Some of this autumn’s coldest weather yet is bearing down on the United States, enveloping the eastern two-thirds of the country in Arctic air on Monday and affecting millions of people.

National Weather Service forecasters said the weather could bring record low temperatures in the U.S. Southeast, including all of Florida, where parts of the state were near 80 degrees just a day ago.

The cold air brought gusty wind and red flag warnings in the Great Plains on Monday, and forecasters said the Great Lakes and Appalachian Mountain regions could see 4 inches to 8 inches of snow.

Around Lake Erie, forecasters warned of possible lake-effect snow, where copious amounts can fall in relatively narrow bands, drastically increasing snowfall near the water while leaving other nearby areas untouched.

Cold weather warnings were issued for Ohio, West Virginia and Kentucky, with freezing temperatures predicted for a large swath farther south, from Texas and Oklahoma to Alabama and Georgia.

The wintry weather contributed to flight delays across the country, including four-hour wait times at airports like the busy Chicago O’Hare International Airport. The cold front compounded the impacts of Federal Aviation Administration’s order to cancel thousands of flights in response to the federal budget shutdown that has forced air traffic controllers to work unpaid for over a month. Some have stopped showing up for work, citing the added stress and need to take second jobs.