Rain, and lots of it: What to know as ‘bomb cyclone’ heads for Northern California

A series of storms hitting Northern California in the next several days will include a powerful “bomb cyclone” system, expected to drop heavy precipitation over the weekend and early next week.

The system is developing off the coast of the Pacific Northwest and is also expected to batter the coasts of Oregon and Washington.

“There’s a big, deep (pressure) drop that’s kind of remaining off of the Pacific Northwest. It’s bringing in multiple waves,” said Emily Heller, a meteorologist at the National Weather Service’s Sacramento office.

First, showery conditions Wednesday and Thursday will bring a lighter round of rain and some snow above summit pass levels, according to weather service forecasts.

Precipitation will intensify a bit Thursday night and into Friday, with heavier amounts falling north of Interstate 80. The weather service says Sacramento could get a half-inch to an inch of rain between Thursday through Friday, as a dusting of snow in the mountains could drop to around 7,000 or 8,000 feet.

The weather service has issued a flash flood watch for areas near the Dixie Fire and 2020 North Complex burn scars, in place 11 p.m. Thursday to 11 a.m. Friday. The warning includes the areas of Greenville, Berry Creek, Feather Falls and along highways 70, 89 and 162 near those communities.

Residents in those areas should be prepared to evacuate if instructed by local emergency officials.

Conditions will calm back down to lighter showers early Saturday before the big storm hits that afternoon, expected to last into Tuesday.

Heller said the heaviest rain is expected in the Sacramento region Sunday and Monday. The capital city could get more than 2 inches. Sacramento only got about 7 inches through all of the last water year, from October 2020 to September 2021, Heller said.

Some northern coastal areas like Eureka and foothills areas including Grass Valley could get 5 inches or more, the NWS Sacramento office said in a video briefing

In the Sierra Nevada mountains, more than a foot of snow could fall at pass level. Forecasters predict 8 to 12 inches at Echo Pass. Three to four feet could drop in the southern Sierra range, around Sonora Pass. Snow levels are expected to drop from around 7,000 feet during the weekend to around 5,500 feet late Monday.

Stormy weather is expected at times through next Tuesday. Valley rain showers and high elevation mountain snow showers will create slick roads and possible ash and debris flows to recently burned areas. Watch this quick briefing to learn more. https://t.co/LE9M4NKB6I #CAwx pic.twitter.com/nonYHJ2uAd

— NWS Sacramento (@NWSSacramento) October 19, 2021

Today is the last day of mild weather before more wet weather returns to #Norcal by tonight. Rain and mountain snow showers are expected at times through next Tuesday! Please plan ahead for slick roads and possible travel delays. #CAWX #CARain pic.twitter.com/gKNcHNptLF

— NWS Sacramento (@NWSSacramento) October 19, 2021

The bomb cyclone storm will bring hazards, including slick roads, possible roadway flooding and mudslides. Californians in areas with recent wildfires may also see ash and debris flows.

The storm should also produce some wind gusts, though Heller said they’ll likely only be around 25 mph near Sacramento, which is weaker than some recent wind storms in the region.

Northern California last experienced a bomb cyclone, or “bombogenesis,” in November 2019, right around Thanksgiving. The previous one before that came in December 2015.

Storm needed for ultra-dry California

The precipitation is much needed: Gov. Gavin Newsom on Thursday officially declared a state of drought across all of California, expanding on earlier declarations that had swelled to include 50 of the state’s 58 counties.

But even with an intense bomb cyclone, it will take more than just a few days of rain to put a dent in the drought.

“One storm is great, but we’re going to need a couple to get us back to a robust and healthy storage condition,” Erik Ekdahl, a deputy director for the State Water Resources Control Board, told board members Tuesday.

Sacramento has only received about 4 1/2 inches throughout all of 2021, meaning the annual total could nearly double in less than a week if the storms hit the high end of forecast expectations.

“It would definitely help in the beginning of this water year,” which started Oct. 1, Heller said.

‘End of fire season’ near?

Heller said the wet weather will “definitely” improve wildfire conditions in Northern California.

“Especially with all of the moisture we’re getting, fuels are going to become pretty much saturated,” Heller said. “We might still see some fires, but it’s probably close to the end of fire season.”

Some of California’s largest wildfires of 2021 are nearing full containment, and the storm will impact fire areas.

In a Wednesday incident update for the Caldor Fire burning near the Lake Tahoe Basin, the U.S. Forest Service said snow could make some areas inaccessible. The blaze is 98% contained, with no spread expected in the next few days.

The Monument Fire near Shasta-Trinity National Forest is “essentially out” and 94% contained, according to another Forest Service update. But this week’s weather will hinder mitigation of tree hazards, and gusts from the storm could knock some over.

Meanwhile, the Dixie Fire burning in parts of Butte and Plumas counties is 95% contained. California’s second-largest wildfire ever at more than 960,000 acres, officials have said previously that its vast burn scars could be susceptible to mud slides in heavy rains.

Highway 70 is a particular area of concern, and is included in the weather service’s flash flood watch. If necessary, the weather service will upgrade the watch to a flash flood warning, which would mean flooding is imminent.

Residents who live on or below hillsides should remain alert, according to the California Department of Conservation.

The Associated Press contributed to this report.