1.   By Saturday morning, cold air had spread over the region, turning the snowpack bulletproof.

2.   And dirty air spreads beyond big cities.

3.   Arctic air will spread into the northern Rockies and western Dakota as a cold front sweeps across these regions.

4.   Arctic air will spread from the upper Midwest into the interior Northeast Saturday in the wake of a cold front.

5.   As a potent disturbance from the Gulf of Alaska moves inland later Sunday, colder air will spread into the northern Rockies and northeast Washington, escorted by snow.

6.   As arctic air spread over the mild lake waters, it was rapidly warmed and moistened.

7.   Behind the front, cooler and drier air will spread into the upper Mississippi Valley.

8.   Behind the front, drier air will spread into the western Tennessee Valley.

9.   Behind the front, unseasonably chilly air will spread into the Northern Rockies with the risk for a few snow showers in the higher mountain peaks of western Montana.

10.   Behind the front, colder and drier air will spread from the southern Plains to the western Gulf of Mexico coast.