Snow cover amplifies the phenomena called a temperature inversion Salt Lake City was a foggy freezer box Wednesday at 18 degrees, while Park City basked in sunny 43-degree weather.

NPR: Sickening Fog Settles Over Salt Lake City Area

The cold waters mean a large temperature contrast between the land and ocean -- conditions that favor the formation of a strong inversion layer that traps smog over cities, such as the Los Angeles, Calif.

CNN: Western U.S. to get smoggy summer, fall