Mount Rainier Weather Page
Mount Rainier Weather Patterns
A Pacific maritime climate characterized by rainy, mild winters and cool, dry summers controls northwest weather patterns. Winter storms, generated out of the Gulf of Alaska, strike the coast from the southwest and bring warm moist air into the Pacific Northwest. In summer, the North Pacific High dominates the weather pattern, bringing winds over cooler water and striking the region from the northwest. The water vapor in this cool air condenses to form fog in the areas in the summer. The driest weather in the region occurs when high pressure systems develop east of the Cascade Mountains, causing warm, dry air from the interior to blow westward toward the coast.
Mountains make their own weather by forcing incoming air masses upward as they strike the mountains. As the air rises it cools at an average rate of 3.5 degrees Fahrenheit per 1000 feet, forming clouds and increasing precipitation as the air rises over the mountains. On the leeward side of the mountains the air descends down slope, warms, and increases the amount of water vapor it can hold. This leeward side of the mountain receives less precipitation, in what is called a "rain shadow."
Mount Rainier lies west of the Cascade Mountains, only 100 miles east of the Pacific Ocean, and rises to an elevation of 14,410 feet. Mount Rainier makes its own weather. Clouds often collect around the mountain forming a cap on the summit, indicating a change in weather. The heaviest snowfall occurs between the 5,000 and 11,000 foot elevations. Year round weather stations are located at Longmire (2761 feet), Ohanapecosh (1949 feet) and Paradise (5400 feet) ranger stations for recording precipitation, temperature, wind direction, and cloud cover. The Paradise Ranger Station is known for its snowfall, holding a record for the most accumulated snowfall in a single year, 1122 inches (93.5 feet) of snowfall in 1971-72.
Visitors should be aware that mountain weather is very changeable. Wet, cold weather can occur anytime of the year. While late-July and August can be the driest, warmest time of the year, summer can also be wet and cool. Snow may 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.