Olney, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 28.5 °F (low) to 54.5 °F (high). Annual precipitation averages 21.3 Inches. Olney is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 21 - May 31 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 14.1 °F | 30.4 °F | 2.22 in. |
| February | 14.9 °F | 36.0 °F | 1.46 in. |
| March | 21.2 °F | 44.4 °F | 1.43 in. |
| April | 27.4 °F | 54.1 °F | 1.4 in. |
| May | 34.9 °F | 64.2 °F | 2.16 in. |
| June | 41.5 °F | 70.3 °F | 3.2 in. |
| July | 44.9 °F | 81.2 °F | 1.51 in. |
| August | 42.6 °F | 81.3 °F | 0.98 in. |
| September | 35.6 °F | 70.0 °F | 1.27 in. |
| October | 27.9 °F | 53.7 °F | 1.5 in. |
| November | 22.0 °F | 38.5 °F | 2.0 in. |
| December | 15.4 °F | 29.7 °F | 2.13 in. |
| Annual | 28.5 °F | 54.5 °F | 21.26 in. |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 4b : -25°F to -20°F |
| Plant Hardiness Zone - 2012 | Zone 4b : -25°F to -20°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |