Sumner, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 43.8 °F (low) to 61.6 °F (high). Annual precipitation averages 41.6 Inches. Sumner is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 35.4 °F | 47.7 °F | 6.17 in. |
| February | 35.2 °F | 50.4 °F | 3.5 in. |
| March | 37.7 °F | 54.6 °F | 4.15 in. |
| April | 41.1 °F | 59.7 °F | 3.04 in. |
| May | 46.7 °F | 66.8 °F | 2.16 in. |
| June | 51.4 °F | 71.3 °F | 1.95 in. |
| July | 54.7 °F | 77.8 °F | 0.75 in. |
| August | 54.8 °F | 78.0 °F | 1.36 in. |
| September | 50.4 °F | 72.2 °F | 1.45 in. |
| October | 44.2 °F | 61.3 °F | 4.27 in. |
| November | 38.6 °F | 52.4 °F | 6.45 in. |
| December | 34.9 °F | 46.8 °F | 6.3 in. |
| Annual | 43.8 °F | 61.6 °F | 41.55 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 40-50 Days |
| Plant Hardiness Zone | Zone 8b : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |