Their feathers, roosting behaviors and adaptability help birds survive the cold, “nature’s proving ground.”

A mass of air called the polar vortex has escaped the Arctic and plunged southward. Some scientists see the fingerprints of climate change.

“So many of you have never seen an event like this,” Louisiana’s state climatologist warned, with New Orleans facing possibly the most snow it has ever seen.

Closures of schools, airports and businesses were taking effect in areas from southern Texas to Florida and South Carolina. Snow and ice could bring major travel disruptions and power outages.

Heavy snow is expected on Sunday in the Northeast before the coldest air in several years descends across much of the country starting on Monday, forecasters warned.

An arctic chill is headed to Washington (and much of the United States) on Monday.

A winter storm was sweeping across a wide swath of the South on Friday. Atlanta’s airport issued a ground stop after a plane was evacuated onto a snowy runway.

Hazardous snow, sleet and freezing rain disrupted travel plans and caused power outages in the Mid-Atlantic region, as bitter cold set in.

All highways in northeastern Kansas were closed on Sunday evening, bringing traffic to a standstill in some parts.

Officials are bracing for a dreadful mix of sleet, snow and freezing rain that is forecast to hit from Kansas to Virginia this weekend.

The Arctic air arrives this weekend and could linger into mid-January.