Forgan, Oklahoma has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 5.6 °C (low) to 21.7 °C (high). Annual precipitation averages 529.8 Millimeters. Forgan is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Apr. 11 - Apr. 20 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.9 °C | 9.1 °C | 13.72 mm |
| February | -5.6 °C | 10.9 °C | 14.73 mm |
| March | -0.7 °C | 16.3 °C | 36.07 mm |
| April | 4.2 °C | 21.3 °C | 47.24 mm |
| May | 10.3 °C | 26.6 °C | 64.26 mm |
| June | 16.3 °C | 31.8 °C | 85.09 mm |
| July | 19.1 °C | 34.6 °C | 67.31 mm |
| August | 18.1 °C | 33.4 °C | 72.9 mm |
| September | 13.4 °C | 29.5 °C | 36.07 mm |
| October | 5.8 °C | 22.4 °C | 49.02 mm |
| November | -1.3 °C | 15.3 °C | 20.32 mm |
| December | -6.1 °C | 9.1 °C | 23.11 mm |
| Annual | 5.6 °C | 21.7 °C | 529.84 mm |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 11 - Apr. 20 |
| Average Days With Frost | 100-125 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Moderate Drought |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |