Polar vortex set to envelop much of US in freezing temperatures

By Hannah Lang and Brendan O'Brien (Reuters) - A blast of Arctic air is set to cover much of the United States with temperatures below freezing starting on Friday and into next week, impacting millions of Americans in nearly all of the contiguous states. Temperatures will reach below 10 degrees Fahrenheit (-12 C) in the Northern Plains and Upper Midwest, into the teens in the central Plains and