If you don't want to bother swapping out wheels twice a year and don't mind giving up a little performance on snow and in the summer, then all seasons work well here.
If you want the best handling in all conditions, or plan to go into the mountains a lot for winter sports or cross the pass into eastern WA, then go with a dedicated winter tire and wheel setup for the 4 months we could see snow. A "
winter performance" tire is perfect for the Model S and our climate. It'll have a silica compound that stays compliant and sticky in freezing temperatures, but not an awful ride when on dry or wet like a full on snow tire or studied snow tire.
Between the two options, it's a question of what you want to maximize: convenience or handling.