Harlowton, Montana has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -0.4 °C (low) to 14.4 °C (high). Annual precipitation averages 351.5 Millimeters. Harlowton 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.11 - Sep. 20.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -9.6 °C | 2.5 °C | 8.13 mm |
| February | -9.4 °C | 3.7 °C | 9.65 mm |
| March | -5.7 °C | 8.4 °C | 14.48 mm |
| April | -1.7 °C | 12.9 °C | 39.88 mm |
| May | 3.1 °C | 17.9 °C | 65.02 mm |
| June | 7.6 °C | 22.9 °C | 70.1 mm |
| July | 10.7 °C | 28.9 °C | 38.86 mm |
| August | 9.6 °C | 28.3 °C | 30.48 mm |
| September | 5.1 °C | 22.6 °C | 29.72 mm |
| October | -0.4 °C | 14.7 °C | 21.08 mm |
| November | -5.4 °C | 7.2 °C | 12.45 mm |
| December | -9.1 °C | 2.3 °C | 11.68 mm |
| Annual | -0.4 °C | 14.4 °C | 351.53 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | 150-180 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 | Severe Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |