The White House said Tuesday that President Obama was "certainly aware of the dramatic weather" gripping most of the nation, while reporting that so far there had been no requests for federal emergency assistance.

A so-called "polar vortex" has much of the Midwest and Northeast fighting sub-zero temperatures this week, with schools and businesses closed across the country. Record lows have crippled travel, closing highways and rail networks and leading to hundreds of flight cancellations.

White House press secretary Jay Carney urged Americans to "be safe and follow directions from local officials."

"If local officials say 'stay off the roads,' avoid travel unless it's an emergency. Depending on the state, depending on the region, local officials have the best insight when it comes to what's the right thing and the safe thing to do," Carney said.

He also said the White House was confident that the Federal Emergency Management Agency would "be on top of it" if an "issue that requires federal assistance" arises.

The president himself acknowledged the chilly temperatures — which fell to single digits in the nation's capital — at an event promoting unemployment insurance on Tuesday, telling attendees he hoped they were "keeping warm."