SAN FRANCISCO (CBS SF) — An atmospheric river fueled by “a fire hose of rich subtropical moisture” grew in intensity off the Northern California coast Friday, carrying with it the threat of potent downpours, flash flooding, mudslides in the burn zones of the September wildfires and blinding blizzards in the Sierra.

A strong pulse of rain rolled through the Bay Area early Friday, triggering treacherous driving conditions for the morning commute. By 5:34 a.m., the California Highway Patrol said it was responding to 26 incidents on local freeways.

While more than a half of inch of rain had fallen by dawn in Santa Rosa and Petaluma, the main event was on tap for Sunday when the atmospheric river arrives.

Downpours In Marin County

Late Thursday morning, the National Weather Service issued a flash flood watch to start late Saturday night for the burns area in Napa and Sonoma counties left behind from the 2020 wildfires.

It’s all part of an extremely turbulent weather pattern developing in the Pacific. Forecasters said a potent weather system known as a ‘bomb cyclone’ would send waves of storms into Washington state and Oregon.

ALSO READ: North Bay Communities Prepare For Major Storm; Flood Concerns In Fire Scarred Areas

Meanwhile, the extreme weather experts at Scripps Institution of Oceanography warned that the atmospheric river headed toward the San Francisco Bay Area was intensifying toward becoming a Category 5 — the highest level in their scale of measurement.

“By Saturday night, a rapidly intensifying Pacific cyclone directing a powerful atmospheric river squarely at the West Coast delivers a fire hose of rich subtropical moisture into California,” the National Weather Service said. “Snow levels will be low enough to blanket the Sierra Nevada in heavy snow on Sunday while prolonged periods of rain soak the coast and valleys of northern and central California.”

“This impressive atmospheric river will result in heavier rainfall amounts and in a shorter time span, leading to more flash flooding and debris flow concerns for burn scarred areas of California.”

Fremont Officials Handing Out Sandbags

 

The rainfall totals from Sunday’s storm will bring welcome relief for the Bay Area, which has been in the grip of an extreme drought for months.

“Rainfall amounts from this event are likely to range from 3-6 inches in the North Bay and down into the Santa Cruz Mountains,” the weather service said. “Isolated amounts in the region`s favored coastal ranges could see amounts in excess of 8 inches, especially in the North Bay.”

A flash flood watch was set to go into effect Sunday for the large burn scars left behind from the wildfires that burned more than 2 million acres in the Sierra in August and September.

“Periods of moderate to heavy rain are expected, especially Monday morning,” the weather service said in its flood watch warning. “These could bring potential mud and debris flows over recent burn scar areas in Madera, Fresno, Tulare and Kern Counties.”

A winter storm watch was also set to go into effect in the Lake Tahoe area on Sunday.

“Heavy snow possible above 8000 feet,” the weather service’s Reno office warned. “Total snow accumulations of 1 to 3 feet with locally higher amounts possible. Light snow accumulations are possible below 8000 feet on Monday. Sierra ridge winds could gust as high as 100 mph.”

Transportation officials said chain requirements will be likely in the mountain passes on Highway 50 and I-80.

When it comes to the drought, even if California were to have above-average rain and snow this winter, warming temperatures mean it still likely won’t be enough to make up for all the water California lost.

This past year, California had its warmest ever statewide monthly average temperatures in June, July and October 2020.

Jeanine Jones, interstate resources manager for the California Department of Water Resources, said people should not think about drought “as being just this occasional thing that happens sometimes, and then we go back to a wetter system.”

“We are really transitioning to a drier system so, you know, dry becomes the new normal,” she said. “Drought is not a short-term feature. Droughts take time to develop, and they usually linger for quite some time.”