Chicago ? Utility crews worked overtime Saturday to restore electrical service to thousands of customers still blacked out by the Midwest’s first big snowstorm of the season.

As temperatures plummeted below freezing, officials said some people could be without power for days. National Guardsmen in Missouri and Illinois went door to door in the St. Louis area to make sure residents were surviving the cold.

The storm was blamed for at least 13 deaths as it spread ice and deep snow from Texas to Michigan and then blew through the Northeast late Friday and early Saturday. Schools and businesses were shuttered, and hundreds of travelers had been stranded by canceled flights.

Nearly 600 Amtrak passengers in Illinois and Missouri were delayed up to 10 hours Friday and Saturday morning, Amtrak spokesman Marc Magliari said. With many tracks still strewn with downed trees and power lines, passengers were eventually taken by bus to their destinations.

Many areas of Illinois, Wisconsin and Missouri got more than a foot of snow, including 16 inches in parts of central Missouri and 17 at Manistee, Mich. Fifteen inches fell as far south as Bartlesville, Okla.