OMAHA, Neb. (AP) — A major winter storm threatened to blanket parts of the middle of the country with more than a foot of snow Monday, promising to disrupt travel and even forcing the closure of some coronavirus testing sites.

The National Weather Service said at least 4 inches (10 centimeters) of snow is expected across most of an area stretching from central Kansas northeast to Chicago and southern Michigan. Parts of southeast Nebraska and western Iowa could get more than three times that much.

Several coronavirus testing sites in Nebraska and Iowa planned to close early Monday because of the snow. More than 6 inches (15 centimeters) of snow had already fallen in parts of eastern Nebraska by midday.

National Weather Service meteorologist Taylor Nicolaisen said 10 to 15 inches (25 to 38 centimeters) of snow is likely between Lincoln, Nebraska, and Des Moines, Iowa, and that it has been at least 15 years since that area received more than a foot of snow in a single storm.

“This is a historic snow,” said Nicolaisen, who is based near Omaha, Nebraska.

Many schools and businesses closed Monday as the storm moved across the region. In western Iowa, Missouri Valley Superintendent Brent Hoesing reworked the lyrics of the 1970s hit “I Will Survive” to tell students in his district to “So Stay Inside.”

Officials urged drivers to stay off the roads during the storm, especially during the heaviest snowfall in the afternoon and evening. Nebraska State Patrol troopers had helped at least 60 drivers who got stuck or slid off the road by midday Monday.

“Do not travel unless it’s absolutely necessary,” said Nebraska State Patrol Col. John Bolduc.

Roughly 250 semi trucks pulled off the road to wait out the storm at the Petro truck stop alongside Interstate 80 in York, Nebraska. Manager Rachael Adamson said she could see knee-high drifts and that the maintenance man had to go out every 30 minutes to shovel the sidewalks to keep up with the snow.

“We haven’t had this much snow in quite a few years,” Adamson said.

Elsewhere in the U.S., a storm moving across the Southwest on Monday and Tuesday was forecast to bring gusty winds and snowfall, the weather service said. Over the weekend, more than a foot of snow fell in Southern California’s mountains, making driving conditions hazardous. Interstate 5 was shut down Monday in the Tejon Pass between Los Angeles and the San Joaquin Valley. Wind, snow and ice also forced the closure of State Route 58 through the Tehachapi Pass.

Until recently, California had been experiencing significantly dry weather accompanied by relentless wildfires. A band of clouds suggested more rain could fall Tuesday in areas north and south of San Francisco Bay, bringing the threat of possible flash floods and landslides in areas scarred by the fires.

Across southern Nevada, light rain and snow at higher elevations was reported Monday.

Forecasters at the Sacramento-area National Weather Service office predict an abundance of snow in the Sierra Nevada between late Tuesday and Friday that will make travel through the mountains difficult.