A powerful storm system that brought high winds to parts of northern Iowa last week has officially been designated a derecho, causing damage to trees, buildings and crops along its path.

Experts with the National Weather Service Storm Prediction Center determined that the storm that rolled through late on July 28 met the criteria to be considered a derecho — a widespread, long-lived storm system that travels at least 400 miles, spans a width of 60 miles or more, and produces sustained winds of at least 58 mph across most of its length, with peak...