Winter Storms and Subzero Temperatures Ahead for Midwest, Northern States

— -- Snowstorms are expected in many parts of the country this weekend, posing hazardous driving conditions for millions of motorists.

On Thursday, slippery roads and low visibility caused multi-vehicle pileups on interstate highways in Pennsylvania, Ohio, Michigan and Nevada.

Lake effect snow continues to slam the Great Lakes region. In Oswego, New York, residents witnessed a unique weather phenomenon late Thursday: a snowstorm that produces lightning.

Seattle and Washington experienced the first measurable snow in two years and Portland, Oregon, has already received more snow than the average amount for the entire month of December.

It will be a snowy weekend for Minneapolis, Chicago, Detroit and Cleveland. Next week, temperatures for these cities are expected to drop to subzero levels.