The first major atmospheric rivers of winter arrived in Los Angeles, and the risk of fires eventually receding, the dangers of serious landslides on burn hills around the city, and the possibility of the southern part of the country. It brings something. The rainy season in California is finally beginning in earnest.
Many explanations of the Palisade and Eton fires are attributed in part to delays in winter rain, partly to its strength, and its framing is not wrong. But it doesn’t answer the basic question: why does Los Angeles receive almost all the rain during the winter?
It seems like a fact of life on the west coast, when summer is dry. In a typical year, LAX receives about 2½ inches of rain over the eight months from April to November. This is less than 20% of the annual average. However, compared to most other countries (and the world), this is an unusual pattern.
Go northeast over Sierra Nevada and head to Salt Lake City. This averages around the same annual rainfall as LA. Instead, we head east to Santa Fe – we also pass around the same annual rainfall – and the wettest months are July and August. As we get far from the Rockies, we head east and steadily wet. Most of them have flat precipitation cycles (for example, none of the month in Boston contains more than 10% of the average annual rainfall) or spikes spring or summer.
The family will walk underwater during sunset on June 13, 2024 at Great Salt Lake near Salt Lake City.
(Rick Bowmer/AP)
It is no coincidence that Cascades, Rockies, and even the relatively modest San Jacinto, such as the western mountains, divide the area into various precipitation patterns. In Joshua Tree National Park, intense summer downpours are occasionally wiped out from the Gulf of California, but the lateral area forms walls and prevents that moisture from reaching Los Angeles.
Similarly, the so-called “Pineapple Express,” which carries warm, humid air from Hawaii to the Pacific coast, is usually spent on the Sierra. The dry condition phenomenon on the leeward side of the mountain range (i.e., the wind-protected side) is known as “rain shadows” and can produce some of the driest conditions on the planet. Chile’s Atacama Desert, downwind in the Andes, has never recorded any rain.
But just as important as the literal ridges that traverse the land are weather ridges present in the atmosphere. Atmospheric ridges are long high pressure areas and are usually associated with hot, dry air. Unlike mountain ridges, they let the air flow around them, creating their own version of the shadows of the rain. One of these ridges (known as “subtropical ridges”) usually circles the Earth at about 30 degrees latitude, creating the deserts of Arabia, Sahara and Sonoran.
During the summer months when the sun warms the North Pacific Ocean, subtropical ridges turn north between Hawaii and California, blocking air that flows from the ocean. During the winter, the oceans are cooled, and the so-called “Aleutian Law” spreads south from Alaska, releasing the paths that bring rain to the west coast. A similar phenomenon occurs in the Atlantic, creating dry summers and wet winters in Lisbon, Rome and Athens. In fact, places with less than 10% annual rain during the summer are said to have a “Mediterranean climate” due to the prevalence of this pattern in southern Europe.
People try to remove snow from the road during a storm in Truckee, California, March 2, 2024.
(Brook Hess Homier/Applications)
Given that the movement of these atmospheric ridges is driven by temperature changes, it is hardly surprising that climate change can have a major impact on them. In recent history, the deep drought that held California between 2011 and 2017 was driven by a phenomenon known as the “ristocratic resilient ridge.” A storm that has come from reaching the west coast during the winter.
Several studies suggest that sustained ridges off the coast, and therefore longer droughts – are many times more frequent due to climate change. These ridge changes can also contribute to a dangerous phenomenon known as “hydrated water. whiplash.” In a year, warm air (which can retain more moisture) can lead to torrential rains that promote vegetation growth. It keeps rain, guides vegetation, drys out, and provides fuel for wildfires.
As the weather warms and extreme weather grows even more extreme, the key question may change from “Why does it rain so much in winter?” “If not, what happens to LA?”
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