Yellowstone

You're going to have a blast. We went 3rd week of May 2013 and had an amazing time. Stayed at Norris in A Loop and LOVED it. Had every kind of weather you can imagine from t-shirt weather to snow to thunder and lightening. Most of the bigger campgrounds were open and the only roads that were closed were up at the Northeast entrance. Tons of wildlife and geyser activity. We stayed a week and still didn't get to see it all. I would go back in a heartbeat.