AFD_CHS

FXUS62 KCHS 201726 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 1226 PM EST Sat Dec 20 2025

.SYNOPSIS...

High pressure will prevail over the weekend, with another cold front forecast to impact the area Monday.

.NEAR TERM /THROUGH TONIGHT/...

Quiet weather will dominate across the SC Lowcountry and SE GA through this afternoon and tonight as surface high pressure holds strong.

Zonal flow will dominate in the mid and upper levels of the atmosphere today, with slight ridging present over the SE states at 850hPa according to the 12Z SPC upper air analysis. Surface analysis from 12Z shows high pressure centered over the southeastern states. As the afternoon progresses the center of high pressure will drift eastward towards the local forecast area. Blended guidance continues to show high temperatures in the low 60s, however given that locations across the region are already around 60, temperatures will likely top off in the mid 60s with upper 60s possible across SE GA.

Tonight will feature winds going light and variable as the center of high pressure resides overhead. Given light winds and clear skies another radiational cooling night is forecast, although temperatures aren't expected to dip quite as low as Friday night/Saturday morning. Lows tonight are forecast to reach into the mid 30s inland with low to mid 40s along the coastal counties.

.SHORT TERM /SUNDAY THROUGH TUESDAY/...

Quasi-zonal upper level flow and a weak surface high pressure will continue the quiet conditions, with afternoon highs in the mid 60s to lower 70s across the area. A weak cold front pushes through during the afternoon hours, though the colder air lags behind overnight into Monday. Overnight lows in the upper 30s to mid 40s expected.

Upper level ridging pushes a surface high pressure onto the east coast north of the area, increasing the surface pressure gradient. This will result in breezy conditions building overnight into Monday, with gusts into the teens to lower 20s throughout the day. With the fresh influx of cooler air, afternoon temperatures will be below normal in the upper 50s to lower 60s.

Winds decrease overnight into Tuesday as the surface high pressure weakens and moves into the Atlantic. As they swing around to become out of the south-southwest, warmer temperatures will be advected back across the region with afternoon highs in the upper 60s to mid 70s expected.

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...

The aforementioned upper level ridge continues into the extended, with another surface high pressure expected to move down into the region end of this holiday week. This will result in above normal temperatures and dry conditions. Afternoon highs look to be in the upper 60s to mid 70s range.

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...

Prevailing VFR through the 18Z TAF period. As the center of high pressure shifts over the forecast area winds tonight are forecast to go light and variable.

Extended Aviation Outlook: VFR expected to prevail through Sunday, with a period of MVFR cigs possible Monday morning in the wake of a frontal passage. Northeasterly winds are expected to be breezy on Monday, with gusts in the 14-18 kt range.

.MARINE...

Today and tonight: Prevailing high pressure will yield northeast winds 5 to 10 kt with transient gusts up to 15 kt across all waters. Seas 2 to 4 ft.

Sunday - Monday: Tranquil conditions continue into Sunday. Overnight into Monday, north-northeasterly winds strengthen with wave heights similarly building. Confidence for wind gusts greater than 25 knots is high for all near and offshore waters, with both the HREF and REFS showing 90%+ probabilities for wind gusts greater than 25 knots, though both ensembles show very low probabilities (<10%) for Gale force winds. For the Charleston Harbor, probabilities for these winds is in the 60-80% range, highest near the entrance and decreasing into the harbor. Wave heights of 6-8 feet are also expected to build into the region overnight into Monday. Thus, a Small Craft Advisory will be needed for the early overnight hours into Monday, though unsure if the Charleston Habor will need to be included, with advisory level winds and seas tapering off overnight into Tuesday. Some indications that the Savannah to Altamaha Sound water from 20-60nm out may hang onto the SCA conditions until late Tuesday afternoon or evening.

Tuesday - Wednesday: No high confidence marine concerns at this time.

.CHS WATCHES/WARNINGS/ADVISORIES...

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

NEAR TERM...CPM SHORT TERM...APT LONG TERM...APT AVIATION...APT/CPM MARINE...APT/CPM