Tijuana’s climate is a semi-arid , with about 231 mm (9.09 in) of annual precipitation, and generally mild to warm weather year-round. It has characteristics of the Mediterranean climate (Csa) found to the immediate north, with most of the annual precipitation falling in the winter, between the months of November and March.
Between November and March, storms originate from fronts entering off of the Pacific Ocean. January is the wettest month of the year for the city and during this time a periodic event, similar to June Gloom, is observed created by marine layer. January is the coolest month, during which temperatures average 13.6 °C (56.5 °F). In the city April signifies the end of winter and the start of Santa Ana winds. Though the daytime highs are generally around 20 °C (68 °F), heat waves can reach up to 33 °C (91 °F). The hottest months in the city are August and September, during which temperatures average 22.0 °C (71.6 °F). Summers are by far the driest time of year since influences from the California Current and the North Pacific High suppress the formation of rainfall caused by the North American Monsoon. As in coastal Southern California, air pollution sometimes occurs during periods of temperature inversion, especially during summer and fall, but (unlike Mexico City) is seldom severe and in recent years has lessened due to cleaner car engines.
Frost and snow are rare phenomena in the city as temperatures are usually well above freezing. Yet, in December 1967, snow fell in the city and in January 2007 feather light snow fell in the east of the city. However, excessive amounts of snow fall have never been recorded in the city. On February 14, 2008 a winter storm caused an unusual snowfall in the upper reaches of the hills of the city.
The record low temperature recorded in the city was −6 °C (21 °F), while the highest was 49 °C (120 °F).