The Associated Press / A person walks her dog along Lake Michigan on Monday as snow covers the ground with fall colors on the trees in Evanston, Ill., a suburb of Chicago.

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 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.

Chill could cause falling iguanas in Florida

In Florida, forecasters said wind chills could dip to the 30s. Whenever it gets that cold in the Sunshine State, many look to the trees: Iguanas, an invasive reptile species, have previously gone into a sort of suspended animation and fallen to the ground when temperatures dip below 40 degrees.

They usually wake up with the sun’s warmth — although it is unclear whether any of the reptiles will tumble from the treetops this time.

Across the south, many local governments opened heated shelters for residents struggling to cope with the cold.

Those resources are invaluable in St. Louis, Missouri, where some people are still waiting for essential repairs on their houses after a powerful EF3 tornado ripped through the region in May. City officials announced Monday that emergency shelters would be open for homeless people as well as those who still dealing with the aftermath.

Hazardous conditions for travel

In Tennessee, temperatures dropped to 30 into Sunday morning, and areas with higher elevation in the eastern part of the state reported that 3 inches of new snow had fallen by 9 a.m., causing some school closures. Snowy roads led to a crash involving multiple vehicles and about an hourlong shutdown on westbound Interstate 40 in Putnam County, east of Nashville, the county sheriff’s office announced.

Further north, as temperatures dropped across the nation’s midsection, meteorologists warned of hazardous travel conditions through winter weather advisories for Michigan, Indiana and Wisconsin. Snow fell Sunday in Michigan’s Upper Peninsula, where meteorologists warned of low visibility and up to a foot of snow by Monday.

In Indiana, weather experts predicted up to

11 inches of snow and “slippery surfaces” for road travel. Up to 6 inches of snow were predicted in parts of Wisconsin.

“Patchy blowing snow” and wind chills hovering near freezing were expected in portions of Minnesota, Nebraska and South Dakota. Some areas got measurable fluff a day earlier, including 4 inches of snow in southwest Minnesota and more than 5 inches in northern Iowa.