Newcastle, California has a Hot-Summer Mediterranean Climate climate (Köppen classification: Csa). Average annual temperatures range from 9.4 °C (low) to 22.9 °C (high). Annual precipitation averages 686 Millimeters. Newcastle is located in USDA Plant Hardiness Zone 9b. The growing season typically runs from the last frost around Feb. 11 - Feb. 20 through the first frost around Dec. 1 - Dec. 10.
| Month | Avg. Low | Avg. High | Avg. Precip |
|---|---|---|---|
| January | 3.7 °C | 12.9 °C | 124.21 mm |
| February | 4.6 °C | 15.2 °C | 116.33 mm |
| March | 6.1 °C | 17.6 °C | 102.87 mm |
| April | 7.3 °C | 20.3 °C | 58.42 mm |
| May | 10.4 °C | 25.2 °C | 37.08 mm |
| June | 13.8 °C | 30.3 °C | 9.65 mm |
| July | 16.4 °C | 34.3 °C | 0 mm |
| August | 16.2 °C | 33.6 °C | 0.76 mm |
| September | 14.1 °C | 30.7 °C | 5.08 mm |
| October | 10.3 °C | 24.9 °C | 35.81 mm |
| November | 6.2 °C | 17.5 °C | 71.88 mm |
| December | 3.3 °C | 12.7 °C | 123.95 mm |
| Annual | 9.4 °C | 22.9 °C | 686.04 mm |
| Average First Frost Date | Dec. 1 - Dec. 10 |
| Average Last Frost Date | Feb. 11 - Feb. 20 |
| 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 | Abnormally Dry |
| Köppen Climate Classification | Csa - Hot-Summer Mediterranean Climate |