Alderton, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.3 °C (low) to 16.3 °C (high). Annual precipitation averages 1095 Millimeters. Alderton 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 | 1.7 °C | 8.6 °C | 156.72 mm |
| February | 1.7 °C | 10.1 °C | 98.55 mm |
| March | 3 °C | 12.4 °C | 115.06 mm |
| April | 4.8 °C | 15.2 °C | 87.38 mm |
| May | 7.9 °C | 19.2 °C | 58.42 mm |
| June | 10.5 °C | 21.7 °C | 51.56 mm |
| July | 12.4 °C | 25.3 °C | 21.08 mm |
| August | 12.4 °C | 25.6 °C | 30.73 mm |
| September | 10 °C | 22.3 °C | 39.88 mm |
| October | 6.6 °C | 16.2 °C | 110.49 mm |
| November | 3.5 °C | 11.2 °C | 166.88 mm |
| December | 1.4 °C | 8.1 °C | 158.24 mm |
| Annual | 6.3 °C | 16.3 °C | 1094.99 mm |
| 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 : -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 |