A period of active weather is coming to South Carolina on Thursday. The cause is a storm centered over Louisiana, which will track northeastward toward Lake Erie. Ahead of it, a warm front will lift northward through our state tonight that will generate some rain, especially over the Upstate. Then, a line of thunderstorms currently in Mississippi and Alabama will move through Thursday with soaking rains and a severe storm risk. A cold front will move through late Thursday with a shower or thunderstorm in spots, followed by cooler air rushing in.
The Storm Prediction Center (SPC) has outlined the entire state as having a risk for damaging thunderstorms during the day on Thursday.
SPC's latest Severe Weather Outlook graphic for Thursday shows most of South Carolina in a level 1 of 5 severe storm risk area; a small part of the Lowcountry is at level 2.
The primary concern for Thursday is for damaging straight-line wind. It will turn blustery across the state as the line of storms approaches, and winds will become strong even outside thunderstorms. However, the best chance for damaging wind gusts will be within the thunderstorms. A lesser concern is that the vertical shear setup favors isolated tornadoes with the thunderstorms. Any tornadoes that occur are likely to be of the short-lived and relatively weak variety, but even these "junior tornadoes" (as I've heard them called in Oklahoma) are still quite dangerous.
Working in our favor is the timing of this event. Storms likely arrive in the western part of the state around daybreak Thursday and progress steadily eastward, exiting over the Atlantic during midafternoon. So, most of the state will be at risk during the coolest and least unstable part of the day. This is why SPC has most of the state at the lowest risk level. The level 2 area in the Lowcountry is justified because it will be warmer and more humid there Thursday morning and midday ahead of the storms. There is a chance this level 2 area will have to be expanded further northeast along our coast.
This loop of simulated radar reflectivity output from the 1800 UTC run of the HRRR model helps to visualize the timing of thunderstorms across South Carolina. The loop begins at 8 p.m. EDT this evening and ends at 8 p.m. EDT Thursday. Remember that this is model output and it will not predict exactly where the most intense storms will occur.
In addition to the severe storm risk, we will see a soaking rain over much of South Carolina through Thursday. Most of the state will see an inch or more, with parts of the Upstate, especially our mountains, seeing 2-3 inches. This could cause minor flooding, especially with it coming on the heels of a solid half-inch or so in that area on Tuesday.
There is a 'what can go wrong' department today. One concern is that the storms might move in earlier than forecast, perhaps reaching parts of the state before daybreak. The other concern is that a scattering of showers and thunderstorms will occur in the Upstate and vicinity with the cold front Thursday afternoon. This activity likely remains below severe levels, but that is not certain. So, stay on your toes Thursday afternoon and early evening in case a storm headed your way decides to go rogue with locally gusty winds and hail.
As always, have two ways to receive warnings, like a weather radio and a properly-configured cell phone weather app. Set this up before you go to bed tonight. You might have to hit the ground running Thursday morning since the storms will arrive early, perhaps even before daybreak.
Gusty westerly winds will follow the cold front Thursday night through Friday, but these will be a nuisance with peak gusts around 35 mph. Of course, that's a major annoyance for motorists and pickleball players, but the wind should not cause damage. Once past Friday, it looks like we'll see tranquility for a while; more about that on Friday.
