Derecho brings 75 mph winds, severe warnings near Storm Lake

Storm Lake and nearby towns were jolted before sunrise by a fast-moving line of severe storms that pushed east at 60 mph and put Buena Vista County in the warning path as winds strengthened across northwest Iowa. The National Weather Service warned at 3:26 a.m. that northeastern Cherokee County and Buena Vista County could see ping pong ball-size hail and damaging winds, with Alta and Aurelia in the storm’s path around 3:30 a.m. and Storm Lake, Lakeside and Truesdale about five minutes later.

A follow-up warning at 3:36 a.m. said the storm was near Alta, about 10 miles northwest of Storm Lake, and still moving east at 60 mph. That warning expanded the list of communities that could be affected to Storm Lake, Alta, Truesdale, Albert City and Newell, underscoring how quickly the system was crossing the county before many residents had fully started their day.

The National Weather Service in Des Moines described the event as part of a damaging wind storm that had derecho-like structure, and the agency’s definition helps explain why the warnings drew so much attention. A derecho is a long-lived swath of thunderstorm winds with gusts of at least 58 mph along most of its length, several separate gusts of 75 mph or more, and a track at least 250 miles long. The agency says derecho winds can exceed 100 mph, reaching the strength of an EF-1 tornado but over a much wider area.

Across Iowa, the storm line tracked from northwest to southeast in the early morning hours of June 17 and produced damaging winds and heavy rain. The weather office described a rainfall swath of 1 to 3-plus inches from central Iowa into southeast Iowa, while gusts over 75 mph were reported across a path stretching more than 360 miles. The system arrived just days after the June 10-11 Midwest severe weather outbreak, adding another round of disruption to a region already dealing with a prolonged stretch of unstable weather.

In Storm Lake, the utility impacts were already visible on MidAmerican Energy’s outage map, which showed the local power area being affected during the storm period and carried a warning about downed power lines. The map was last updated at 4:12 p.m. on June 17, a reminder that the storm’s effects extended beyond the warning sirens and into daily life for Buena Vista County households and businesses. The National Weather Service’s archive of past Iowa derechos, including July 11, 2011 and August 10, 2020, offers a sobering comparison for a storm pattern that once again put northwest Iowa on alert.