AFD_CHS

FXUS62 KCHS 152323 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 623 PM EST Thu Jan 15 2026

.WHAT HAS CHANGED...

The aviation section has been updated for the 00z TAF issuance. Expanded the Cold Weather Advisory to now include Berkeley County. Otherwise, confidence remains low in regard to frozen precipitation on Sunday.

.KEY MESSAGES...

- 1) Dry conditions and low relative humidity values expected

Friday.

- 2) Very cold temperatures will occur Friday morning, with lows

in the upper teens to lower 20s away from the beaches.

- 3) Potential for snow mixing with rain Saturday night into

Sunday morning as coastal low tries to develop on Sunday. &&

.DISCUSSION...

KEY MESSAGE 1: Dry conditions and low relative humidity values expected Friday.

The center of the dry air mass will build across the Southeast U.S. on Friday. RH values should fall to the upper teens to around 20 percent very far inland, and around 25 percent closer to the coast. Fortunately, High pressure overhead should only support winds between 5-10 mph. No Fire Danger Statements are expected.

KEY MESSAGE 2: Very cold temperatures will occur Friday morning, with lows in the upper teens to lower 20s away from the beaches.

A Cold Weather Advisory remains in effect from 8 PM this evening to 9 AM EST Friday morning. It was expanded to include Berkeley County. Surface High pressure over the southern MS Valley late this afternoon will quickly move east and become located over the Southeast U.S. by Friday morning. This will cause winds across our area to become very light or go calm late tonight into early Friday morning. Additionally, the High will usher in very cold temperatures and dry conditions. The combination of clear skies, light to calm winds, and dry conditions will lead to near ideal radiational cooling. Expect low temperatures in the upper teens west of I-95 and in the typical colder spots. Along and east of I-95 to about US Highway 17, expect low temperatures in the lower to mid 20s. Along the beaches, expect low temperatures in the mid to upper 20s (including the Charleston Peninsula). Temperatures will be below freezing for 8 to 12 hours.

KEY MESSAGE 3: Potential for snow mixing with rain Saturday night into Sunday morning as coastal low tries to develop on Sunday.

A Rex Block will gradually to loose cohesion as a wave situated over the eastern Pacific approaches from the west. In response to this downstream effect, a substantial shortwave trough will dive southeast out of Manitoba and approach the region Sunday morning. This shortwave could potentially take on a more negative tilt as it approaches the coastline. As this story unfolds, a coastal low may develop offshore of the Carolinas, and its exact position will be extremely important to how conditions evolve from Saturday night into Sunday morning. There's a couple different scenarios at play, let's walk through them.

(1) Coastal low forms offshore of the Carolinas *This appears to be the most likely scenario at the moment,

with support from CMC, GEFS (GFS ensemble), and 06Z EPS (ECMWF ensemble). This would favor a rain/snow mix solution away from the coastline with rain along the coastline as the placement of the low would yield warmer temperatures. There is a chance of brief snow (not a mix) for the inland counties in the morning.

(2) Coastal low forms far east/northeast of SC/GA *Some support with this solution as 06Z/12Z GFS (deterministic)

and EC-AIFS supporting this scenario. This would favor a warm and wet (mostly rain) solution as the low would be forming far offshore away from the Carolinas.

(3) Coastal low forms along the SC/NC coastline *Not much support with this scenario with the latest guidance,

however some of the ensembles still indicating this as a possibility. This would again favor a warm and wet (mostly rain) solution.

There remains a considerable amount of uncertainty with this system, as it hinges on a multitude of factors: the placement of this coastal low, how far south this trough shifts, and how quickly it develops a negative tilt. Taking a look at the 15.00Z WPC Cluster Analysis (e.g., 50% of the GEFS being contained in Cluster 1), it appears the ensemble guidance is becoming less dispersive as time goes on. This reveals that the majority of the uncertainty remains with the dueling shortwaves on the western and eastern flanks of the Rex Block (e.g., Cluster 3 and 4). Also, the combination of warm ground temperatures and marginally cold air present on Sunday is really the main factor working against this system. Nevertheless, the probabilistic Winter Storm Severity Index (WSSI-P) continues to show a 5-10% chance of experiencing minor impacts from winter weather on Sunday. Therefore, with this in mind, it's important to remember to exercise caution here as the forecast can change, and will likely change.

Behind this cold front, temperatures will again be seasonably cold on Monday morning with low to mid 20s (with upper 20s near the coastline). Out ahead of the high pressure settling into the region, wind speeds remain on the light side (near 5 kts). This will be enough to kick wind chills into the upper teens to low 20s across the region, with the highest probabilities (40-50%) across the the furthest inland counties. Therefore, a Cold Weather Advisory might be needed for Monday morning. Highs on Monday remain below normal as temps. only reaching into the upper 40s to low 50s.

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...

VFR conditions will prevail at KCHS, KJZI, and KSAV through 00z Saturday.

Extended Aviation Outlook: VFR conditions will continue for KCHS, KJZI and KSAV through the majority of Saturday, before another system could impact the region late Saturday night.

.MARINE...

Tonight: Winds will remain elevated and gusty across the local waters as high pressure continues to build in from the west this evening. Winds will continue to gust into the 25-30 knot range, especially early in the evening, supporting the ongoing Small Craft Advisories in effect for all waters outside Charleston Harbor. Beginning early Friday morning, winds and seas will quickly improve as the pressure gradient relaxes. All Small Craft Advisories should be down by sunrise.

The center of a large area of high pressure will arrive on Friday and may linger into Saturday, supporting southwesterly winds at 10 to 15 kts with gusts up to 20 kts. Seas will ease back from Friday with the 2 to 3 ft expected. There is potential for an area of low pressure to develop offshore of the Carolinas on Sunday, yielding gusty winds and building seas yet again. It's possible that Small Craft Advisories might be needed across a portion of the waters on Sunday. Thereafter, high pressure should settle over the region early next week, allowing conditions to remain less than Small Craft Advisory criteria.

.CHS WATCHES/WARNINGS/ADVISORIES...

GA...Cold Weather Advisory until 9 AM EST Friday for GAZ087-088-

099>101-114-115.

SC...Cold Weather Advisory until 9 AM EST Friday for SCZ040-042>045-

047.

MARINE...Small Craft Advisory until midnight EST tonight for AMZ350-352-

354. Small Craft Advisory until 4 AM EST Friday for AMZ374.