1.   But, icy air from the Canadian tundra is only a wind shift away.

2.   The Arctic chill that reaches the United States forms over the Canadian tundra when clear skies and calm winds allow the ground to rapidly lose energy.

3.   The strengthening March sun steadily warms the equatorial regions while arctic air lingers over Canadian tundra.

4.   The strengthening late-winter sun steadily warms the equatorial regions, while arctic air lingers in the Canadian tundra.

5.   Thereafter, the jet stream became contorted, drawing cold air from Canadian tundra into the East.

6.   Winters can be bitter in the northern Plains where northerly winds direct arctic cold from the Canadian tundra.