Los Angeles Mayor Karen Bass said the city will start moving unhoused people to hotels and motels. Meanwhile, she signed an executive order to hasten the process of building affordable housing.

The winter solstice is the shortest day of the year, and happens when the Northern Hemisphere is pointing away from the sun.

Forecasters are warning of treacherous holiday travel and life-threatening cold for much of the nation as an arctic air mass blows into the already-frigid southern United States.

Hawaiian Airlines' chief operating officer said the airline had not experienced "an incident of this nature in recent history," calling it an isolated and unusual event.