A deadly arctic deep freeze enveloped the US Midwest with record-breaking temperatures, triggering widespread closures of schools and businesses. According to the US National Weather Service, temperatures plunged as low as -48.3 degrees in northern Illinois, -37.2 degrees in the central part of the state and -31.6 degrees in southern Illinois. According to the Flightaware flight tracking website, snowfalls caused a flurry of cancellations and delays at Chicago's two major airports. US Postal Service had to take the rare step of suspending mail delivery service to a wide swath of the region. See the images of how residents are weathering the arctic cold.