Science & Tech Editor
No, this is not another sequel to a Seth Rogen movie. Pineapple Express is the name given to the weather phenomenon that has caused the abnormal amounts of precipitation in California this past week.
The main consequence of this Pineapple Express is the moist atmosphere that is causing downpours across most of the state. The higher elevations of the Sierra Nevada mountain range had anomalous amounts of snowfall, closing many ski areas and shutting down many roads. Mammoth Lakes reported 48 inches of snowfall in less than 48 hours.
The name Pineapple Express was the term used by sailors to describe the fast winds that propel the ships from Hawaii to the West Coast, as they were often carrying pineapples from the islands.
Known as an atmospheric river, these fast winds bring the moist, rising air from the tropical Pacific – the Hawaiian and other islands – to California. With this flow of moist air, precipitation follows. The Pineapple Express has brought the rainfall typical of tropical environments to the arid regions of California.
The phenomenon starts with the high pressure difference between the polar jet stream and the rainstorms of equatorial pacific. As the heavy rains move east with the fast winds, the low pressure forms in the North Pacific. The moisture with this rain converges with the low pressure system, creating the perfect conditions for anomalous rainfall.
In addition, this system results from an atmospheric cycle known as the Madden-Julian oscillation. This oscillation causes a shift in rainfall areas in the Pacific, similar to that of El Niño, but on a different temporal scale. Associated with anomalous rainfall, this cycle, combined with the propagating forces of the Pineapple Express, is causing the downpours falling onto California.
However, these levels of rain in a typically dry region can have high costs. The last time this event transpired, in 2005, it caused an estimated $300 million in damages, according to the National Oceanic and Atmospheric Administration. Massive amounts of flooding shut down freeways, filled streets with water and even created an ephemeral lake in the desert of Death Valley.
Although this water is much needed for the draining reservoirs of the state, the storm systems can bring about powerfully destructive events. The large amounts of rain that hit Santa Barbara as a result of the Pineapple Express system in 2005 severely eroded the coastline. The level of moisture in typically arid soils causes unstable conditions. The saturated cliff fell apart in a catastrophic landslide above the town of La Conchita. The collapse of this cliff destroyed almost 30 homes, with almost a dozen resulting fatalities. Driving on the 101, you can still see the damage of this landslide, with some houses still buried and a large crater in the cliff.
The types of clouds present in the area are also indicative of the Pineapple Express atmospheric event. The storms bring in clouds not typical of Californian climate. Much fluffier clouds which form distinct lines in the sky, especially around sunset have been making the top of Snapchat stories and Instagram posts.