Mount Rainier National Park weather in September
September in Mount Rainier National Park: cold, rainy, with clean air — an excellent time to visit.
#3 of 12 months in Mount Rainier National Park · #289 of 604 destinations to visit in September · comfort 81/100 (tier A)
Updated June 2026 · climate normals from ERA5 reanalysis
Mount Rainier National Park climate normals — September
| Daytime high | 11°C / 52°F | 🧥 cold |
|---|---|---|
| Nighttime low | 1°C / 33°F | |
| Feels like (high) | 8°C / 46°F | |
| Rainfall | 87 mm / 3.4 in | 🌧 rainy |
| Rainy days | 11 days | |
| Humidity | 69% | 💧 humid |
| Dew point | -1°C / 30°F | |
| Sunshine | 9.6 h/day | |
| Daylight | 12.5 h | |
| Wind | 11 km/h / 7 mph | |
| Snowfall | 0.8 cm / 0.3 in | |
| Air quality (US AQI) | 33 | 🍃 good |
Monthly averages from ERA5 reanalysis. AQI is the mean US Air Quality Index for the month.
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Mount Rainier National Park in September — FAQ
- Is September a good time to visit Mount Rainier National Park?
- September in Mount Rainier National Park: cold, rainy, with clean air — an excellent time to visit. It ranks #3 of 12 months for Mount Rainier National Park on SeasonMap's comfort score (81/100).
- What is the weather like in Mount Rainier National Park in September?
- In September, Mount Rainier National Park averages a daily high of 11.2°C and a low of 0.7°C, with about 86.5 mm of rain over roughly 10.6 rainy days.
- What is the air quality in Mount Rainier National Park in September?
- Mount Rainier National Park has a mean US Air Quality Index of about 33 in September.