What is atmospheric river? Here's how it can dump more snow, rains on California

A new 'atmospheric river' is expected to bring weather chaos to the gates of California. Parts of the US state are still digging out from massive amounts of snow that left mountain communities buried for weeks. Now the situation can worsen as these atmospheric rivers are set to hit the state on Thursday. According to forecasters, northern and central California is set to receive most of the rain this weekend and there are chances of even flash floods.

As per the National Weather Service, California will see moderate to heavy rain, flooding, and gusty and heavy snow in high elevations through the weekend.

Atmospheric River in California

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The atmospheric rivers, sometimes described as ‘rivers in the sky’, are expected to blanket higher elevations with heavy snow and to bring heavy rain across portions of California, with lighter rainfall in the Los Angeles area.

Forecasters expect the worst, as seven inches of rain can cause flooding in the area with mudslides everywhere. The rain is especially concerning in the regions that have already received a near-record run of snow this winter, including at low elevations in the Sierra Nevada foothills.

What is an atmospheric river? Is it a new term?

Atmospheric rivers are relatively long and narrow regions in the atmosphere that transport most of the water vapour outside of the tropics. In other words, it is a narrow corridor of concentrated moisture (specifically hydrosphere) in the atmosphere. There are many names that are given to this phenomenon, such as tropical plume, tropical connection, moisture plume, water vapour surge, and cloud band.

These corridors of vapour move with the weather, carrying an amount of water vapour equivalent to the average flow of water at the mouth of the Mississippi River. When the atmospheric rivers make landfall, they often release this water vapour in the form of rain or snow.

The first atmospheric river is expected to move into California on Thursday, and another is forecast to arrive on Monday. Unlike other storms this year, more of the precipitation is expected to be rain which prompts concerns over snowmelt in areas like the Sierra Nevada.

The term ‘atmospheric river’ is not new. It was coined back in the 1990s by researchers Reginald Newell and Yong Zhu of the Massachusetts Institute of Technology. These rivers can be several thousand kilometres long. Some of them can even carry a greater flux of water than Earth’s largest river, the Amazon River.

Snowstorm weather forecast: California

According to weather.com, the storm will produce its most significant impacts on Thursday and Friday. In the central states, the greatest chance for light to moderate accumulations is from the Dakotas into parts of Minnesota, Iowa Wisconsin, northern Illinois, Michigan, northern Indiana and northern Ohio. That includes northern Chicago, Detroit, Milwaukee and Minneapolis St. Paul.

Snowfall in the Northeast will be light to moderate, with the most accumulations to the west of Interstate 95 in southwestern New York and Pennsylvania.

(With inputs from agencies)

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