The cold air invaded the northwestern U.S. during New Years day and was accompanied by accumulating snow to near sea level in Washington. Cold air will hang on much of the week in the Northwest.
Over the Southwest, including Southern California and southern Arizona, the chilly weather will continue into Thursday, as temperatures will moderate late in the week. Cold air will hang on much of the week in the Northwest.

"The main thrust of the cold air will extend from the northern Rockies to the northern Plains and the Upper Midwest," according to AccuWeather Meteorologist Evan Duffey.

By the middle of the week, actual temperatures will bottom as low as 20 degrees Fahrenheit below-zero and will rival the coldest air of the season so far over the northern tier of the Central states. AccuWeather RealFeel® Temperatures over part of the northern Plains and Rockies can dip as low as minus 40 for a time.