Ag Weather Forum

Heat and humidity have been the talk of the weather scene across the Central and Eastern United States for the last week as an upper-level ridge of high pressure has been building across these areas. On the northern edge of these heat ridges, there is good potential to produce thunderstorms that form clusters, often called a mesoscale convective system, or MCS.

MCSs often produce severe weather in the form of damaging wind gusts. One of these may develop later Monday, July 28, and that could turn into an extremely damaging windstorm called a derecho for parts of the North-Central U.S.

The Storm Prediction Center has a moderate risk of severe weather (four out of five on the severity index) for this potential in eastern South Dakota and southwestern Minnesota late Monday afternoon and evening.

Scattered thunderstorms have already formed in the Northern Plains early Monday across Montana and into western North Dakota. These storms will be watched as they migrate southeast throughout the morning and afternoon. They are likely to build as they get deeper into the Dakotas, reaching where the heat and humidity are maximized south of a front that is draped across South Dakota and southern Minnesota and becoming an MCS if it hadn't already.

Tapping into this extreme amount of energy will likely cause the storm clusters to rapidly intensify. Winds coming out of the storm could be very significant once they do. If the wind speeds can consistently be in the severe category (at least 58 mph) for at least 240 miles and include some hurricane-force wind gusts over 74 mph, then whatever MCS forms here would likely be labelled as a derecho. Other than the extreme winds, areas of hail and tornadoes will be possible as well as heavy rainfall that may produce flooding.

The development of a derecho may be complicated by other thunderstorms developing in the heat as the cluster approaches, as well as recovery from overnight storms over Iowa and southern Minnesota. That could extend severe potential farther south into northeastern Nebraska and Iowa, and these areas will need to be watched closely as well. And, though the setup does appear to be favorable for producing a derecho, it does not mean that one is guaranteed.

Derechos produce widespread damage, but MCSs do not need to be labelled a derecho to do so. Regardless of classification, those living in the North-Central U.S. will need to be weather aware Monday. Though the threats are less likely for the rest of the week, the front will get pushed southward where severe storms and heavy rain will be possible for much of the country.

The U.S. sees one or two derechos each year on average. It could be argued that the Northern Plains already saw a derecho on June 20, 2025, as severe winds approaching 100 mph were noted in North Dakota and northern Minnesota.

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John Baranick can be reached at john.baranick@dtn.com

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