Monticello, Minnesota has a Humid Continental Mild Summer, Wet All Year climate (Köppen classification: Dfb). Average annual temperatures range from 1.5 °C (low) to 12.2 °C (high). Annual precipitation averages 790.7 Millimeters. Monticello is located in USDA Plant Hardiness Zone 4b. The growing season typically runs from the last frost around May 1 - May 10 through the first frost around Oct. 1 - Oct. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -15.3 °C | -5.5 °C | 19.81 mm |
| February | -13.4 °C | -2.8 °C | 21.08 mm |
| March | -6.4 °C | 4.2 °C | 43.18 mm |
| April | 0.9 °C | 12.7 °C | 70.1 mm |
| May | 8.1 °C | 20 °C | 105.66 mm |
| June | 14.1 °C | 25.3 °C | 113.54 mm |
| July | 16.5 °C | 27.7 °C | 99.82 mm |
| August | 14.9 °C | 26.4 °C | 103.63 mm |
| September | 10.3 °C | 22.2 °C | 80.26 mm |
| October | 3.1 °C | 14 °C | 68.58 mm |
| November | -3.9 °C | 5.1 °C | 36.07 mm |
| December | -11.2 °C | -2.6 °C | 28.96 mm |
| Annual | 1.5 °C | 12.2 °C | 790.69 mm |
| Average First Frost Date | Oct. 1 - Oct. 10 |
| Average Last Frost Date | May 1 - May 10 |
| Average Days With Frost | 150-180 Days |
| Plant Hardiness Zone | Zone 4b : -31.7°C to -28.9°C |
| Plant Hardiness Zone - 2012 | Zone 4b : -31.7°C to -28.9°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | Dfb - Humid Continental Mild Summer, Wet All Year |