What is an atmospheric river? California declares State of Emergency due to potentially ‘life-threatening’ flood

Sunday, February 4, 2024, saw the arrival of a second strong atmospheric river in Southern California. According to the National Weather Service’s Los Angeles office, it brought torrential rain and a “high risk for life-threatening and damaging flooding” with it.

This powerful, protracted river has caused extensive power disruptions, the possibility of mudslides, and potentially fatal flooding. As a result, warnings of “one of the most dramatic weather days in recent memory” have left nearly 500,000 Californians without electricity.

Atmospheric rivers are long, narrow regions in the atmosphere that resemble rivers in the sky. Most of the water vapor outside the tropics is transported via these. Although the size and strength can vary widely, these typical rivers contain about the same volume of water vapor as the average flow of water at the Mississippi River’s mouth.

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An atmospheric river is a natural phenomenon that can happen anywhere on the planet

As per PBS, forecasters issued warnings for hazardous flooding, significant snowfall in the mountains, and an increased chance of avalanches and mudslides from February 4 to February 6, 2024. This is due to the strong atmospheric river which is headed towards California. The river is the most recent one to bring heavy rains to the West Coast.

As per the National Oceanic and Atmospheric Administration (NOAA), an atmospheric river is a slender passageway or filament of concentrated water vapor carried through the atmosphere. It resembles a river that can stretch up to 1,000 kilometers across the sky.

The moisture these rivers carry cools and condenses when they encounter mountains or local atmospheric dynamics. This water vapor is frequently released by these rivers as rain or snow when they touch down on land.

This phenomenon comes in a variety of forms and dimensions. However, the ones with the highest concentrations of water vapor and the strongest winds have the potential to produce extremely high rainfall and flooding. These occurrences have the potential to obstruct traffic, trigger mudslides, and result in severe harm to people and property.

While they are most prevalent in the mid-latitudes, this phenomenon can be found almost everywhere. These originate over warm water, usually tropical oceans, and are directed towards the coast ahead of cold fronts of extratropical cyclones by low-level jet streams.

Atmospheric rivers can bring extreme weather and flood events. They are predicted to become more intense and frequent in certain regions of the world due to changes in heat and humidity in the atmosphere brought on by climate change. It is anticipated that this will be particularly noticeable in Canada and the Western US.

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California will likely witness "life-threatening" floods on Tuesday: Reports

As per CNN, continuous rain has stalled over Southern California and Los Angeles, increasing the likelihood of flooding on Monday, February 5. The National Weather Service office in San Diego has said that by Tuesday, February 6, Orange County could see torrential rain and "locally catastrophic" floods.

Lindsey P. Horvath, the Chair of the Los Angeles County Board of Supervisors, as reported by CBS News, said:

"Los Angeles County is taking action to protect our communities during the storm and to recover from any impacts that may result.”

On the other hand, BBC reported that strong gusts and rain are already pounding the area from Santa Barbara to Los Angeles in California. The outlet has also reported that "life-threatening" flooding is possible through Tuesday, so 94% of the population, or around 37 million people, are currently under flood alert.