Area Forecast Discussion
Issued by NWS Charleston, SC

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549 FXUS62 KCHS 210000 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 800 PM EDT Tue May 20 2025 .SYNOPSIS... A cold front will push offshore Wednesday afternoon into Wednesday evening, followed by high pressure through the weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Quiet conditions as the boundary layer stabilizes and we return to a southwesterly flow at the surface. Winds will be picking up as the surface pressure gradient increases ahead of an approaching cold front. Low temperatures will be in the 70s.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... Wednesday: A broken line of showers/tstms ahead of an approaching cold front will be in a weakening phase as it approaches the far interior areas prior to daybreak. Some remnant shower/tstm activity could push into interior Southeast Georgia just after daybreak, but confidence in anything meaningful happening is low. Guidance still shows little in the way of significant forcing ahead of the front with model cross sections showing the corridor of strongest UVVs displaced to the north where a passing shortwave/vorticity lobe will traverse North Carolina. Some low-level forcing is noted, likely along/near the frontal surface itself, but the best 850 hPa theta-e pooling will occur south of I-16 during peak heating and this is where the best overlap of instability and theta-e will occur. Given the westerly low-level flow ahead of the front within an environment without any strong forcing mechanisms, it is unclear exactly how much coverage of showers/tstms will occur during the afternoon hours and its very possible convection will remain largely absent through FROPA. A blend of the latest HREF and 13z NBM was favored to construct pops, which yields rain chances of 10-30%, highest across the Georgia coastal counties. The front should clear the coast during the evening hours which will end any chance for measurable rain. Modified soundings do show modest to locally strong mixed- based instability within a belt of around 30 kt of 0-6km bulk shear. This could support an isolated severe tstm with damaging winds and large hail, but an organized severe weather event seems highly unlikely at this time. Highs will warm into the lower-mid 90s, a bit cooler at the beaches where a pinned sea breeze will be late to form. Thursday and Friday: A modest cyclonic flow aloft will prevail through the period as high pressure tries to be build into the region. A weak, secondary cold front will push offshore Thursday evening which will help to reinforce the relatively cooler and drier airmass that will filter in on Thursday. The front will pass through dry with no meaningful moisture return occurring prior to is passage. Highs will warm into the upper 80s/lower 90s Thursday with 80s for Friday (maybe even a few upper 70s across the far interior adjacent to the CSRA). Lows Friday morning will drop into the lower 60s well inland to around 70 at the beaches and Downtown Charleston. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Mostly quiet conditions will prevail for much of the extended period. Rain chances will increase slightly Sunday into Monday as a weak warm front lifts north through the area ahead of a developing storm system to the west. Temperatures will start out near to slightly below normal over the upcoming weekend, then begin to recover back to levels slightly above normal. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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00Z TAFs: Mainly VFR. A cold front may bring some showers and thunderstorm on Thursday. But probabilities will be too low to warrant mention in the TAFs. Additionally, gusty winds are expected late in the TAF time period. Extended Aviation Outlook: There are no concerns with a >50% confidence level.
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&& .MARINE...
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Tonight: S winds will veer to the SW overnight. Seas will average 2-3 ft. Wednesday: Southwest winds will increase ahead of an approaching cold front. Winds could get as high as 15-20 kt over the South Santee-Edisto Beach nearshore leg and Charleston Harbor during the afternoon hours. Gusts could get close to 25 kt, but its duration is somewhat uncertain. For this reason, a Small Craft Advisory has not been issued. The need for an advisory will be reevaluated overnight. Winds will shift offshore during the evening hours as a cold front shifts offshore. Seas will build 2-3 ft, except 4-5 ft over the South Santee-Edisto Beach nearshore leg. Thursday through Sunday: There are no major concerns. Offshore winds will turn back more southwesterly Thursday before returning offshore Thursday night as a reinforcing cold front shifts offshore. Offshore winds will persist through Friday before turning northerly Saturday ahead of a developing warm front. Winds will then veer southerly Sunday as the warm front lifts north.
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&& .CLIMATE...
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Record High Minimum Temperatures: May 20: KCHS: 72/2022 KCXM: 76/2022 KSAV: 73/1896 May 21: KCHS: 74/2022 KCXM: 78/1998 KSAV: 74/2017
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&& .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE...