I run through winter, but I have my limits.
My drop dead low temperature for running is -5°F. Beyond that, any amount of wind creates a sub-30-minute frostbite risk. I don’t want to take any chances by running outside for any length of time, since given icy conditions I will likely have to travel some distance on foot to find a suitable running path.
My drop dead low temperature for any kind of outdoor anything is -10°F. Even if covered up, even with no wind, the temperature by itself begins to pose a frostbite and hypothermia risk, regardless of how well you’re bundled up.
(Much respect to my Canadian, Maritime, Dakotan, Montanan, New English, Mongolian, Siberian, Antarctican, et ceteran readers who regularly experience temps far colder. You also have the benefit of generations of biology that we southerners lack. I have grown to handle extreme cold but despite my best efforts I still have physical limits.)