The recent severe weather in California was driven by an atmospheric river, a column of moisture that reached from the Pacific Ocean to close to Hawaii. Let’s explore this event further:

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What is an atmospheric river?

Atmospheric rivers are long and relatively narrow bands of water vapor that form over an ocean and flow through the sky, transporting much of the moisture from the tropics to northern latitudes.

These events are present worldwide, but have a particular impact on the West Coast of the United States. They account for 30% to 50% of yearly rainfall and are crucial for water resources. However, they can also result in severe storms, leading to floods and mudslides, as reported by the National Oceanic and Atmospheric Administration.

Atmospheric rivers, created by winds from cyclones, usually measure between 250 and 375 miles (400 and 600 kilometers) wide and are affected by other weather patterns.

Several atmospheric river occurrences are not very strong, but the ones that pack a punch can move an incredible amount of moisture. Research has revealed that they can transport seven to 15 times more water than the average daily discharge of the Mississippi River, as reported by the U.S. Geological Survey.

The Center for Western Weather and Water Extremes at Scripps Institution of Oceanography reported that a total of 46 atmospheric rivers reached the U.S. West Coast in water year 2023. Among them, nine were considered strong, two were extreme, and one was exceptional. This led to severe flooding and heavy snowfall in California.

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What occurs when an atmospheric river makes landfall?

According to NOAA, when air with a lot of moisture travels over mountain ranges like the Sierra Nevada near the border of California and Nevada, the water vapor rises and cools. This results in a large amount of precipitation in the form of rain or snow.

Although the Sierra snowpack is typically formed by cold winter storms from the north Pacific, atmospheric rivers are warmer. While there may still be snow at higher elevations, the lower elevations usually experience rain on the existing snowpack. This can lead to rapid melting, runoff, and flooding, resulting in a decrease in the snowpack necessary for California’s water resources.

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Can you explain what a Pineapple Express is?

This is a moniker given to a powerful atmospheric river located in the tropical Pacific region near Hawaii.

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What is the origin of the term “atmospheric river”?

The term is derived from a study conducted in the 1990s by Yong Zhu and Reginald E. Newell, researchers from the Massachusetts Institute of Technology. These weather phenomena are commonly known as ARs.

Source: wral.com