California snow video: Balcony jumping, bridge shoveling, turkey spotting
The winter of 2023 isn’t finished yet. Not by a long shot.
An atmospheric river storm is likely to hit Northern California late Thursday into Friday, meteorologists and climate scientists said Monday, bringing high chances of heavy rain in the Bay Area, 1 to 3 feet of new snow at higher elevations in the Sierra, and an increased risk of flooding as the warm rain hits the state’s massive snowpack.
Details about the storm, a classic “pineapple express” event barreling in more than 2,000 miles from Hawaii, are still not certain.
But this past weekend, computer models began to show its likelihood increasing from about 10% to now about 70%, said Daniel Swain, a climate scientist at UCLA.
“There’s a lot of uncertainty at this point regarding how intense it will be, how prolonged it will be, and the impacts it will likely have,” Swain said, “as well as whether it will be followed by additional warm storms or not. All of that is up in the air. However, confidence has grown that a warm rain event of some magnitude will occur later this week.”
This storm is most likely to be a 3 on a scale of 1 to 5, potentially a 4, said Marty Ralph, director of the Center for Western Weather and Water Extremes at UC San Diego and one of the nation’s leading experts on atmospheric rivers.
“It will be felt as far south as San Diego and up to the Russian River,” Ralph said.
Ralph and Swain both said that the latest storm by itself won’t likely be enough to cause major melting of the immense Sierra snowpack — which on Monday was 192% of its historic average, the most snow in 30 years — because the deep snow can absorb a fair amount of rain.
But computer models are also showing that two or three more atmospheric river storms could be lining up over the next 10 days, Ralph said.
“It could be like January where we had back-to-back-to-back atmospheric rivers,” he said. “That’s what I’m looking out for. The chance for having another sequence of atmospheric river storms where this is the one to kick it off is where the greatest risk is.”
Many of the state’s largest reservoirs still have room to hold the incoming water. Their levels fell so low during three years of drought that the biggest ones still aren’t all the way full. On Monday, Shasta Lake near Redding, the largest reservoir in California, was 61% full. The second largest, Oroville, in Butte County, was 74% full.
That wasn’t the case in 2017 when Oroville got filled to the top and its spillway failed, forcing the evacuation of more than 180,000 nearby residents.
Hoping to reduce the chances of a similar event, dam operators in recent weeks have been increasing water releases from some reservoirs, such as Folsom, northeast of Sacramento, and Millerton, near Fresno, to create more space.
“We’ve got a lot of reservoirs in the state in a good position going into this storm,” Ralph said.
How much rain is expected? Thursday night through Sunday, the National Oceanic and Atmospheric Administration is expecting 2 to 3 inches of rain in San Francisco, Oakland and San Jose, with 4 to 6 inches in the Santa Cruz Mountains and Big Sur — enough to cause flooding on roads and some small streams.
There will be 1 to 3 inches in the Central Valley and 3 to 6 inches in the Sierra foothills, said Katrina Hand, a meteorologist with the National Weather Service in Sacramento. The snow level will be 5,000 to 6,000 feet, she said.
California’s massive snowpack is a bounty that will melt and continue to fill the state’s biggest reservoirs through the spring. But flood experts also have been eyeing it nervously.
They worry that a series of warm tropical storms could melt it faster than normal, triggering the kind of catastrophic flooding that was seen in 1997.
That year, several warm “Pineapple Express” storms drenched the Sierra around New Year’s Day. Yosemite Valley experienced its worst floods in a century. Entire campgrounds washed away. Half of Yosemite Lodge was destroyed. Across the Central Valley, big reservoirs filled to the top and released water uncontrollably. Levees broke, causing major flooding in Marysville, Yuba City and other communities. When it was over, 48 of California’s 58 counties were declared disaster areas, and damage totaled $1.8 billion.
Friday’s storm won’t do that by itself, Hand said.
“We are not looking at a repeat of 1997,” she said. “This storm is not nearly as strong or as warm.”
California’s severe 3-year drought has been largely broken in many northern and coastal areas, after nine atmospheric river storms between Christmas and mid-January raised reservoir levels and caused serious flooding that killed at least 21 people, caused more than 750 landslides, wrecked roads and prompted a visit from President Biden to survey the damage.
Much of February was dry. But over the past two weeks, several powerful new storms have dumped more rain on urban areas from the Bay Area to Los Angeles and smothered the Sierra Nevada in 16 feet of new snow, closing Yosemite National Park, Interstate 80, Highway 50 and even ski resorts for several days that couldn’t operate chairlifts during blizzard conditions.
Swain noted that Friday’s storm could cause “unusual problems” in some mountain communities, including the risk of roofs collapsing due to the weight of built-up snow, with rain making it heavier.
“It will most certainly cause some flooding, at least minor or moderate flooding,” in Sierra foothills communities and some urban areas, Swain said, adding “I think the Friday-Saturday event will produce less flooding than the events we saw in January.”
But he said he is watching next week’s forecasts very closely.
“A prolonged storm train and successive waves of warm rain on top of the huge snowpack, that would be a significant problem,” Swain said.
