Climate - California (United States)

Index:

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• Introduction
• Temperatures
• Precipitation
• Sunshine
• Sea temperature
• Floods and hurricanes
• Best Time

Introduction

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In much of California, a state located in southwestern United States and overlooking the Pacific Ocean, the climate is sub-tropical.
Along the coast, the climate is mild with cool summers. In areas near the coast but more sheltered, such as Silicon Valley, the climate is Mediterranean. In the central Valley, the climate is similar to that of the Mediterranean, but it is more arid and continental, while in Los Angeles, it is mild to pleasantly warm and sunny most of the year.
In southeastern California, the climate is desert. To the east of Los Angeles, we find the Mojave desert (in which we find the Death Valley, one of the hottest places in the world), while to the east of San Diego, we find the Sonoran desert. From the deserts, a warm wind called Santa Ana can blow towards the coasts, especially the southern ones (see Los Angeles, San Diego). The Santa Ana winds blow more likely in autumn.
In California, we find some of the hottest areas in North America. First of all, the Death Valley, which is probably the hottest place on the planet. Then, the lower course of the Colorado River, which crosses low-altitude valleys: the Mohave Valley (see Needles), on the border with Nevada and Arizona, and the Palo Verde Valley (see Blythe), on the border with Arizona. Further south, we find the Coachella Valley (see Palm Springs, Indio, Coachella, Indian Wells, Palm Desert, La Quinta, Thermal) and, near the border with Mexico, the Imperial Valley (see Brawley, Imperial, El Centro, Calexico).
In the mountainous areas, the climate becomes colder. In the north, we find the Klamath Mountains (whose highest peak is Mount Eddy) and the Cascade range (whose highest peak in California is Mount Shasta). In the east, we find the Sierra Nevada (where the parks of Yosemite, Kings Canyon and Sequoia are found), while in the southeast, we find the San Jacinto Mountains.
Fog (called "tule fog") can form in the Central Valley due to cold air stagnation in the winter months. Along the coast, on the other hand, fog can form due to the cold current flowing in the ocean. In the southern part of the coast (see Los Angeles, San Diego), fog forms at night and in the early morning in May and June ("May gray" and "June gloom"), while in the central-northern part (see San Francisco), fog is formed especially in summer.

Temperatures

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Along the coast, temperatures vary little between winter and summer. For example, in Eureka, in the northern part, the average temperature ranges from around 9 °C (48 °F) in December to 14.5 °C (58 °F) in August. So summer is very cool. Here are the average temperatures.

As you proceed south, temperatures gradually increase. For example, in San Francisco (which is not right on the west coast but in an inner bay) the maximum temperature ranges from 14.5 °C (58 °F) in December and January to 24 °C (75 °F) in September. In the southern part, in San Diego, winter is by now very mild, and summer is mild or pleasantly warm: in practice, the weather is spring-like most of the year. Here are the average temperatures.



In inland areas, the temperatures become decidedly warmer in summer, because the cooling effect of the ocean is reduced or completely canceled. Already in the Central Valley of California, many torrid days occur in the summer. For example, here are the average temperatures in Fresno.

In the inland areas of the southeast, where we find the California deserts, winter is very mild (although it can be cold at night), while summer is very hot. Here are the average temperatures in Palm Springs, in the desert area south-east of Los Angeles.

At high altitudes, the temperature naturally decreases. In Alturas , in the northeast and 1,300 meters (4,260 ft) above sea level, there are strong differences between night and day, so there are frequent night frosts in winter, while in summer, nights are cool, but it gets hot during the day.

At even higher altitudes, the winter is freezing, while the summer is mild in the day and cold at night. Here are the average temperatures near Ellery lake, at almost 3,000 meters (9,800 ft) above sea level, in Yosemite National Park.

Precipitation

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Precipitation in California follows a Mediterranean pattern, that is, it is more abundant in winter and scarcer (or completely absent) in summer; it is generally scarce or moderate at low altitudes, except for the north-west, where it exceeds 1,000 millimeters (40 inches) per year, even in the plains. In Crescent City, on the coast near the Oregon border (which is located at the 42nd parallel), 1,500 mm (58 in) of rain fall per year, which become about 1,170 mm (46 in) slightly further south, in Eureka, and 950 mm (37.5 in) in Medoncino. This happens because weather fronts of the Pacific pass more frequently and for a longer period the more you go north. Here is the average precipitation in Eureka.

Continuing south along the coast, rainfall drops to 500 mm (20 in) per year in San Francisco (at the 37th parallel), to 360 mm (14 in) in Los Angeles (at the 34th parallel), and to 260 mm (10.2 in) in San Diego, at the border with Mexico (at the 32nd parallel). In the Channel Islands, the islands located off the southern coast of California, annual rainfall ranges from 300 mm (12 in) in the northernmost ones to 200 mm (8 in) in the southernmost ones. Here is the average precipitation in Los Angeles.

Also in the Central Valley of California, precipitation decreases from north to south, ranging from almost 850 mm (33.5 in) per year in Redding, to 675 mm (26.5 in) in Chico, to 460 mm (18 in) in Sacramento, to 340 mm (13.3 in) in Stockton (east of San Francisco), and finally, to only 160 mm (6.3 in) per year in Bakersfield, therefore at a desert level.
In mountainous areas, precipitation increases with altitude. And so, at the highest altitudes of the northern mountains, but also of the Sierra Nevada, heavy snowfalls occurs, and there are ski resorts. On Mount Shasta, in the southern part of the Cascade Chain, 4,316 meters (14,161 ft) high, 12 and a half meters (41 feet) of snow fall per year, and the snow on the top is preserved even in summer. Further south, at Lake Tahoe, 1,900 meters (6,200 ft) above sea level, in the Sierra Nevada, almost 5 meters (16 feet and a half) of snow fall in the northern part and almost 3 meters (10 ft) in the southern part. Further south, and still in the Sierra Nevada, at Mammoth Lakes, 2,400 meters (7,900 ft) above sea level, 5 meters and 25 cm (17.2 ft) of snow fall per year (generally, from November to April).



In eastern California, rainfall is define scarce at low altitudes. In the north-east, in Alturas, 1,400 meters (4,600 ft) above sea level, rainfall amounts to 315 mm (12.5 in) per year. Further south, east of the Sierra Nevada, and in the south-east, east of the Transverse Ranges, the climate is decidedly desert. In Death Valley, it amounts to just 55 mm (2.2 in) per year, in Needles, in Mohave Valley, to 110 mm (4.3 in), in Palm Springs, in Coachella valley, to 115 mm (4.5 in), and in El Centro , in Imperial Valley, to 60 mm (2.4 in). Here is the average precipitation in Palm Springs.

Sunshine

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California is a sunny state. In Eureka, in the northern part of the coast, there are almost 2,500 hours of sunshine per year (therefore, roughly as in Rome, Italy). Further south, in San Francisco, there are about 3,000 hours of sunshine per year, and in Los Angeles, 3,200 hours. Here are the hours of sunshine per day in Los Angeles.

In the central valley, despite the winter fogs, sunshine duration is about 3,500 hours per year. The desert areas of the south-east reach almost 4,000 sunshine hours per year: we are therefore in one of the sunniest areas in the world.

Sea temperature

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As mentioned, a cold current flows along the California coast. In the northernmost part of the coast, the temperature of the Pacific Ocean fluctuates between 11 °C (52 °F) and 14 °C (57 °F), while in San Francisco, it fluctuates between 12 °C (54 °F) and 14 °C (57 °F). Therefore, the sea remains decidedly cold even in summer.
In southern California, the sea is less cold, although it never gets pleasantly warm for swimming. Here are the average sea temperatures in Santa Monica, on the coast west of Los Angeles, where they range between 14.5 °C (58 °F) and 18.5 °C (65 °F).

In San Diego, in the southernmost part, the ocean is slightly milder, and its temperature fluctuates between 15 °C (59 °F) and 20.5 °C (69 °F).

Floods and hurricanes

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Occasionally, in winter, there can be particularly intense waves of bad weather, which can cause floods. A phenomenon that causes heavy rain is called Pineapple Express, and occurs when a "train" of warm, humid air from the Hawaii area reaches California and western United States, as happened for example in January-February 2017.
Every now and then, from June to November, but with a higher probability from August to October, the southernmost part of California (see San Diego, Imperial Valley) may be affected by the remains of a hurricane coming from the Pacific west of Mexico. Typically, the main effects are heavy rain or scattered thunderstorms. However, hurricanes are rare in June, the month in which they are most frequent is September, and historically, they have never occurred in November.

Best Time

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To visit California you can choose the spring, especially in April. In this way, you can avoid the summer heat of the inland and desert areas, but also the rains that can affect the whole state in winter, and the cold that mainly affects the mountainous areas in winter.
In autumn too, temperatures are generally acceptable, however, in the central-southern areas, the Santa Ana wind is more likely to blow.

See also the temperatures by month.