Charlo, Montana has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.6 °C (low) to 14.1 °C (high). Annual precipitation averages 372.4 Millimeters. Charlo is located in USDA Plant Hardiness Zone 6a. 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 | -5.9 °C | 1.3 °C | 25.4 mm |
| February | -5.7 °C | 3.3 °C | 20.83 mm |
| March | -2.7 °C | 8.9 °C | 20.83 mm |
| April | 0.6 °C | 13.4 °C | 35.56 mm |
| May | 4.5 °C | 18.8 °C | 43.69 mm |
| June | 8.2 °C | 22.5 °C | 61.21 mm |
| July | 11 °C | 28.8 °C | 25.15 mm |
| August | 10.3 °C | 28.7 °C | 22.35 mm |
| September | 6.3 °C | 22.4 °C | 28.19 mm |
| October | 1.3 °C | 13.8 °C | 33.53 mm |
| November | -2.9 °C | 5.6 °C | 29.97 mm |
| December | -5.9 °C | 1.1 °C | 25.65 mm |
| Annual | 1.6 °C | 14.1 °C | 372.36 mm |
| 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 6a : -23.3°C to -20.6°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 |