Talk:Climate of Los Angeles

Assessment as Start class
Despite its length, the "Overview" section is nothing but a list of statistics, something that wikipedia is not. Dropped the class to C because of this, because it doesn't have much to say, besides its length. There is surprisingly little text in the article...could have gone Stub if it wasn't for the proper article structure. Thegreatdr (talk) 18:52, 6 February 2011 (UTC)

El Nino Prediction
The article claims the Climate Prediction Center "predicted" rain. The "prediction" is a misnomer. They give statistics based on what is more or less likely, not a yes or no. If I say there is a 60% it is going to rain, and it doesn't, that does not mean I was wrong. That should be updated.

Moving article to "Climate of Los Angeles"
I'm going to go ahead and be bold and move this article to "Climate of Los Angeles." Half of the current article addresses areas that are not technically in the Los Angeles Basin—the basin is generally accepted to be the coastal plain seaward of the mountain ranges. This definition would exclude the San Fernando Valley, San Gabriel Valley, and all of the Inland Empire from San Dimas/Pomona eastward. Since this article seems to want to be about the climate of the whole Los Angeles region (which conforms to the convention of other "Climate of..." articles), I'm going to change the article name to reflect that. It doesn't make much sense to have an article on the climate of the coastal basin leaving out the immediate surroundings. Darkest Tree  Talk  18:24, 3 February 2015 (UTC)

Climate classification
The intro currently says that all of Los Angeles is either Csb or Csa, but by my calculations, many of the locations with temperature and precipitation tables on the page are actually subtropical semi-arid (based on the Koeppen threshold of the average annual temperature times 20): LAX, Culver City, Long Beach, Santa Ana, and Anaheim. Other locations are above the threshold and qualify as Cs: USC, Santa Monica Pier, Canoga Park, and Burbank. — Eru·tuon 04:05, 17 August 2016 (UTC) Drbits (talk) 21:54, 17 June 2020 (UTC)
 * LAX, Culver City, Santa Monica Pier, and Long Beach are adjacent to the Pacific Ocean. They are CSb
 * Santa Ana and Anaheim in Orange County are separated from the Los Angeles basin (a large valley).
 * USC (University of Southern California) is in downtown Los Angeles and is the official source location (QCT) for the temperature data for downtown Los Angeles since 1921. A nearby location was used prior to 1921. USC is Csa.
 * Canoga Park and Burbank are in the San Fernando Valley, a separate microclimate from downtown Los Angeles. They are Csa.
 * The San Fernando Valley is usually 5°C to 10°C (9F to 18F) warmer (July through September) than Downtown Los Angeles (personal observation from various weather stations).
 * Santa Monica and Long Beach are usually 5°C to 10°C (9F to 18F) cooler (July through September) than downtown Los Angeles (personal observations).

Csa or Csb with only 311mm? Is the same that Alicante, Spain, and Alicante is semi arid Bsk or Bsh Hinzel 15:43, 28 April 2022 (UTC) — Preceding unsigned comment added by Hinzel (talk • contribs)

Santana (Santa Ana) Winds
The discussion of climate in the Los Angeles region is incomplete without discussing the mountain ranges, plateaus, and valleys that comprise the region and the surrounding areas.

The article mentions the temperature increase caused by high pressure over the "Great Basin," but mistakenly excludes the Central California "High Deserts." A wind coming into the Los Angeles region from between North by North East and East comes over the San Gabriel Mountains. As the air descends from the mountains into the San Gabriel Valley, it undergoes "Adiabatic heating" (the air is heated by compression). This air is very dry and often carries the smell of wildfires, so the winds were named Satanás (Satan) Viento by the Spanish settlers -- later English speaking settlers thought the Spaniards were saying "Santa Ana Winds." These winds travel across the San Gabriel Valley to the San Fernando Valley and the Los Angeles Basin.

The Santana winds are further heated in the Western San Fernando Valley as they are compression heated when they meet the Santa Susanna Mountains.

When the winds are on-shore (coming from between the West and the South), they tend to cool most of the Los Angeles Region. However, in the Eastern San Gabriel Valley, the winds press against the San Gabriel Mountains and are compression heated. This compression also traps air pollution in the area.

A similar effect in the San Francisco area is called the Diablo (devil) Winds.

Inversion Layers
When the winds are relatively calm, an "Inversion Layer" often forms over the Los Angeles Basin (and sometimes over the adjacent valleys). In most of the world, cold air moves under a mass of warm air or warm air moves over a mass of cold air (the heavier cold air is below the warm air). An inversion layer forms when a mass of warm air develops under a mass of cold air. The multi-valley structure of the Los Angeles Region keeps air near the ground from moving away. Sunlight heats the air near the ground while leaving the cold air above unchanged. This traps hot, dry air near the ground. The thermocline (where the warm and cold air meet) forms a barrier to air movement. The thermocline prevents the escape of polluted air and pollution is concentrated in the warm air mass near the ground. Under those conditions, one can often see the extent of the warm air mass, because it is brown when compared to the air above. Fortunately, air pollution in the Los Angeles Region has been considerably reduced over the past 20 years. The trapped pollution used to cause serious health problems and even deaths.

The Los Angeles Basin formed inversion layers even before the European invasion. Some Indigenous people referred to what is now Downtown Los Angeles as "The valley of the smokes," because smoke from campfires (and wildfires) was concentrated by the inversion layer. The ground level heating problem has been increased by the replacement of light-colored sand and vegetation with asphalt and darker buildings.

Local Greenhouse Effect
Most US cities have a local greenhouse effect because of the darker surfaces and the generation of greenhouse gasses by local industry, electrical generation, home heating, and transportation. This greenhouse effect causes a dome of warm air to form over the city (an inversion layer). At night, the city lights tend to reflect off of the dome-shaped thermocline above the city and these domes can be seen from low-flying aircraft. There is a small group of people from southern cities trying to change cities from heat-absorbing surfaces to more heat reflective surfaces. Los Angeles has started installing light gray coatings on some blacktop roads.

When the city of London, England was heated mostly by coal, an intense local greenhouse effect heated the city in the winter (and the particles of soot created the famous London fogs). In the summer, the local greenhouse effect trapped pollution near the ground, forming smokey fog (the origin of the word "smog"). This smog contained sulfuric acid droplets from the sulfur in the coal and in some years caused a significant number of deaths by respiratory failure. When most of London changed from coal to natural gas and petroleum products, the greenhouse gasses remained, but the soot and acid disappeared. London is now several degrees colder in the winter and the London Fogs are mostly gone. Drbits (talk) 02:46, 9 November 2017 (UTC) Drbits (talk) 22:07, 17 June 2020 (UTC) (update)