Vacaville's winters are cool and variable, with temperatures often dropping below freezing in January, February, and December. Spring brings mild temperatures, gradually warming up through March, April, and May, with average highs reaching the mid-30s by late spring. Summer is relatively mild, with temperatures mostly in the 20s and low 30s from June to August, although July's cooler days are an exception. Autumn is similar to spring, with temperatures gradually cooling down through September and October before dropping again in November and December. Overall, Vacaville's climate is characterized by moderate temperatures, with minimal extreme heat or cold.