Hillsboro, Oregon has a Warm-Summer Mediterranean Climate climate (Köppen classification: Csb). Average annual temperatures range from 6.5 °C (low) to 17.3 °C (high). Annual precipitation averages 1009.9 Millimeters. Hillsboro is located in USDA Plant Hardiness Zone 8b. The growing season typically runs from the last frost around Apr. 1 - Apr. 10 through the first frost around Nov. 1 - Nov. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 1.9 °C | 8.3 °C | 154.43 mm |
| February | 1.9 °C | 10.5 °C | 107.7 mm |
| March | 3.3 °C | 13.2 °C | 104.14 mm |
| April | 5 °C | 16.1 °C | 73.41 mm |
| May | 8.1 °C | 20.2 °C | 54.1 mm |
| June | 10.4 °C | 23 °C | 35.81 mm |
| July | 12.7 °C | 27.4 °C | 8.64 mm |
| August | 12.6 °C | 27.8 °C | 13.46 mm |
| September | 10.2 °C | 24.6 °C | 32.51 mm |
| October | 6.6 °C | 17.7 °C | 84.33 mm |
| November | 3.7 °C | 11.4 °C | 152.15 mm |
| December | 1.6 °C | 7.8 °C | 189.23 mm |
| Annual | 6.5 °C | 17.3 °C | 1009.91 mm |
| Average First Frost Date | Nov. 1 - Nov. 10 |
| Average Last Frost Date | Apr. 1 - Apr. 10 |
| Average Days With Frost | 50-75 Days |
| Plant Hardiness Zone | Zone 8b : -9.4°C to -6.7°C |
| Plant Hardiness Zone - 2012 | Zone 8b : -9.4°C to -6.7°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Csb - Warm-Summer Mediterranean Climate |