Biggest storm in weeks is coming
The biggest storm in the region in five weeks is forecast to bring widespread rain across Northern California on Tuesday and Wednesday. There could be thunder, lightning and even some hail, forecasters say, just like winter weather is supposed to behave.
What is expected to be the wettest storm since Feb. 2 is likely to deliver up to 2 inches of rain to coastal mountains, about half an inch or slightly more to Bay Area cities, and 1 to 2 feet of new snow in the Sierra Nevada.
“It should be moderate rainfall, not like what we saw during the atmospheric river in January,” said Brayden Murdock, a meteorologist with the National Weather Service in Monterey. “It’ll be above a drizzle but below a downpour.”
In Woodland, the forecast shows cloudy weather with 60% chance of showers on Tuesday.
The rain is welcome, and much needed. But it’s probably too little too late, experts say, to make much of a difference in this winter’s very dry overall trend — the second dry winter in a row, and one that has California heading back toward tight water supplies and elevated fire risk this summer.
“We’re in drought unless we get a super-miracle March. And that’s unlikely,” said Jay Lund, director of the UC Davis Center for Watershed Sciences. “This is California. You should always be in a water con
servation mindset. And now we see why.”
The math is stark and simple. San Francisco has received 7.3 inches of rain since Oct. 1. The city’s historical average by this date is 18.7 inches. So San Francisco needs at least 11 inches more in the next few days — which would be a historic deluge, with massive flooding — just to bring it up to average. Yet 11 inches is more than three times the city’s historical average for the entire month of March. And this storm is expected to bring half an inch.
“Any progress is progress,” Murdock said. “But we’re still less than half of normal for the water year. Adding half an inch isn’t going to change that by too much.”
On Monday, San Francisco had received 39% of its historical rainfall for that date. Other cities were in similarly dry predicaments, with San Jose at 37% of normal precipitation and Oakland at 38%. Sacramento was at 43%, Los Angeles at 39% and San Diego at 44%. Forecasts call for dry weather Thursday, Friday and Saturday, which some chance of modest rain again perhaps on Sunday. But the winter weather season traditionally ends at the beginning of April.
Water agencies around Northern California say they will make decisions on summer water restrictions — whether to ask for voluntary cutbacks or announce mandatory restrictions with penalties for excessive use — in late March and early April.
Big picture, California should expect high fire risk again this summer, Lund said. Farmers will be pumping more groundwater from underground basins that still haven’t fully recovered from the 2012-2016 drought, he added. Urban areas are somewhat better prepared for drought now than during the last five-year drought, he said, because water use in many places is still below where it was before that drought, due to conservation measures like paying people to remove lawns and offering rebates to install more waterefficient toilets, dishwashers, washing machines and other appliances.
“For most people in urban areas, they aren’t going to see it in a profound way this summer,” Lund said. “It will affect your lawn watering and make your energy bills go up a little because we won’t have as much hydropower. But it will affect rural areas that rely on groundwater, and wildfire season will probably start early.”
Hang on to your masks, he added. Even after most of society is vaccinated, you may need them for wildfire smoke this summer and fall.
For now, the storm moving in from the Pacific Northwest is expected to bring rain beginning Tuesday morning, starting first in the North Bay, and sweeping down through the rest of the Bay Area by lunchtime. Rain is forecast to continue, with heavy bursts at times, through Tuesday night and most of Wednesday before clearing up Thursday.
The Sierra Nevada snowpack, the source of nearly one-third of California’s water supply, was at 58% of normal on Monday. The National Weather Service issued a winter storm watch for the Sierra Nevada and Lake Tahoe area from noon Tuesday to 6 pm Wednesday. Difficult driving conditions and chain controls are expected on Sierra roads during those two days with 1 to 2 feet of snow possible for the storm, which could bump the overall snowpack up into the low-to-mid 60% range.
As important for the state’s water picture, reservoir levels are below average around much of the state. A drenching winter in 2017 filled them, causing flooding in some areas, like Oroville Dam. But after a dry year last year, levels have fallen.
Shasta Lake, the state’s largest reservoir, near Redding, is currently 50% full, or 67% of normal for this time of year. Lake Oroville, in Butte County, is 39% full, or 54% of normal. New Melones Lake, in the Sierra Foothills of Calaveras and Tuolumne counties, is in better shape, at 65% full, or 105% of its historic average. And San Luis Reservoir, near Los Banos, is 57% full, or 66% of its historical average.
With the worst from COVID-19 pandemic probably already passed, Californians and residents in other Western states will need to address another crisis, water scarcity, this summer.
According to the U.S. Drought Monitor, a weekly federal report, 90% of California is in at least a “moderate drought,” now while 29% is in an “extreme drought,” including Napa, Solano, Inyo and San Bernardino counties, along with much of the Sacramento Valley.
“Gosh, I was hoping we weren’t going to have another drought this year,” Lund said. “It would have been nice to have a year to relax. But I’m afraid the world doesn’t seem to work that way.”