Winter storms threaten Thanksgiving travel in US

Passengers wait to pass through security gates at San Francisco International Airport in San Francisco, Tuesday, Nov. 26, 2019. Northern California and southern Oregon residents are bracing for a 'bomb cyclone' that's expected at one of the busiest travel times of the year. (AP Photo/Jeff Chiu)

A City of Greeley snowplow plows the westbound lanes of 20th Street during a winter storm in Greeley, Colo. Tuesday, Nov. 26, 2019. The storm is expected to dump at least a foot of snow on Greeley by Tuesday night and caused the closure of school districts, the Greeley and Weld County government offices, and the University of Northern Colorado. (Alex McIntyre/The Greeley Tribune via AP)

University of Northern Colorado facilities management staff Francis Garza, left, and Tina Longoria shovel snow from the steps and entranceway to Sabin Hall during a winter storm in Greeley, Colo. Tuesday, Nov. 26, 2019. The storm is expected to dump at least a foot of snow on Greeley by Tuesday night and caused the closure of school districts, the Greeley and Weld County government offices, and the University of Northern Colorado. (Alex McIntyre/The Greeley Tribune via AP)

DENVER — Heavy snow and wind shut down highways Tuesday in Colorado and Wyoming, closed schools in Nebraska and forced more than 1,000 travelers to sleep overnight in Denver’s airport after hundreds of flights were canceled just as Thanksgiving travel moved into high gear.