Map from Google - Los_Angeles

The climate of Los Angeles is temperate, with very mild and relatively rainy winters, and warm and sunny summers.
The climate is even milder than the Mediterranean one: the city is located at a lower latitude than the Mediterranean coasts, so it has milder winters; on the other hand, it is located on the Pacific coast, along which a cool current flows (the California Current), therefore the summer is a bit cooler than in the Mediterranean Sea. So this is a really mild climate, as well as kissed by the sun most of the year.
There are, however, different microclimates depending on area, since the city covers a wide surface, is situated on the coast, and is surrounded by hills and mountains.
Here are the average temperatures of downtown Los Angeles.
Average temperatures - Los Angeles
Los AngelesJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)9101112141618181715119
Max (°C)202021232426282928262320
Min (°F)485052545761646463595248
Max (°F)686870737579828482797368

The city is quite polluted, and pollutants can accumulate in the air especially in the dry season, from May to October.
In addition to the possible bad weather in winter, a nuisance in the climate of Los Angeles is represented by the Santa Ana, a hot and dry wind from the northeast, which blows for a few days from the deserts of California and Arizona, after passing over the mountains, from which it descends. This wind is more likely to blow in autumn and winter, but it can blow all year round, bringing temperatures above 25 °C (77 °F), and sometimes even 30 °C (86 °F), in the middle of winter, and above 35 °C (95 °F), and sometimes even 40 °C (104 °F), from April to October. Heat waves, due to this wind, occur more often in September, followed by August, July and October; the highest temperature was recorded on 27 September 2010, when the thermometer measured 45 °C (113 °F) in the city centre and 41 °C (106 °F) at the airport, which is located on the coast. The San Fernando Valley, north-west of the city, and closed between the hills, is even hotter, in fact here the highest records are about 46/47 °C (115/117 °F). Sometimes, the Santa Ana winds can cause fires.

Los Angeles, map of the metropolitan area by Google

Rainfall is quite scarce, amounting to about 375 millimetres (15 inches) per year, and has a similar pattern to that of the Mediterranean climate, but with a drier autumn, since most of the rain falls from December to March, while in summer it almost never rains. The wettest month is February. For brevity of the rainy season, the climate is actually semi-arid. Sometimes, however, some waves of bad weather can be more intense than usual, and there may be heavy rains, from December to April.
Here is the average precipitation.
Average precipitation - Los Angeles
Los AngelesJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec. (mm)8095602572017152560377
Prec. (in)

Winter, from December to March, is very mild, and it actually looks like spring. There are many nice and sunny days, with daytime temperatures around 20 °C (68 °F). However, after the rare cold air outbreaks, the night temperature can approach freezing (0 °C or 32 °F). The rains occur in short periods of bad weather, and are generally not abundant, although as mentioned sometimes there can be waves of bad weather more intense than usual. However, to the north of the city, the San Gabriel Mountains, whose highest peak is Mount San Antonio, 3,067 metres (10,062 feet) high, are quite often covered with snow, offering a nice view on the horizon.
As mentioned, sometimes the Santa Ana blows also in winter, raising the temperature to about 25 °C (77 °F) or above.

Spring, from April to June, is pleasantly warm and sunny. In June, and sometimes in May, in the morning the phenomenon called "June gloom" can occur: this is a kind of cloudy and damp weather, sometimes foggy, accompanied by a sort of drizzle, which is formed on the sea and later can invade the mainland and therefore the area of Los Angeles. The phenomenon is due to the contrast between the sea, which is still cold, and the mainland, which is getting increasingly warmer.

Summer, from July to September, is hot and sunny. In summer, the ocean acts like a kind of natural air conditioner: on the coast, for example in Santa Monica, at the Los Angeles International Airport or in Long Beach, daytime temperatures are quite cool, and remain around 24/25 °C (75/77 °F); they are higher, but they don't reach 30 °C (86 °F), in the central districts of the city (see the table above), although they slightly exceed this value in areas located further away from the sea (see Pasadena), not to mention the eastern ones, which are closer to the desert. On the hills above the city, there is often a torrid heat, even though at lower altitudes, on the coast, the temperature remains around 25 °C (77 °F). On the other hand, if you decide to take a trip to the desert, remember that the temperature gradually increases, and already in San Bernardino highs are normally around 35/36 °C (95/97 °F), while in Palm Springs, far away from Los Angeles, there's a scorching heat, and highs are normally around 40/42 °C (104/108 °F). However, in the city proper of Los Angeles, the temperature in summer is acceptable, except when the Santa Ana blows: in these cases, all these differences are reduced, and it's hot everywhere.
Sometimes the June gloom can also occur in July and August, especially in the years of La Niña, when the sea is colder than usual.

Autumn, in October and November, is very mild or pleasantly warm; in November, daytime temperatures are still around 23 °C (73 °F). In this season, mild and sunny days alternate with hot days, in which the annoying Santa Ana blows, and also with the first periods of bad weather.

The amount of sunshine in Los Angeles is really great, since there are 3,200 hours of sunshine per year. The sky is often clear in all seasons, but even more so in summer.

Disneyland is located in Anaheim, about 20 kilometres (12 miles) away from the sea, to the south-east of downtown Los Angeles, and has the same climate as the city centre.

Los Angeles

For swimming, the temperature of the sea is very cool, if not cold, even in summer, since it reaches 17 °C (63 °F) in July and August, and 18 °C (64 °F) in September. In June, it is still around 15 °C (59 °F). However, you can sunbathe for a long period, from June to September, but often also in April, May and October.
Here are the average sea temperatures.
Sea temperature - Los Angeles
Los AngelesJanFebMarAprMayJunJulAugSepOctNovDec
Sea (°C)141414141415171718171615
Sea (°F)575757575759636364636159

When to go

The best time to visit Los Angeles is spring, from April to June, being a mild or pleasantly warm and sunny period, and with a very low risk of hot days. Summer, from July to September, is usually a good period as well, being warm but not too much (at least if you stay in the city and don't move towards the desert) and sunny; occasionally, however, there can be hot days, when the Santa Ana blows. Autumn, in October and November, is generally a good season as well, although the Santa Ana is quite common, and you can see the first rains, especially in November.