AFD_CHS

FXUS62 KCHS 121816 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 116 PM EST Mon Jan 12 2026

.WHAT HAS CHANGED...

This is the first issuance of the Key Message format AFD. Timing of the cold front Wednesday night/Thursday continues to be further refined.

.KEY MESSAGES...

1) Dry high pressure will dominate through Tuesday, yielding low relative humidity values both Monday and Tuesday afternoons.

2) Dangerous fire weather and marine conditions possible as gusty winds and low humidity arrive behind a mostly dry cold front Thursday into Friday.

3) Very cold temperatures will occur Friday morning, with lows in the upper teens to lower 20s away from the beaches.

.DISCUSSION...

KEY MESSAGE 1: Dry high pressure will dominate through Tuesday, yielding low relative humidity values both Monday and Tuesday afternoons.

Surface high pressure centered over the southeastern states on Monday will slowly drift towards Texas on Tuesday. Aloft, broad troughing will dominate over the eastern CONUS into mid-week as a closed low north of New England on Monday pushes northeastward. Given the northwesterly flow aloft, much drier air will be advected into the region. This is shown through multiple model forecast soundings, depicting a very dry column of air across southeastern SC and southeastern GA. The drier air will yield RH values on the order of 20-30% across the region. With the surface high pressure centered over the southeastern states, winds across southeast SC and southeast GA will top out only around 5 to 10 mph Monday and Tuesday afternoons. While the criteria for a fire weather headline is met in regards to the RH values, wind speeds are significantly below Fire Danger Statement/Red Flag Warning criteria. While no fire weather headlines are anticipated at this time, individuals should be cautious as fires can spread quickly under these conditions.

KEY MESSAGE 2: Dangerous fire weather and marine conditions possible as gusty winds and low humidity arrive behind a mostly dry cold front Thursday into Friday.

Approaching shortwave Tuesday night will encourage the development of weak low pressure within a front over the Bahamas, which will lift north well off our coast Wednesday. Current expectation is very dry air in the low levels will limit the potential for any significant rainfall over land, though a few showers could work back over the beaches.

A strong cold front associated with low pressure lifting across New England will then approach from the west Wednesday night, crossing the area early Thursday. Low level moisture is limited ahead of the front, and, with only modest upper forcing coinciding with the strongest frontogenesis Thursday morning, the overall rainfall potential with the front looks very limited.

Of greater concern is the strong gradient in the wake of the front as high pressure builds in from the west. This, in combination with peak mixing and downsloping flow in the low and mid levels, will likely result in wind gusts Thursday afternoon on the higher end of the guidance envelope, with 25 to 30 mph gusts likely, with some gusts to 35 mph possible over land. A Lake Wind Advisory will likely be necessary, with wind over the coastal waters possible gusting to Gale Force (~10-30% chance) into Thursday night. Additionally, RH values will be rapidly dropping through the afternoon and evening, and critical RH's (<25%) could be approached by late Thursday afternoon. A faster frontal passage would result in a greater potential for adverse fire weather conditions later Thursday afternoon/evening.

Very dry air remains in place Friday, with the 30-50% probability of RH values of <25% away from the immediate coast. However, the gradient will be much weaker Friday, so Red Flag Warning conditions currently look unlikely.

KEY MESSAGE 3: Very cold temperatures will occur Friday morning, with lows in the upper teens to lower 20s away from the beaches.

Strong cold and dry air advection will occur in the wake of a cold front Thursday afternoon and evening. Then, overnight Thursday night, the gradient will weaken significantly and radiational cooling will ensue. The guidance envelope shows most likely lows away from the immediate coast in the upper teens to lower 20s. If several hours of radiational cooling occurs, lows on the lower end of the envelope, potentially in the mid to upper teens, are very realistic given dew points in the lower teens. With light winds, the wind chill will generally be the same as the temperature, so Cold Weather Advisories could be needed for much of the area.

.AVIATION /18Z MONDAY THROUGH SATURDAY/...

18Z TAFs: VFR. NE winds around 5 to 10 knots will dominate this afternoon before going light and variable tonight at all terminals. Tuesday morning will see winds out of the N around 5-10 knots.

Extended Aviation Outlook: VFR conditions prevail for KCHS, KJZI and KSAV through late week. NW winds could gust to 25 to 30 kt Thursday afternoon as chilly high pressure builds in quickly behind a strong cold front.

.MARINE...

Conditions will remain below Small Craft Advisory criteria through Wednesday as surface high pressure dominates over the forecast area and adjacent marine waters.

Weak low pressure passes off the coast Wednesday, but a weak gradient on the west side of the low keeps benign marine conditions in place despite increased shower chances.

A strong cold front will cross the area late Wednesday night into Thursday morning, with gusty NW winds developing behind the front Thursday through Thursday evening. There is currently a low (10-30%) chance for Gale Force gusts, but at the very least Small Craft Advisories are likely. Winds and seas subside quickly Friday morning as high pressure builds in from the west.

.CHS WATCHES/WARNINGS/ADVISORIES...

GA...None. SC...None. MARINE...None.

CEB/CPM