In photos: Boiling water freezes, train tracks lit on fire in severe cold

Temperatures overnight sank into the negative double digits in nearly a dozen states, with the polar vortex descending on the Midwest and threatening to break all-time cold records.

The big picture: Mail deliveries have been suspended, schools and businesses closed, and Midwesterners warned that the frigid cold is not to be trifled with. Even so, some brave souls have ventured outside to test out the temperatures.

Go deeper:

• Polar vortex to set painful all-time records
• USPS suspends delivery in 11 states, citing safety concerns
• Polar vortex preys on the Midwest with coldest air in a generation