Severe weather is expected to bring subzero temperatures the northern Plains as soon as Thursday, then reach the Mississippi Valley, the Northeast and the Ohio Valley by Sunday.

Winter Storm Fern was forecast to spread heavy snow, sleet and dangerous ice to tens of millions of Americans across two dozen states beginning on Friday, Jan. 23, and continuing into the weekend.

The National Weather Service has issued winter storm watches and warnings spanning more than 2,000 miles, and more than a dozen states have declared states of emergency.