textproduct: Charleston

WHAT HAS CHANGED

A Marine Dense Fog Advisory has been issued for all of the nearshore waters through 10 AM, not including the Charleston Harbor at this time.

KEY MESSAGES

- 1) Areas to widespread fog anticipated across the majority of southeast South Carolina and southeast Georgia tonight into early this morning.

- 2) Unseasonably warm temperatures continue into the middle of next week, with increasing rain chances during the later half of this weekend.

DISCUSSION

KEY MESSAGE 1: Areas to widespread fog anticipated across the majority of southeast South Carolina and southeast Georgia tonight into early this morning.

Given the above normal temperatures observed on Thursday, fog is once again a threat across the region tonight into early this morning. Condensation pressure deficits from the HRRR are very supportive of fog developing across the SC Lowcountry and Southeastern GA. Other guidance continues to show solid support for fog, however this is taken with a grain of salt. It appears that a lot of the Hi-Res models are not initializing well, with almost all guidance showing that there should be ongoing dense fog, which there is not. A Special Weather Statement or Dense Fog Advisory may be required at some point for some locations. While fog is expected to form, the onset timing and intensity is a very low confidence forecast. The fog that is able to develop will likely mix out very quickly after sunrise.

KEY MESSAGE 2: Unseasonably warm temperatures are expected through the middle of next week.

Deep-layer high pressure will continue to strengthen over the Western Atlantic today and persist into early next week. Ensemble situational awareness tables show that geopotential heights at various levels peak at or above the 90th percentile wrt climatology over the coming days, leading to well above normal temperatures in the upper 70s to mid 80s. Despite sufficient moisture, persistent subsidence associated with this pattern will suppress majority of shower/thunderstorm development. The exception is for areas well west of the I-95 corridor, as high resolution convection allowing models (CAMs) do suggest an isolated shower/thunderstorm may be possible on the edge of the ridge axis both Friday afternoon and again Saturday afternoon.

As the ridge begins to flatten Sunday, afternoon/evening rain chances will expand eastwards to include the rest of the forecast area, partly due to a diurnally formed sea-breeze. A series of weak shortwaves move through Sunday into Monday, with an additional wave possible on Tuesday, which could provide additional forcing for showers and thunderstorms as deep moisture remains in place. No severe weather or flooding expected at this time.

Well above normal temperatures linger into the second half of next week. The latest forecast ties record warm low temperatures early next week, with afternoon high temperatures remaining shy of daily records.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

VFR will start off the 06Z TAF period at KCHS/KJZI/KSAV. Fog is expected to impact the terminals later tonight and into early this morning, bringing reduced cigs/vsbys. Conditions will improve quickly after sunrise, with VFR prevailing through the remainder of the day.

Extended Aviation Outlook: Restrictive ceilings are possible overnight into the early morning hours each night through the weekend due to low stratus/fog. Chances for scattered showers and thunderstorms return Sunday afternoon/evening, leading to chances for temporary flight restrictions.

MARINE

Satellite imagery shows that sea fog is starting to develop off of the coastline as of 1:30AM. Given the strong guidance support for the continuing development of the sea fog a Marine Dense Fog Advisory has been issued for all nearshore waters through 10AM. The advisory does not currently include the Charleston Harbor, although it is possible it will need to be expanded to include the harbor later tonight.

High pressure will remain centered over the western Atlantic into the weekend, continuing easterly/southeasterly flow on Saturday. Winds are then expected to shift out of the southwest Sunday through early next week, though may begin to exhibit diurnally driven fluctuations. Both winds and seas are expected to stay below Small Craft Advisory levels.

Sea fog will continue to be a recurring concern as warm, moist air moves over the cooler shelf waters. Periods of fog may redevelop frequently and could persist through the weekend, remaining possible into early next week. The fog could become dense at times, reducing visibility for mariners. Additional Marine Dense Fog Advisories could be needed.

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...None. MARINE...Dense Fog Advisory until 10 AM EST this morning for AMZ350-352- 354.