Inland areas like El Cajon can receive over 20 inches (51В cm) 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 40 inches (100В cm) of rainfall per year.ДЄt the National Weather Service office, there are an average of 41 days with measurable precipitation.

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. While hurricanes are very rare, San Diego receives more tropical storms and remnants of tropical storms than anywhere else in California. Rainfall is highly variable from year to year and from month to month, and San Diego is subject to both droughts and floods. While the summer months are virtually rainless, subtropical moisture from the North American Monsoon usually results in increased humidity and thunderstorms for at least a few days each summer. 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. The average annual precipitation is less than 12 inches (30В cm), resulting in a borderline arid climate. San Diego has on average 146 sunny days and 117 partly cloudy days a year. Several cities near San Diego, including Los Angeles, broke their all-time records that day. The record high temperature was tied only once and happened on September 27, 2010, 47 years and two days after the set record. The record low temperature was 25В вЏ (в€’4В вЊ) on January 7, 1913. The record high temperature at the National Weather Service office in San Diego of 111В вЏ (44В вЊ) was on September 26, 1963. For example, the months with the highest record high temperatures are September at 111В вЏ (44В вЊ) and October at 107В вЏ (42В вЊ). Although confusing to tourists, newcomers, and out-of-the-region newscasters, this makes October the fire season for San Diego and the rest of Southern California due to low precipitation and sporadic heat waves that the average monthly temperatures do not immediately show. Temperatures soar to very high readings only on rare occasions, chiefly when easterly winds (known as the ' Santa Ana winds') bring hot, dry air from the inland deserts.

The local sayings 'May gray' and 'June gloom' refer to the way in which San Diego has the most trouble shaking off the early morning fog during those months, and cool, cloudy conditions often last into the afternoon or even all day. Marine layer conditions linger until the heat of the sun becomes strong enough to evaporate the clouds. San Diego experiences marine layer clouds, most often between May and August, which cause cool temperatures, cloudy weather and fog in the morning. Snow and ice are rare in the wintertime, typically occurring only inland from the coast when present. Temperatures occasionally reach 90В вЏ (32В вЊ) or higher.

Late summer and early autumn are typically the hottest times of the year with an average high of 78В вЏ (26В вЊ) in August and 77В вЏ (25В вЊ) in September. On average, 344 days a year are hotter than 60В вЏ (16В вЊ), but only 25 days are hotter than 80В вЏ (27В вЊ). Average monthly temperatures range from 57.3В вЏ (14.1В вЊ) in January to 72В вЏ (22В вЊ) in August.

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