FXUS62 KCHS 181158 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 658 AM EST Thu Dec 18 2025
.SYNOPSIS...
A warm front will shift north across the area today before a cold front arrives tonight. High pressure will then prevail during the weekend. Another cold front could shift across the area Monday, before high pressure returns and prevails into the middle of next week.
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.NEAR TERM /THROUGH TONIGHT/...
Today and Tonight: Aloft, a southwest flow will be in place to start the day ahead of a southern stream shortwave tracking across the Deep South and northern Gulf Coast region. At the sfc, a coastal trough is anticipated to shift onshore as warm front early, eventually lifting north of the local area by late morning and keeping the region warm-sectored through the afternoon prior to a cold front arriving tonight. Breezy south- southwest winds will help advect deep moisture into the area (PWATs approaching 1.5 to 1.75 inches) and mild air (high temps in the upper 60s/lower 70s), setting the stage for numerous to widespread rain/showers and even a few embedded thunderstorms. Precip coverage appears most widespread late afternoon and early evening when the combination of deep moisture and forcing (strong upper lvl jet, h5 vort energy and isentropic lift) align prior to the cold front arriving from the west. The front looks quite progressive with a high amplitude mid-upper lvl trough forcing it to the Eastern Seaboard after midnight tonight. Expect rain/showers and perhaps a few embedded thunderstorms (non-severe) to persist during evening and overnight hours until fropa occurs late, although the mid-upper lvl trough could spawn a few showers post front late night. Total rainfall amounts in the 1/2 to 1 inch range should be common, highest along and east of the I-95 corridor, particularly near the Southeast South Carolina coast late day/evening. Overnight lows remain mild despite fropa, generally in the low-mid 50s inland to upper 50s near the coast.
Lake Wind: Low-lvl wind fields will strengthen across the area today as a cold front approaches the area overnight. A warm air advection regime could limit mixing of stronger winds across the lake today, but eventually lead to gusts upwards to around 25 kt tonight. A Lake Wind Advisory could eventually be needed late evening and overnight.
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.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Friday: Broad mid-lvl troughing will extend from the Ohio River Valley into the Deep South as an associated cold front marches offshore by mid to late morning. A band of weakening stratiform precipitation will likely be present along the frontal boundary in the early morning hours as it passes through the region. Thereafter, skies should quickly clear as post-frontal conditions should limit forcing at the surface and promote subsidence. This will yield temperatures in the low to mid 60s across the Lowcountry. Overnight lows will be a bit cooler than the previous night with temperatures dropping into the low 30s across the interior counties and upper 30s to low 40s closer to the coastline.
Saturday and Sunday: A shallow upper-lvl trough could pass over the Eastern CONUS this weekend within the return of quasi-zonal flow aloft. At the surface, high pressure will be centered across the Mid- Atlantic and will yield warm and dry conditions across the Southeast. As subsidence continues to envelope the region, skies will remain mostly clear and temperatures will moderate back to near normal. This is nothing to write home about, but it's possible a weak seabreeze could develop on Saturday afternoon. Some of the recent model guidance continues to signal that another cold front could approach the region on Sunday night and winds will likely become a bit breezy ahead of it (esp. in the evening and into overnight). It's important to note that no precipitation is expected with this frontal passage. Considering the absence of clouds in the sky this weekend, strong radiational cooling will likely be the main driver of the overnight lows with temps. falling into the upper 30s to low 40s.
Lake Wind: Southwesterly flow expected to surge near/behind a cold front Thursday night into early Friday morning, and then become more westerly behind the front on Friday mid to late morning. There could be a short window of time where gusts could be reach near and above 25 knots across Lake Moultrie, and a Lake Wind Advisory could be needed.
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.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Expect quiet and rain-free weather through the period as broad upper- lvl ridging dominates the forecast through the middle of the week. Temperatures on Monday will be a bit cooler than the rest of the week with the passage of the cold front, however temperatures will quickly rebound and reach near to above normal values thereafter.
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.AVIATION /12Z THURSDAY THROUGH MONDAY/...
At CHS/JZI, VFR conditions should prevail through late morning, even with coastal showers shifting onshore and impacting the terminals. TEMPO MVFR conditions are anticipated between 18-22Z as rain and/or shower activity increases this afternoon. Gusty winds to around 20 kt could also accompany precip activity. The bulk of rain/showers and possibly a thunderstorm come between 22Z and 06Z tonight, which likely lead to additional rounds of MVFR conditions late afternoon and during evening hours. Guidance has come in quite a bit stronger with gusty winds and IFR cigs with fropa overnight, thus have been added between 04-12Z Friday. Prior to the gusty winds, LLWS is possible late afternoon/evening as well.
At SAV, VFR conditions prevail during the next couple hours while light rain/shower activity associated with a coastal shifts onshore along the Georgia coast. MVFR cigs prevail late morning into early afternoon with light/moderate rains anticipated. There could be a period of VFR conditions late day, but conditions will likely lower to MVFR early evening, then followed by even lower conditions after 04Z tonight. Guidance has come in quite a bit stronger with gusty winds and IFR cigs with fropa overnight, thus have been added between 04-12Z Friday. Prior to the gusty winds, LLWS is possible during evening hours as well.
Extended Aviation Outlook: Periods of MVFR possible Friday morning as light showers might result in lower ceilings and vsbys. However, conditions should rapidly improve in the late morning as the front pushes offshore.
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.MARINE...
Today and Tonight: A weak coastal trough will shift onshore early, then lift north as a warm front early to mid morning. Winds should become more southerly behind this feature, gradually increasing throughout the day as the pressure gradient slowly tightens well in advance of a cold front arriving during the second half of the night. Although wind fields increase throughout the day, low-lvl mixing could be an issue early on within a warm air advection regime, but wind speeds should gradually top out in the 15-20 kt range by late day. Additionally, some guidance suggests a window of opportunity for sea fog to develop late afternoon/early evening as sfc winds become more parallel to the coast and sfc dewpts surge into the lower 60s over slightly cooler waters. Chances appear highest across nearshore waters along and south of Edisto Island, SC to the Altamaha River, GA. However, winds do pick up speed during this time, which should limit the potential.
Seas will build today, reaching 6 ft across outer Georgia waters late afternoon, but even more likely early evening (including off the Charleston County Coast). Given the arrival of larger seas, Small Craft Advisories have been issued for outer Georgia waters starting late afternoon and across northern South Carolina waters off the Charleston County Coast starting starting early evening. Southern South Carolina nearshore waters also features a Small Craft Advisory tonight, although with a later start time based on the arrival of larger seas. Southwest winds could top out near 25-30 kt across zones already included in Small Craft Advisories overnight and should persist into early Friday. Seas should also build to 6-8 ft, largest across outer Georgia waters and northern South Carolina nearshore waters. A brief period of Small Craft Advisories could eventually be needed across the Charleston Harbor and nearshore Georgia waters as well, but the event would be based on more marginal conditions and will need to be reevaluated later today.
Friday through Monday: Expect a cold front to pass over the local waters mid to late morning and yield west-southwesterly winds at 15 to 20 kts with gusts up to 25 kts. Also, a weakening band of showers associated with the front could pass through as well early Friday morning. By Friday afternoon, winds should shift more northwesterly and wind speeds should decrease to 10 to 15 kts. East-southeasterly swell continues to mix into the waters with seas ranging from 6 to 8 ft on Friday morning, and then quickly taper back to 4 to 6 ft by the afternoon. Thereafter, expect seas to range 2 to 3 ft over the weekend, before another swell tries to settle into the waters on Monday. Small Craft Advisories have been issued for nearshore South Carolina waters and the outer Georgia waters until Friday evening given the elevated marine conditions.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None. SC...None. MARINE...Small Craft Advisory from 7 PM this evening to 7 PM EST Friday
for AMZ350. Small Craft Advisory from 10 PM this evening to 1 PM EST Friday for AMZ352. Small Craft Advisory from 4 PM this afternoon to 7 PM EST Friday for AMZ374.
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NEAR TERM...DPB SHORT TERM...Dennis LONG TERM...Dennis AVIATION...Dennis/DPB MARINE...Dennis/DPB