AFD_CHS

FXUS62 KCHS 310550 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 1250 AM EST Wed Dec 31 2025

.SYNOPSIS...

High pressure will prevail for the remainder of the week. A low pressure system will move through on Saturday, followed by a cold front later this weekend.

.NEAR TERM /THROUGH TONIGHT/...

Through Daybreak: The boundary layer decoupled quickly Tuesday evening, but has started to show signs to recoupling again across parts of Southeast Georgia into far southern South Carolina in response to a tightening pressure induced by the formation of a lee-side trough east of the Southern Appalachians. Temperature falls have slowed a bit where the wind has picked up, but are still dropping at a modest rate across interior Southeast South Carolina up into coastal parts of Beaufort, Charleston and Colleton Counties where calm winds persist. Still expect lows to bottom out in the mid-upper 20s inland with mid 30s at the beaches. Where winds pick up, wind chills could drop into the lower-mid 20s with the lowest values occurring across far interior Southeast Georgia. Incoming data suggest wind chills could drop as low as 20 degrees in a few spots, but durations still look brief, similar to what transpired Tuesday morning. The situation looks too marginal to justify a Cold Weather Advisory where wind chills hit 20, but trends are being monitored. The issuance of a Special Weather Statement highlighting brief advisory conditions will be considered should wind chills approach 20 degrees.

Today: A deep longwave trough will remain across the eastern CONUS today with the local area positioned between high pressure over the Gulf and a lee-side trough to the northwest. This will keep a modest pressure gradient over the area today. Some mountain wave induced cirrus off the Southern Appalachians could brush mainly the central and northern counties this morning, otherwise sunny skies will prevail. Highs this afternoon will range from the lower-mid 50s, consistent with full sun low-level thickness schemes and 31/01z NBM output.

Tonight: A dry cold front will push offshore later this evening ushering in a reinforcing shot of cool/dry air. Guidance is similar in showing a brief yet modest burst of cold air advection behind the front. The will keep the conditions fairly well mixed through the night with lows Thursday morning dropping into the lower 30s inland to the upper 30s/lower 40s at the beaches. Wind chills will bottom out in the 25-30 degree range. Another round of mountain wave induced cirrus could brush northern areas late, but clear to mostly clear conditions should prevail for most areas.

Lake Winds: Winds are expected to surge over Lake Moultrie late this evening with the passage of a dry cold front. RAP soundings showing profiles becoming increasingly favorable for vigorous mixing as low-level lapse rates steepen and lake water temperatures hold in the mid 50s. Soundings support frequent gusts as high as 25-30 kt with sustained winds closer to 15-20 kt. A Lake Wind Advisory has been posted 10 PM to 10 AM Thursday per coordination with WFO Columbia. Waves are expected to peak around 2 ft with the highest winds and the most significant wave action occurring over the central and eastern parts of the lake.

.SHORT TERM /THURSDAY THROUGH SATURDAY/...

A weak front moves through on Thursday, bringing a resurgence of westerly winds across the area which become marginally gusty in the teens, along with high temperatures in the upper 50s to lower 60s. Overnight into Friday, radiational cooling brings overnight temperatures back into the mid 30s inland and up to the lower/mid 40s along the coast. Temperatures continue to moderate on Friday as a warm front lifts across the region, but with cloud coverage increasing, afternoon temperatures won't warm too much but are still expected in the lower to mid 60s. Behind the warm front, overnight lows into the weekend will be much warmer in the mid 40s to lower 50s.

Weak shortwaves in the mid levels begin to traverse the area overnight, with a surface low pressure beginning to move across the deep south ahead of the main shortwave. This will bring chances for light to moderate rain showers along with isolated thunderstorms starting early Saturday morning and ending overnight into Sunday ash the surface low moves offshore. Ensemble clustering analysis shows that model agreement remains fairly high, with the two dominant clusters showing 70-80% probabilities for a quarter inch of rain now for all areas across the region. Probabilities have similarly risen for half an inch, up to 40-50% across the region, while probabilities for an inch remain low at about 10%. With CAPE values looking to remain below 500 J/kg, severe thunderstorms are not expected. SPC and the various AI/ML output agree, and do not show chances for severe weather across the area. Despite the rain, afternoon temperatures in the lower to upper 60s are expected.

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...

Northwesterly flow aloft moves in behind the exiting shortwave, with a cold front moving through overnight into Sunday resulting in temperatures cooling into the mid 50s to lower 60s on Sunday. For the beginning of next week, a surface high pressure moves into the northeast, with the region warming up into the lower to mid 60s on Monday and mid 60s to lower 70s on Tuesday.

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...

31/06z TAF Discussion: KCHS/KJZI/KSAV: VFR through 01/06z.

Extended Aviation Outlook: VFR conditions expected to prevail through the rest of the week. Chances for rain return on Saturday, along with possible flight category restrictions from both lowered cigs and vsbys.

.MARINE...

Through Tonight: Quiet conditions will give way to increasing winds and seas tonight as a dry cold front pushes offshore. Confidence is increasing that winds will surge to Small Craft Advisory levels overnight as a period of modest cold air advection pushes through and steepening low-level lapse rates become increasing favorable for strong mixing. West winds will increase to 20-25 kt with gusts to 30 kt across the South Carolina nearshore and Georgia offshore waters and Small Craft Advisories have been posted to account for these conditions. The situation looks a bit more marginal over the Georgia nearshore waters and Charleston Harbor, but still expect winds to reach 15-20 kt with a few gusts to 25 kt possible. If the risk for higher winds or more frequent gusts to 25 kt increases, the Small Craft Advisories may have to be expanded into these zones.

Thursday through Sunday: Westerly winds will be decreasing to below Small Craft criteria throughout the morning hours, but will remain gusty throughout the day before weakening further overnight into Friday. Chances for showers and isolated thunderstorms return on Saturday as a low pressure system moves through, with gusty southwest winds near Small Craft Criteria possible, particularity in the outer Georgia waters Saturday morning/afternoon. Winds become northerly on the backside of the aforementioned surface low, remaining breezy on Sunday.

.CHS WATCHES/WARNINGS/ADVISORIES...

GA...None. SC...None. MARINE...Small Craft Advisory from 11 PM this evening to 10 AM EST

Thursday for AMZ350-352-374.