Yellowstone Park technically never closes, but most of the roads do. Beginning November 1 there are just two gates open (weather permitting) throughout the winter.
"Winter hours" doesn't mean limited access to the Boiling River. We were surprised to read how EARLY in the morning you can soak in the warm water down near Gardiner.
We know that we're living on a ginormous caldera (Yellowstone Park) that theoretically could blow at any time. Want to see the earthquake data in real time?