast while a weak surface front approaches the local forecast area. Temperatures are still forecast to be above normal (mid 90s), but heat index values look to fall short of Heat Advisory criteria across most of the region. The only locations that could see heat index values of 108 or greater would be along the coastal counties, especially in SC. However, given the increased coverage of precipitation there is little confidence in hitting the heat advisory criteria. Therefore, one has not been issued at this juncture. This weekend into early next week: Temperatures will cool slightly, with highs in the low 90s (still above normal for this time of year). The extended forecast looks to be heat-headline free with heat index values topping out in the 100-103 range each afternoon. KEY MESSAGE 2: Increased risk for showers and thunderstorms into the weekend. Friday: A more appreciable change in the pattern is expected on Friday as this mid-lvl ridge finally breaks down and broad troughing begins to build across the eastern half of the CONUS. Several embedded shortwaves are forecast to round the base of this trough while a slow-moving surface front approaches the region from the west and northwest. This will provide greater convection coverage than the previous day (Thursday). Scattered showers and thunderstorms are expected to develop mid- day/early afternoon, before becoming numerous and widespread in the afternoon/evening hours. Expect moisture to increase substantially ahead of this approaching front, with PWAT values forecast to rise above 2 inches (near the 90th percentile for late August at KCHS). Despite somewhat greater cloud cover and temperatures several degrees lower than the previous couple days, sufficient heating should still yield moderate to locally strong instability. The combination of instability, abundant moisture, and appreciable DCAPE values will support another risk for strong to severe storms. Thus, the SPC has highlighted the majority of the region in a Marginal Risk (Level 1/5) for severe thunderstorms on Friday. Again, damaging wind gusts will be the greatest threat (within the stronger storms), along with localized flooding possible. Saturday: Another scattered to numerous shower and thunderstorm day as the front stalls near the region. The exact corridor of greatest coverage is less certain and will depend heavily on the frontal position. Strong wind gusts remain possible again, but training storms and localized flash flooding could become an increasing concern given PWATs near 2 inches and storms potentially tracking parallel to the boundary. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... 21/00z TAFs: KCHS/KJZI/KSAV: VFR for much of the period. Risk for showers/tstms will increase late in the afternoon. PROB30s were introduced after 21z to account for this at all terminals. Extended Aviation Outlook: A front in our vicinity will bring showers and thunderstorms Friday into the weekend, leading to occasional flight restrictions. && .MARINE... Tonight: No significant marine concerns are expected across the local waters through tonight, with winds and seas remaining below Small Craft Advisory criteria. A typical summertime pattern will dominate with generally south-southwesterly flow around 10 kt and seas 2-3 ft. Friday through Tuesday: Outside of showers and thunderstorms, overall marine conditions will remain fairly typical for late summer, with south-southwesterly winds generally 5-15 kt with seas ranging from 2-4 ft through early next week. The main concern for mariners will be the increasing thunderstorm threat through the weekend as a front approaches and then stalls nearby. && .CLIMATE... Record High Minimum Temperatures: 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...None. SC...None. MARINE...None. && $$