Olney, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1.9 °C (low) to 12.5 °C (high). Annual precipitation averages 540 Millimeters. 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 | -9.9 °C | -0.9 °C | 56.39 mm |
| February | -9.5 °C | 2.2 °C | 37.08 mm |
| March | -6 °C | 6.9 °C | 36.32 mm |
| April | -2.6 °C | 12.3 °C | 35.56 mm |
| May | 1.6 °C | 17.9 °C | 54.86 mm |
| June | 5.3 °C | 21.3 °C | 81.28 mm |
| July | 7.2 °C | 27.3 °C | 38.35 mm |
| August | 5.9 °C | 27.4 °C | 24.89 mm |
| September | 2 °C | 21.1 °C | 32.26 mm |
| October | -2.3 °C | 12.1 °C | 38.1 mm |
| November | -5.6 °C | 3.6 °C | 50.8 mm |
| December | -9.2 °C | -1.3 °C | 54.1 mm |
| Annual | -1.9 °C | 12.5 °C | 539.99 mm |
| 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 : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |