McMillin, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 43.5 °F (low) to 61.4 °F (high). Annual precipitation averages 43.4 Inches. McMillin is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 35.2 °F | 47.6 °F | 6.18 in. |
| February | 35.0 °F | 50.3 °F | 3.99 in. |
| March | 37.5 °F | 54.4 °F | 4.6 in. |
| April | 40.9 °F | 59.3 °F | 3.51 in. |
| May | 46.4 °F | 66.3 °F | 2.36 in. |
| June | 51.0 °F | 70.8 °F | 2.0 in. |
| July | 54.4 °F | 77.6 °F | 0.84 in. |
| August | 54.4 °F | 78.0 °F | 1.08 in. |
| September | 50.1 °F | 72.2 °F | 1.57 in. |
| October | 44.0 °F | 61.1 °F | 4.38 in. |
| November | 38.4 °F | 52.2 °F | 6.66 in. |
| December | 34.7 °F | 46.6 °F | 6.19 in. |
| Annual | 43.5 °F | 61.4 °F | 43.36 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 50-75 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 |