Autumn weather can be pleasant, although temperatures average 10 to 20 degrees lower than summer readings--highs in the 40s to 60s (5-20C). Over-night temperatures can fall into the teens and single digits (10 to -20C). Snowstorms increase in frequency and intensity as the weeks go by. At any time of year be prepared for sudden changes; unpredictability, more than anything else, characterizes Yellowstone's weather.
Sudden storms can cause a drop in temperature or result in precipitation. Always carry extra clothing when hiking. Good walking shoes and layers of clothing are recommended throughout the year. If you plan to visit Yellowstone during spring or fall, call ahead for current weather and road information since sudden storms may result in cold temperatures, snow and/or temporary road closures.