DENVER (AP) — A storm dumping heavy snow buried highways in Colorado and Wyoming Tuesday, prompted school closures in Nebraska and forced more than 1,000 people to sleep overnight in Denver’s airport after hundreds of flights were canceled just as the busy Thanksgiving week travel period went into high gear.

That storm was heading toward South Dakota, Iowa, Michigan, Minnesota and Wisconsin — and another storm in the Pacific Ocean was moving toward California and Nevada, where heavy snow was predicted to start falling in mountainous areas Tuesday night and mountain pass road closures were planned.

At Denver International Airport, about 7 inches (18 centimeters) was on the ground by Tuesday morning with more expected in the afternoon. Windy conditions reduced visibility, prompting the cancellation of about 30 percent of the airport’s average daily 1,600 flights.

About 1,100 travelers spent the night at the airport, including many cadets from the Air Force Academy near Colorado Springs who either missed flights or wanted to get to the airport before road conditions deteriorated, said airport spokeswoman Alex Renteria.

Airport workers handed out blankets, diapers, baby formula, toothbrushes and toothpaste to the airline passengers who camped out for the night on floors and in chairs. Officials said they were hopeful that flight conditions would be back to normal by the afternoon.

More than 2 feet (60 centimeters) of snow had fallen in northern Colorado and about a foot (30 centimeters) fell in southern parts of Wyoming by midmorning — forcing the closures of long stretches of Interstates 70 and 76 in Colorado and Interstate 80 in Wyoming. Parts of I-80 were buried under snow drifts of up to 4 feet (121 centimeters), officials said.

“We are mindful that this is a holiday travel week and we are working as fast and as quickly as possible to reopen the roads, and we will do that once the roads are safe for travelers,” said Wyoming Department of Transportation spokeswoman Aimee Inama.

Many government offices in the Denver area and in Cheyenne, Wyoming closed along with colleges and schools not already on holiday break. In Nebraska, several school districts canceled classes Wednesday and the southwestern city of Sidney had received about 8 inches (20 centimeter) of snow. George Lapaseotes, the city’s airport manager, said he spent much of the morning clearing the runway in case it was needed for medical emergency flights.

Blizzard and wintry weather warnings extended into the Great Lakes states with the storm expected to bring high winds and snow to Michigan, Minnesota and Wisconsin later Tuesday and a chance of snow over the weekend for parts of New England, said Alex Lamers, a National Weather Service meteorologist.

“That could be a coast-to-coast storm,” he said.

It also could mean disappointment for fans of the larger-than-life balloons flown at Macy’s Thanksgiving Day Parade in New York.

Organizers were preparing for the possibility that of grounding the iconic balloon characters because of 40-50 mph (64-81 kph) gusts in the forecast. Rules put in place after several people were injured by a balloon years ago require lower altitudes or full removal if sustained winds exceed 23 mph (37 kph) and gusts exceed 34 mph (54 kph). The decision will be made on parade day.

The Minneapolis-St. Paul metropolitan area could see its biggest November snowfall in nearly a decade, and travel is northwestern Wisconsin “is going to be chaotic,” said National Weather Service meteorologist Brent Hewett.

The Minneapolis airport could be hit by snow but Chicago and its two big airports should only see rain from the storm, weather service officials said.

The second storm developing in the Pacific Ocean was expected to slam the West Coast of the U.S. on Tuesday evening, bringing snow to the mountains of California and Nevada and wind and rain along the coasts of California and Oregon.

Forecasters also warned of “difficult to impossible travel conditions” across much of northern Arizona later this week as that storm dumps about 2 feet (61 centimeters) on areas that include Interstate 40. The approaching storm accelerated the annual winter closure of the highway leading to the North Rim of the Grand Canyon by five days.

This month, AAA predicted that the number of travelers over a five-day stretch starting Wednesday will be the second-highest, behind only 2005, despite rising costs for a road trip.

At the start of the week, a gallon of regular gas cost $2.59 on average, up 3 cents from a year ago, and rental cars averaged around $75 a day — their highest Thanksgiving price since AAA started keeping track in 1999.

For those flying, the airlines expect traffic to be up about 4% from this time last year. Airlines added about 850 flights and 108,000 seats per day on average to handle the increase over last year’s crowds, according to the trade group Airlines for America.

American Airlines plans to operate 7,046 flights Sunday, just one less than on Aug. 8, its heaviest schedule this year. In all, 22 of American’s 23 busiest days occurred during the summer vacation season, with this Sunday being the only exception.

“Everybody talks about Thanksgiving being a busy travel time, but summer is Thanksgiving week for the entire summer,” said Ross Feinstein, a spokesman for the airline.