Large portions of the United States were experiencing dangerously low temperatures on Monday morning, with wind chills poised to hit some 40 degrees Fahrenheit below zero in certain areas.

The National Weather Service issued wind chill advisories in parts of 16 states, warning that gusty winds and low temperatures could lead to frostbite in as little as 20 minutes in some areas.

The warnings covered portions of Montana, North Dakota, Minnesota, Wisconsin, Michigan, Iowa, Missouri, Illinois, Indiana, Ohio, Pennsylvania, West Virginia, Virginia, North Carolina, Kentucky and Tennessee. Temperatures were expected to remain below 20 degrees in almost all of the advisory areas, and large portions were expecting sub-zero or single-digit temperatures.

Wind gusts in the high teens drove the perceived temperature down further, the service said. People affected by the extreme cold were advised to dress warmly and cover all exposed skin.

The National Weather Service said the temperatures were “below-normal” and would shift further east over the next two days. Lake effect snow warnings were in effect for portions of Michigan, Ohio, Pennsylvania and New York, and the service said there was a chance of heavy snow before Tuesday night. Some parts of New York could receive up to 20 inches, forecasts say.