Tumwater, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 5.5 °C (low) to 16 °C (high). Annual precipitation averages 1467.6 Millimeters. Tumwater is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 11 - Oct. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.5 °C | 8.2 °C | 216.66 mm |
| February | 1.2 °C | 9.8 °C | 140.21 mm |
| March | 2.3 °C | 12.3 °C | 157.99 mm |
| April | 3.9 °C | 14.9 °C | 107.95 mm |
| May | 6.8 °C | 18.8 °C | 65.28 mm |
| June | 9.3 °C | 21.3 °C | 47.24 mm |
| July | 11.2 °C | 25.1 °C | 17.78 mm |
| August | 11.2 °C | 25.5 °C | 29.46 mm |
| September | 8.9 °C | 22.4 °C | 52.58 mm |
| October | 5.8 °C | 15.9 °C | 145.03 mm |
| November | 2.9 °C | 10.7 °C | 256.79 mm |
| December | 1.2 °C | 7.6 °C | 230.63 mm |
| Annual | 5.5 °C | 16 °C | 1467.6 mm |
| Average First Frost Date | Oct. 11 - Oct. 20 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 75-100 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 |