A massive winter storm dumped sleet, freezing rain and snow across much of the U.S. on Sunday, bringing subzero temperatures and paralyzing air and road traffic. Power lines were draped in ice, and hundreds of thousands of people in the Southeast were left without electricity.

The ice and snowfall were expected to continue into Monday in much of the country, followed by very low temperatures, which could cause “dangerous travel and infrastructure impacts” to linger for several days, the National Weather Service said.

Heavy snow was forecast from the Ohio Valley to the Northeast, while “catastrophic ice accumulation” threatened from the Lower Mississippi Valley to the Mid-Atlantic and Southeast.