A powerful winter storm was sweeping east from the Plains on Sunday, driven by what meteorologists describe as an intense cyclone, setting off a chain reaction of snow, ice, rain and severe weather expected to affect much of the country. Snow and strengthening winds spread across the Upper Midwest on Sunday, where the National Weather Service warned of whiteout conditions and possible blizzard conditions that could make travel impossible in some areas. Snowfall totals were expected to exceed a foot across parts of the upper Great Lakes, with up to 2 feet (61 centimeters) possible along the south shore of Lake Superior.