FXUS62 KCHS 211831 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 131 PM EST Wed Jan 21 2026
.WHAT HAS CHANGED...
The aviation section has been updated for the 18z TAF issuance. There are now two key messages, removing the previous first key message referencing morning (today, Wednesday) low temperatures.
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.KEY MESSAGES...
- 1) Widespread precipitation is expected to occur this
weekend, bringing the potential for a winter weather event across portions of the region.
- 2) Very cold temperatures will occur early next week.
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.DISCUSSION...
KEY MESSAGE 1: Widespread precipitation is expected to occur this weekend, bringing the potential for a winter weather event across portions of the region.
Focus on the forecast remains the potential for a winter weather event across portions of southeast South Carolina and Georgia this weekend. The overall synoptic pattern remains fairly confident, however there are many details in the evolution of this pattern that are not certain. This is causing a fairly high spread in model guidance on p-types location and timing.
Synoptic Pattern/Diagnosis:
On Thursday, a decaying omega block will be located across Alaska with two upper level lows undercutting the block (forming a quasi rex block). The upper level low of concern will be located just southwest of California. Simultaneously, a long wave trough will be centered southwest of the Hudson Bay with a trailing shortwave extending across Saskatchewan and Alberta. How this shortwave interacts with the cutoff low is the linchpin to how this weekend unfolds for the central/ eastern United States. The general idea is that the shortwave will dive southeast out of Canada and then begin to pickup the closed low in the main flow. By late Saturday/ early Sunday, the closed low will open up with fragments of PV ejecting east/ northeast. As this occurs, surface low pressure will form somewhere across the southern United States or northern Gulf. Over the Canadian Maritimes, a closed low will be ejecting east and will help push a surface cold front through the area Saturday. As winds near the surface turn from the northeast and low level flow remains out of the southwest, isentropic upglide will commence. This working in tandem with the fragments of PV moving overhead will quickly cause vertical profiles to saturate with precipitation beginning late Saturday morning/ early Saturday afternoon. On Sunday, surface low pressure will eject northeast with precipitation continuing across the region. The main uncertainty will be the track of the surface low. More on this below. Monday morning, a surface cold front will sweep through all zones with precipitation coming to an end from west to east.
Model Confidence:
The latest 00z EPS and GEPS have seen a real translation northwards of the freezing rain, sleet, and snow precipitation types with the 00z GEFS still holding on to the colder solution. Taking a look at the WPC Cluster Analysis reveals that the GEFS now is the least dispersive with 67% of GEFS members in Cluster 2 with only 18% of EPS and 10% of GEPS members a part of that clustering. Meaning the EPS and GEPS now appear much closer in the solution space. The issue appears to be with the development of the surface low and how it evolves. The GEFS solutions show a strong CAD in place with surface low pressure forming off of the southeast South Carolina coast. The latest run of the EPS and GEPS shows a much weaker CAD in place with surface low pressure moving over central Georgia and South Carolina, effectively putting the region temporarily in a warm sector. This change in the EPS from a colder ensemble suite to a warmer ensemble suite is not completely unexpected. Taking a look at the WPC Ensemble Sensitivity Analysis Webpage reveals that most of the model spread is coming from the shortwave diving south out of Canada as well as how mid-level heights respond to that incoming wave over the central/ eastern United States. Most of these details will not be resolved until Friday. This means that changes in deterministic and ensemble members (possibly drastic at times) are possible over the next 24 to 48 hrs.
Potential Impacts/Timing:
Colder/GEFS Solution: Precipitation starting late Saturday morning with freezing rain possible Saturday evening into Sunday morning. This colder solution would favor the potential for freezing rain to the South Carolina coast and areas of inland GA. Precipitation would then come to an end late Monday morning.
Warmer/EPS and GEPS Solution: Precipitation starting Saturday afternoon with a warm front and surface low pressure moving overhead Sunday evening. A brief break in the precipitation would be possible with this solution Sunday afternoon. The chances for freezing rain would be confined to far inland Berkeley, Dorchester, Colleton, and Allendale counties.
Confidence on which solution set, or a blend of the two, actually occurs is low. Now is the time to prepare for the potential for minor impacts from a winter storm.
KEY MESSAGE 2: Very cold temperatures will occur early next week.
Arctic high pressure will settle overhead through the first part of next week with some of the coldest temperatures of the season possible.
Monday night/Tuesday morning: Low temperatures in the upper teens to lower 20s with wind chills in the lower to middle teens are currently forecast for Tuesday morning. Cold Weather Advisories appear likely at this point with probabilities of meeting or exceeding criteria at 50 - 75%.
Tuesday night/Wednesday morning: Wednesday morning low temperatures will be in the lower to mid 20s with morning wind chills in the upper teens to lower 20s. Confidence on needing a Cold Weather Advisory is less for Tuesday night/ Wednesday morning with probabilities of meeting or exceeding criteria at 20 to 50%.
It should be noted that model confidence is fairly high at this range with the IQR (or core 50% of guidance) only showing a 3 - 6 degree spread for lows Tuesday and Wednesday mornings of next week. However, changes in the synoptic pattern mentioned in Key Message 1 will have impacts on the timing of the cold air for Tuesday into Wednesday and if cold air persists into the later half of the next work week.
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.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
VFR conditions are expected to prevail at KCHS, KJZI, and KSAV through 18z Thursday.
Extended Aviation Forecast: There is a low end probability for some fog across the area Friday morning, otherwise VFR will prevail through Friday. Expect increasing chances of MVFR and IFR conditions through the weekend as a storm system impacts the area. There continues to be a threat for a period of winter precipitation, primarily beginning late Saturday night and into Sunday and mainly at KCHS and KJZI.
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.MARINE...
Tonight: Quiet conditions will continue with light northerly flow through the overnight. Wind speeds should mostly be around 5 knots, but up to 5-10 knots in the outer GA waters. Seas will mostly average 2-3 feet, but could be up to 4 feet in the outer reaches of the outer GA waters.
Thursday and Friday: Continued quiet conditions across the local waters for the late week time period. Wind speeds should be no more than 10 knots throughout, with seas 2-3 feet across the nearshore waters and up to 4 feet in the outer waters.
Friday night through Monday: Overall, expect hazardous marine conditions to occur this weekend. A strong cold front is forecast to push across the waters Friday night as high pressure builds in across inland areas. This will drive a strong northeast surge beginning late Friday night which will continue through Saturday and into Saturday night. As we head into Sunday, an area of low pressure is expected to develop just offshore and lift to the northeast into Sunday night. Finally a cold front will sweep through from the west by Monday. Winds and seas will ramp up to solid Small Craft Advisory (SCA) conditions early Saturday morning across all waters. As of now, peak winds look to occur late Saturday. Peak wind gusts are currently forecast to be around 30 knots, through there continues to be some support for potential gales in the Charleston County waters. There could be a bit of a lull in conditions (mainly winds) late Sunday as the gradient diminishes when the surface low pulls away from the area. However, winds should ramp back up a bit for Monday as the cold front from the west moves through.
In summary, SCA's will likely be needed for all waters (possibly Charleston Harbor as well) from late Friday night through Monday for both wind and sea conditions. There is still a low chance for a period of gales in the Charleston County waters in the late Saturday time period and it is possible that a Gale Watch/Warning could eventually be needed.
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.EQUIPMENT...
The Beaufort/Green Pond NOAA Weather Radio transmitter (WXJ-23) is operating at low power with diminished service. Repairs are scheduled to be made today or Thursday to restore full service.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None. SC...None. MARINE...None.
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BSH/Haines