Tumwater, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 42 °F (low) to 60.9 °F (high). Annual precipitation averages 57.8 Inches. 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 | 34.7 °F | 46.7 °F | 8.53 in. |
| February | 34.2 °F | 49.7 °F | 5.52 in. |
| March | 36.2 °F | 54.2 °F | 6.22 in. |
| April | 39.0 °F | 58.9 °F | 4.25 in. |
| May | 44.3 °F | 65.9 °F | 2.57 in. |
| June | 48.8 °F | 70.4 °F | 1.86 in. |
| July | 52.2 °F | 77.1 °F | 0.7 in. |
| August | 52.1 °F | 77.9 °F | 1.16 in. |
| September | 48.0 °F | 72.4 °F | 2.07 in. |
| October | 42.4 °F | 60.6 °F | 5.71 in. |
| November | 37.3 °F | 51.3 °F | 10.11 in. |
| December | 34.2 °F | 45.7 °F | 9.08 in. |
| Annual | 42 °F | 60.9 °F | 57.78 in. |
| 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 : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8a : 10°F to 15°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |