Allyn, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.2 °C (low) to 16.1 °C (high). Annual precipitation averages 1358.4 Millimeters. Allyn 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 Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 2 °C | 8.5 °C | 205.49 mm |
| February | 1.7 °C | 9.9 °C | 134.62 mm |
| March | 2.8 °C | 12.4 °C | 153.42 mm |
| April | 4.6 °C | 15.2 °C | 103.12 mm |
| May | 7.7 °C | 19.1 °C | 59.94 mm |
| June | 10.1 °C | 21.2 °C | 42.67 mm |
| July | 12.1 °C | 25.1 °C | 17.53 mm |
| August | 12 °C | 25.2 °C | 27.94 mm |
| September | 9.7 °C | 22.1 °C | 46.23 mm |
| October | 6.4 °C | 15.3 °C | 131.06 mm |
| November | 3.4 °C | 10.9 °C | 224.03 mm |
| December | 1.7 °C | 7.9 °C | 212.34 mm |
| Annual | 6.2 °C | 16.1 °C | 1358.39 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |