California's 'Atmospheric River' Will Flood These Areas Hardest

  • California is facing an incoming storm that is forecasted to dump more than 5 inches of rain in some areas and will cause flooding in the Sierra Nevada foothills.
  • The National Weather Service has warned those living below 5,000 feet elevation to be aware of the flood risk.
  • The increased rainfall and snowpack melt has removed all of California from the extreme drought category.
  • Over 17 million people are under flood watches due to the incoming storm.

Millions of California residents will again face severe weather as an atmospheric river is forecasted to dump more than 5 inches of rain in some areas in central California Thursday night and into Friday.

It has been a tumultuous few months for the Golden State, which faced torrential rainfall in January and a first-ever blizzard warning in Los Angeles County in February that left higher-elevation households stranded without supplies for days. The increased moisture has proved beneficial to the state's wildfire threat, but it brings a different kind of danger to people in the highest flood-risk areas.

Those residing in the Sierra Nevada foothills are most at risk for flooding, the National Weather Service (NWS) Prediction Center tweeted, as the atmospheric river dumps excessive rain and increased temperatures from the warm storm system can cause an increased rate for snow melt in the mountains.

Cars drive through flooded California road
Cars pass through a flooded section of road in Mill Valley, California. Millions of residents are under flood watches as an atmospheric river threatens to dump more than 5 inches of precipitation on some areas. Getty

"A storm arriving Thursday will bring a threat of flooding from a combination of heavy rain and snowmelt to lower elevations and foothills in California, especially below 5000 feet," NWS Weather Prediction Center tweeted. "And heavy, wet snow at higher elevations will lead to difficult travel and impacts from snow load."

AccuWeather senior meteorologist Paul Pastelok told Newsweek that meteorologists are "very nervous" about the incoming storm. Pastelok said the past few weeks have been chilly for California, leaving snow that hasn't melted.

"When you put rain, 2 or as much as 5 or 6 inches of rain on top of that, that snow is not deep enough to absorb water, so it runs off very fast," Pastelok said. "This has a higher potential of producing more flooding in the lower elevations of the western Sierra [mountains]. We are very nervous about that and concerned on the flood situation."

What Is An Atmospheric River?

The National Oceanic and Atmospheric Administration (NOAA) described an atmospheric river as a "long, narrow region in the atmosphere—like rivers in the sky— that transport most of the water vapor outside of the tropics."

The atmospheric rivers can carry excessive vapor that is equivalent to the Mississippi River's average flow. The atmospheric river is anticipated to make landfall Thursday and impact the northern two-thirds of California. The NWS Weather Prediction Center warned that those residing below 5,000 feet elevation are at risk for floods, with the most severe risk concentrated around the foothills of the Sierra Nevada mountains.

Much of the state is forecast to receive 3 to 5 inches of precipitation, with some of the state slated to receive less—1 to 3 inches. Part of the state can expect to see more than 5 inches, mostly in the east-central parts of California.

NWS Weather Prediction Center warned that heavy, wet snow will be likely in higher elevations of the Sierra Nevada mountains in northern California and could disrupt travel.

The Affect On California's Drought

The increased rain and snowpack melt has removed all of California from the extreme drought category, as documented weekly by the U.S. Drought Monitor Map.

Three months ago, the map showed more than 40 percent of the state battling extreme drought and more than 12 percent of the state battling exceptional drought. As of the March 9 map, none of the state was classified as battling extreme or exceptional drought.

However, the increased rainfall and flood risk bring a different danger to people residing in the affected area. NWS Weather Prediction Center tweeted a map that showed people in east-central California faced the biggest risk with the precipitation, labeling the risk as causing extreme impacts and substantial disruption to daily life.

In January, when California battled torrential rain, Time reported that 17 people had been killed and millions were urged to evacuate. CNN reported with the incoming storm, more than 17 million people are under flood watches.