Forecasters believe the rains in California are the result of a “true Pineapple Express,” a specific type of typical meteorological phenomenon that resembles a moisture conveyor belt.
Over the last two weeks, California and other portions of the West Coast have been hammered by a series of atmospheric rivers, which are long, narrow regions of the atmosphere that convey the majority of the water vapor outside the tropics.
“Like rivers in the sky,” according to the National Oceanic and Atmospheric Administration.
Is ‘Pineapple Express’ a common phenomenon?
These sky rivers are most common on the West Coast, although they can occur everywhere, including the eastern United States, where they frequently channel moisture from the Caribbean. They also transport a lot of moisture — enough water vapor to match or perhaps exceed the normal flow of the Mississippi River near its mouth in the Gulf of Mexico.
When moisture interacts with the land, it can fall as rain or snow. Precipitation is often copious, as it has been recently in California since these atmospheric rivers supply a continual flow of moisture.
Although atmospheric rivers come in a variety of shapes and sizes, for one to be a “true Pineapple Express,” location is critical. The tail end, in which moisture is drawn into the atmosphere, must begin near Hawaii. The river must then flow continually through the atmosphere to the West Coast of the United States.
As a result, what happens?
Whether or not an atmospheric river is a Pineapple Express, the consequence is something akin to a precipitation conveyor belt. As a result, they are critical to the livelihood of coastal states that rely significantly on precipitation for water supply: According to the NOAA, a few atmospheric river episodes cause between 30% and 50% of the yearly precipitation on the West Coast.
However, when the rivers are extremely strong — or arrive back-to-back in what are known as “atmospheric river families” — the consequences can be severe, such as the widespread flooding that California is currently experiencing.
