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The weather in Southern California is divided between wet and dry seasons. People who have lived here for a number of years can detect the change of seasons, but a newcomer would only notice rain/drought, longer/shorter days and around a 15°F change in temperatures from Winter to Summer.
In the cities the palms and lawns are always green and there is always something blooming year round.
But there is a lot more to the weather story of Southern California. I should begin by saying that for practical purposes there is no weather here, it's the lack of it that makes things nice.

Here is a breakdown of some of the subtle and not so subtile causes of the weather, when we have it:
In the Winter, you can always pick out the vacationers from the Midwest by their shorts-no shirts. At the same time, some locals may be wearing parkas.
Hop in a car, get out of the irrigated city and check out the countryside. In the Winter the hills are green, in the Summer they are brown, dried-out and dead.
The further you go inland or the higher you go, you will encounter more extremes.
Mt. Wilson, which is a 30 minute drive, or 16 miles from Downtown L.A. has a climate more akin to Switzerland than to L.A. - drive a few miles down and inland from there and it is more like Phoenix.

It is all part of the phenomenon called "Picking your Climate". Yes, when you live here, if you don't like the climate where you are, you pick another climate a few miles down the road.
This is reflected in the bible of gardening, Sunset's New Western Gardening Book, that shows L.A. County having more than 20 different climate zones ranging from Mediterranean to nearly Arctic.
The weatherman on TV here refers to things like "High desert", "Low desert", "Beaches", "Inland valleys" and of course "Mountains", they are all within an hour or two drive from Downtown.

The main drive of the Southern California weather machine is the Pacific Ocean. The Pacific's current runs from North to South along the coast and is called the Alaskan Current. The water temperature ranges from the low 70°'s in late Summer to the high 50°'s in Winter. It is L.A.'s air conditioner.
Since the wind prevails from West to East for most of the year, the southeasterly flow over it keeps the climate moderate all year long.
The closer you are to this powerful BTU machine, the more you benefit from cooler Summer days and warmer Winter nights than you would if you were further inland.
Few people along the coast need or even have air-conditioning. Heaters are used only occasionally in Winter. It can be very damp and chilly along the coast even in May and June. The beaches are among the world's prettiest, but you won't want to stay in the water for long periods of time without insulation. In the Summer, hundreds of thousands of Arizonans rush to Southern California Beaches to cool off.

The second factor that greatly affects L.A.'s weather is the highly stratified winds that generally blow from NW to SE. In this part of the Pacific there are rarely broken clouds to create updrafts and downdrafts.
You never see cumulus clouds or thunderstorms over this part of the Pacific. Since temperature in laboratory conditions is supposed to drop a certain amount the higher the elevation, the Eastern Pacific is very close to a laboratory.
The drop in temperature from altitude is much more predictable and consistent here than the Appalachian Mountains or the Alps where the air is much more mixed before it arrives. A city here that is 2000 ft. in elevation 10 miles inland would have a distinctly different climate than a beach city or even a nearby city of 500 ft.

Spring here is like Spring everywhere with the most prolific floral covering around April with wildflowers changing the color of the coastal foothills to green with patches of amber and rust. In late Spring thru June a phenomenon occurs called the Marine Layer.
It is caused by the desert air, 100 miles East, heating up and rising, pulling in cool air off the Alaskan Current.
The air mixes and condenses overnight causing ominous Nubian skies every morning. Sometimes the Marine Layer can be so thick that it may drizzle or mist, but rarely is there a significant runoff of water. We call this period June Gloom. The cloud layer which can range from a few hundred to several thousand feet thick burns off from the heat of the sun from the East to the West, sometimes leaving the beaches hazy all Summer long, but it also caused Palm Springs a reason to exist as it is the place to go to see some sun when the coast is socked in with clouds. A German would never recognize June Gloom, other than that he would wake up and think that it is going to rain, but it never does and usually sees a hazy-to-sunny afternoon, depending on how far he is from the ocean.
June Gloom may extend into August and begin in May, but I have seen June Gloom pop up occasionally for a day or two at any time of the year. Most newcomers flying into LA during June Gloom think it is smog and start coughing when they land.

From May to November the weather is pretty much the same. Usually the weatherman is questioning his right to exist. Once in a while November and December can be wet from early storms.
More often, it is the tail end of a hurricane that has fallen apart in September or October that can drop some substantial rain, but hardly every year.
Hurricanes can't survive in the cool Alaskan Current. Usually what is left of them is nothing more than a few broken high clouds with no precipitation, but the humidity can rise to uncomfortable levels and thunderstorms may materialize inland over the deserts and mountains.
Sometimes Southern California creates its own weather. As the winds more or less parallel the coast, certain projecting topographies such as Point Conception block the air stream enough to create a low pressure area downwind.
The low is usually centered over Catalina Island and is called a Catalina Eddy. No weather anywhere for hundreds of miles and a low comes out of nowhere and it just sits there ruining golf games.

Nothing really happens weatherwise... until around Thanksgiving. By this time Seattle and Portland have drifted into their endless grayness and drizzle that won't disappear until Spring. San Francisco may have already had a few rainshowers and some of the passes through the Sierra Nevadas may be closed for the season. Some of our local mountain communities may be experiencing 80 ° days and below freezing nights with cloudless skies. Then finally a storm makes its way all the way to Santa Barbara... and then... Oh ! the day of the first storm!

You would think that the world was coming to an end. The weatherman is warning that the snow level is dropping to the 5,000 ft. level.
He hasn't said anything at all for the last 8 months and now he is jumping up and down. Hundreds of traffic accidents, people not showing up for work, a city in distress with, maybe... a quarter of an inch of rain.
Later on stronger storms do arrive and it can pour. Three inch storms are not unusual. By then people are used to driving on a wet road again. The worse part of the rains is from Mid-January to Mid-March. Cold Alaskan air mixes with warm tropical air well out at sea and streams into California from as far away as Hawaii. The cold air is always the winner as the days after a Pacific storm are always crisp and clear with nearly limitless visibility.
If there was not much tropical air, the temperature just drops. A storm without rain and maybe without clouds... another Southern California phenomenon.

In the Fall, the desert begins to cool. The ocean breezes fall flat and sometimes Santa Ana Winds (winds from the desert) predominate. It is all caused by a high pressure system over Utah. Since the desert-sucking-pacific air machine is no longer operating; there is nothing to keep the heavy air over the high-desert from finding its way down into the L.A. basin.
On a November day the temperature could be 95° with the humidity at 10%. Oddly, the winds may be perfectly still in some areas, but a steady gale of 50 mph a few miles away. It all depends on which path the heavy air is forced over the San Gabriel and San Bernardino Mountains take to the sea.
As it drops, it heats-up. Drop a match and it becomes a 50 foot wall of fire swirling and eating everything in its path, including homes. If you are out of the air current and in the calm, temperatures can very noticeably as you walk a few steps. It is quite eerie and ominous and you can hear a pin drop a mile away. Surfing is bad as the waves are flattened by the off-shore breezes. Life is tough.

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