San Diego predominately has a semi-arid steppe climate (Koppen climate classification) with mild , sunny weather throughout the year. It is said that San Diego has the best year-around climate in the United States.Average monthly temperature range from 57 degrees (14C) in January to 72 degrees (22C) in July, although summer and early autumn are typically the hottest times of the year. The average daily temperature is 70.5 (21.4C) degrees. Snow and freezing temperatures are virtually nonexistent in the wintertime, only occurring in inland valleys and not along the coast. Average water temperatures range from 57 degrees (14C) in December to 69 (20.5C) degress in August. The warmest water is usually found in the small coves in La Jolla where it can be around 72 (22C) degrees in August.
“May gray and June gloom”, a local saying, refers to the way in which San Diego sometimes has trouble shaking off the marine layer, a cloudy layer typically higher in the atmosphere than 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 front the inland deserts to the coast that are call “Santa Anas.” The “sea breezes” off the Pacific Ocean are Mother Nature’s air conditioner.
The highest temperature on record at the San Diego Airport is 111 degrees (44C) on September 26th, 1963 and the coldest is 25 degrees (-4C) on January 7th, 1913.
The average annual precipitation is less than 12 inches (300mm), resulting in a borderline arid climate. Rainfall is concentrated in the colder half of the year, particularly the months of December through March, although precipitation is lower than any other part of the west coast. Summer months are virtually rainless. Many times when it rains in the San Diego is for only a few days but can be heavy and some flooding occurs. Thunderstorms are rare the moisture from a weakening tropical storm or hurricane off the Baja Coast moves north into the area.
Measurable snowfall has never occurred in downtown San Diego, snow flurries were reported at the airport in January 1949/1979. Light amounts of snow have occurred in higher locations within the city limits.
Climate in the San Diego area often varies dramatically over short geographical distances, due to the city’s topography (the Bay, the Pacific Ocean, numerous hills, mountains and canyons): frequently, particularly during the late spring and early summer mounts with the cool/humid hang-on for the entire day along the coast. If the marine layers is deep enough, light more drizzle occurs. Just inland 5-15 miles the skies clear in mid-morning and sun shines the remainder of the day.
