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Strong to severe storms may become widespread ahead of a cold front Thursday

/ March 17, 2021 at 6:07 PM

Severe weather appears to be in the cards for Thursday as a cold front approaches the area in the afternoon and early evening hours. This cold front is expected to be bringing a squall line with it, and the atmosphere ahead of the line will become increasingly favorable for sustaining severe weather. Temperatures will surge to near 80° especially away from the immediate coast before being tamped down later in the day. Even outside of thunderstorms, it will be windy, with gusts 30-40 MPH possible thanks to a strengthening low-level jet, which will help contribute to increased shear to help organize severe thunderstorms.

The squall line is the main concern, though. The line could enter western portions of the Tri-County as early as 1-2 PM, and may exit as late as 8 PM, based on the National Weather Service’s latest timing estimates. The line is slowly starting to take shape across Louisiana, and we will want to watch its progress closely over the next 24 hours to ensure timing and forecast is on track. A somewhat later arrival could mean more time for the atmosphere to destabilize, increasing the severe weather threat.

Hazards with the line include the risk for widespread damaging straight-line winds as well as a few tornadoes — a couple of which could be on the strong side, particularly near the I-95 corridor. Quarter-size hail is a possibility as well. Additionally, while not explicitly modeled in our area, we’ll want to keep an eye on any storms that might try to get going ahead of the line as those could pose a higher tornado risk.

Finally, it’s most important to note that not all of you will see severe weather tomorrow. There are limiting factors at play, including the role that the cooler Atlantic shelf waters may play in stabilizing the atmosphere closer to the coast and just how unstable the atmosphere can ultimately get here due to cloud cover. Severe weather forecasts are rarely a slam dunk in the Lowcountry because of our unique geography. With all that said, though, let’s be ready for the worst, but hopeful for a relatively quiet day.

What is a “moderate risk”?

Weather Twitter has been abuzz about the “moderate risk” for severe weather across much of South Carolina in the Storm Prediction Center’s convective outlook . These are rare in this part of the world — the last one was in 2019. (Yes, April 13th was only an “Enhanced Risk.”) The Moderate Risk designation indicates confidence in scattered to widespread severe thunderstorms. For our area, the outlook calls for a 45% chance of wind damage within 25 miles of a point and a 15% chance of a tornado within 25 miles of a point. These are pretty substantial probabilities for this area, and is certainly worthy of our attention.

Additionally, the atmosphere will be capable of producing strong, long-tracked tornadoes, with a 10% chance of a strong (EF-2 or greater) tornado within 25 miles of a point. This risk extends from Georgia through the Carolinas into southern Virginia, further calling attention to the volatile environment expected tomorrow.

What I will say, though, is that thunderstorms really don’t care about these risk categories. In fact, these risk categories originally weren’t even designed for public consumption — they are first and foremost guidance to local National Weather Service offices when they consider the forecast for their areas of responsibility.

Regardless of whether the risk heads up or down with subsequent updates, you should be ready for severe weather tomorrow as the atmosphere will certainly be capable of damaging thunderstorms.

What to do tonight

There are a few things you can get together tonight:

What to do tomorrow

Knowing the difference between a watch and a warning is so important on days like tomorrow.

Cooler and drier for Friday

Once the front is offshore late Thursday/early Friday, the severe weather threat will end and high pressure will build back into the area. We should see some sunshine during the day Friday before clouds increase as a coastal trough sharpens. Temperatures will run in the upper 60s on Friday, much cooler than where we expect to be tomorrow. Right now, the weekend is looking chilly by recent standards, with mostly cloudy skies and the risk for a passing shower each day. (More on this tomorrow.)


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