The 2011 Groundhog Day blizzard was a powerful and historic winter storm that affected large swaths of the United States and Canada from January 31 to February 2, 2011, especially on Groundhog Day. During the initial stages of the storm, some meteorologists predicted that the system would affect over 100 million people in the United States. The storm brought cold air, heavy snowfall, blowing snow, and mixed precipitation on a path from New Mexico and northern Texas to New England and Eastern Canada. The Chicago area saw 21.2 inches (54 cm) of snow and blizzard conditions, with winds of over 60 mph (100 km/h). With such continuous winds, the blizzard continued to the north and affected Eastern and Atlantic Canada. Blizzard conditions affected many other large cities along the storm's path, including Tulsa, Oklahoma City, Kansas City, St. Louis, Springfield, El Paso, Las Cruces, Des Moines, Milwaukee, Detroit, Indianapolis, Dayton, Cleveland, New York City, New York's Capital District, and Boston. Many other areas not normally used to extreme winter conditions, including Albuquerque, Dallas and Houston, experienced significant snowfall or ice accumulation. The central Illinois National Weather Service in Lincoln, Illinois, issued only their fourth blizzard warning in the forecast office's 16-year history. Snowfall amounts of 20 to 28 inches were forecast for much of Northern and Western Illinois.

A winter storm is an event in which wind coincides with varieties of precipitation that only occur at freezing temperatures, such as snow, mixed snow and rain, or freezing rain. In temperate continental and subarctic climates, these storms are not necessarily restricted to the winter season, but may occur in the late autumn and early spring as well. A snowstorm with strong winds and other conditions meeting certain criteria is called a blizzard.