FXUS62 KCHS 131838 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 138 PM EST Tue Jan 13 2026
.WHAT HAS CHANGED...
Strong post-frontal winds have trended a bit weaker on Thursday, and the probability for a Lake Wind Advisory on Thursday afternoon has diminished. A fourth key message was added to cover the concerns for this upcoming weekend.
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.KEY MESSAGES...
1) High pressure over the region will keep conditions dry through the remainder of the day, with relative humidity values dropping to low levels this afternoon.
2) Dangerous fire weather and marine conditions possible Thursday into Friday as gusty post-frontal winds combine with low humidity.
3) Very cold temperatures will occur Friday morning, with lows in the upper teens to lower 20s away from the beaches.
4) Dry and cooler temperatures for the second half of the weekend into early next week.
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.DISCUSSION...
KEY MESSAGE 1: High pressure over the region will keep conditions dry through the remainder of the day, with relative humidity values dropping to low levels this afternoon.
Dry surface high pressure will continue to dominate the forecast across the Southeast today. As of 1630Z, observations have been showing dewpoints in the mid 20s to upper 20s range with some locations showing values in the low 30s. Weak southwest flow will yield dewpoints in the mid 30s by the afternoon, spreading inland from the coastline. Minimum RH values will occur in the afternoon hours, prior to dewpoint recovery. Forecast min. relative humidity values will fall into the mid to upper 20 percent range west of I- 95, with low to mid 30 percent range and and east of I-95. High temperatures are forecast to range around 10 degrees warmer than yesterday, with temps. reaching into the upper 50s to low 60s.
KEY MESSAGE 2: Dangerous fire weather and marine conditions possible Thursday into Friday as gusty post-frontal winds combine with low humidity.
A rex block will be well-established over the Western CONUS on Thursday, as broad downstream amplified trough exists across the Eastern CONUS. This trough should slowly deamplify as a closed mid- lvl low pushes eastward across the Great Lakes, yielding lower heights out ahead of it. Despite the magnitude of these dropping heights, precipitation chances remain limited (less than 10%) with the approaching surface cold front. This mainly due to location of the LFQ of the subtropical jet streak on Thursday early morning, and most of the precipitation will be located offshore.
Post-FROPA conditions will yield strong low-lvl CAA and expect 850 mb temps. to drop from 0C to -8C on Thursday morning. This combined with peak mixing and downslope flow in the low to mid lvls will likely result in breezy northwesterly flow on Thursday afternoon with 20 to 25 mph gusts possible. It's possible that a Lake Wind Advisory might be needed for Thursday afternoon, however probabilities of winds reaching 25 kt has dropped down to 20-25%.
Additionally, expect dewpoints to drop rapidly into the low to mid teens behind the cold front allowing relative humidity values to drop below 30% west of I-95 on Thursday afternoon. It's important to note that the Wambaw and Glissons Pond RAWS sites have both had fuel moisture values in the single digits on the previous Sunday and Monday afternoons.
Walking into Friday morning, surface high pressure will settle across the region and keep dewpoints in the low to mid teens through Friday evening, before dewpoint recovery. The latest LREF probs. indicate 40-50% chance of RH values less than 25% west of I-95.
Also of note is that lingering upper lift associated with the strongest DPVA will pass over the area late Wednesday night into Thursday morning, coincident with low-lvl temps well below freezing. Very dry mid to upper-lvl air advecting overhead is very likely to preclude any potential for precip., with cluster analysis revealing that only outlier guidance showing a much greater amplitude upper- lvl trough shows potential for flurries mainly across the Low Country. Take home message here is that we are very likely to remain dry Wednesday night/early Thursday, with the worst case scenario being some brief flurries.
KEY MESSAGE 3: Very cold temperatures will occur Friday morning, with lows in the upper teens to lower 20s away from the beaches.
There is very good agreement in calm winds emerging as the surface ridge axis builds overhead Thursday evening and overnight. Temps away from the coast drop below freezing within a few hours after sunset, then continue to steadily cool through the night as dew points remain in the lower teens. Lows will likely be in the upper teens inland of US Hwy 17 corridor, and low-to-mid 20s closer to the coast. As such the potential for lows of 20 or less is generally likely (50-80%) inland of the US Hwy 17 corridor, 10-40% along the US Hwy 17 corridor, including much of the inland portions of the Charleston and Savannah Metro areas, and less than 10% for areas near the beaches.
Key Message 4: Dry with cooler temperatures for the second half of the weekend into early next week.
As an upper level trough moves towards the region, a cold front sweeps through Saturday night into Sunday. Overnight lows dip into the mid 20s to lower 30s for inland areas, and into the mid 30s along the coast. Probabilities for overnight temperatures at or below 20 degrees F are very low, only 10% for interior Georgia. The upper level trough axis pushes through on Sunday, with ensemble clustering showing the majority of solutions keep the region dry given the lack of moisture. If moisture were to become more plentiful, the ptype would largely remain rain given warm thermodynamic profiles, with afternoon highs in the mid 40s to lower 50s. However, the probabilistic Winter Storm Severity Index (WSSI-P) does show a 5-10% chance for a trace of snowfall from the colder solutions, but again moisture looks to be lacking so we most likely won't see any falling precipitation.
Coldest temperatures move down overnight into Monday as a surface high pressure builds into the region, with overnight lows down into the mid 20s for furthest inland areas and up into the lower 30s along the coast. Given a decent radiational cooling set up which may lead to further cooling, probabilities for temperatures at or below 20 degrees are in the 40-50% range for those furthest inland, and down to 5% along the coast. Ahead of the approaching high pressure, winds may remain just strong enough (near 5 knots) where wind chills may dip into the 15 to 20 degrees range, with highest probabilities again for the furthest inland areas right at 50%, dropping to 25% along the coast. A Cold Weather Advisory may be needed. Highs on Monday remain below normal, in the lower to upper 50s.
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.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
VFR conditions prevail at CHS/JZI/SAV terminals through 12Z Wednesday. It's possible to see flight restrictions Wednesday afternoon as showers develop ahead of the approaching cold front, however confidence remains low with this.
Extended Aviation Outlook: VFR conditions Friday.
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.MARINE...
Broad surface high pressure remains across the marine zones through tonight, yielding 5 to 10 kts and seas between 2 to 3 ft. Conditions remain below Small Craft Advisory criteria through early Thursday morning.
A strong cold front will march across the local waters late Wednesday night into Thursday morning, yielding gusty post-frontal northwesterly winds Thursday mid-day through Thursday evening. Expect seas to gradually build to 3 to 5 ft across the nearshore waters with possible 6 footers peaking into the offshore Georgia waters on Thursday afternoon into the evening. Therefore, Small Craft Advisories seem likely for Thursday mid- day into the evening.
Expect improved marine conditions for Friday as upper-lvl ridging settles overhead, yielding light to moderate winds and seas mainly 1 to 2 ft.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None. SC...None. MARINE...None.
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APT/CEB/Dennis