Cold and snow linger into April and May, although temperatures gradually climb. Average daytime readings fall in the 40s to 50s (5-15C), reaching the 60s and 70s (15-25C) by late May and June. Over-night temperatures fall below freezing and may plunge near zero (-20C). These are statistical averages; actual conditions can be vastly different from longterm norms. At any time of year, be prepared for sudden changes; unpredictability, more than anything else, characterizes Yellowstone's weather. Storms in late May and early June may result in significant accumulations of snow--up to a foot of snow in 24 hours is not uncommon.
We recommend that you bring a warm jacket and rain gear. Spring visitors should be prepared for any type of weather. Call ahead for current weather and road information since sudden storms may result in cold temperatures, snow and/or temporary road closures. Yellowstone's weather is always unpredictable. Carry extra clothing when hiking. Good walking shoes and layers of clothing are recommended throughout the year.