Portola, California has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Annual precipitation averages 587.5 Millimeters. Portola is located in USDA Plant Hardiness Zone 6b. The growing season typically runs from the last frost around Jun. 11 - Jun. 20 through the first frost around Sep.1 - Sep. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | -6.4 °C | 6.6 °C | 107.44 mm |
| February | -5 °C | 8.4 °C | 93.98 mm |
| March | -2.9 °C | 11.6 °C | 89.92 mm |
| April | -1 °C | 14.3 °C | 41.15 mm |
| May | 2 °C | 19.2 °C | 30.23 mm |
| June | 5.3 °C | 25 °C | 11.94 mm |
| July | 7.8 °C | 30.3 °C | 4.83 mm |
| August | 6.8 °C | 29.6 °C | 5.84 mm |
| September | 3.7 °C | 26.2 °C | 11.18 mm |
| October | -0.3 °C | 19.2 °C | 26.42 mm |
| November | -4 °C | 11.6 °C | 53.34 mm |
| December | -6.4 °C | 5.9 °C | 111.25 mm |
| Annual | -0 °C | 17.3 °C | 587.52 mm |
| Average First Frost Date | Sep.1 - Sep. 10 |
| Average Last Frost Date | Jun. 11 - Jun. 20 |
| Average Days With Frost | Over 180 Days |
| Plant Hardiness Zone | Zone 6b : -20.6°C to -17.8°C |
| Plant Hardiness Zone - 2012 | Zone 6b : -20.6°C to -17.8°C |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |