Blog Article
Severe Storms Threaten Great Lakes After SD Derecho
A Slight Risk for severe storms spreads into the Midwest and Great Lakes today, with an even more organized threat set up for Monday across Ohio and Michigan.
Severe Storms Take Aim at the Great Lakes Again After That 92 MPH Gust in South Dakota
Alright y'all, let's talk about what South Dakota went through last night, because it sets the stage for today. A Particularly Dangerous Situation Severe Thunderstorm Watch went up over central and eastern South Dakota as a big MCS came together, and it delivered. Tea, SD measured a 92 mph gust. Harrisburg and Ireton, IA weren't far behind at 81 and 82 mph. That's not garden variety wind. That's roof-tearing, tree-snapping wind, and it followed a month that's already given us a 105 mph gust in Huron back on July 2. This has been a rough July for the Dakotas.
Today, that same general energy shifts east, and the Storm Prediction Center has a Slight Risk posted from the Upper Midwest and Great Lakes down into Nebraska.
What's driving today's threat
An upper ridge is holding steady over the western US, and that's funneling energy along its northeastern flank into the Midwest. SPC's discussion points to large to very large hail, damaging winds (they specifically flag the potential for 75+ mph gusts in a hatched zone), and an isolated tornado risk this afternoon into tonight. Chicago, Milwaukee, Minneapolis, Madison, and Grand Rapids all sit inside that Slight Risk. About 27.6 million people are covered by it, and CAPE and shear values are plenty sufficient for organized storms if the cap breaks.
If you've got a Twins game at Target Field this afternoon, or you're headed to a Brewers-Rockies game in Milwaukee, keep half an eye on the sky as the day wears on. Same goes for the Cubs-Pirates game up in Pittsburgh and the White Sox-Astros matchup in Chicago. Day games should be fine early, but the timing on this risk skews toward afternoon into tonight, so evening activities are the ones to watch.
Tomorrow is the bigger story
Here's the thing about Monday. SPC's Day 2 outlook actually raises the stakes. The Slight Risk shifts into the Great Lakes and Ohio Valley, covering Chicago, Columbus, Indianapolis, Detroit, and Louisville, and it's paired with a 30% probability (Level 3) area for numerous damaging wind reports across lower Michigan into Indiana and Ohio. That 30% number is a meaningful step up from today's 15% max. MLCAPE values in the 2,500 to 3,500+ J/kg range with 40-50+ knot effective shear are the kind of numbers that support a fast-moving, wind-dominant complex, not unlike the derecho analogs our team flagged for this stretch. We're not saying Monday repeats the July 2019 Wisconsin derecho or the July 2024 Great Lakes event, but the ingredients rhyme enough that Detroit, Chicago, and the Ohio Valley need to have a plan for strong, possibly damaging thunderstorm winds Monday evening into the overnight hours. A Marginal Risk also stretches from New York to Nashville, so don't tune out if you're along that corridor either.
The heat is climbing in the north
While the Midwest deals with storms, the Northern Plains are baking. Montana into the Dakotas are running 10 to 15 degrees above average, which is a serious heat load layered on top of ground that's still recovering from last night's wind damage. For comparison, Minneapolis normally tops out around 83 in late July, so numbers well above that are stressing crews trying to clear storm debris and stressing anyone without reliable AC.
Rain risk hugs the Southeast coast
Separately, WPC has a Slight Risk for excessive rainfall along coastal South Carolina into Florida today, tied to a lingering quasi-stationary front and a moisture-rich air mass. This isn't the same setup driving the Midwest severe threat, it's a slower, wetter pattern that favors localized flash flooding rather than wind damage. Anyone in Charleston, Savannah, or the Florida coast should watch for ponding on roads through Monday morning. A separate Slight Risk also develops Tuesday from New York into the Mid-Atlantic as an upper low organizes, with precipitable water values pushing close to 2 inches.
What we're watching
- Whether today's Upper Midwest storms organize into another MCS overnight, similar to Saturday's South Dakota derecho
- The Monday Great Lakes/Ohio Valley setup and whether SPC upgrades any of that Slight Risk to Enhanced as the 12z data comes in
- Continued critical fire weather over the northern Sierra, the Harney Basin, and far northern Montana, where dry fuels and strong flow aloft keep spread risk elevated
- The Northern Plains heat wave and how long that 10-15 degree anomaly hangs around
- Coastal Southeast flash flood potential tied to that stalled frontal boundary
Bottom line
If you're anywhere from Nebraska through the Upper Midwest and Great Lakes today, have a way to get severe weather alerts this afternoon and evening. Large hail and damaging wind are the headline threats, with an isolated tornado not off the table. Monday looks like the more organized day for the Great Lakes into the Ohio Valley, so Chicago, Detroit, Columbus, and Louisville should treat this as a multi-day watch, not a one-off. Coastal Florida and the Carolinas need to watch for standing water on the roads rather than wind. And if you're up in Montana or the Dakotas, this isn't just uncomfortable heat, it's the kind of stretch that raises real health risk if you're outside for long.