A cross-country storm, a blast of Arctic air and an outbreak of showers and thunderstorms are threatening to snarl traffic and pile up delays at airports through the Thanksgiving holiday weekend, one of the nation's busiest travel periods.

A winter storm has moved into Colorado's mountains, bringing widespread snow, with 1 to 3 feet of accumulation possible by Wednesday afternoon. Rain will transition to snow overnight tonight for the Denver metro,

The snowstorm bearing down on Colorado has already produced a winter storm warning and avalanche warning for much of the mountains.