Annex, Oregon has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 4.1 °C (low) to 18.4 °C (high). Annual precipitation averages 312.7 Millimeters. Annex is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -5.3 °C | 2.7 °C | 44.45 mm |
| February | -3.2 °C | 7.4 °C | 31.75 mm |
| March | 0.3 °C | 13.7 °C | 31.5 mm |
| April | 3.2 °C | 18.1 °C | 23.88 mm |
| May | 7.8 °C | 23.4 °C | 30.48 mm |
| June | 11.6 °C | 28.1 °C | 24.38 mm |
| July | 15.6 °C | 34.2 °C | 7.11 mm |
| August | 14 °C | 33.3 °C | 4.32 mm |
| September | 8.9 °C | 27.4 °C | 9.4 mm |
| October | 2.8 °C | 18.9 °C | 18.8 mm |
| November | -1.9 °C | 9.6 °C | 33.53 mm |
| December | -5 °C | 3.4 °C | 53.09 mm |
| Annual | 4.1 °C | 18.4 °C | 312.69 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 7a : -17.8°C to -15°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |