McMillin, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.4 °C (low) to 16.3 °C (high). Annual precipitation averages 1101.3 Millimeters. 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 | 1.8 °C | 8.7 °C | 156.97 mm |
| February | 1.7 °C | 10.2 °C | 101.35 mm |
| March | 3.1 °C | 12.4 °C | 116.84 mm |
| April | 4.9 °C | 15.2 °C | 89.15 mm |
| May | 8 °C | 19.1 °C | 59.94 mm |
| June | 10.6 °C | 21.6 °C | 50.8 mm |
| July | 12.4 °C | 25.3 °C | 21.34 mm |
| August | 12.4 °C | 25.6 °C | 27.43 mm |
| September | 10.1 °C | 22.3 °C | 39.88 mm |
| October | 6.7 °C | 16.2 °C | 111.25 mm |
| November | 3.6 °C | 11.2 °C | 169.16 mm |
| December | 1.5 °C | 8.1 °C | 157.23 mm |
| Annual | 6.4 °C | 16.3 °C | 1101.34 mm |
| 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 : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |