My family and I drove up from Phoenix one spring day wearing shorts and got to Flagstaff where it was 30 degrees cooler, kinda neat, reminded me of Iowa, besides the beautiful scenery.
Personally, I learned all I need to know when we left Omaha on Christmas day and it was -22F and when we landed a few days before the Insight.com bowl win in Phoenix , it was 60F there and they were complaining like the ice age was coming.
You will have to get used to dry heat. You never really sweat, but you get dehydrated very quickly.
You might want to rethink the dark colored automobile with dark leather seats.
I would take the weather in eastern washington over the weather in Iowa any day. 300 days of sunshine. Cool nights and warm days with low humidity during the summer. Snow during the winter, not freezing rain, not sleet, snow. High in the 20's and 30's all winter (occasionally 40's) with lows in the teens and twenties. No wild fluctuation in temps. A gradual warm up in the spring and a gradual cool off in the fall. No tornado's, really not any earthquakes (felt two the entire time I lived there and one was from Seattle area), and if your smart, wildfires are that big of an issue (take it from a firefighter from the most fire pron county in Washington).