What are atmospheric rivers? The science behind them


Cruz Medina explains the science behind atmospheric rivers.
Published: Jan. 10, 2023 at 5:29 PM CST
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NASHVILLE, Tenn. (WSMV) - Over the past week or so, there has been a lot of talk about atmospheric rivers due to the current weather conditions unfolding in California and other parts of the west coast.

An atmospheric river is a phenomenon that typically impacts the west coast during the fall and winter months and forms when tropical moisture is transported northward from the Pacific Ocean in narrow bands (also thought of as rivers) ahead of the traveling cold front.

Oftentimes, the flow between high and low pressure can accelerate the rate at which the moisture is transported.

The high moisture content, or water vapor, interacts with the higher terrain on the coast and causes the water vapor to cool and condense as it is forced upward. The upward motion will not only form clouds but also squeezed out the moisture in the form of rain and snow.

While higher elevations can receive feet of snow, lower elevations can receive destructive amounts of rain that can lead to urban flooding, landslides, and mudslides.

Imagine before these heavy rain events that soil is on a slanted surface on top of a compact layer of soil that is beneath the surface. The top layer is where vegetation is found, such as trees and grass. This layer can easily become unstable if saturated during heavy rain. When the top layer becomes saturated and unstable, it can give way, given that it is already on a sloped surface. This would then turn into a mudslide which often occurs during these atmospheric river events. Mudslides can be destructive to property and roadways and can also threaten life.

The heavy rain over the past week has caused a lot of flooding in urban areas, especially throughout the state of California. Strong atmospheric rivers, like the one currently affecting the west coast, can typically cause damage upwards of hundreds of millions of dollars. Even the places we consider the quietest in the country, as far as weather is concerned, are not immune to the wrath of mother nature.