Allyn, Washington has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 43.1 °F (low) to 60.9 °F (high). Annual precipitation averages 53.5 Inches. 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 | 35.6 °F | 47.3 °F | 8.09 in. |
| February | 35.0 °F | 49.9 °F | 5.3 in. |
| March | 37.1 °F | 54.4 °F | 6.04 in. |
| April | 40.2 °F | 59.4 °F | 4.06 in. |
| May | 45.8 °F | 66.3 °F | 2.36 in. |
| June | 50.1 °F | 70.2 °F | 1.68 in. |
| July | 53.7 °F | 77.1 °F | 0.69 in. |
| August | 53.6 °F | 77.3 °F | 1.1 in. |
| September | 49.5 °F | 71.8 °F | 1.82 in. |
| October | 43.6 °F | 59.6 °F | 5.16 in. |
| November | 38.2 °F | 51.6 °F | 8.82 in. |
| December | 35.0 °F | 46.3 °F | 8.36 in. |
| Annual | 43.1 °F | 60.9 °F | 53.48 in. |
| 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 : 15°F to 20°F |
| Plant Hardiness Zone - 2012 | Zone 8b : 15°F to 20°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |