Welcome to the Polar Vortex! - 2019-02-01 2:44 AM
https://en.wikipedia.org/wiki/Polar_vortex
This is the first time I've heard the term "Polar Vortex". But wind-chill factor of 50 below zero is rather unusual, and not something I recall ever occurring in my 55 years of experiencing winter weather.
It's already credited with 7 deaths in the U.S., and even puts emergency police/fire/medical people at risk, trying to help people who are going out in this severe cold and end up needing rescued.