I'm in that boat, upper midwest, one day in 50s, next day snowing in 30s. Having done PPA last year, I know the majority of the time during the event is a long fast hike, not running (something only the elite runners with access to mountains do). So get out there and do long slow runs and long fast hikes. Consider hiking with a weighted vest or backpack to simulate fatigue better. Keep your aerobic threshold high, and just do the best you can!