How a week of weather extremes upended the lives of millions of Americans

It was a week of fire and ice. It began with millions of people across the U.S. shivering amid blizzard conditions and frigid air that lasted for days, thanks to a jet stream that slips out of its usual path more often these days. Then, catastrophe in California, with wind-whipped flames taking off in a landscape parched by months of drought to become Los Angeles' worst-ever wildfires.