As mentioned here already, layers and an electric vest are the way to stay warm. This is my ensemble, good for down to -25C/-13F, after which the helmet becomes useless...
Two pairs wool socks, thermal long johns, thermal undershirt, roofer's kneepads, track pants, Gerbing electric vest w/heated collar, Kenora Dinner Jacket (long sleeved quilted lumberjack shirt), snow pants and snow jacket rated to -50C, neoprene full face mask, insulated winter gloves, all weather motorcycle flip-up helmet, mukluk style winter boots.