Going west in the spring YMMV. In the summer the 1st thing you need to do is get out of the Midwest. A few years back I cut north from Kentucky to Cincinnati to South Dakota, thinking if only I kept going north, it would get cooler. It doesn't. It's one big weather system and I learned to my chagrin that most of SD is actually a swamp. Native peoples used an extensive river system in the state and there's a pretty cool archaeological site in Mitchell, SD if you happen to go through there.
Once you hit WY things will cool down, but you may very well have the opposite problem at the various higher altitudes. Too cold! The Bighorn wasn't defrosted and Yellowstone had 12 ft. of snow over the southern approach. I didn't have any cold weather gear at the time. I looked at a US map and said, hey, look at all these National Forests I can go camping in. Didn't realize lots of 'em were at high elevation and would be fairly cold. That year had lotsa moisture, lotsa flooding, supersaturated soils so trees could fall down at a moment's notice, embankments and roadsides could disappear. I saw the remnants of a few places where it had happened, where parts of roads next to rivers were just gone.
The possibility of trees falling was the biggest real threat I faced that year. One night I did something dumb, I camped in this NF with all these trees, which I realized had orange marks on them! I thought oh no, maybe the rangers have been marking trees for removal that are likely to fall. So I packed up camp and left. Um, turned out the markings on trees mean a timber sale. They're either trees to be sold or trees to leave alone, depending. I left for nothing. And my driving that night was dangerous, I was so tired. I finally just pulled over at some business in the middle of nowhere, slept, and cleared out shortly before dawn. Ah the learning curve of the early days.
Once I got to Seattle and had some time to think, I acquired some of the necessary mild winter / high altitude style gear, like polyester thermals. I had these British military wool pants from the 1950s. The fabric held up but all the buttons popped off because the thread was weak. I had a great time in the arid Eastern Cascades and really want to go back. In later seasons I acquired a more serious winter mummy bag, and a comforter, so now the dog and I can handle 20*F although I don't choose to stay in that for long. A pair of hand-me-down ski pants from my Dad has been my preferred cold weather bottom gear.
BLM land is typically too hot in the day for my taste, you start frying at 8 AM. I tried to rig up some shade with a 25' tarp, and I just created a 25' foot low slung oven. The BLM land is excellent as a "sleep and scoot" place at night though, just leave in the morning. Especially outside Cody WY, last stop before Yellowstone.
