Portola, California has a Humid Continental Climate - Dry Cool Summer climate (Köppen classification: Dsb). Average annual temperatures range from 31.9 °F (low) to 63.2 °F (high). Annual precipitation averages 23.1 Inches. 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 | 20.5 °F | 43.8 °F | 4.23 in. |
| February | 23.0 °F | 47.2 °F | 3.7 in. |
| March | 26.8 °F | 52.8 °F | 3.54 in. |
| April | 30.2 °F | 57.8 °F | 1.62 in. |
| May | 35.6 °F | 66.5 °F | 1.19 in. |
| June | 41.5 °F | 77.0 °F | 0.47 in. |
| July | 46.1 °F | 86.5 °F | 0.19 in. |
| August | 44.2 °F | 85.3 °F | 0.23 in. |
| September | 38.7 °F | 79.1 °F | 0.44 in. |
| October | 31.4 °F | 66.5 °F | 1.04 in. |
| November | 24.8 °F | 52.8 °F | 2.1 in. |
| December | 20.5 °F | 42.7 °F | 4.38 in. |
| Annual | 31.9 °F | 63.2 °F | 23.13 in. |
| 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 : -5°F to 0°F |
| Plant Hardiness Zone - 2012 | Zone 6b : -5°F to 0°F |
| Current Drought Conditions | Abnormally Dry |
| Köppen Climate Classification | Dsb - Humid Continental Climate - Dry Cool Summer |