A heavy fall snowstorm hit the Midwestern United States on Saturday, blanketing states from South Dakota to Wisconsin with as much as 16 inches of snow, and was forecast to travel east into the Great Lakes region, according to the National Weather Service.

Some 4 to 8 inches of snow was forecast from northern Illinois through central Michigan with snow expected to continue into Sunday.

Forecasters warned that trees that had not already dropped their leaves could be damaged by the heavy, wet snow.

"We have snow across the area with heavier amounts across northern Illinois," said Amy Seeley, a meteorologist with the National Weather Service office in Chicago.

While it is uncommon for the Midwest to see such heavy snowfall so early in the year, the storm is not unprecedented, Seeley said, noting that an early November storm in 1951 dropped 9.3 inches of snow.

"This has happened before, but obviously it's not as common to have this much snow in November," she said.

Snow was forecast to continue into the early evening hours, with single-digit Fahrenheit temperatures hitting parts of the northern Midwest overnight, she said.

The storm affected air travel, with 457 U.S. flights canceled by Saturday morning, with Chicago's O'Hare International and Midway International airports the hardest hit. One in three Midway departures had been canceled by 9:30 a.m.

The Illinois and Michigan Departments of Transportation warned that snow and ice-covered roads would slow travel.