A major winter storm is threatening to blanket parts of the middle of the country with more than a foot of snow, promising to disrupt travel and even closing some coronavirus testing sites. The snow that began in some parts of the Midwest Monday morning was forecast to stretch from central Kansas northeast to Chicago and southern Michigan throughout the day. Some of the heaviest snow was expected in southeast Nebraska and western Iowa. Officials are urging drivers to stay off the roads. Several coronavirus testing sites in Nebraska and Iowa closed early on Monday because of the storm. Elsewhere, a major highway in California was closed as a storm moving across the Southwest dumped snow in the Tejon Pass between Los Angeles and the San Joaquin Valley.