Theclimate of California varies widely fromhot desert toalpine tundra, depending onlatitude,elevation, and proximity to the Pacific Coast.California's coastal regions, theSierra Nevada foothills, and much of theCentral Valley have aMediterranean climate, with warmer, drier weather in summer and cooler, wetter weather in winter. The influence of theocean generally moderates temperature extremes, creating warmer winters and substantially cooler summers in coastal areas.

The cool offshore, enhanced byupwelling of cold sub-surface waters, often creates summerfog near the coast, creating a warm-summerMediterranean climate (Köppen climate classificationCsb). Farther inland, the climate becomes morecontinental, with some areas turningsemi-arid (KöppenBSk), with colder winters and markedly hotter summers. Low-lying inland valleys, especially theCentral Valley, have a hot-summer Mediterranean climate (KöppenCsa), withsubtropical temperatures but a well-defined sunny summer season and a foggy winter season.

The temperature gradient between immediate coast and low-lying inland valleys in the south is about 7 °F or 3.9 °C in winter, the coast being warmer, and in summer roughly 20 °F or 11.1 °C, the interior being hotter. For example, the average daily high inSan Francisco in July and August is between 62 and 68 °F (17 and 20 °C),^[1][2] and inWalnut Creek, some 20 miles (32 km) inland, the average daily high in July and August is 84 °F (28.9 °C): a temperature gain of more than one degree (Fahrenheit) per mile.^[3] InSouthern California, the temperature differences are approximately 4 °F or 2.2 °C in winter and 23 °F or 12.8 °C in summer. At the coast inSanta Monica, the average high in August is 75 °F (24 °C), while inBurbank, approximately 10 miles (16 km) inland, the average high in August is 95 °F (35 °C): a temperature gain of about two degrees Fahrenheit per mile.^[4]

During the cooler winter months (October–March), theCoachella Valley regularly has the warmest winter temperatures out of any place west of the Rocky Mountains.East Los Angeles, theGateway Cities, and parts of theSan Gabriel Valley average the warmest winter high temps (72 °F, 22 °C) in all of the western U.S., and Santa Monica averages the warmest winter lows (52 °F, 11 °C) in all of the western U.S.Palm Springs, a city in the Coachella Valley, averages high/low/mean temperatures of 75 °F/50 °F/63 °F, (24 °C/10 °C/17 °C) respectively during the period of cooler weather from November to April.^[5] The extreme southwest, aroundSan Diego, has a borderline mediterranean/semi-arid or steppe climate (Köppen "Csa"/"BSk") as winters are drier there.

The southeastern regions have ahot arid climate (KöppenBWh), similar to that of the Sahara Desert. In the northern portion of theMojave Desert on the east side of the state isDeath Valley, which has recorded temperatures among the highest in the world. It is common in the summer for temperatures in the valley to surpass 120 °F (49 °C). The highest reliably recorded temperature in the world,^[i] 134 °F (56.7 °C), was recorded in Death Valley on July 10, 1913. Temperatures of 130 °F (54.4 °C) or higher have been recorded as recently as 2005. The 24-hour average July temperature in Death Valley is 101.8 °F (38.8 °C)^[ii].

In contrast, the high Sierra Nevada has a much cooler climate with extremediurnal temperature variation.Bodie, at an altitude of 8,379 feet or 2,554 metres, has never had a freeze-free month in a record dating back to 1895, and can expect only about 60 minima above freezing annually.

Alturas Bakersfield Bishop Bodie Death Valley Eureka Fresno Los Angeles Needles Redding Riverside Sacramento San Diego San Francisco San Jose Santa Rosa South Lake Tahoe class=notpageimage| Map of locations in the table below

The highest temperature ever recorded in California was 134 °F (56.7 °C) in Death Valley on July 10, 1913. This is also the highest temperature ever recorded on Earth. The lowest was −45 °F (−42.8 °C) inBoca on January 20, 1937.

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The prevailing westerly winds from the oceans also bringmoisture, and the northern parts of the state generally receive higher annual rainfall amounts than the south. California's mountain ranges influence the climate as well: moisture-laden air from the west cools as it ascends the mountains, dropping moisture; some of the rainiest parts of the state are west-facing mountain slopes. Northwestern California has atemperate climate with rainfall of 15 inches (380 mm) to 50 inches (1,300 mm) per year. Some areas ofCoast Redwood forest receive over 100 inches (2,500 mm) of precipitation per year.

The Central Valley has a wide range of precipitation. The northern parts of the Central Valley receive substantially greater precipitation from winter storms which sweep down from thePacific Northwest, while the southernmost regions of the Central Valley are near desert-like because of a lack of precipitation.

The high mountains, including theSierra Nevada, theCascade Range, and theKlamath Mountains, have amountain climate withsnow in winter and mild to moderate heat in summer. Ski resorts atLake Tahoe,Mammoth Lakes, andMount Shasta routinely receive over 10 feet (3.0 m) of snow in a season, and some years, substantially more – leading, for example, to annual ski races on theFourth of July.

On the east side of the mountains is a drierrain shadow. California'sdesert climate regions lie east of the high Sierra Nevada and southern California'sTransverse Ranges andPeninsular Ranges. The low deserts east of the southern California mountains, including the Imperial and Coachella valleys and the lowerColorado River, are part of theSonoran Desert, with minimal frost in the winter; the higher elevation deserts ofeastern California, including theMojave Desert,Owens Valley, and theModoc Plateau, are part of theGreat Basin region, which has a more continental climate. During the summer months, especially from July through early September, the region is affected by theMexican Monsoon (also called the "southwest monsoon"), which drives moisture from the tropical Pacific,Gulf of California, and/orGulf of Mexico into the deserts, setting off brief, but often torrential thunderstorms, particularly over mountainous terrain.

TheENSO cycle has a huge effect on rainfall and snowfall patterns in California, especially during the winter and spring seasons. During the El Niño phase, the jet stream is located south through California, allowing for warmer temperatures and more heavy rains to occur, particularly in the southern portions of the state. During the La Niña phase, the jet stream is much further north, and therefore the far northern portions of California are wetter, while the southern half stays cool and dry.

Incidences of dense fog in Los Angeles have been decreasing over time; researchers surmise the change may be a consequence of both theurban heat Island effect and decreased air pollution.^[54]

In the Central Valley during the winter months and in times of clear skies and light winds, the moisture from the Pacific can produce thetule fog, which is exceptionally thick fog that is visible on satellite imagery.^[55] The tule fog, named after the localtule grass wetlands, can reduce visibility to near zero, making it the primary cause of weather-related traffic accidents in the state. On November 3, 2007, a sudden patch of dense fog alongCalifornia State Route 99 (SR 99) resulted in a traffic crash involving 108 vehicles in Fresno, which killed two people and at least 36 injuries. Following the accident, the California Department of Transportation (Caltrans) developed a fog warning system along a 13 mi (21 km) section of SR 99.^[56][57]

Across the state,tornadoes develop in three main regions – the Los Angeles area, the deserts of Southern California, the Central Valley. However, they are typically weaker and shorter-lived than tornadoes in the central United States.^[58][59] Because of their irregular and short-lived nature, the San Diego National Weather Service considers it "nearly impossible to forecast a Southern California tornado before it touches down." The agency utilizes a volunteer group of more than 1,300 volunteers to report local severe weather.^[60] The most California tornadoes on a single day in the state was seven, which occurred on November 9, 1982.^[59] In July 2004, a twister touched down inSequoia National Park at an altitude of around 12,156 ft (3,705 m), making it the highest elevation for a confirmed tornado in the United States.^[61]

Despite its long coastline, California is not vulnerable totropical cyclones. Because of the coldCalifornia Current from the North Pacific Ocean and the fact that the storms tend to "steer" west, California has only been hit with threetropical storms in recorded history, a storm which came ashore in 1939 and dumped heavy rainfall on theLos Angeles area and interior deserts. The remnants of tropical systems will affect California more commonly, every several years.

Summers in inlandCalifornia can see temperatures well over 100 °F (38 °C) during the day and less than 0.3 in (7.6 mm) of monthly rainfall, particularly in the southern areas. This makes them prone towildfires. These can be life-threatening and causeevacuation. Wildfires are less common along the coast because of the cooler, more humid summers, but can occur in autumn when themarine layer is less common, making temperatures warmer and humidity drop significantly.

On occasion,fire whirls or fire tornadoes can develop within wildfires. One such event was rated an EF3, which developed inRedding inShasta County within theCarr Fire. The fire whirl produced winds over 143 mph (230 km/h), killing four people and injuring six others.^[62]

In February 2017, a winter storm produced a wind gust of 199 mph (320 km/h) at Ward Peak inAlpine Meadows ski resort.^[63]

The following are terms used to describe local or regional weather events.

• "Earthquake weather": Any nonseasonal, uncomfortable weather, typically hot and more humid than usual, and often associated with high and mid-level clouds, is spoken of as "earthquake weather", although there is no scientific basis for that relationship.^[64]
• Marine layer: The cool, moist layer of air coming in from the ocean which typically includes fog. A standard weather phenomenon along the northern and central California coast from late spring to early fall.
• May Gray/June Gloom: A characteristic weather pattern of late spring (May and June) in which a combination of inland heat, off-shore cool water, and prevailing wind patterns bring foggy and overcast weather to coastal regions. FromPoint Conception northwards the gloom continues until early autumn. (See also:Catalina eddy)
• Pineapple Express: A complex combination of events, bringing high levels of torrential precipitation to California. The Pineapple Express occurs when thejet stream dips across California, and warm, humid air from the mid-Pacific (from the vicinity ofHawaii–hence, the name) is drawn towards California. The resulting combination can cause extraordinarily heavy rains. A January 2005 Pineapple Express dropped nearly 25 inches (63.5 cm) of rain inSanta Barbara County.
• Santa Ana winds: Santa Anas are hot, high winds that blow from the eastern mountains and deserts towards coastalsouthern California, usually in thespring andfall. They are the result ofair pressure buildup between theSierra Nevada and theRocky Mountains. This air mass spills out, is pulled bygravity, and circulates clockwise around the high pressure area, bringing winds from the east and northeast; as the air descends in elevation, it heats up and thehumidity plummets to less than 15 percent. It is often said that the air is heated and dried as it passes through the nearby deserts, but according tometeorologists this is a popular misconception (it is actually due toadiabatic compression as the air flows from the higher elevations down to sea level); during Santa Ana conditions, it is typically hotter along the coast than in the deserts. As the Santa Ana winds are channeled through the mountain passes they can approach hurricane force. The combination of speed, heat, and dryness turns thechaparral into explosive fuel forwildfires.
• Tule fog: A thick groundfog that settles in theSan Joaquin Valley andSacramento Valley areas of theCalifornia Central Valley. Tule fog forms during the midfall, winter to early spring after the first significant rainfall. This phenomenon is named after thetule grass wetlands of the Central Valley. Tule fog can extend fromBakersfield toChico. Accidents caused by the tule fog are the leading cause of weather-related deaths in California; visibility is usually less than an eighth of a mile (about 600 feet or 183–200 m), but can be less than 10 feet (3 m).

• Climate change in California
• Climate of southern California
• Floods in California
• List of wettest known tropical cyclones in California

• More about the climate of CaliforniaArchived July 21, 2009, at theWayback Machine
• Climate of Northwest California

• Climate of California
• Climate of the United States by state

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