textproduct: Charleston

WHAT HAS CHANGED

All sections updated.

KEY MESSAGES

- 1) Unsettled weather will continue through this weekend. Locally heavy rainfall is possible.

DISCUSSION

KEY MESSAGE 1: Unsettled weather will continue through this weekend. Locally heavy rainfall is possible.

Rest of Today: The region is currently positioned within an area of troughing aloft, sandwiched by two areas of high pressure, one over western Texas and the other over Bermuda. At the surface a stationary front was analyzed by WPC over the SC Midlands. Between the troughing aloft and the front in the vicinity the stage has been set for scattered to numerous convection this afternoon. However, thick cloud cover across the entire forecast area from this morning has lingered into this afternoon. These clouds will likely limit convection this afternoon, with storms relying on outflow boundaries for initiation. The environment across the region is very moist, with the KCHS 12Z RAOB Sounding setting a new SPC Climatology daily maximum of 2.31". Heavy rainfall cannot be ruled out with any storm that is able to develop this afternoon. There is a minimal severe risk this afternoon as SPC Mesoanalysis only depicts around 300-400 J/kg of DCAPE across the region. However, a strong wind gust cannot be completely ruled out this time of year.

Tonight: Convection is expected wane fairly quickly this evening. As inland areas cool and low-level winds back, a corridor of modest convergence is forecast to develop along mainly the lower South Carolina coast from roughly midnight through daybreak Sunday. With such a warm and moist atmosphere in place, it will not take much to initiate additional showers/tstms during the early morning hours. There is a potential for some convective training to occur within the plume of PWATS >2" and the 29/00z HREF are showing some elevated probabilities for >1"/3-hr in the vicinity of Downtown Charleston. This will need to be monitored as a quick inch in Downtown Charleston is known to cause flash flooding.

Sunday: Surface high pressure will re-establish early Sunday morning after the stationary front dissipates. Diurnal heating will yield moderate instability, with SBCAPE values 2500-3000 J/kg. However, weak environmental flow aloft will limit storm organization, keeping the overall threat for severe weather low. Convection will remain largely mesoscale-driven, with the sea breeze boundary primarily initiating isolated afternoon showers and thunderstorms. There remains a threat for localized heavy rain/flooding Sunday, but not as widespread as previous days' due to the anticipated lack in coverage. Forecast soundings reflect a classic heavy-rainfall profile with PWATs 2.1-2.2 inches and weak steering aloft (~10 kt). Because these storms will move relatively slowly, rain rates possibly exceeding 1 to 2 inches per hour could dump heavy rain in a short window. To note, HREF probabilities currently only show a couple spots with a 20-40% chance of 2+ inches of rain. Nonetheless, minor flooding is possible in low-lying and flood-prone/urban areas.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

MVFR cigs have held strong at KCHS/KJZI/KSAV through the start of the 18Z TAF period. Cigs are forecast to lift to VFR levels later this afternoon, with showers and thunderstorms impacting all terminals. However, this is a very low confidence forecast. The lingering MVFR cigs will likely limit the overall coverage of convection, so the longer MVFR cigs last the lesser the threat for thunderstorms. Showers/tstorms are forecast to wane with nightfall, but another round of precipitation is possible late tonight/early Sunday morning at KCHS/KJZI.

Extended Aviation Outlook: Brief flight restrictions are possible within showers and thunderstorms, especially during the afternoons.

MARINE

Through Tonight: Onshore winds will linger through tonight with directions near the beaches likely backing more east to northeast late. Speeds will remain less than 15 kt through tonight with seas 1-3 ft.

Sunday through Thursday: Expect benign marine conditions overall. Light and variable prevailing flow will shift onshore each afternoon as the sea breeze circulation develops along the coast.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...None.