Scattered showers and thunderstorms are expected to close out 2020 and welcome in 2021. The chance of a few strong to severe storms will be possible through the holiday weekend.
A complicated weather system is setting up to welcome in the New Year with a pair of upper level low pressure systems moving in from the southwest. The first low pressure system was moving over northern Mexico and into the Texas Gulf Coast Thursday afternoon and will continue to track northeastward, dragging a slow cold front across the Deep South through New Year's Eve. A second low pressure system is expected to develop early Friday morning over the southern Appalachians which will likely strengthen the slow-moving cold front associated with the first low pressure system.
While these two low pressure systems continue to develop and track eastward a stationary front will drape itself over the Palmetto State which will help to lift moisture into the region and keep rain chances present across the state to close out 2020.
Beginning Friday and lasting into Saturday the cold front associated with the first low pressure system, which should be near the Ohio River Valley, will likely move into the area before stalling over the state delivering rounds of showers and isolated thunderstorms.
High temperatures will vary widely Friday afternoon with 50s in the Upstate and 70s towards the LowCountry and Pee Dee regions. The best chance for strong convection Friday will likely take place in the warmer pockets which should be along and south of the I-20 corridor according to the National Weather Service in Columbia.
The Storm Prediction Center on Thursday issued a Marginal Risk (risk level 1 out of 5) for the Midlands and western parts of the Pee Dee and LowCountry for late Friday afternoon and overnight into Saturday. The primary threat with some storms is expected to be damaging wind gusts. However, an isolated tornado cannot be ruled out.
Showers should decrease for a short period by early Saturday morning as the first low pressure system passes to the north of the state. However, the cold front is expected to remain stalled over the region but will gradually weaken to start off Saturday. The second low pressure system is anticipated to strengthen and lift from the southern Appalachians and track into the state beginning Saturday night. This system will help to amplify the stationary cold front over South Carolina and showers and thunderstorms should resume by late in the day as deep tropical moisture advects northward.
The Storm Prediction Center has shifted the Marginal Risk towards the Atlantic coast for Saturday as the cold front inches eastward towards Pee Dee and the LowCountry. Strong storms are possible but the main threat will be the heavy rainfall. Weather models have been indicating near record rainfall levels with amounts of 2 to 4 inches possible.
Drier conditions and near seasonal temperatures are expected to surge in after the passage of the slow cold front. Temperatures are forecast to return into the 50s in the Upstate and 60s for the Midlands and out towards the coast for Sunday.