Royal, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 36.2 °F (low) to 56.5 °F (high). Annual precipitation averages 30.9 Inches. Royal is located in USDA Plant Hardiness Zone 5a. The growing season typically runs from the last frost around Apr. 21 - Apr. 30 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 7.5 °F | 25.1 °F | 0.7 in. |
| February | 11.6 °F | 29.3 °F | 0.83 in. |
| March | 23.6 °F | 42.5 °F | 1.63 in. |
| April | 35.2 °F | 57.6 °F | 3.38 in. |
| May | 47.9 °F | 69.6 °F | 4.27 in. |
| June | 58.8 °F | 79.8 °F | 4.83 in. |
| July | 62.4 °F | 83.2 °F | 3.55 in. |
| August | 59.7 °F | 80.7 °F | 3.78 in. |
| September | 51.0 °F | 74.7 °F | 3.17 in. |
| October | 38.0 °F | 60.9 °F | 2.34 in. |
| November | 24.9 °F | 44.3 °F | 1.44 in. |
| December | 13.6 °F | 30.3 °F | 0.96 in. |
| Annual | 36.2 °F | 56.5 °F | 30.88 in. |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | Apr. 21 - Apr. 30 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 5a : -20°F to -15°F |
| Plant Hardiness Zone - 2012 | Zone 5a : -20°F to -15°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |