Monmouth, California has a Cold Semi-Arid Climate climate (Köppen classification: BSk). Average annual temperatures range from 9.7 °C (low) to 24.8 °C (high). Annual precipitation averages 271.3 Millimeters. Monmouth is located in USDA Plant Hardiness Zone 9b. The growing season typically runs from the last frost around Feb. 1 - Feb. 10 through the first frost around Dec. 1 - Dec. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 3.3 °C | 13.4 °C | 57.15 mm |
| February | 4.8 °C | 16.7 °C | 49.28 mm |
| March | 6.4 °C | 20.2 °C | 46.48 mm |
| April | 8.1 °C | 23.4 °C | 23.37 mm |
| May | 11.8 °C | 27.9 °C | 11.18 mm |
| June | 14.8 °C | 32.6 °C | 3.05 mm |
| July | 17.8 °C | 35.8 °C | 0.76 mm |
| August | 17.1 °C | 35.4 °C | 0 mm |
| September | 14.5 °C | 32.6 °C | 2.29 mm |
| October | 10.3 °C | 26.7 °C | 11.94 mm |
| November | 5.4 °C | 19.1 °C | 22.1 mm |
| December | 2.6 °C | 13.5 °C | 43.69 mm |
| Annual | 9.7 °C | 24.8 °C | 271.29 mm |
| Average First Frost Date | Dec. 1 - Dec. 10 |
| Average Last Frost Date | Feb. 1 - Feb. 10 |
| Average Days With Frost | 10-20 Days |
| Plant Hardiness Zone | Zone 9b : -3.9°C to -1.1°C |
| Plant Hardiness Zone - 2012 | Zone 9b : -3.9°C to -1.1°C |
| Current Drought Conditions | Normal |
| Köppen Climate Classification | BSk - Cold Semi-Arid Climate |