ARLINGTON, Va. − Two powerful weather systems were careening across the nation Tuesday, threatening to dump up to a foot of snow in some areas while snarling traffic, clogging roadways, shuttering schools and shutting down government offices.

As the Midwest and Northeast dig out from back-to-back winter storms, new systems are building and are expected to dump more snow from the middle of the country to the East Coast this week. Plenty of cold air remains is in place to the north,