AFD_CHS

FXUS62 KCHS 311126 AFDCHS

Area Forecast Discussion National Weather Service Charleston SC 626 AM EST Sat Jan 31 2026

.WHAT HAS CHANGED...

Near term guidance is beginning to show some consistency on the possible formation of a cyclonic band of moderate snow setting up later today roughly in the Metter-Savannah Metro corridor. Should this band form, it could push snow totals to 2". An upgrade to a Winter Storm Warning may be needed for Tattnall, Evans, Inland Liberty, Inland Bryan and Inland Chatham later today if confidence on the timing and placement of this band increases. The aviation discussion was updated for the 12z TAFs.

.KEY MESSAGES...

- 1) A significant winter storm is expected to bring moderate to

major impacts across portions of the South Carolina Lowcountry and Southeast Georgia through Sunday morning. Winter Storm Warnings and Winter Weather Advisories are in effect.

- 2) Extremely cold temperatures are expected this weekend into

early next week. Historically cold wind chills are expected Saturday night into Sunday morning and an Extreme Cold Warning has been issued for the entire area.

.DISCUSSION...

KEY MESSAGE 1: A significant winter storm is expected to bring moderate to major impacts across portions of the South Carolina Lowcountry and Southeast Georgia through Sunday morning. Winter Storm Warnings and Winter Weather Advisories are in effect.

The synoptic reasoning has changed little since Friday. Cyclogenesis is expected to initiate offshore of the Carolinas today and tonight in response to intense Gulf Stream low-level baroclinicity interacting with the approach of a powerful upper-level system. This system is forecast to dig across the Carolinas and Georgia tonight as it closes off. Intense DCVA ahead of the digging shortwave/upper low will steadily increase across the region. This will result in widespread precipitation breaking out over much of northern/central portions of South Carolina and Georgia later this morning which will spread east and southeast through the afternoon while gradually changing over to snow. A period of rather intense snow could occur over the Charleston Tri-County into Colleton County this evening as the upper low barrels through and the deformation axis along the backside of the cyclone pivots south into parts of the Lowcountry. The snow will gradually end from southwest-northeast through the night as the as the upper low clears the area and a pronounced dry slot rotates through.

Timing/Snow Amounts/Mesoscale Details: Temperatures will peak at various times through the day as cold air filters south and precipitation overspreads the area. Most of the hourly temperature guidance is likely too warm given their usual bias of underplaying the impacts of diabatic cooling. Near term adjustments were made to account for this. This results is a slightly quicker transition to snow from west-east this afternoon. Snow should mix with and quickly to change to snow by mid/late morning well inland with the change over reaching the Georgia coast by late afternoon. Forecast soundings suggest sub-freezing temperatures may initially outpace the saturation of the Dendritic Growth Zone (DGZ) well inland, so precipitation may briefly start out as a rain/freezing rain/sleet mix, mainly across far northern portions of Colleton, Dorchester and Berkeley Counties. But this mixed p-type transition should not last long before turning to all snow as full cloud ice nucleation occurs. By sunset, all areas should have transitioned to all snow.

There are increasing signals that a band of heavy snow associated with the deformation zone along the northwest flank of the upper low could pivot south into the Lowcountry this evening as the upper low pivots through. This could enhance snowfall rates across portions of the Charleston Tri-County into Colleton County for about a 3-6 hour period this evening. Near term guidance has trended upwards because of this with updated storm totals (utilizing an initial SLR of 12-16:1 increasing to 18-20:1 by this evening) ranging from 4-7" across parts of the Charleston Tri-County. Elsewhere, amounts will range from 2-4" the Jenkins-Colleton region with up to 2" in the Candler- Beaufort region. Winter Storm Warnings are in effect for these areas. South of I-16, including the Savannah Metro Area, up to 1" of snow is expected and a Winter Weather Advisory remains in place.

In addition to deformation enhancement, some of the higher resolution data sets suggest a few bands of locally heavier snows could impacts areas south of I-16 later this afternoon/evening. This may result in localized amounts in excess of 2 inches. These bands are associated with pockets of enhanced frontogenesis. Frontogenetic bands, especially in the presence of negative EPV values, are notorious for enhancing snowfall rates. This is something that will have to be watched through the day and an expansion of the Winter Storm Warning south may be needed.

Snow Impacts: Moderate to major impacts are expected in the Winter Storm Warning area with the most significant impacts occurring in the Charleston Tri-County. Dangerous to impossible driving conditions are likely there. Closures and disruptions of infrastructure may also occur. Minor impacts are likely in the Winter Weather Advisory area where slick spots could make for hazardous driving conditions. Vsbys could drop as low as 1/2 mile across parts of the Charleston Tri-County as an area moderate to heavy snow associated with the aforementioned deformation axis settles in for about a 3-6 hour period this evening. As winds begin to gust to 30-35 mph late this afternoon and overnight in response to strong cyclogenesis offshore, areas of blowing snow could occur, especially with SLRs likely remaining above the critical threshold of 12:1 resulting in a very dry/powdery snow. The risk for impacts from blowing snow will greatest across the Charleston Tri-County where the highest snow amounts will likely be found. New snowfall records could be set at both the KCHS and KSAV airports for January 31 and February 1. See the climate section below for details.

Lake Moultrie: Winds on Lake Moultrie will increase late this afternoon and evening. Speeds will reach 20-25 kt with gusts as high as 30-35 kt. Waves will peak 2-3 ft with local sets in excess of 4 ft. Lake Moultrie is a fresh water lake. As winds become gusty and sub-freezing temperatures (30 deg or lower) settle in, the risk for freezing spray will increase over the open lake waters and along the downwind side of the lakeshore, including Pinopolis and Short Stay. This could result in a glaze of ice on trees, piers and other structures, in addition to the expected snow.

KEY MESSAGE 2: Extremely cold temperatures are expected this weekend into early next week. Historically cold wind chills are expected Saturday night into Sunday morning and an Extreme Cold Warning has been issued for the entire area.

Through Sunday: Bitterly cold temperatures will settle into the region tonight as gusty northwest winds persist through daybreak. Lows overnight have trended down just a bit, ranging from the mid teens inland to around 20 at the beaches. Wind chills Sunday morning are expected to bottom out in the 0-5 degree above zero range which is is an extremely rare occurrence this far to the south. Highs Sunday will be heavily influenced by a lingering snow pack, especially across the Charleston Tri- County. Highs will only peak in the lower-mid 30s in the Charleston Tri-County to the lower 40s near the Altamaha River. Despite full sun, some areas in the deepest snow pack may not get above freezing. Some further downward adjustments in the highs may be needed pending the final area/depth of the snow pack.

Sunday Night through Tuesday: The mid-levels will consist of a very strong trough over the East Coast Sunday night into early Monday, followed by it shifting offshore later Monday into Tuesday. This will generate northwest flow over our area. At the surface, High pressure will be over the Lower MS Valley Sunday night. It'll gradually shift eastward, passing over FL on Tuesday. Sunday night, the combination of west northwest winds ushering colder temperatures in, cooled further by a fresh snowpack (especially for our SC counties), and plenty of radiational cooling due to mostly clear skies will cause temperatures to bottom out in the teens across most of our area, except the lower 20s along the immediate coast, and a tad warmer at the beaches. But winds will be light, which will generally keep the wind chill only a few degrees colder than the temperatures. But Cold Weather Advisories will still be needed everywhere. Monday, there should be a noticeable spread in high temperatures, mostly due to a remaining snowpack over our SC counties. They'll range from around 40 degrees near the Santee River, to around 50 degrees near the Altamaha River. Monday night, very light southwest winds are expected. Skies will start out clear in the evening, but clouds will gradually increase from south to north overnight. This may limit some of the radiational cooling. Lows should range from the lower 20s inland to near freezing at/near the beaches. Since winds will be very light, it doesn't appear wind chills will drop to 20 degrees or lower, so we probably won't need Cold Weather Advisories. Tuesday, temperatures moderate further with highs ranging from near 50 degrees near the Santee River to the lower 60s near the Altamaha River.

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...

21/12z TAF Discussion: KCHS/KJZI: Conditions will deteriorate through the day as precipitation spreads over the terminals. Rain should mix with/change to snow by early afternoon then become all snow by late afternoon. An area of moderate to heavy snow with IFR conditions could impact both KCHS/KJZI after sunset with vsbys possibly dropping to airfield minimums. Blowing snow could also have an impact as gusty winds in excess of 25 kt occur and a snow pack forms. High snow-to-liquid ratios support a dry/powdery snow which should be easily lofted. Vsbys 1/2SM SN BLSN were highlighted at both terminals 23-05z. This is also when any deicing operations will could be at their peak.

KSAV: Conditions will deteriorate through the day as precipitation spreads over the terminal. Rain should mix with snow by early afternoon then become all snow late afternoon and linger into this evening as activity diminishes. Conditions looks to mostly remain MVFR once lower cigs settle in. The risk for any snow impacts looks greatest from 21-04z. Wind gusts in excess of 25 kt are likely.

Extended Aviation Outlook: A cold front may bring flight restrictions Wednesday, mainly due to rain showers.

.MARINE...

Through Sunday: There is a high probability of gales for all waters from late this afternoon into Sunday morning. Gale Warnings are in effect for all legs as a result. Gusts could get close to storm-force over the the Georgia offshore waters and the outer portions of the South Santee-Edisto Beach nearshore leg. An upgrade to a Storm Warning may be needed if confidence for frequent storm-force gusts increases.

Sunday Night through Wednesday: Surface High pressure will be over the Lower MS Valley Sunday night. It'll gradually shift eastward, passing over FL on Tuesday, then shift offshore Tuesday night into Wednesday. A cold front will approach from the west on Wednesday. Winds and seas will be trending lower Sunday night into Monday. Any remaining marine headlines (most likely for the GA waters beyond 20 nm) should come to an end by Monday evening. Winds and seas are expected to remain below Small Craft Advisory criteria through Wednesday, followed by deteriorating conditions Wednesday night.

.CLIMATE...

Record Low Temperatures:

February 1: KCHS: 21/1977 KCXM: 23/1900 KSAV: 23/1977

February 2: KCHS: 19/1980 KCXM: 17/1917 KSAV: 18/1917

Record Low Maximum Temperatures:

February 1: KCHS: 38/1980 KCXM: 36/1900 KSAV: 38/1900

February 2: KCHS: 38/1980 KCXM: 38/1898 KSAV: 38/1951

Record Snowfall:

January 31: KCHS: 0.6/1977 KSAV: 1.3/1977

February 1: KCHS: no record established KSAV: no record established

.EQUIPMENT...

The KCLX radar is operational, but could go down at any time. Additional repairs are needed.

.CHS WATCHES/WARNINGS/ADVISORIES...

GA...Winter Storm Warning until 1 PM EST Sunday for GAZ087-088-

099>101. Extreme Cold Warning from 4 PM this afternoon to 1 PM EST Sunday for GAZ087-088-099>101-114>119-137>141. Winter Weather Advisory from 10 AM this morning to 7 AM EST Sunday for GAZ114>119-137>141.

SC...Winter Storm Warning until 1 PM EST Sunday for SCZ040-042>045-

047>052. Extreme Cold Warning from 4 PM this afternoon to 1 PM EST Sunday for SCZ040-042>045-047>052. Lake Wind Advisory from 6 PM this evening to 10 AM EST Sunday for SCZ045.

MARINE...Gale Warning from 6 PM this evening to 7 AM EST Sunday for

AMZ330. Gale Warning from 4 PM this afternoon to 10 AM EST Sunday for AMZ350-352. Gale Warning from 1 PM this afternoon to 10 AM EST Sunday for AMZ354. Gale Warning from 1 PM this afternoon to 1 PM EST Sunday for AMZ374.

ST/-