textproduct: Charleston

WHAT HAS CHANGED

Key Message 1 has been introduced for fog potential tonight. Minor changes to Key Message 2 have been made for warming weather through early next week. The Aviation Section has been updated for the 18Z TAF issuance. The Marine Section has been updated to include sea fog potential tonight into late week.

KEY MESSAGES

- 1) Areas to widespread fog anticipated across much of the Southeast South Carolina and Southeast Georgia tonight into Thursday morning.

- 2) Unseasonably warm temperatures are expected through early next week with increasing rain chances beginning this weekend.

DISCUSSION

KEY MESSAGE 1: Areas to widespread fog anticipated across much of the Southeast South Carolina and Southeast Georgia tonight into Thursday morning.

The region will remain along the western periphery of high pressure extending across the Atlantic today through Thursday morning, setting up the stage for an inversion to develop quickly this evening, then persisting through a few hours after daybreak. The pattern will be quite similar to the previous night with sfc winds that decouple early evening, light 1000 mb geostrophic winds from the south and a bulk of guidance indicating favorable condensation pressure deficits as well as sfc dewpts in the upper 50s during the second half of the night through daybreak. Given the setup, another round of areas to widespread fog is possible, with many areas potentially experiencing dense fog a few hours prior to and post daybreak until the inversion breaks mid-late Thursday morning. Latest HREF guidance indicates a 40-60% of vsbys reduced to 1/4 mile (dense fog) across parts of Southeast South Carolina and Southeast Georgia late night/around daybreak Thursday. Special Weather Statements and/or Dense Fog Advisories could eventually be needed

KEY MESSAGE 2: Unseasonably warm temperatures are expected through early next week with increasing rain chances beginning this weekend.

The forecast area will remain west of strong H5 ridge from Thursday through Wednesday. In fact, NAEFS indicates that mid-level ridge will generally remain two units of standard anomaly through the period. At the sfc, high pressure centered over the western Atlantic will provide the region with steady ESE winds, supporting mild llvl thicknesses across the forecast area. Temperatures on Thursday through Saturday will peak in the upper 70s to mid 80s across SE GA and the SC Lowcountry. Sunday through Wednesday, highs will favor values in the low to mid 80s, with upper 80s possible across SE GA on Sunday and Monday.

Conditions are forecast to remain dry on Thursday and Friday. Generally, diurnal isolated to scattered showers, with occasional thunderstorms, expected from Saturday through Wednesday. Given ESE winds and unseasonably warm temperatures, convection may initiate or focus along afternoon and evening sea breezes. No severe weather expected.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR conditions will prevail at CHS/JZI/SAV terminals through at least 00Z this evening. Guidance suggests MVFR conditions returning at all terminals by 06Z Thursday, possibly a few hours earlier, then continuing to deteriorate to IFR/LIFR by around 09Z Thursday due to low clouds and/or fog. IFR conditions should then prevail at all terminals until the inversion breaks around 14Z Thursday. VFR conditions quickly return thereafter and persist through 18Z Thursday.

Extended Aviation Outlook: Restrictive ceilings are possible overnight into the early morning hours each night through late week due to low stratus/fog.

MARINE

Today and Tonight: High pressure will remain the dominant weather feature across local waters, extending across the western Atlantic through Thursday morning. Winds/seas are expected to remain below Small Craft Advisory levels, with sfc winds becoming more onshore around 10 kt or less and seas generally in the 2-4 ft range nearshore to 4-5 ft across offshore Georgia waters. The main issue should arrive during overnight hours, when the risk for sea fog returns as upper 50/lower 60 dewpts result across local waters while 1000 mb geostrophic winds are light from the south and southeast sfc winds remain light through the night. Dense Fog Advisories could eventually be needed over a portion of local waters overnight into early morning hours Thursday.

High pressure will remain centered over the western Atlantic through the weekend. Winds should favor a ESE direction Thursday through Saturday, with speeds 10 kts or less. Winds may shift from the south by Sunday. Both winds and seas are expected to stay below Small Craft Advisory levels.

Sea fog will continue be a recurring concern this week as warm, moist air moves over the cooler shelf waters. Periods of fog may redevelop frequently and could persist through the weekend. The fog could become dense at times, reducing visibility for mariners. Additional Marine Dense Fog Advisories could be needed in the coming days. Winds are then forecast to shift out of the south/southwest by early next week, which could prolong the sea fog threat into that period.

CHS WATCHES/WARNINGS/ADVISORIES

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