The recent record-breaking rainfall totals already for the 2023-2024 wet season in California are largely due to a series of storms bringing precipitation in a form known as atmospheric rivers.
Atmospheric rivers are long, narrow bands of highly concentrated moisture in the atmosphere that can transport large amounts of water vapor from the tropics to other parts of the world. Nicknamed “rivers in the sky”, atmospheric river events can be thousands of kilometers long and a few hundred kilometers wide, and they are responsible for a significant portion of the global transport of water vapor. The term “atmospheric river” was coined in 1994.
When atmospheric rivers make landfall, they can produce heavy precipitation, strong winds, and flooding. While atmospheric rivers can also bring drought relief to dry regions by delivering much-needed moisture, the precipitation overload can also wreak havoc by causing flooding, toppling trees, down power lines, and trigger landslides. The high winds and precipitation that arrives with atmospheric rivers make these storms some of the most damaging types of mid-latitude storms according to researchers. The mid-latitudes are the latitudes between the tropics and polar regions.
California’s location along the western coast of the United States means that the state is affected by atmospheric rivers that originate in the tropical Pacific Ocean. These atmospheric rivers tend to form along the east side of the subtropical high-pressure system that is centered over the Pacific Ocean and are often directed towards the west coast of North America by the prevailing westerly winds. The combination of moist air from the tropics and the high terrain of the Sierra Nevada mountains can lead to the formation of strong, moisture-laden atmospheric rivers that can bring heavy rain and snowfall to California.