A furious storm unleashed from a “bomb cyclone” over the Pacific Ocean slammed ashore Sunday in drought-plagued Northern California, blasting a wide swath of the West Coast with heavy rain, damaging winds, flooding and mudslides.
Flooding across the San Francisco Bay Area closed streets in Berkeley and inundated the Bay Bridge toll plaza in Oakland. The National Weather Service in Sacramento warned of “potentially historic” rain for the city’s downtown.
“Conditions will continue to deteriorate,” the National Weather Service’s Weather Prediction Center warned on Twitter. “Strong winds, high surf, and heavy rain will lead to major impacts. Heavy snow in the Sierra starting tonight.”
The storm was forecast to pound some areas with a foot of rain while dumping up to 8 feet of snow over the mountains, forecasters said. Areas burned by wildfires were vulnerable to mudslides, and debris flows were forcing road closures.
“If you are near a burn scar, it may be too late to evacuate,” the weather service in Sacramento announced on Twitter. “Do not attempt to cross a debris flow. Take shelter in the highest floor of your home.”
A bomb cyclone forms when air pressure rapidly drops as the storm explosively strengthens. The phenomenon was pulling deep tropical moisture from the Pacific, creating an “atmospheric river,” AccuWeather Meteorologist Jon Porter said. He described the river as a “firehose of moisture in the sky” capable of unleashing intense rain and mountain snow.
The storm was most severe in the northern and central portions of California and part of southern Oregon, with the greatest intensity lasting into Monday, he said. Rainfall of up to 2 inches an hour may come “too fast and too furious,” leading to serious flooding and mudslides that could threaten lives and property, Porter added.
The National Weather Service Bay Area issued a plethora of flash flood watches, saying on Twitter: “Main concern will be 2020 burn scars but urban and small stream flooding likely as the heavy rain band passes through Sunday afternoon and night.”
“Flooding, rock slides, chain controls, overturned vehicles – and that was just this morning,” the California Transportation Department tweeted Sunday. “This atmospheric river storm is expected to intensify with heavy rain and significant snow into tomorrow. Do NOT drive if you don’t have to.”
Parts of Oregon were under siege from strong winds and heavy rains. Pacific Gas & Electric said it had thousands of workers ready to respond to outages.
Southern California was not exempt. Parts of western Santa Barbara County were under an evacuation warning in the area recently burned by the Alisal Fire, now 97% contained but not before it burned through 25 square miles.
The region needs the rain. California Gov. Gavin Newsom just last week declared a drought emergency for the entire state, citing three years of drought across the West.
Seventeen major wildfires are burning in California, Idaho, Montana, Oregon and Washington, according to the National Interagency Fire Center. Wildfires have burned almost 2 million acres in California in 2021 alone. The storms will effectively end the wildfire season in much of the region, AccuWeather’s Porter said.
“This rainfall is coming about a month ahead of average and will be very welcome in fighting the remaining fires, particularly in Northern California,” Porter said.
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Snow will begin to fall at elevations above 8,000 feet, but then drop down to elevations around 6,000 feet by Monday, AccuWeather said.
“Given the amount of moisture aiming at the northern and central Sierra Nevada, there can easily be 60-100 inches of snow at levels above 8,000 feet,” AccuWeather Senior Storm Warning Meteorologist Rich Putnam said.