Firth, Idaho has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 31.9 °F (low) to 58.1 °F (high). Annual precipitation averages 10.7 Inches. Firth is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 13.7 °F | 30.5 °F | 0.87 in. |
| February | 16.8 °F | 35.4 °F | 0.62 in. |
| March | 25.8 °F | 47.8 °F | 0.95 in. |
| April | 31.1 °F | 57.6 °F | 1.07 in. |
| May | 38.8 °F | 66.9 °F | 1.57 in. |
| June | 45.2 °F | 75.7 °F | 1.09 in. |
| July | 50.8 °F | 86.1 °F | 0.48 in. |
| August | 49.2 °F | 85.7 °F | 0.59 in. |
| September | 41.6 °F | 75.3 °F | 0.94 in. |
| October | 31.9 °F | 60.4 °F | 1.03 in. |
| November | 22.7 °F | 44.2 °F | 0.71 in. |
| December | 14.6 °F | 31.6 °F | 0.8 in. |
| Annual | 31.9 °F | 58.1 °F | 10.72 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Extreme Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |