Lake Mary Ronan, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from -1.3 °C (low) to 12.4 °C (high). Annual precipitation averages 469.2 Millimeters. 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 | -9.1 °C | 0.1 °C | 39.12 mm |
| February | -8.9 °C | 2 °C | 30.99 mm |
| March | -6 °C | 7.2 °C | 32.51 mm |
| April | -2.6 °C | 11.5 °C | 40.89 mm |
| May | 1.6 °C | 17 °C | 48.26 mm |
| June | 5.1 °C | 20.7 °C | 70.36 mm |
| July | 8.4 °C | 27.1 °C | 28.45 mm |
| August | 7.9 °C | 26.9 °C | 23.88 mm |
| September | 3.9 °C | 20.6 °C | 32.51 mm |
| October | -1.3 °C | 11.8 °C | 40.39 mm |
| November | -5.5 °C | 4.4 °C | 41.66 mm |
| December | -8.6 °C | -0.6 °C | 40.13 mm |
| Annual | -1.3 °C | 12.4 °C | 469.15 mm |
| 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 : -26.1°C to -23.3°C |
| Plant Hardiness Zone - 2012 | Zone 5b : -26.1°C to -23.3°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |