A ferocious storm system that swept across the Midwest left hundreds of thousands of customers without electricity on Thursday, with hundreds of houses, barns and buildings damaged and one man dead after a gust of wind overturned his tractor-trailer on an Iowa highway.
Less than a week after a string of deadly tornadoes devastated six states, Wednesday night brought weather that was extremely unusual for the Midwest in December: 70-degree temperatures, wildfires, tornadoes and winds that surpassed 75 miles per hour.
“In the middle of December, it’s obviously extraordinary, unprecedented,” said Mike Fowle, a meteorologist for the National Weather Service, noting that the city of Des Moines broke a record by reaching a temperature of 74 degrees.
Before Wednesday, Mr. Fowle said, there had been only five confirmed tornadoes in the month of December in Iowa, dating back to 1950. On Wednesday alone, there were at least five tornadoes across the state.
Storm teams from the National Weather Service were crisscrossing the Midwest on Thursday surveying the damage, and the extent was still coming into full view.
The storm system, which was moving into Canada on Thursday, came five days after tornadoes whipped through Kentucky and five other states, killing at least 88 people, whichmay have prompted many people in the Midwest to take a cautious approach when faced with storms on Wednesday night.
What prompted the unusual December weather events is unclear. The ingredients that give rise to tornadoes include warm, moist air at ground level; cool dry air higher up; and wind shear, which is the change in wind speed or direction. Each of these factors may be affected differently by climate change.
Residents of communities across Michigan, Wisconsin and Iowa were still struggling with widespread power outages on Thursday. Most were in Michigan, with more than 235,000 customers without power by late morning, according to PowerOutage.us, which aggregates data from utilities across the country. Another 128,000 experienced outages in Wisconsin, and nearly 38,000 customers were without power in Iowa.
In western Wisconsin, the police department of the city of Stanley wrote on Facebook that there was devastation throughout the community from storms overnight, with roofs of buildings sheared off by winds, streets filled with rubble and power lines downed. As emergency workers and residents worked to clean up on Thursday morning in 24-degree temperatures, a light snow began to fall, with wind gusts of 40 miles per hour predicted.
Despite few reports of injuries or major damage, the main air traffic control tower at Kansas City International Airport was temporarily evacuated early Wednesday evening.
The National Weather Service said there had been at least 55 wind gusts of at least 75 miles per hour across the country on Wednesday, the highest daily number since 2004.
In the West and Plains regions, dust storms whipped through Colorado and Kansas, and a tornado was spotted in Lincoln, Neb. Images circulating on social media showed damage to hangars and small planes at the Santa Fe Regional Airport in New Mexico.
In Iowa, transportation officials shut down bridges and warned drivers to stay off roads. And in Omaha, meteorologists for the Weather Service briefly suspended their work as they sheltered from a storm.
The storm system also spawned wildfires and winds of up to 100 m.p.h. in Kansas, the local authorities said.
As storms moved through South Dakota, the Weather Service office in Sioux Falls issued its first tornado warning on record for the month of December.
And in Iowa, where schools closed early and some areas saw wind gusts of up to 90 m.p.h., high temperatures reached the lower 70s. On average, high temperatures in December throughout much of the state are in the 30s, according to the Weather Service.