California entered 2017 hoping a wet winter could end the state’s six-year drought.
Be careful what you wish for.
Northern California, the San Joaquin Valley and foothills are bracing for potential flooding this weekend, as a massive weather system known as an atmospheric river builds off the coast. Forecasters say that by Monday, rainfall and river flows could reach totals not seen in more than a decade.
Already, some regions north of Sacramento are issuing voluntary evacuation orders and several northern counties, including Sacramento, are readying sandbag stations.
In Eastern Madera County, sandbags are available at several locations through the Madera County Sheriff’s Office of Emergency Services. On Thursday, Paul Lassos and Jacob Wheeler, facilities director and assistant director at Sugar Pine Christian Camp, were taking advantage of the free bags and sand at Madera County Fire Station 12 in Oakhurst.
“We need whatever we can get for this storm,” said Lassos, noting Sugar Pine is a nonprofit organization. “It’s fantastic that we have the sand and bags here when we need them. We’ve already got some leaks in some buildings, so hopefully this will help us make it through the rain.”
The National Weather Service issued a flood watch Thursday, stretching from Saturday afternoon through Monday, for 24 counties. Officials warned of flooding in streams and creeks that normally aren’t much more than a trickle. The Sacramento River is expected to roar with its highest flows since 2006 and send a huge gush of water into the Yolo Bypass, the massive floodplain west of Sacramento engineered to prevent the city from getting swamped.
Flash flood warnings
The area of the state likely to be hardest hit is farther south. If the storm follows its current trajectory, forecasters say it could send an impressive - and possibly dangerous - cascade of water to the drought-ravaged southern Sierra Nevada and San Joaquin Valley. Fresno, Madera, Mariposa, Tulare and Tuolumne counties are under a flash-flood warning.
Any water is welcome news to a region home to some of the most iconic images of California’s lingering drought: millions of dead trees in the mountains near Yosemite National Park, and dusty, impoverished farm communities whose wells have gone dry.
But the prospect of too much water too fast has officials on edge, nonetheless.
“We definitely welcome the rain but wish it were distributed more evenly,” said Reed Schenke, an engineer at Tulare County’s Resource Management Agency.
An atmospheric river is a weather phenomenon in which a narrow band of strong wind sweeps eastward across the Pacific Ocean, gathering moisture as it goes. These storms often make landfall in California and historically have produced some of the state’s worst weather-related disasters.
A single atmospheric river can transport 10 to 20 times the flow of the Mississippi River. The state typically sees five or six of these storms every year, and while potentially damaging, they also provide as much as half of California’s annual rainfall.
Central California’s rainfall has already been 35% above normal this season, and this storm could be particularly powerful. Michelle Mead of the National Weather Service said areas south of Interstate 80 could see their largest rainfalls in 15 to 25 years. “It’s going to hit the foothills quite hard and the eastern Valley pretty good,” she said.
In Eastern Madera County, meteorologists said some areas could get up to seven inches of rain by the time the storm passes on Monday.
The flood risks are exacerbated by warm temperatures in the mountains, which could send a rush of snowmelt downstream. While the storm is expected to start out cold, bringing several feet of snow to Sierra ski resorts, temperatures will quickly warm up.
“By the time Sunday rolls around it should be rain all the way up to 8,000 feet,” Mead said.
Also problematic from flood risks are the potential for rock slides and road closures. On Friday morning, the stormy conditions necessitated a Caltrans crew be sent to the Rocky Cut area of Highway 41, north of Road 208, to check on a potential rock slide.
Caltrans spokesman Cory Burkarth said that turned out to be a large puddle of mud, and traffic was not delayed, but the area would be surveyed throughout the day to prepare for any possible mudslides or other effects.
“Our guys are ready for this storm,” Burkarth said. “They may have to work a lot this weekend, but they’re ready for it.”
In Coarsegold, a rock slide did take place Thursday and caused closure of the highway for about an hour, when a boulder fell on a moving big rig truck.
For updates on road conditions in Eastern Madera County, call Caltrans at (559) 444-2409 or toll free at 1-800-427-7623.
It also appears more likely that Yosemite National Park will temporarily close its gates. On Friday, officials announced all roads to Yosemite Valley would close at 5 p.m. that afternoon.
In a release issued earlier in the week, park officials said they’ll monitor forecasts and decide in the next few days whether to close all entrances out of safety concerns. They added the park could see floods reminiscent of 1997, when devastating flows caused millions of dollars in damages and closed the park for two months. Those with plans to visit the park are strongly encouraged to consider alternate arrangements until the storms pass next week.
Badger Pass Road was scheduled to be closed at 5:30 p.m. Friday, alongside a full closure of Yosemite Ski and Snowboard Area until the weather is clear.
For updating road conditions in Yosemite, dial (209) 372-0200 and press the number 1, or visit www.nps.gov/yose.
Storm a boost for reservoirs
The rain likely will melt a portion of the precious Sierra snowpack, which on Thursday hit slightly above average levels for the first time this winter. And that won’t help the state’s water supply in the long term. A healthy snowpack acts as an additional set of reservoirs, bolstering the state’s overall water supply. In a decent year, the snowpack contributes about 30% of the state’s supplies, gradually refilling reservoirs and canals through summer and fall.
When winter precipitation falls as heavy rain rather than snow in the mountains, the state’s water network can get overwhelmed. With the ground already saturated, much of the rainfall will run off into rivers and streams – and too quickly to be safely stored in many reservoirs.
U.S. Bureau of Reclamation officials increased releases from Folsom Lake, pouring more water into the American River in anticipation of huge amounts of water cascading into the reservoir from upstream.
At Friant Dam in Fresno County, for the first time since 2011, water is spilling over in a controlled release that began Tuesday. Millerton Lake was 73% full on Thursday at 378,000 acre feet.
Other key reservoirs in the state still have plenty of room, particularly south of the Sacramento-San Joaquin Delta, stark evidence of the drought. New Melones Reservoir on the Stanislaus River, the state’s fourth-largest reservoir, was just one-quarter full Thursday. The hope is it could fill substantially if the central Sierra gets inundated with rain.
Operators of the state and federal pumping stations in the Delta, which deliver Northern California water to the San Joaquin Valley and millions of Southern Californians, also plan to ramp up pumping operations to capacity over the next few days. That, along with unusually heavy rain south of Sacramento, could bolster reservoirs and groundwater basins in the San Joaquin Valley and Southern California, bringing long-awaited relief to some of the driest areas of the state.
Mark Evan Smith of the Sierra Star contributed to this report. He can be reached at email@example.com.