Lake Mary Ronan, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 29.7 °F (low) to 54.3 °F (high). Annual precipitation averages 18.5 Inches. Lake Mary Ronan is located in USDA Plant Hardiness Zone 5b. The growing season typically runs from the last frost around Jun. 1 - Jun. 10 through the first frost around Sep.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 15.6 °F | 32.2 °F | 1.54 in. |
| February | 15.9 °F | 35.6 °F | 1.22 in. |
| March | 21.2 °F | 44.9 °F | 1.28 in. |
| April | 27.4 °F | 52.7 °F | 1.61 in. |
| May | 34.9 °F | 62.6 °F | 1.9 in. |
| June | 41.2 °F | 69.3 °F | 2.77 in. |
| July | 47.2 °F | 80.8 °F | 1.12 in. |
| August | 46.3 °F | 80.4 °F | 0.94 in. |
| September | 39.0 °F | 69.1 °F | 1.28 in. |
| October | 29.6 °F | 53.2 °F | 1.59 in. |
| November | 22.1 °F | 39.9 °F | 1.64 in. |
| December | 16.5 °F | 31.0 °F | 1.58 in. |
| Annual | 29.7 °F | 54.3 °F | 18.47 in. |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | Jun. 1 - Jun. 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5b : -15°F to -10°F |
| Plant Hardiness Zone - 2012 | Zone 5b : -15°F to -10°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |