Rainier, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 5.3 °C (low) to 15.9 °C (high). Annual precipitation averages 1272.3 Millimeters. Rainier is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.1 °C | 7.9 °C | 180.34 mm |
| February | 0.9 °C | 9.6 °C | 122.68 mm |
| March | 2.1 °C | 11.9 °C | 138.94 mm |
| April | 3.7 °C | 14.8 °C | 101.6 mm |
| May | 6.7 °C | 18.8 °C | 60.96 mm |
| June | 9.2 °C | 21.3 °C | 51.05 mm |
| July | 11.2 °C | 25.2 °C | 17.02 mm |
| August | 11.2 °C | 25.7 °C | 26.67 mm |
| September | 8.8 °C | 22.3 °C | 49.53 mm |
| October | 5.5 °C | 15.9 °C | 121.16 mm |
| November | 2.6 °C | 10.4 °C | 210.82 mm |
| December | 0.9 °C | 7.3 °C | 191.52 mm |
| Annual | 5.3 °C | 15.9 °C | 1272.29 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8a : -12.2°C to -9.4°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |