Make sure you warm up the interior before blasting the power washer at it, some of those places have some decently warm water and a blast of that onto an icy window may not be good. Otherwise any days with decent sun / above 30 I will take advantage and hose everything down.
Sometimes I leave the truck running, just because. I like to turn the AC on as well multiple times throughout the winter just to keep everything functional.
Water only, no need for soap to scum up and freeze.....Just trying to get any salt and build up sprayed off. Hose from top down and then drive around for a bit to get everything air drying.
We are lucky up here and have one wash bay that has a garage door that closes behind you. The water is warm and the bays are heated. Good place to hide out for an hour while the truck thaws out.