On long commutes, you can get 60-75mpg even with temperatures as low as -5 degrees in my experience, with only a radiator block. Under decent conditions, of course.
On short commutes of less than 10 miles, it starts to get difficult. 45-60mpg.
On even shorter commutes, 45-50mpg.
If it's snowy and you have snow tires on, 45-50mpg.
If it's super rainy, 45-50mpg.
If you're diamondlarry, add 20mpg to all of those.