Round two of a three-day severe weather outbreak across the eastern half of the United States is getting ready to unfold across the Midwest this evening and tonight. The atmosphere is getting antsy, and it looks primed to produce more destructive straight-line winds and maybe even a strong tornado or two. The storms also have the potential to develop into another derecho, much like the one we saw today.
Mesoscale convective systems—or a squall line, which is an organized line of thunderstorms—are nothing if not impressive. Monday’s severe weather event played out much as forecasters expected, with a couple of intense supercells in western Minnesota and eastern North Dakota merging into a potent squall line that continues to chug along as of the writing of this post. You can see the progression of the squall line above (times in CDT)—as of 4:00 PM EDT, the squall line is still producing damaging winds in excess of 60 MPH as it sweeps through eastern Kentucky on its way toward the Appalachians.
If you were wondering, the storm has likely produced enough damage over a long enough path to be considered a derecho. A derecho is a long-lived, intense squall line that produces significant wind damage over a path at least 250 miles long.
Risk Level: 4 out of 5, or a moderate risk
Hazards: Destructive straight-line winds, a couple of strong tornadoes, hail larger than golf balls in any supercells that form.
Storm Modes: A handful of intense supercells at first, morphing into a dangerous squall line this evening that will last through tomorrow as it races southeast. The storms have the potential to become a derecho if they last long enough.
Select Cities at Greatest Risk: Chicago, Peoria, Champaign, Lafayette, Indianapolis, Terre Haute, Louisville, Evansville, Lexington.
Discussion: Just like we saw yesterday, supercells will likely develop near the Mississippi River in Iowa, Illinois, and Wisconsin—these discrete storms will be intense, and if they have the right interaction with surface features (like outflow boundaries), they could produce some strong tornadoes. These supercells will congeal into a squall line in northern Illinois, which will make its way southeastward just like the one still raging today.
Here’s a look at the threat for damaging winds this evening. The black hatching indicates the risk for significant wind gusts of 75 MPH or stronger. Higher percentages equate to a greater risk for strong, damaging winds.
Stay alert if you live in or around the edges of a higher risk area—the threat for wind damage will follow the path of the storms (thank you, Captain Obvious), so the storms (and the strongest winds) may wobble beyond the areas forecast. Nature often does things we don’t expect.
We can’t ignore the threat for tornadoes, especially in the supercells that form as a precursor to the squall line. The Storm Prediction Center has a 10% risk for strong tornadoes across portions of northern Illinois, which doesn’t sound like much, but it’s a lot more significant than a 10% chance of rain.
I hope you’ll forgive me if I copy and paste a few paragraphs from the post I wrote about yesterday’s severe weather. The majority of the storms that unfold during this second outbreak will occur at night. Nighttime storms are even more dangerous than ones that occur during the day because people just aren’t paying attention.
Severe thunderstorms are dangerous enough, but what’s most concerning is that the majority of the storms anticipated over the next couple of days will unfold overnight when people are tuned-out or asleep. Every year, people stumble to the nearest news camera and shout out “WE HAD NO WARNING” when their homes are demolished at 3:00 AM, and without fail, news organizations manage to spin “we had no warning” into a failure on the part of meteorologists instead of a failure on the part of residents in the path of the storms.
You need to be proactive about your own safety. Make sure you have a way to receive alerts both day and night, ensuring you can quickly act if dangerous storms threaten even if you’re dead asleep. Go to Walgreens or Walmart or Lowe’s or Home Depot and buy a weather radio that, when properly set-up, automatically activates a loud tone when a warning is issued for your county. The baseline models are $20-$30, but they’re well worth the cost. Email me if you can’t figure out how to set it up and I’ll gladly guide you through it.
The risk for severe thunderstorms will continue on Tuesday, dependent on how much rain and clouds linger in the area as a result of tonight’s event. If the atmosphere is able to recover from today’s leftovers, all signs point to another dangerous severe weather day, this time across much of the southeast.
The Storm Prediction Center has issued a three out of five—or enhanced—risk for severe weather in the southeast in anticipation of a widespread risk for severe thunderstorms capable of producing damaging winds and large hail. The greatest risk for severe weather as of this afternoon’s forecast is along and west of the Appalachians in the enhanced risk zone, but any severe thunderstorm is dangerous.
Pay attention to the weather tonight and tomorrow, especially if you live in an area at heightened risk. Make sure you have a way to receive alerts tonight. You can keep up with the latest severe weather alerts for your area by frequently checking the Storm Prediction Center and your local National Weather Service office.
[All maps by the author—please let me know if you have suggestions on how I can improve them.]