Great trip report--and you did all that in an S60! That shows the utility of the Supercharger network. Musk got that right.
I remember early June in Yellowstone in '68. I was hitchhiking and had to sleep in one of those heated restrooms
as we didn't have the gear for snow.
Hah! Back when I was a scoutmaster I had my entire troop sleep in the restroom at Grover Hot Springs S.P. in Markleeville sometime in the '80s. It was supposed to be a ski camping trip, but it rained all the way over Carson Pass and down to Markleeville. We were still hoping the temps would drop overnight and it would be safe to take them out to ski and camp, so slept in the bathroom to keep everyone from starting out with wet, heavy tents and gear the next day. Temps stayed in the high 30s or low forties the next day while it continued to rain/sleet with an occasional snow flurry, so we bagged the skiing, spent the morning soaking in the hot spring, and then drove over to Sorensen's resort and got a cabin for the rest of the weekend. Probably a good thing, as the senior scout responsible for the food planning had decided he was going to try and make fondue (on a backpacking stove), which would have been an ordeal by itself if done in a tent vestibule. The fondue was quite good, though!
Oh, and nice photos of DGP's trip. I've only been to Yellowstone once around '90, with a friend who'd worked there for a summer or two in the '70s or '80s, as he also wanted to see how the place was recovering from the '88 fires. Were the usual tourist idiots ignoring the risks and trying to pose themselves/their kids next to/on buffalo, or did the weather keep them away?
Can't say Yellowstone is really my kind of place, as I prefer to be above timberline so I can see long distances (we'd been backpacking in the Wind Rivers, and then spent a couple of days in the Tetons before Yellowstone), although I expect I'd like it a lot more in winter. , At least I would if they banned snowmobiles. They've apparently toned things down a bit since the bad old days: https://www.npr.org/2013/10/22/239705610/new-rules-mean-more-and-cleaner-snow-mobiles-in-yellowstone