Explosive Thunderstorms, Possible Derecho Threat Across Iowa, Wisconsin, and Northern Illinois

A possibly volatile severe weather event is unfolding across the Upper Midwest this afternoon (7/26) into early Tuesday (7/29) morning, with the potential for a rare and destructive derecho sweeping across Iowa, Wisconsin, and parts of Illinois.

According to recent posts from the Midwest Weather Facebook Page, future-casts show a rapidly organizing cluster of thunderstorms is expected to intensify over parts of the Dakotas and Minnesota, then evolve into a fast-moving Mesoscale Convective System (MCS). As it bows out and accelerates southeastward, this system is forecast to produce widespread damaging wind gusts, potentially exceeding 80 to 100 mph in some areas, strong enough to cause power outages, tree damage, and even structural impacts.

This complex is expected to reach eastern Iowa and southern Wisconsin by late evening, pushing into northern Illinois overnight. Areas along and just north of Interstate 80, as well as along the I-35 and I-39 corridors, should prepare for dangerous nighttime storms with little warning. Some weakening is expected by the time it reaches areas east of the Mississippi River, but it may still maintain damaging potential well into Illinois.

A derecho is a long-lived, widespread windstorm associated with a line of rapidly moving storms. To qualify, the system must produce wind damage over at least 400 miles and include multiple reports of severe wind gusts (58+ mph). Today’s setup meets many of these criteria and is being monitored closely.

Get our free mobile app

Residents in the path of this system should have multiple ways to receive weather alerts, especially after dark, and be prepared to take shelter quickly. Watches and warnings will be issued throughout the evening. If your phone alerts, don’t wait until it’s too late.