| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 14.6° | 4.2° | 126.2mm | 12.6 | 58 |
| February | 16.5° | 4.6° | 122.9mm | 10.1 | 69 |
| March | 18.2° | 5.5° | 88.6mm | 10.6 | 73 |
| April | 19.9° | 6.7° | 41.7mm | 6.2 | 87 |
| May | 22.3° | 8.7° | 22.6mm | 3.5 | 93 |
| June | 25.9° | 10.5° | 4.8mm | 1.1 | 98 |
| July | 27.4° | 11.6° | 0.2mm | 0.1 | 98 |
| August | 27.6° | 11.9° | 1.1mm | 0.3 | 97 |
| September | 27.7° | 11.1° | 3.1mm | 1.1 | 95 |
| October | 24.7° | 8.9° | 33.8mm | 3.5 | 93 |
| November | 18.7° | 6° | 71.1mm | 7.9 | 80 |
| December | 14.7° | 4° | 140.1mm | 12.7 | 58 |
January in Petaluma averages a daily high of 14.6°C with nights around 4.2°C. Expect roughly 12.6 wet days totalling 126.2mm. Generally workable, with some weather to plan around.
February in Petaluma averages a daily high of 16.5°C with nights around 4.6°C. Expect roughly 10.1 wet days totalling 122.9mm. Generally workable, with some weather to plan around.
March in Petaluma averages a daily high of 18.2°C with nights around 5.5°C. Expect roughly 10.6 wet days totalling 88.6mm. Generally workable, with some weather to plan around.
April in Petaluma averages a daily high of 19.9°C with nights around 6.7°C. Expect roughly 6.2 wet days totalling 41.7mm. Comfortable conditions for being outdoors all day.
May in Petaluma averages a daily high of 22.3°C with nights around 8.7°C. Expect roughly 3.5 wet days totalling 22.6mm. Comfortable conditions for being outdoors all day.
June in Petaluma averages a daily high of 25.9°C with nights around 10.5°C. Rain is rare — about 1.1 wet days and 4.8mm across the month. Comfortable conditions for being outdoors all day.
July in Petaluma averages a daily high of 27.4°C with nights around 11.6°C. Rain is rare — about 0.1 wet days and 0.2mm across the month. Comfortable conditions for being outdoors all day.
August in Petaluma averages a daily high of 27.6°C with nights around 11.9°C. Rain is rare — about 0.3 wet days and 1.1mm across the month. Comfortable conditions for being outdoors all day.
September in Petaluma averages a daily high of 27.7°C with nights around 11.1°C. Rain is rare — about 1.1 wet days and 3.1mm across the month. Comfortable conditions for being outdoors all day.
October in Petaluma averages a daily high of 24.7°C with nights around 8.9°C. Expect roughly 3.5 wet days totalling 33.8mm. Comfortable conditions for being outdoors all day.
November in Petaluma averages a daily high of 18.7°C with nights around 6°C. Expect roughly 7.9 wet days totalling 71.1mm. Comfortable conditions for being outdoors all day.
December in Petaluma averages a daily high of 14.7°C with nights around 4°C. Expect roughly 12.7 wet days totalling 140.1mm. 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. Petaluma peaks at 98.
Based on 30 years of records, May–October scores highest for comfort in Petaluma, balancing daytime temperature against rainfall.
September is the warmest, averaging a daily high of 27.7°C.
December is the wettest, averaging 140.1mm of rain across roughly 12.7 wet days.
January is the coolest month, with average daily highs around 14.6°C.