Sinclair, Wyoming has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from -0.7 °C (low) to 13.6 °C (high). Annual precipitation averages 241.3 Millimeters. Sinclair is located in USDA Plant Hardiness Zone 5a. 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 | -10.4 °C | 0.1 °C | 12.7 mm |
| February | -9.7 °C | 1.4 °C | 9.91 mm |
| March | -5.3 °C | 7.1 °C | 22.35 mm |
| April | -2.2 °C | 11.7 °C | 25.4 mm |
| May | 2.7 °C | 17.7 °C | 37.59 mm |
| June | 7.2 °C | 24.6 °C | 22.1 mm |
| July | 11.1 °C | 29.2 °C | 18.54 mm |
| August | 10 °C | 27.9 °C | 19.3 mm |
| September | 5.2 °C | 22.6 °C | 20.83 mm |
| October | -0.6 °C | 14.2 °C | 22.61 mm |
| November | -5.7 °C | 6.1 °C | 14.99 mm |
| December | -10.3 °C | 0.1 °C | 14.99 mm |
| Annual | -0.7 °C | 13.6 °C | 241.31 mm |
| Average First Frost Date | Sep.11 - Sep. 20 |
| Average Last Frost Date | May 21 - May 31 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 5a : -28.9°C to -26.1°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 |