July in West Yellowstone is the sunniest and the warmest month of the year. In July, the weather in West Yellowstone is typically warm. Average daily high temperature in July is about 21 degrees above zero. On average, West Yellowstone has 19 sunny, 9 partly cloudy, and 3 rainy days in July. The rains are usually light. July as well as August is considered the most comfortable time to visit West Yellowstone.