A 1-2 punch of weather systems will bring severe thunderstorms to the Palmetto State, with the first one hitting this afternoon and evening and the second one hitting Friday afternoon and evening.
An upper-level disturbance that was over the Tennessee Valley at midday is responsible for today's severe weather. It will arrive later this afternoon and touch off thunderstorms. Locally damaging wind and large hail are the primary concerns. The Storm Prediction Center (SPC) has the entire state in at least a level 1 of 5 severe storm risk area, with much of the state in a level 2 area.
The setup over the western Carolinas favors supercell thunderstorms at the start of the event, which are the kind of storms that produce most tornadoes. However, the setup isn't great for tornadoes, with most of the wind shear that leads to supercells found well above the surface. There's a low-end tornado risk in the Upstate, but the risk is near zero elsewhere.
However, supercells also cause damaging straight-line winds and large hail, and a non-tornadic supercell is often a prolific hail producer. So, large hail (think golf ball-sized and perhaps larger) is a concern along with the damaging wind risk. That's a highly destructive combination where we might pair the two together. Ask the people of Rock Hill how miserable wind-driven hail can make you! Eventually, storms should consolidate into a squall line that primarily causes locally damaging winds as it crosses the rest of the state.
So, keep your eyes peeled this afternoon and evening, especially if you live along and north of the I-20 Corridor, and be prepared to take shelter as thunderstorms move your way. If you have a garage, this will be a day to put your car in, thanks to the hail threat. (That is, if you can find room among the lawn mower, old washing machines, and stuff you've meant to go through for three years. Not judging or anything; there's a reason I'm so oddly specific.) Be sure you have at least two ways to receive warnings for your area, such as the emergency alerts on your mobile device and a weather radio. These are the storm prep basics; you'll find complete storm prep advice at scemd.org and on the National Weather Service's website.
Friday will bring a cold front into South Carolina, causing our second round of locally severe thunderstorms. SPC has most of the state at a level 1 of 5 severe storm risk area.
The risk area is subject to change and may be kicked up a notch for parts of the state once forecasters examine the situation early Friday. Once again, locally damaging wind and hail will be the primary risks as the front moves into the Upstate Friday afternoon, with a near-zero tornado risk. Storms will shift southward into the Coastal Plain as we go into the evening.
Once we reach Saturday, the front will become stationary to our south or over the Lowcountry. Then, we'll wait for a wandering storm system now across the southwestern states and northern Mexico to reach us. Timing is uncertain on when that storm system will start to affect us, but when it does finally get here (likely sometime Saturday, but maybe it's by daybreak, or maybe Saturday is dry until late afternoon or evening; hopefully there is more clarity in another 24 hours), we're in for an extended stretch of wet weather. That will bring us some drought relief at the expense of localized minor flash flooding where repeated downpours occur and perhaps a few more gusty thunderstorms.
My usual Friday edition will cover the second round of severe storms and the soaking rains to follow in more detail.