Under the Köppen climate classification, Guadalajara has a humid subtropical climate (Cwa) that is quite close to a tropical climate, featuring dry, warm winters and hot, wet summers. Guadalajara’s climate is influenced by its high altitude and the general seasonality of precipitation patterns in western North America.
Although the temperature is warm year-round, Guadalajara has strong seasonal variation in precipitation. The northward movement of the Inter-Tropical Convergence Zone brings a great deal of rain in the summer months, whereas, for the rest of the year, the climate is rather dry. The extra moisture during the wet months moderates the temperatures, resulting in cooler days and nights during this period. The highest temperatures are usually reached in May averaging 33 °C (91 °F), but can reach up to 37 °C (99 °F) just before the onset of monsoon season. March tends to be the driest month and July the wettest, with an average of 273 millimeters (10.7 in) of rain, over a quarter of the annual average of about 1,002 millimeters (39.4 in).
During the summer, afternoon storms are very common and can sometimes bring hail flurries to the city, especially toward late August or September. Winters are relatively warm despite the city’s altitude, with January daytime temperatures reaching about 25 °C (77 °F) and nighttime temperatures about 10 °C (50 °F). However, the outskirts of the city (generally those close to the Primavera Forest) experience on average cooler temperatures than the city itself. There, temperatures around 0 °C (32 °F) can be recorded during the coldest nights. Frost may also occur during the coldest nights, but temperatures rarely fall below 0 °C (32 °F) in the city, making it an uncommon phenomenon. Cold fronts in winter can sometimes bring light rain to the city for several days in a row. Snowfall is extraordinarily rare, with the last recorded one occurring in December 1997, which was the first time in 116 years, as it had previously last fallen in 1881.