Yellowstone National Park
However, the main reason (as explained above) is that the caldera is the biggest volcanic system in North America. It sits on top of a hotspot in the Earth's crust. In summer, there are temperatures of about  in the lower areas, but they can go up to  sometimes. There are many thunderstorms during the afternoons. There are relatively low temperatures during the night; they can get below zero in the mountains. Normal temperatures in winter are between .