According to the National Oceanic and Atmospheric Administration, an atmospheric river is essentially a long, flowing body of water vapor in the sky. They form here in Southern California when winds take evaporated water from the equator north.
Lowell Stott, a professor of earth sciences at USC, said atmospheric rivers are necessary for California.
“Atmospheric rivers are the normal way that California receives the bulk of its precipitation during the winter season,” Stott said. “So typically, these river events happen three, four, maybe even five times during the winter season.”
Although atmospheric rivers are less frequent in Southern California compared with Central and Northern California, local rainfall is still fairly common in the winter -- most of the time. This year’s rainy season got off to a slow start, and dry weather contributed to last month’s deadly wildfires in Pacific Palisades and Altadena. Now, these wildfire areas are at risk for mudslides.
“There’s a special circumstance right now, and that is the burns that denuded the landscape here in Southern California and exposed that landscape to this heavy rainfall,” said Scott. “So in that regard, no, we’re not prepared for that.”
Don’t put your umbrellas away just yet because based on climate models, Stott believes Thursday’s atmospheric river isn’t the only one Southern California will see in the near future.
“Decision makers have to pay close attention to what the climate scientists are telling us about how this system is going to respond in the future,” Stott said. “And that should help shape decision-making about such things as how to rebuild in those areas that were affected by the burn and now by this heavy rainfall.”
Potential flooding is also an issue. Ryan Kittell, a meteorologist for the National Oceanic and Atmospheric Administration, said people should be extra careful when driving.
“Especially this particular storm, just anticipate the roads to be a little bit of a mess,” warned Kittell. “If you do not need to travel on the roads, definitely allow extra time. Be extra patient. Don’t be distracted by anything. Just focus and get to where you need to go.”
Rain is expected through the night, so be safe out there.