NPS, Steve Redman
Weather patterns at Mount Rainier are strongly influenced by the Pacific Ocean, elevation, and latitude. The climate is generally cool and rainy, with summer highs in the 60s and 70s. While July and August are the sunniest months of the year, rain is possible any day, and very likely in spring, fall, and winter.
Visitors should be aware that mountain weather is very changeable. Wet, cold weather can occur anytime of the year. Although late-July and August are generally the driest and warmest time of the year, summer can also be wet and cool. Snow will remain at the 5,000 to 8,000 feet elevation well into mid-July.
Hikers and mountain climbers should be prepared for changing weather. Pay attention to weather forecasts, both one day and long range, avalanche warnings, and special weather alerts. Have extra clothing, rain gear, and a tent for protection against storms anytime of the year. Know the weather forecast and plan your trip accordingly.
Average Monthly Temperatures at Mount Rainier: