Key Points:
- South Carolina will be on the fringe of a major severe thunderstorm and tornado outbreak through Sunday.
- The risks include damaging wind, isolated tornadoes, damaging hail, and flash flooding as the thunderstorms impact us Saturday night and Sunday.
- There is some uncertainty about the timing. Check the forecast occasionally through the weekend for updates specific to your area.
- Before the storms, take some time to review tornado safety tips (see the last paragraph and the links therein).
- Those traveling to the Midwest and middle Mississippi Valley tonight or Tennessee, Arkansas, Louisiana, Mississippi, Alabama, and Georgia Saturday through Saturday night must remain on high alert for severe thunderstorms with damaging winds, violent tornadoes, and large hail.
By now, you probably have heard that a mighty storm currently swirling over the Intermountain West and Plains will cause a major outbreak of severe thunderstorms and tornadoes over parts of the country through Sunday. The worst of this will occur in areas to our west, but South Carolina will have a risk for damaging winds and tornadoes later Saturday night through Sunday.
The setup is like the one we had last Wednesday; the storm center will track toward the Great Lakes and pull a cold front across the South. The difference here is that a much warmer and more humid air mass will be in place ahead of the front, an air mass laden with thunderstorm fuel. Also, the setup this time will be more favorable for tornadoes to occur with the thunderstorms.
I'll show a wide-angle view of the Storm Prediction Center's (SPC) Severe Weather Outlooks to give y'all an idea of the magnitude of the coming severe weather outbreak. Day 1 covers today and tonight, Day 2 covers Saturday and Saturday night, and Day 3 covers Sunday and Sunday night.
As I've mentioned before, level 3 (enhanced) and higher risk areas are the areas where you need to stand up and pay attention, and that's especially true when they appear on the outlooks for Days 2 and 3. At least for now, we don't have much of that over South Carolina except for a part of Oconee County. My point in showing the whole country this time is that those who have travel plans to the Midwest and Mississippi Valley this afternoon and tonight, or on Saturday to the lower Mississippi Valley, Tennessee Valley, Gulf Coast, and points in between, need to be ready for a serious severe storm and tornado outbreak. SPC is particularly bullish on the threat of violent, long-tracked tornadoes across Louisiana, Mississippi, and Alabama for Saturday afternoon and night. If you travel to those areas, you'll want to remain alert to the severe storm and tornado threat and know what to do when a warning comes out.
South Carolina may be on the fringe of this outbreak, but the severe storm danger is real for us, starting later Saturday night and lasting through Sunday. There is some uncertainty on the event's timing because squall lines like what we expect to see move through this weekend tend to move faster than our computer model guidance indicates. The front causing the severe storms will also slow down as it approaches the East Coast, which adds more timing uncertainty.
Our primary concern will be locally damaging winds. Like last Wednesday, it will be pretty windy even outside the thunderstorms, but the storms will cause the strongest wind gusts. The next concern is isolated tornadoes; the tornado risk is higher this time around. Damaging hail may occur in a few spots as well.
Slower-moving storms add one more concern to the situation: flash flooding. Some areas may see prolonged downpours or training storms. The risk will be greatest in the Upstate because some rain will fall ahead of the storms Saturday and Saturday evening due to upsloping moisture-bearing southwesterly winds.
The current estimate is for the thunderstorms to arrive in the Upstate around 2 a.m. Sunday and march across the Upstate through daybreak. The line of storms likely stretches from Rock Hill to Aiken at 7 a.m. Sunday. By midday, the line should be over the Central Savannah River Area, Midlands, and possibly the upper Pee Dee, but it's around this time that the progression slows down considerably. I expect it to move more slowly through the Coastal Plain through the rest of the day. If this timing is correct, the storms reach the Coastal Plain during the warmest and most unstable part of the day, so this may be where the greatest severe weather risk occurs.
We'll also have to watch for a second wave of potentially severe thunderstorms to develop to our west on Sunday and move through the Upstate during the midday or afternoon hours.
The thunderstorms and severe weather risk should exit out to sea late Sunday or early Sunday night, but lingering showers could hang around past midnight Sunday night.
Cooler and dry air will return to the Palmetto State behind the cold front, and a few pleasant days should follow during the first part of next week, though I can't rule out a pop-up shower or two on Monday in the Pee Dee. The next chance for rain comes on Thursday as another cold front arrives, which could be another thunderstorm situation, depending on the timing. The thunderstorm risk would be higher if the front reaches us in the afternoon.
A chilly-for-March air mass could move behind Thursday's cold front. On Friday or Saturday morning, there is a chance for a freeze in parts of the Upstate.
This weekend offers the best chance for severe storms and tornadoes so far this year. Unfortunately, parts of the state could be hit in the middle of the night or early in the morning, when most people are sleeping. So, it's essential to prepare in advance this time. Decide on your best shelter (interior room, basement, under a staircase, etc.) ahead of the storm so that you can react when you get the alert for a tornado warning; you may not have time to evaluate shelter options at that point. Be sure you have at least two ways to receive warnings (mobile device emergency alerts, mobile apps, a weather radio, SCEMD's CodeRED alerts, etc.), and they need to be LOUD so they wake you if you're sleeping. Also, having some protective items in your shelter, such as a bicycle or motorcycle helmet (head trauma is common in tornadoes), work gloves, sturdy clothes, and shoes, would be nice. Finally, take some time to review tornado safety information from the National Weather Service and SCEMD to get more prep tips.