OMAHA, Neb.—A major winter storm threatened to blanket parts of the middle of the country with more than a foot of snow Monday, promising to disrupt travel and forcing the closure of some coronavirus testing sites. The National Weather Service said at least 4 inches (10 centimeters) of snow is expected across most of an area stretching from central Kansas northeast to Chicago and southern Michigan. Parts of southeast Nebraska and western Iowa could get more than three times that much by Tuesday morning. Several coronavirus testing sites in Nebraska and Iowa were closing early Monday because of the snow. More than 10 inches (25 centimeters) of snow had already fallen in parts of eastern Nebraska by Monday evening. National Weather Service meteorologist Taylor Nicolaisen said 10 to 15 inches (25 to 38 centimeters) of snow was likely between York, Nebraska, and Des Moines, Iowa, and that it has been …