Then again, WI and MN are much colder but no one is out there building in -40 degrees.
It actually does get that cold in parts of Colorado.
Here is a screen shot I took of Craig's (where I live) weather summary in February 2011:
On the 2nd, it was officially -40F at the weather station and -48F at my house. Maybell, 30 miles west has a record low of -61F, colder than the record lows in MN or WI.