Forecasters say two rounds of bone-chilling air blowing across the nation this week are the coldest so far this winter.  

An arctic air mass will push through the eastern half of the U.S. this week, bringing wind chills that will keep much of the country below freezing.

The first round of cold air is keeping temperatures in the teens throughout the Great Lakes region, with wind chill factors well below zero.

A second wave of frigid air due Wednesday will push arctic air further south.

Below-freezing highs are expected as far south as Amarillo.

Forecasters say much of the east coast will have highs in the teens by Thursday morning.