Irwin, Missouri has a Humid Subtropical Climate climate (Köppen classification: Cfa). Average annual temperatures range from 46.2 °F (low) to 67.4 °F (high). Annual precipitation averages 46.4 Inches. Irwin is located in USDA Plant Hardiness Zone 7a. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Oct. 21 - Oct. 31.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 23.2 °F | 42.8 °F | 1.82 in. |
| February | 27.0 °F | 48.0 °F | 2.09 in. |
| March | 35.3 °F | 57.9 °F | 3.24 in. |
| April | 44.8 °F | 67.5 °F | 4.86 in. |
| May | 55.3 °F | 75.7 °F | 6.7 in. |
| June | 64.7 °F | 84.6 °F | 5.81 in. |
| July | 68.9 °F | 89.3 °F | 4.4 in. |
| August | 67.0 °F | 88.9 °F | 3.53 in. |
| September | 58.4 °F | 81.2 °F | 4.6 in. |
| October | 46.7 °F | 70.1 °F | 3.62 in. |
| November | 35.8 °F | 57.1 °F | 3.2 in. |
| December | 27.0 °F | 46.2 °F | 2.55 in. |
| Annual | 46.2 °F | 67.4 °F | 46.42 in. |
| Average First Frost Date | Oct. 21 - Oct. 31 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 75-100 Days |
| Plant Hardiness Zone | Zone 7a : 0°F to 5°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Cfa - Humid Subtropical Climate |