Mill Creek, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.7 °C (low) to 14.9 °C (high). Annual precipitation averages 1125 Millimeters. Mill Creek is located in USDA Plant Hardiness Zone 9a. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 2.2 °C | 7.9 °C | 144.78 mm |
| February | 2.2 °C | 9.2 °C | 111 mm |
| March | 3.5 °C | 11.4 °C | 121.67 mm |
| April | 5.3 °C | 13.8 °C | 91.95 mm |
| May | 8.2 °C | 17.6 °C | 68.07 mm |
| June | 10.3 °C | 19.7 °C | 52.07 mm |
| July | 12.3 °C | 23 °C | 23.11 mm |
| August | 12.6 °C | 23.5 °C | 28.45 mm |
| September | 10.7 °C | 20.6 °C | 54.61 mm |
| October | 7.3 °C | 14.8 °C | 105.16 mm |
| November | 3.9 °C | 10.3 °C | 171.96 mm |
| December | 2.1 °C | 7.4 °C | 152.15 mm |
| Annual | 6.7 °C | 14.9 °C | 1124.98 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 30-40 Days |
| Plant Hardiness Zone | Zone 9a : -6.7°C to -3.9°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 |