AFD_CHS

FXUS62 KCHS 211709 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 1209 PM EST Sun Dec 21 2025

.SYNOPSIS...

High pressure continues to prevail today, with a cold front then expected to dive across the region tonight into Monday. High pressure then returns Tuesday, resulting in above normal temperatures and dry conditions for the remainder of the holiday week.

.NEAR TERM /THROUGH TONIGHT/...

Expect pleasant conditions this afternoon as a surface high pressure builds into the region, with ridging occurring aloft resulting in high temperatures in the mid 60s to lower 70s. As the aforementioned surface high pressure moves in, a cold front moves through later this afternoon. The colder air lags behind the front a couple hours, but as it moves in this evening gusty conditions develop due to a combination of pressure rises and cold air advection. Gusts into the 15 to 25 mph range are expected and with temperatures in the mid 30s to lower 40s, the wind chills dip down into the 30s overnight and early Monday morning.

Lake Winds: Given the unfavorable northeasterly wind direction, expecting winds to remain below critical thresholds, with winds sustained in the 15 to 19 kt range and gusts in the 20 to 24 kt range. This will continue to be monitored, and updated as needed.

.SHORT TERM /MONDAY THROUGH THURSDAY/...

Monday: Surface high pressure will be centered over the Piedmont of North Carolina with high clouds streaming overhead. Low level winds will be gusty at times in the morning hours with the nocturnal low level jet expected to peak around 30 mph with some surface wind gusts of 20 to 25 mph possible. As the day progresses, winds will become less gusty as the low level jet significantly weakens.

In the mid levels of the atmosphere a potent shortwave will be quickly exiting New England with surface high pressure following suite. This means by late Monday, the surface high will already be off of the coast of North Carolina with a coastal trough moving inland over Georgia and South Carolina. No precipitation is forecast with the coastal trough as an uptick in dewpoints (and relative humidity) are the only sensible weather changes forecast. High clouds will be streaming overhead through the day, but mostly sunny skies are still expected with highs in the lower 60s. Monday night expect lows in the lower 40s with some guidance hinting at the potential for fog or stratus development as higher dewpoints surge west.

Tuesday through Thursday: Another mid-level wave will dive southeast across Ontario and Quebec late Tuesday which will spell the end of the surface high pressure and the ageostrophic convergence comes to an end. Expect warming temperatures Tuesday as the air mass quickly starts to modify. To put it into perspective, 1000/850mb thicknesses Monday are forecast to be around 1340m, and by Tuesday afternoon are expected to be 1365 - 1370m. This means temperatures will rapidly rise into the 50s by mid Tuesday morning with highs around 70 degrees forecast. Temperatures will further warm into the lower to mid 70s for Wednesday and Thursday. The latest run of the NBM shows a high degree of confidence with these temperatures as the interquartile range (IQR) for highs Wednesday - Friday is only 2 - 4 degrees. No precipitation is forecast. &&

.LONG TERM /THURSDAY NIGHT THROUGH SATURDAY/...

The forecast for Friday remains high confidence with above normal temperatures continuing. Forecast confidence starts to decrease Saturday thanks to a potent mid-level low just east of the Hudson Bay. This low could potentially push a strong cold front through the area Saturday with temperatures returning to more seasonable values.

However, model guidance varies with the strength and position of this low. Some ensemble members show a stronger mid-level low and slower movement of the wave northeast, while other members show a much weaker wave and quicker movement to the northeast. The deeper wave would favor near normal to slightly below normal temperatures Saturday into Sunday, while the less amplified wave and faster movement would favor seasonable temperatures again moderating to above normal. Taking a look at the latest WPC Cluster Analysis reveals around 65% of model solutions favoring the faster/ less amplified pattern with 20% showing a highly amplified solution and around 15% advertising a blend between these solutions. Either way, no precipitation is forecast.

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...

18Z TAFs - VFR expected for the rest of the day, with variable winds as a front moves through. Overnight, north-northeasterly winds become increasingly breezy as a cold front moves in. Along the front, can't rule out some isolated MVFR cigs, but cloud coverage itself is looking to be rather meager.

Monday and Tuesday: Mostly VFR conditions. Two periods of MVFR cigs or lower are possible with the first being Monday morning behind the cold front. The second chance will be Tuesday morning as moisture rich air returns to the region. These restrictions will be possible due to fog or stratus development.

Wednesday and Thursday: VFR conditions.

.MARINE...

Through Tonight: Tranquil conditions expected for the rest of the afternoon hours. This evening into the overnight period, north- northeasterly winds strengthen with wave heights similarly building. Confidence remains high for wind gusts greater than 25 knots for all near and offshore waters, keeping the Small Craft Advisory in good shape. The exception is for the Charleston Harbor where winds are borderline but currently expected to remain below advisory criteria. This will continue to be monitored, and updated as needed. As for wave heights, they'll be building towards 5 to 6 feet by daybreak, with the highest waves remaining 10+ nm away from the coast.

Monday and Tuesday: Breezy northeast winds behind a cold front are expected Monday morning with gusts 25 to 30 kt. Seas 4 to 7 ft. The northeast winds will then start to relax late Monday morning with seas slowly starting to come down Monday afternoon. All nearshore water Small Craft Advisories will be done by late Monday evening with the offshore Georgia waters remaining through Tuesday afternoon due to the potential for 6 ft seas.

Wednesday and Thursday: High confidence in no marine headlines. Wind gusts 15 kt or less with seas 2 to 3 ft.

.CHS WATCHES/WARNINGS/ADVISORIES...

GA...None. SC...None. MARINE...Small Craft Advisory from 9 PM this evening to midnight EST

Monday night for AMZ350. Small Craft Advisory from midnight tonight to midnight EST Monday night for AMZ352-354. Small Craft Advisory from 9 PM this evening to 6 PM EST Tuesday for AMZ374.

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