
The National Weather Service's forecast low temperatures for the United States on April 21, 2021.
An upper-level trough dipping over the Great Lakes is responsible for the belated touch of winter spreading across much of the country this week. The cold front producing the snow and ushering in the cold air extends off of a low-pressure system up in southern Quebec.
Snow fell as far south as Tulsa, Oklahoma, on Tuesday afternoon as the front moved through the region. The National Weather Service expected a "slushy" couple of inches of snow from northern Illinois to western New York, and winter weather alerts are in place for southern Ontario where the Greater Toronto Area could see a dusting of snow by the end of the precipitation.
Comment: Outsiders Weather and Ice Age Watch: Record freezing temperatures felt across the globe