The climate of San Diego, California is categorized as a semi-arid Mediterranean climate (Köppen climate classification BSh). It enjoys mild, sunny weather throughout the year.
Temperatures
Average monthly temperatures range from 57.3 °F (14.1 °C) in January to 72 °F (22 °C) in August, although late summer and early autumn are typically the hottest times of the year with temperatures occasionally reaching 90 °F (32 °C) or higher. Snow and ice are rare in the wintertime, typically occurring only inland from the coast when present. "May gray and June gloom", a local saying, refers to the way in which San Diego sometimes has trouble shaking off the fog that comes in during those months. Temperatures soar to very high readings only on rare occasions, chiefly when easterly winds bring hot, dry air from the inland deserts (these winds are called "Santa Ana winds"). Although confusing to tourists, newcomers, and out-of-the-region newscasters, this makes October San Diego's and the rest of Southern California's fire season and often causes heat waves in October that the weather data cannot show easily.
The record high temperature at the National Weather Service office in San Diego of 111 °F (44 °C) was on September 26, 1963. The record low temperature was 25 °F (âˆ'4 °C) on January 7, 1913. The record high temperature was tied only once and happened on September 27, 2010, 47 years and two days after the set record. Several cities near San Diego broke their all-time records that day.
Precipitation
San Diego has on average 146 sunny days and 117 partly cloudy days a year. The average annual precipitation is less than 12Â inches (300Â mm), resulting in a borderline arid climate. Rainfall is strongly concentrated in the cooler half of the year, particularly the months December through March, although precipitation is lower than any other part of the U.S. west coast. The summer months are virtually rainless, although subtropical moisture from the North American Monsoon usually results in increased humidity and thunderstorms for at least a few days each summer. Rainfall is highly variable from year to year and from month to month, and San Diego is subject to both droughts and floods. Hurricanes are very rare, although San Diego receives more tropical storms and remnants of tropical storms than anywhere else in California. Famous examples include the 1858 San Diego Hurricane and the 1939 California tropical storm, as well as the remnants of Hurricane Kathleen in 1976, all of which brought several inches of rain and high winds to San Diego. Inland areas like El Cajon can receive over 20 inches per year on average; further inland at higher elevations in the Cleveland National Forest receive more yet, and some areas like Palomar Mountain average more than 40Â inches of rainfall per year.
At the National Weather Service office, there are an average of 41 days with measurable precipitation. The wettest year was 1941 with 24.93 inches (63.3Â cm) and the driest year was 1953 with 3.23 inches (8.2Â cm). The most rainfall in one month was 9.09 inches (23.1Â cm) in January 1993. The most rainfall in 24 hours was 3.23 inches (8.2Â cm) on April 5, 1926.
Snow
Snow has been recorded falling on lowland San Diego communities only five times in over 125 years of record-keeping. Snow flurries were last seen in San Diego on February 14, 2008 around 1,700 to 1,800 feet (520 to 550 m), and the last measurable snowfall to hit various neighborhoods and suburbs around the city fell on December 13, 1967. In winter, light snow is common in mountainous regions of east and north San Diego County above 3,000â€"4,000 feet (910â€"1,220 m).
Variation
Climate in the San Diego area often varies dramatically over short geographical distances, due to the city's topography (the Bay, and the numerous hills, mountains, and canyons), thus exhibiting microclimate: frequently, particularly during the "May gray / June gloom" period, a thick "marine layer" cloud cover will keep the air cool and damp within a few miles of the coast, but will yield to bright cloudless sunshine between about 5 and 15 miles (8.0 and 24.1 km) inlandâ€"the cities of El Cajon and Santee for example, rarely experience the cloud cover.
Compared to national averages
On average San Diego sees 21 days with some precipitation while the rest of the country sees about 110. The national average for mostly sunny days is 213 while San Diego's is 267. San Diego's annual snowfall is 0 inches per year while the nation usually sees an average of 24.2 inches (610 mm) per year. The United States average for days above 90 °F (32 °C) is 37.9 days while San Diego's is only 2.5 days, and there are, on average 0 days below 32 °F (0 °C) in San Diego, while the national average is 88 days. The average low temperature in January for the country is 26.5 °F (âˆ'3.1 °C), and for San Diego it is 50 °F (10 °C). The average high temperature in July for San Diego is 76 °F (24 °C). The national average is 86.8 °F (30.4 °C).
Monthly averages
Sea temperatures
Average annual temperature of sea is 65 °F (18 °C), from 59 °F (15 °C) in January to 72 °F (22 °C) in August.
Santa Anas
The months of September through February bring warm winds from the desert called "Santa Anas". Occurring about 10 days out of the year, these winds bring sometimes hot, but always dry conditions. Inland, and in mountain passes and canyons, they can burst out in gusts of 100 miles per hour (160Â km/h) and can lower relative humidity to single digits, although by the coast they rarely see gusts of over 40 miles per hour (64Â km/h). They can spread and worsen wildfires. Because these winds blow from east to west, common perception is that they are pulling hot air from the desert. However, it is not uncommon during a Santa Ana condition for the coast to be even hotter than the desert regions. The Santa Ana winds are actually warm due to barometric pressure increases: As the air is pulled down to sea level from the higher altitudes of the Great Basin and Rocky Mountains to the east, it is compressed and its temperature rises.
Hurricanes
San Diego is only 3° further north than New Orleans, and technically within reach of East Pacific hurricanes. However, the cold California Current off the coast keeps ocean water significantly colder than in the Gulf of Mexico and western Atlantic. As a result, virtually all northbound hurricanes dissipate over Baja California and fail to bring any precipitation to San Diego. The only tropical cyclone known to impact San Diego as a hurricane in around 200 years of record-keeping was the 1858 San Diego Hurricane. Two more cyclones managed to bring tropical storm-force winds to Southern California: the 1939 California tropical storm and the Hurricane Kathleen (1976).
May and June clouds
During the months of May and June, a common natural occurrence brings a thin layer of clouds that covers coastal and inland communities. Some call it "May Gray", or "June Gloom".
Southern Oscillation
San Diego's wet winter season is influenced by the El Niño Southern Oscillation. During the El Niño phase, San Diego receives more winter storms with warmer and more humid conditions. During the La Niña phase, San Diego becomes drier with cooler and less humid conditions. Late spring and early summer fog is also known to be more common during the La Niña phase.
See also
- Climate of California
- Horse latitudes
Notes
References
External links
- USTravelWeather.com: San Diego Weather and Climate
