Royal, Iowa has a Humid Continental Hot Summers With Year Around Precipitation climate (Köppen classification: Dfa). Average annual temperatures range from 2.3 °C (low) to 13.6 °C (high). Annual precipitation averages 784.4 Millimeters. 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 | -13.6 °C | -3.8 °C | 17.78 mm |
| February | -11.3 °C | -1.5 °C | 21.08 mm |
| March | -4.7 °C | 5.8 °C | 41.4 mm |
| April | 1.8 °C | 14.2 °C | 85.85 mm |
| May | 8.8 °C | 20.9 °C | 108.46 mm |
| June | 14.9 °C | 26.6 °C | 122.68 mm |
| July | 16.9 °C | 28.4 °C | 90.17 mm |
| August | 15.4 °C | 27.1 °C | 96.01 mm |
| September | 10.6 °C | 23.7 °C | 80.52 mm |
| October | 3.3 °C | 16.1 °C | 59.44 mm |
| November | -3.9 °C | 6.8 °C | 36.58 mm |
| December | -10.2 °C | -0.9 °C | 24.38 mm |
| Annual | 2.3 °C | 13.6 °C | 784.35 mm |
| 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 : -28.9°C to -26.1°C |
| Plant Hardiness Zone - 2012 | Zone 5a : -28.9°C to -26.1°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dfa - Humid Continental Hot Summers With Year Around Precipitation |