Petaluma's winters are mild, with temperatures ranging from around freezing to the mid-20s Celsius in January and December, averaging around 12-13°C. As spring arrives, temperatures gradually warm up, reaching averages of around 14-17°C by May and June, with occasional heatwaves pushing highs into the low 30s. Summer months are relatively cool, with average highs only slightly above those of spring, but without the dramatic temperature swings of autumn. Autumn brings a return to cooler temperatures, with averages dropping back down to around 16°C by October, before plummeting to around 10°C in December. Overall, Petaluma's climate is characterized by mild temperatures year-round, with minimal extreme fluctuations.