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Here’s what you need to know about Northern California’s atmospheric river weather event

A car drives through standing water in Sacramento's Oak Park neighborhood Monday, Dec. 13, 2021.
Andrew Nixon
A car drives through standing water in Sacramento's Oak Park neighborhood Monday, Dec. 13, 2021.

Just on the heels of a record-breaking heat wave, California saw the onset of an atmospheric river this past weekend. It’s expected to break rainfall records throughout Northern California.

Atmospheric rivers have become known for bringing heavy rainfall, and with it, flooding concerns. The same is true for this storm: The Sacramento office of the National Weather Service has warned residents of the potential for localized flooding throughout Northern California.

Amounts of rainfall from the atmospheric river might vary in different parts of the region, according to the weather service. In a recent tweet, the agency explained that while some areas may see bursts of rain, others may see no rain at all.

Although atmospheric rivers have garnered more attention in recent years, they aren’t new to the West Coast. However, their intensity is ramping up. Experts say that this “whiplash” pattern of moving from extreme heat to heavy precipitation is becoming more intense because of climate change.

“That [pattern], if we measure it, has been increasing over the past few decades,” said Katerina Gonzales, a climate adaptation researcher at the University of Minnesota who studies atmospheric rivers. “So it’s kind of a situation where we are learning to expect the unexpected.”

Gonzales said that while this rainfall might do some good for California, intense precipitation can also have devastating flooding effects. It could create danger in areas that have recently seen fire, as that heavy rainfall can trigger debris flows and landslides in burn scar areas.

There’s a flash flood watch in effect for the area of the Mosquito Fire burn scar. Forecasts say there is also the potential for thunderstorms in the area.

There is some good news, though: While it doesn’t seem like the storm will quench the fire, experts say that it could help firefighters with their efforts to contain the blaze.

“The rain, of course, is going to keep the fire relatively in place where it is,” said Jonathan Pangburn, a fire behavior analyst with Cal Fire, in a recent nightly community briefing. “We’re not expecting any rapid growth.”

This storm also hit Alaska with force this past weekend. Governor Mike Dunleavy issued a disaster declaration on Sept. 17, allowing state resources to be directed toward recovery in impacted coastal communities.

Meanwhile, a devastating hurricane hit Puerto Rico this past weekend and is dumping huge amounts of rain on the island. Gonzales said that, while unrelated, seeing these two weather events manifest at the same is a reminder of what will become even more common with climate change.

“The fact that our country is being hit… [and] the resources are being strained at the same time is very emblematic of the climate change of now and the climate change that we expect in the future,” she said.

While atmospheric rivers have historically helped replenish California’s water supply, Gonzales said that their increased intensity is a cause for concern.

“We rely on them,” she said. “And at the same time, they’re becoming more hazardous.”

The National Weather Service office in Sacramento will continue to provide updates on the storm via social media.

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