"Glad you are thinking of making the trip to Alaska. About your timing for Yellowstone, if you arrive there in late April or early May, campgrounds or services may still be closed. Roads may still be closed or impassable. Spring/summer comes late there (usually). We have been there in June and experienced enough snowfall for the Rangers to confine us to our immediate area for the day. It can snow and dip below freeing any month there. So if stopping by Yellowstone, I would suggest calling ahead to see what is open and what is not. Good luck and hope you have a great trip".
Thank you for the information. I plan to make a couple stops before hitting Yeellowstone, so I might not even get there until middle/end May. BTW, I am originally from Phila area.