| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 15° | 4.6° | 158.4mm | 14.5 | 55 |
| February | 17° | 4.6° | 154.6mm | 11.7 | 67 |
| March | 18.6° | 5.7° | 108.9mm | 11.2 | 73 |
| April | 21.1° | 6.9° | 55.3mm | 7.6 | 85 |
| May | 23.3° | 9° | 40mm | 4.8 | 90 |
| June | 26.6° | 11° | 4.4mm | 1.1 | 98 |
| July | 27.9° | 11.8° | 0.3mm | 0.3 | 96 |
| August | 28.5° | 11.9° | 1.5mm | 0.6 | 93 |
| September | 28.6° | 11.2° | 4.1mm | 1.5 | 91 |
| October | 25.2° | 9.2° | 46.1mm | 4 | 92 |
| November | 18.8° | 6° | 95.4mm | 9.4 | 77 |
| December | 14.8° | 4.3° | 179.9mm | 13.2 | 57 |
January in Santa Rosa averages a daily high of 15°C with nights around 4.6°C. Expect roughly 14.5 wet days totalling 158.4mm. Generally workable, with some weather to plan around.
February in Santa Rosa averages a daily high of 17°C with nights around 4.6°C. Expect roughly 11.7 wet days totalling 154.6mm. Generally workable, with some weather to plan around.
March in Santa Rosa averages a daily high of 18.6°C with nights around 5.7°C. Expect roughly 11.2 wet days totalling 108.9mm. Generally workable, with some weather to plan around.
April in Santa Rosa averages a daily high of 21.1°C with nights around 6.9°C. Expect roughly 7.6 wet days totalling 55.3mm. Comfortable conditions for being outdoors all day.
May in Santa Rosa averages a daily high of 23.3°C with nights around 9°C. Expect roughly 4.8 wet days totalling 40mm. Comfortable conditions for being outdoors all day.
June in Santa Rosa averages a daily high of 26.6°C with nights around 11°C. Rain is rare — about 1.1 wet days and 4.4mm across the month. Comfortable conditions for being outdoors all day.
July in Santa Rosa averages a daily high of 27.9°C with nights around 11.8°C. Rain is rare — about 0.3 wet days and 0.3mm across the month. Comfortable conditions for being outdoors all day.
August in Santa Rosa averages a daily high of 28.5°C with nights around 11.9°C. Rain is rare — about 0.6 wet days and 1.5mm across the month. Comfortable conditions for being outdoors all day.
September in Santa Rosa averages a daily high of 28.6°C with nights around 11.2°C. Rain is rare — about 1.5 wet days and 4.1mm across the month. Comfortable conditions for being outdoors all day.
October in Santa Rosa averages a daily high of 25.2°C with nights around 9.2°C. Expect roughly 4 wet days totalling 46.1mm. Comfortable conditions for being outdoors all day.
November in Santa Rosa averages a daily high of 18.8°C with nights around 6°C. Expect roughly 9.4 wet days totalling 95.4mm. Comfortable conditions for being outdoors all day.
December in Santa Rosa averages a daily high of 14.8°C with nights around 4.3°C. Expect roughly 13.2 wet days totalling 179.9mm. Generally workable, with some weather to plan around.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. Santa Rosa peaks at 98.
Based on 30 years of records, May–October scores highest for comfort in Santa Rosa, balancing daytime temperature against rainfall.
September is the warmest, averaging a daily high of 28.6°C.
December is the wettest, averaging 179.9mm of rain across roughly 13.2 wet days.
December is the coolest month, with average daily highs around 14.8°C.