Weather

Looks like maybe some people are reading from Salt Lake, thanks for the interest. Most of you are from the Northwest somewhere, I need advice on how the weather is from the 15th of May going into summer. Are we going to end up like the Donner party? We're starting in Astoria, Oregon and going east to Bozeman, the south through Yellowstone. I'm thinking there are generally tailwinds, right? And no snow. Please confirm.