Granted that in my area anything below 35 degrees Fahrenheit is considered extremely cold, I think a waterproof helmet cover could work for you. You'd still need to do something about your face and ears, but I find that my helmet cover is like wearing a space heater on my head. I bought it for rainy commutes, but I found that rain or shine, I arrive at work with my head dripping with sweat in even the coldest of days. I gave up using it for rain, and now I use it for warmth on very cold days.