“This is very unusual for this time of year,” Jeff Ormond, Allstate spokesperson for the insurer's regional office overseeing Ohio, Michigan and Indiana, told PC360. “Usually the region would see like weather in the warmer months of May through September. We did have tornados in Henryville, Indiana and Dexter, Michigan in March 2012, which was very unusual at that time too.”

Illinois saw the worst devastation, says Aon. National Weather Service (NWS) meteorologists recorded an EF-4 twister that completely wiped a farmhouse off its foundation, killing an elderly man and his sister. An EF-2 tornado tracked across Grundy and Will counties, and a deadly tornado in the Peoria region destroyed homes and an apartment complex. Other touchdowns destroyed homes, structures and mobile homes.

Local news reported hospitals were treating patients for severe storm-related trauma injuries.

Thunderstorms, hail and thousands of power outages in the Chicago area grounded flights at O'Hare and midway international airports and delayed an NFL game between the Baltimore Ravens and Chicago Bears at Soldier Field. Fans were evacuated during the game's first quarter.

At least 12 counties in Indiana reported tornado damage, with states of emergency declared in Howard County, home to the towns of Kokomo, Russiaville and Greentown. Severe damage was also reported in Lafayette, Washington and Lebanon cities. One tornado in Logansport caused gas leaks that prompted several complexes to be evacuated.

Eight Kentucky counties reported tornado touchdowns. The Great Lakes were also affected, primarily by straight-line winds that left 253,000 customers without electricity in Michigan. Similar winds of up to 70 mph were felt in Missouri, Ohio and Wisconsin.

Meteorologists from Weather Underground and the Weather Channel say tornadoes are possible in the Ohio Valley and Midwest early Monday, with subsiding but still-strong winds to move into the Northeast by evening.

It is too early to tell the scope of the losses, says Loretta Worters, spokesperson for the Insurance Information Institute, but expects that “hundreds of homes and businesses were damaged or destroyed.”

“Insurers stand ready to help policyholders with the recovery process. Claims adjusters have already begun to help policyholders file claims,” said Jim Whittle, chief claims counsel for the American Insurance Association, in a statement. “AIA's member companies have begun communicating with policyholders through a variety of channels, including Facebook and Twitter.”

Ormond says Allstate has mobile claims units en route to several of the affected locations, where agents have seen severe windstorm damage.

Until Sunday, economic and insured losses from severe weather in 2013—the quietest U.S. tornado year since 1988—were slightly below the 10-year average, records the Storm Prediction Center.

U.S. thunderstorms cost $14.9 billion insured losses in 2012, reports Munich Re. The U.S. experiences more tornadoes than any other country worldwide.