The storm has caused severe air travel disruptions. According to FlightAware, more than 1,800 flights in and out of the U.S. have been canceled so far, including nearly 500 at Reagan National and more than 250 at Chicago's O'Hare International Airport, which issued a temporary ground stop earlier Monday due to snow and ice.

Millions were under weather advisories as the storm stretched from southern Illinois to Washington, D.C. Snow could fall at 1-2 inches per hour.

Tens of millions of Americans are bracing for a massive winter storm Sunday, which is forecast to bring the heaviest snowfall and coldest temperatures to parts of the country in over a decade. The polar vortex has already prompted states of emergency in the Plains,

Tens of millions of people were bracing Sunday for a massive winter storm forecast to bring the heaviest snowfall and coldest temperatures in over a decade to parts of the country.

Storm Blair is throwing travel plans into chaos as it tears across the United States, with thousands of flights and trains either canceled or delayed. Blair is bringing an unpleasant mix of freezing temperatures mixed with snow and ice across the country,