A powerful polar vortex has unleashed a wave of life-threatening cold across the lower 48 states, plunging much of the nation into a deep freeze. Arctic air has surged southward, bringing dangerously low temperatures from the Northern Plains all the way to the Gulf Coast. Residents are facing extreme conditions, with wind chills plummeting to as low as -50°F in some northern states. Even southern cities are struggling, with temperatures barely reaching single digits.