Climate of California

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California's climate varies widely, from arid to subarctic, depending on latitude, elevation, and proximity to the coast. Most of the state has a Mediterranean climate, with rainy winters and dry summers. The influence of the ocean generally moderates temperature extremes, creating warmer winters and substantially cooler summers, especially along the coast.

Contents 1 Temperature range 2 Precipitation 3 Glossary 4 Notes 5 External Links

[edit] Temperature range

The cool California Current offshore, enhanced by upwelling of cold sub-surface waters, often creates summer fog near the coast, creating a moderate oceanic climate (Koppen climate classification Cfb) on the northern coast and a moderate Mediterranean climate (Koppen Csb) from about Cape Mendocino southward. Further inland, the climate becomes more continental, while remaining semi-arid (Koppen BSk), with colder winters and markedly hotter summers. Low-lying inland valleys, especially the Central Valley, have a hot Mediterranean climate (Koppen Csa), with subtropical temperatures but a well-defined summer dry season.

The temperature gradient between immediate coast and low-lying inland valleys in the north is about 7 °F (4 °C) in winter (the coast being warmer) and in summer roughly 25 °F (14 °C) (the interior being warmer). The temperature difference is most dramatic nearer the coast For example, the average daily high in San Francisco in July and August is 68 °F (20° C), and in Walnut Creek, some 20 miles (32 km) inland, the average daily high in July and August is 87 °F (31° C); a temperature gain of approximately one degree (Fahrenheit) per mile.^[1] In the south, the figures are approximately 4 °F and 23 °F (2 °C and 13 °C), respectively. In Santa Monica the average high in August is 81 °F (27° C), while in Burbank, approximately 10 miles (16 km) inland, the average high in August is 90 °F (32° C); again, a temperature gain of approximately one degree (Fahrenheit) per mile.^[2] At its most extreme, there is a 4 °F and 35 °F (2 °C and 20 °C) temperature difference between Santa Barbara and Death Valley. The extreme southwest, around San Diego, has a semi-arid warm steppe climate (Koppen BSh) as winters are drier there.

The southeastern regions have an hot arid climate (Koppen BWh), which grades into a temperate arid climate (Koppen BWk) farther north. In the northern portion of the Mojave Desert on the east side of the state is Death Valley, which is the hottest spot on the Western Hemisphere. It is common in the summer for temperatures in the valley to reach 120 °F (49 °C). The highest temperature in the Western Hemisphere, 134 °F (56.6 °C), was recorded in Death Valley on July 10, 1913. Temperatures of 130 °F (54 °C) or higher have been recorded as recently as 2005. The 24-hour average July temperature in Death Valley is 101 °F (38 °C) (1961–1990 standard).

[edit] Precipitation

Westerly winds from the ocean also bring moisture, 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 a temperate climate with rainfall of 15–50 inches (400–1,270 mm) per year. Some areas of Coast Redwood forest receive over 100 inches of precipitation per year (2,540 mm).

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 the Pacific Northwest, while the southernmost regions of the Central Valley are near desert-like because of a lack of precipitation. Parts of the Valley are occasionally filled with thick fog (known locally as "tule fog)."

The high mountains, including the Sierra Nevada, the Cascade Range, and the Trinity Alps, have a mountain climate with snow in winter and mild to moderate heat in summer. Ski resorts at Lake Tahoe, Mammoth Lakes, and Mt. Shasta routinely receive over 10 feet (3 m) of snow in a season, and some years, substantially more – leading, for example, to annual ski races on the Fourth of July.

On the east side of the mountains is a drier rain shadow. California's desert climate regions lie east of the high Sierra Nevada and Southern California's Transverse Ranges and Peninsular Ranges. The low deserts east of the southern California mountains, including the Imperial and Coachella valleys and the lower Colorado River, are part of the Sonoran Desert, with hot summers and nearly frostless mild winters; the higher elevation deserts of eastern California, including the Mojave Desert, Owens Valley, and the Modoc Plateau, are part of the Great Basin region, with hot summers and cold winters. During the summer months, especially from July through early September, the region is affected by the Mexican Monsoon (also called the "southwest monsoon"), which drives moisture from the tropical Pacific, Gulf of California, and/or Gulf of Mexico into the deserts, setting off brief, but often torrential thunderstorms, particularly over mountainous terrain.

Despite its long coastline, California is not vulnerable to tropical cyclones. Because of the cold California Current from the North Pacific Ocean and the fact that the storms tend to "steer" West, California has only been hit with one tropical storm in recorded history, a storm which came ashore in 1939 and dumped heavy rainfall on the Los Angeles Area and interior deserts. Uncommonly, the remnants of a tropical system will affect California after becoming extratropical.

[edit] Glossary

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

• Santa Ana winds: Santa Anas are hot, high winds that blow from the eastern mountains and deserts towards coastal Southern California, usually in the spring and fall. They are the result of air pressure buildup between the Sierra Nevada and the Rocky Mountains. This air mass spills out, is pulled by gravity, 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 the humidity plummets to less than 15%. It is often said that the air is heated and dried as it passes through the nearby deserts, but according to meteorologists this is a popular misconception; 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 the chaparral into explosive fuel for the infamous wildfires the region is known for.

• Pineapple Express: A complex combination of events, bringing high levels of torrential precipitation to California. The Pineapple Express occurs when the jet stream dips across California, and warm, humid air from the mid-Pacific (from the vicinity of Hawaii–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 in Santa Barbara County.

• Tule fog: A thick ground fog that settles in the San Joaquin Valley and Sacramento Valley areas of the California Central Valley. Tule fog forms during the late fall and winter after the first significant rainfall. This phenomenon is named after the tule grass wetlands of the Central Valley. Tule fog can extend from Bakersfield to Chico. 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).

• June Gloom: A characteristic weather pattern of late spring (May and June) in Southern California, in which a combination of inland heat, off-shore cool water, and prevailing wind patterns bring foggy and overcast weather to coastal regions.

• Marine layer: Cool, moist air coming in from the ocean, typically as fog. A standard weather phenomenon along the central and southern California coast from late spring to early fall.

• "Earthquake weather:" Any unseasonal, uncomfortable weather, typically hot and dry, and often associated with high winds, which is spoken of (usually jokingly) as "earthquake weather."

[edit] Notes