DALLAS—A destructive storm ripping across the U.S. spawned tornadoes that killed a young boy and his mother in Louisiana and threatened the South with more severe weather Wednesday. Meanwhile, the huge storm system delivered blizzard-like conditions to the Great Plains and was expected to push more snow and ice into Appalachia and New England. In…

SIOUX FALLS, S.D.—A massive storm blowing across the country spawned tornadoes in parts of Oklahoma and Texas, including the Dallas-Fort Worth area, as much of the central United States from the Rocky Mountains to the Midwest braced Tuesday for blizzard-like conditions. An area stretching from Montana into western Nebraska and Colorado was under blizzard warnings,…