Vallejo's winters are cool and mild, with temperatures ranging from near-freezing to the mid-20s Celsius, averaging around 11-12 degrees. As spring arrives, temperatures gradually warm up, reaching averages of 13-16 degrees by April and May. Summer months bring hot temperatures, with June to August averages hovering around 18-20 degrees, but also experiencing occasional heatwaves above 40 degrees. Autumn brings a return to milder conditions, with September averaging around 19 degrees before cooling down again in the winter months. The overall temperature range is characterized by moderate lows and highs, making it suitable for outdoor activities year-round.