Nick Nientimp, Amelia Burch and other bystanders help push a stuck car out of the snow on Tuesday, Dec. 29, 2020, in downtown Des Moines, Iowa. Up to 8 inches of snow is expected around central Iowa as a winter storm moves through the state. (Olivia Sun/The Des Moines Register via AP)

DES MOINES, Iowa (AP) — A strong winter storm made its way across the Upper Midwest Tuesday, creating treacherous travel conditions, spurring warnings urging people to stay off the roads and closing coronavirus testing sites.

The National Weather Service issued winter storm warnings for parts of Nebraska, Iowa, Kansas, Missouri, South Dakota, Wisconsin and Illinois.

Snow was so heavy in western Nebraska Tuesday morning that Interstates 80 and 76 were closed for several hours in both directions after numerous accidents, and the Nebraska Department of Transportation warned people to avoid unnecessary travel.

By 4 p.m. Tuesday, the storm had mostly moved out of Nebraska. The Nebraska State Patrol said troopers responded to more than 150 weather-related incidents, including 129 motorist assists.

Many government buildings and properties closed ahead of the storm, including COVID-19 testing sites in Norfolk, O’Neill, Nebraska City, Beatrice, Bassett and Auburn.

Heavy snowfall of up to a foot, and perhaps more in some spots, was forecast in parts of Iowa, where the state Department of Transportation urged people to delay travel plans.

The city of Des Moines had more than 200 employees from public works, parks and recreation, and wastewater reclamation departments on snow removal duty.

Wisconsin was also bracing for up to 10 inches of snow in some areas. The forecast called for 3 to 6 inches of snow in the Milwaukee area.

AccuWeather said parts of southeast Nebraska, northeast Kansas, northern Missouri and southern Iowa could see ice accumulations of up to a quarter of an inch, which could weigh down power lines and branches and cause power outages.

Forecasts showed the storm would move into the Southern Plains later in the week, when parts of Texas and Oklahoma could receive snow or a wintry mix Wednesday and Thursday.