Weather Averages in San Diego
San Diego has one of the top-ten best climates according to the Farmers’ Almanac and has one of the two best summer climates in America as scored by The Weather Channel. Under the Köppen–Geiger climate classification system, the San Diego area has been variously categorized as having either a semi-arid climate (BSh in the original classification and BSn in modified Köppen classification) or a Mediterranean climate (Csa and Csb). San Diego’s climate is characterized by warm, dry summers and mild winters, with most of the annual precipitation falling between December and March. The city has a mild climate year-round, with an average of 201 days above 70 °F and low rainfall.
The climate in San Diego, like most of Southern California, often varies significantly over short geographical distances, resulting in microclimates. In San Diego, this is mostly because of the city’s topography (the Bay, and the numerous hills, mountains, and canyons). Frequently, particularly during the “May gray/June gloom” period, a thick “marine layer” cloud cover keeps the air cool and damp within a few miles of the coast, but yields to bright cloudless sunshine approximately 5–10 miles inland. Sometimes the June gloom lasts into July, causing cloudy skies over most of San Diego for the entire day. Even in the absence of June gloom, inland areas experience much more significant temperature variations than coastal areas, where the ocean serves as a moderating influence. Thus, for example, downtown San Diego averages January lows of 50 °F and August highs of 78 °F. The city of El Cajon just 10 miles inland from downtown San Diego, averages January lows of 42 °F and August highs of 88 °F.
A sign of global warming, the average surface temperature of the water at Scripps Pier in the California Current has increased by almost 3 degrees since 1950, according to scientists at Scripps Institution of Oceanography.
Annual rainfall along the coast averages 10.65 inches and the median is 9.6 inches. The months of December through March supply most of the rain, with February the only month averaging 2 inches or more. The months of May through September tend to be almost completely dry. Although there are few wet days per month during the rainy period, rainfall can be heavy when it does fall. Rainfall is usually greater in the higher elevations of San Diego; some of the higher areas can receive 11–15 inches per year. Variability from year to year can be dramatic: in the wettest years of 1883/1884 and 1940/1941 more than 24 inches fell, whilst in the driest years there was as little as 3.2 inches. The wettest month on record is December 1921 with 9.21 inches.
Snow in the city is so rare that it has been observed only five times in the century-and-a-half that records have been kept. In 1949 and 1967, snow stayed on the ground for a few hours in higher locations like Point Loma and La Jolla. The other three occasions, in 1882, 1946, and 1987, involved flurries but no accumulation.