Doors and Windows - frozen lock

I have an exterior door with a dead bolt lock the freezes in the winter. What should I use to free it up and prevent freeze ups? Will powdered graphite work the best?

Powdered graphite will certainly work better than any spray lubricant. Is this lock exposed to the elements, so that moisture (rain or snow) can get blown into the cylinder? Is it freezing so that you can't insert the key, or could it be that the jamb is swelling and making the lock difficult to turn?

Yes the lock is exposed to the elements. It's a foam core door with no storm door in front of it. I'm not sure if the jam is swelling.

You need to determine if it's the lock mechanism that is freezing, or if it's the bolt being put in a jamb because the jamb is swelling.

Do this. Next time it's frozen, open the door and use the key to lock and unlock the deadbolt. If that works fine (with the door open), the problem is the door jamb or strike plate. Use a file to enlarge the opening in the strike plate a little, so that the bolt will not be rubbing on it.

If you can't operate the deadbolt with the key when the door is open, then it's the lock mechanism getting moisture in it and freezing. Powdered graphite might help that.