California has four seasons: flood, fire, earthquake, and riot. More seriously, most of California really doesn’t have any weather, just a relentless series of minor variations on a rather sunny theme. For six to nine months of the year in most of California you can confidently forecast the next day’s weather (and the next week’s weather, and, often enough, the next month’s weather) by simply looking out the window and describing what you see outside right at that moment. The endless procession of mild dry sunny days near the coast can get a bit creepy after a while….
The majority of California has only two real seasons: a short cool winter wet season, and a long (six to nine months) dry season. In most of California it simply doesn’t rain at all during the dry season (roughly May to November); if it rains in the San Francisco Bay Area in (say) July it is quite literally front page news, with breathless live reports heading the evening television newscasts.
On the coast, temperatures are usually mild the year round, with summer often being cooler (due to fog) than late spring or early autumn in the northern parts. In San Francisco and nearby coastal areas, it actually gets quite cold and grey in summer when the fog rolls in off the ocean (Mark Twain supposedly once wrote that he’d spent the longest winter of his life one summer in San Francisco, which seems about right). We locals just love the sight of tourists in T-shirts and shorts freezing on the Golden Gate bridge or at Fisherman’s Wharf as the fog and wind reduce the outside temperatures to the 40’s or 50’s (Fahrenheit) in the middle of summer. Elsewhere near the coast, most days of the year are fine and sunny, sometimes with a bit of morning fog that burns off by lunch time, or evening fog that creeps in off the cold Pacific in the afternoon and early evening. The L.A. area is warmer, dryer, and somewhat less foggy, but as long as you’re within visual distance of the sea, the temperatures are still fairly mild, the weather clear (they get their own version of “June Gloom” down there as well). The north coast (above about Mendocino) is correspondingly cooler, foggier, and wetter (it actually rains quite a lot north of Mendocino; it’s sort of where Seattle weather begins for most of us Californians). One thing that surprises newcomers and visitors is that except in the southern-most parts of the state, the Pacific Ocean along the coast is cold — usually too cold to swim in without a wetsuit (the water’s circulating down from Alaska). This makes for beautiful fog banks and relatively mild summers, but it’s quite a shock when you first rush down that alluring ocean beach and dive into the water… (hint: look at that lovely beach and beautiful waves. Why is no one swimming?!).
Away from the coast, temperatures can be ferociously hot during late spring, summer, and much of autumn (fall), especially in the Central Valley and the deserts. If you’re driving in these areas, a car with good air-conditioning is recommended, particularly if you’re from a cooler climate like Europe or Britain. The same places can get remarkably cold in winter; the Californian high country and Sierra regions also get lots of snow in the wet season.
Most of California doesn’t have storms in the sense that many of us from elsewhere are used to. For example, along the coast thunderstorms are very rare; in the years I’ve been here, I think there’s been an average of about one or two thunderstorms per year in the Bay Area (and none of them were anything like the spectacular displays I remember as a child in Sydney or London). When you hear the words “storm warning” (or similar) on weather forecasts for California, the word “storm” is being used in the meteorologically-correct sense of “disturbance” — the incoming “storm” will usually be little more than some rain and wind with a low-hanging cloud cover.