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 over the Thanksgiving holiday weekend, one of the nation's busiest travel periods.

Parts of New York, Vermont, New Hampshire and Maine are under winter storm warnings, and precipitation is expected to begin as early as 1 a.m. on Thanksgiving Day. Higher elevations, including area ski resorts, will see snowfall that could continue through 1 a.m. on Black Friday.