Nice! My best friend lives in Billings and I went out to see him. We hiked Mt Rearguard which was my first hike up to a 12kft peak (and highest significant hike over 9k). The elevation absolutely whooped my butt but it was worth it. The first night in Yellowstone there was a tinge of frost on the meadow and we dropped to 33/34º, super super nice.
I got off the plane on my second, and unplanned, connection in DC from Denver and the humidity hit me in the face for the first time in a week. No fun.