Cromwell, Oklahoma has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 9.8 °C (low) to 22.6 °C (high). Annual precipitation averages 1063.5 Millimeters. Cromwell is located in USDA Plant Hardiness Zone 7b. The growing season typically runs from the last frost around Mar. 21 - Mar. 31 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -2.3 °C | 10.4 °C | 46.23 mm |
| February | -0.3 °C | 12.7 °C | 52.32 mm |
| March | 4.4 °C | 17.7 °C | 78.23 mm |
| April | 9.1 °C | 22.4 °C | 106.68 mm |
| May | 14.5 °C | 26.3 °C | 141.48 mm |
| June | 19.5 °C | 31 °C | 127.51 mm |
| July | 21.6 °C | 34.1 °C | 97.03 mm |
| August | 20.8 °C | 34.1 °C | 81.28 mm |
| September | 16.5 °C | 29.8 °C | 105.16 mm |
| October | 10 °C | 23.7 °C | 97.03 mm |
| November | 4.2 °C | 17.2 °C | 70.36 mm |
| December | -0.7 °C | 11.3 °C | 60.2 mm |
| Annual | 9.8 °C | 22.6 °C | 1063.51 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Mar. 21 - Mar. 31 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 7b : -15°C to -12.2°C |
| Plant Hardiness Zone - 2012 | Zone 7b : -15°C to -12.2°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |