Caldwell, Idaho has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 3.9 °C (low) to 18.3 °C (high). Annual precipitation averages 278.9 Millimeters. Caldwell is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -4.6 °C | 3.4 °C | 40.64 mm |
| February | -2.9 °C | 7.9 °C | 24.38 mm |
| March | 0.1 °C | 13.7 °C | 29.72 mm |
| April | 2.7 °C | 17.8 °C | 27.69 mm |
| May | 7.3 °C | 22.9 °C | 29.97 mm |
| June | 11.1 °C | 27.6 °C | 16.26 mm |
| July | 14.7 °C | 33.5 °C | 6.86 mm |
| August | 13.4 °C | 32.8 °C | 4.83 mm |
| September | 8.6 °C | 27 °C | 10.92 mm |
| October | 2.9 °C | 18.9 °C | 19.56 mm |
| November | -1.7 °C | 9.7 °C | 25.15 mm |
| December | -4.6 °C | 3.8 °C | 42.93 mm |
| Annual | 3.9 °C | 18.3 °C | 278.91 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |