Millions of Americans face an artic blast, including the first-ever blizzard warning for parts of the Gulf Coast.

Flight cancellations are mounting as a historic winter storm sweeps across the Gulf Coast. Already, the storm has brought air traffic to a virtual standstill at several airports across parts of Texas and Louisiana.

Millions of people across the northern Gulf Coast braced Tuesday for a rare winter storm that’s expected to scatter heavy snow, sleet and freezing rain around the Deep South as a blast of Arctic air plunges much of the eastern U.S. into a deep freeze.

Houston’s two major airports, George Bush Intercontinental and Hobby, are also closed Tuesday, while Hartsfield-Jackson Atlanta International Airport, the world’s busiest, is pretreated roadways and airfield surfaces in preparation for the winter weather, according to spokesperson Andrew Gobeil.

A powerful winter storm that dumped heavy snow and glazed roads with ice across much of Texas and Oklahoma lumbered eastward into southern U.S. states Friday, prompting governors to declare states of emergency and shuttering schools across the region.