Fallon, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 31.3 °F (low) to 58.9 °F (high). Annual precipitation averages 13.9 Inches. Fallon is located in USDA Plant Hardiness Zone 4a. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Sep. 21 - Sep. 30.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 5.6 °F | 29.4 °F | 0.28 in. |
| February | 9.7 °F | 34.3 °F | 0.31 in. |
| March | 20.1 °F | 46.1 °F | 0.52 in. |
| April | 31.1 °F | 58.4 °F | 1.44 in. |
| May | 41.4 °F | 68.6 °F | 2.63 in. |
| June | 51.2 °F | 78.5 °F | 2.45 in. |
| July | 57.0 °F | 88.3 °F | 2.0 in. |
| August | 54.7 °F | 87.6 °F | 1.25 in. |
| September | 44.1 °F | 76.8 °F | 1.27 in. |
| October | 32.4 °F | 60.5 °F | 1.01 in. |
| November | 19.5 °F | 44.9 °F | 0.37 in. |
| December | 9.2 °F | 32.9 °F | 0.32 in. |
| Annual | 31.3 °F | 58.9 °F | 13.85 in. |
| Average First Frost Date | Sep. 21 - Sep. 30 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4a : -30°F to -25°F |
| Plant Hardiness Zone - 2012 | Zone 3b : -35°F to -30°F |
| Current Drought Conditions | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |