More than 18 million people are under winter weather alerts across the West and Midwest as storms are forecast to bring heavy snows and bitter winds. 

A strong system is producing heavy snow across the Northern Rockies, where higher peaks may pick up a foot or more through Saturday, according to CBS Meteorologist Andrew Kozak. As the low moves east, snowfall expands into the Northern Plains and Upper Midwest from South Dakota to northwest Illinois, with 4 to 6 inches likely and locally higher totals. 

A winter weather advisory is in place for Chicago with up to 2 to 5 inches of snow expected, CBS Chicago reported, leading to slick roadways and sidewalks by the morning hours. 

Bitter cold will follow, with subzero lows possible in the Dakotas and Minnesota by Sunday night into Monday. Another snow system is expected to move through the metro and southern part of the state starting Saturday afternoon, CBS Minnesota reported, with bitter temperatures expected. 

The National Weather Service predicts moderate to heavy snow over parts of the Upper/Middle Mississippi Valley on Saturday night.

Winter storm warnings and winter storm advisories are in effect for Colorado, Colorado CBS reported, with the mountains set to be hammered by snow. 

The Pacific Northwest is set to be pummeled by a series of Pacific systems arriving late Sunday into Monday, bringing widespread heavy rain to western Washington and Oregon, Kozak said. 

Flash flooding is likely as saturated ground quickly converts new rainfall to runoff and flood watches are already in place. The heavy rain threat continues over the next 5-10 days.