This along with what is the safest month to climb Mt. Rainier is a popular questions from our members. Late spring and summer are when conditions are best, starting in May and ending in September. Realize conditions on the mountain change weekly and may be different from year to year but generally you can expect the following in each month:
Much of the mountain is still in deep snow, even at the parking lot. Most of the crevasses are covered making the route to the top more direct. The weather can still bring large amounts of moisture and wet snow, avalanche danger is typically high. One benefit of going in May is that there aren’t many climbers, so if you seek solitude you’ll enjoy it more.
The weather starts improving with more clear days than May. Night time temperatures are still bone chilling cold but days tend to be warm, especially below 9000 feet. Climbers higher up tend to experience icy conditions with melting and refreezing at night. Crevasses start opening up. Avalanche danger can still be high and rock fall seems more noticeable as the mountain thaws out. Chances of securing a last minute campsite at Camp Muir or Schuman are better.
One of the most popular months to climb and for good reason. Conditions are generally good although bad weather can still occur. July and August tend to be the safest options. Snow still remains on lower snowfields making for great glissading and easy decent.
Similar good conditions to July more crevasses are exposed making the routes more circuitous and longer. The snow on the upper mountain is firmer. Many first time climbers like August because it allows them to improve fitness on lower peaks earlier in the season while still providing generally good weather and glacier conditions.
More crevasses are exposed, longer routes, and nights tend to get cold again. The crowds start to dissipate after Labor Day (in first week of Sep). Another advantage is the firm snow makes for easier climbing; usually the trails below the Muir Snow field on DC route and Glacier Basin on Emmons route are free of snow. Chances of securing a last minute camp site at Camp Muir or Schurman are better.
Lastly realize experienced climbers have and continue to summit in winter months. If your going to tackle a winter accent makes sure you have the experience, skills, equipment, and can weather extreme storms and winter conditions. Winter climbers will have to get special permission from the National Park Service.