Fairfield, Idaho has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 27.5 °F (low) to 56.6 °F (high). Annual precipitation averages 13.2 Inches. Fairfield is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Jun. 11 - Jun. 20 through the first frost around Aug. 21 - Aug. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.8 °F | 30.3 °F | 1.9 in. |
| February | 10.4 °F | 34.3 °F | 1.18 in. |
| March | 20.0 °F | 43.2 °F | 1.28 in. |
| April | 28.5 °F | 54.5 °F | 1.07 in. |
| May | 35.6 °F | 64.6 °F | 1.67 in. |
| June | 40.6 °F | 73.3 °F | 0.79 in. |
| July | 47.2 °F | 84.9 °F | 0.19 in. |
| August | 45.3 °F | 84.1 °F | 0.2 in. |
| September | 37.5 °F | 74.7 °F | 0.44 in. |
| October | 28.2 °F | 60.5 °F | 0.96 in. |
| November | 19.1 °F | 43.6 °F | 1.33 in. |
| December | 9.4 °F | 30.7 °F | 2.19 in. |
| Annual | 27.5 °F | 56.6 °F | 13.2 in. |
| Average First Frost Date | Aug. 21 - Aug. 31 |
| Average Last Frost Date | Jun. 11 - Jun. 20 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |