Can Atmospheric River Storms Relieve the California Drought?

Several strong storms are heading towards central and northern California and will bring much-needed rain to the drought-stricken areas from Thursday evening, but also carry fears of flooding in fresh scars.

A large depression floating off the coast of the Pacific Northwest is causing repeated rounds of rainfall in northern California and ushering in the first major storm of the season, National Weather Service meteorologists said.

What is known as the “atmospheric flow” pumps continuous moisture over the area, said Ryan Kittell, a meteorologist with the Meteorological Service’s Oxnard station.

Isolated showers were reported in central and northern California on Thursday morning and more storms are looming. A storm system that arrives in the evening and lasts through Friday is expected to be “significant,” said Emily Heller of the Sacramento Weather Station.

The northern Sierra Nevada had already received about 10 inches of snow earlier this week, and 1 to 2 feet more could be dumped in the area early next week, Heller said.

Weather officials said the Sacramento area and north could receive half an inch to 2 inches of rain, with the majority falling along and north of Interstate 80. Mountain areas could reach up to 4 inches. About half an inch could fall over San Francisco, and 1 to 5 inches of rain could fall in the northern coastal areas, including parts of Counties Sonoma and Trinity.

Another storm, which Heller called the “really heavy racket”, is expected to rise on Sunday night and become even stronger.

It is forecast that approximately 3 to 4 inches of rain will fall over the Sacramento and San Francisco areas from Saturday night through Tuesday, with most precipitation falling from Sunday to Monday. When the sky clears next week, mountain areas could see up to 10 inches.

While most of the rain will fall in the north, the storm system will drift into southern California as well. Weather officials predict there could be about half an inch of rain in the Los Angeles County metropolitan areas and 1 to 1 1/2 inches in the mountains.

Graphic illustration showing the plume of moisture in an atmospheric river rising over coastal mountains and the Sierra Nevada, dropping rain and snow.

(Paul Duginski / Los Angeles Times)

Heller described the atmospheric flux as bringing long rains into the atmosphere in a narrow moisture corridor.

“It’s almost like a front, except [where the moisture is] is just more focused. ”The one that Northern California hits is considered moderate to strong.

“The way it usually works is that we just let this band of moisture flow down the coast. And that’s the kind we’re going to see in Southern California, ”said Kittell. “But up there they actually have it where it comes to a standstill.” The storm system could hover over the central part of the state for days.

Storms at this time of year aren’t uncommon, Heller said, but it’s been several years since they arrived this early.

And not a moment too soon. California just had its driest water year in a century. The state’s average rainfall for the 2021 water year was roughly half what experts consider typical.

Earlier this week, Governor Gavin Newsom declared a nationwide drought emergency and pleaded with Californians to save water in the face of one of the most severe droughts in the state.

There are cautious hopes that the coming rains will bring relief and reduce the risk of fire in the arid regions of the state, but they are not expected to end the drought.

“Unfortunately two years of drought – a storm won’t fix that,” said Heller. Sacramento typically receives 12.63 inches of rain per water year. Last year it was closer to 7 inches.

The rain could be useful, but it also carries risks. The National Weather Service issued a flood watch for northern scars from Thursday afternoon through Friday morning, including the Dixie Fire and the North Complex from 2020.

There are also fears that the influx of heavy rain “could bring potential ash and debris flows over the recent burn scars in Shasta, Tehama, Butte and Plumas counties,” the weather service said in a statement.

Concerns are lower in Southern California, where comparatively less rain is expected and some burn scars are older and therefore less prone to landslides and flooding, weather officials said.

But officials are “moderately concerned” about the area charred from the recent Alisal fire in western Santa Barbara County that ignited October 11.

“It’s really fresh,” said Kittell. “There are some endangered areas where any kind of mud and debris flow would cause problems.”

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