Storm to dump up to 3 feet of snow in 3 days for Tahoe region

Skiers take a snowy ride Monday up the slopes at Northstar California Resort near Lake Tahoe. Weather forecasters are expecting one to three feet of snow in three days. Skiers take a snowy ride Monday up the slopes at Northstar California Resort near Lake Tahoe. Weather forecasters are expecting one to three feet of snow in three days. Photo: Northstar California Resort Photo: Northstar California Resort Image 1 of / 13 Caption Close Storm to dump up to 3 feet of snow in 3 days for Tahoe region 1 / 13 Back to Gallery

A string of downpours converging on the Bay Area will also unleash as much as three feet of snow in three days on the Lake Tahoe region, forecasters said Wednesday.

If one more powerful storm arrives in March after this system departs, resort officials say, the Sierra mountains could easily see the best spring ski conditions since 2011. And that spells good news for California’s parched reservoirs, too.

“This new pattern is just going to open up the storm door for us this weekend,” said Bryan Allegretto, a snowboarder who writes forecasts for the Lake Tahoe region on the website OpenSnow. “There’s nothing to stop this storm. There’s nothing to weaken this storm.”

Showers will begin early Thursday morning in the Bay Area, but the bulk of powder farther northeast won’t arrive until Saturday evening. Above 7,500 feet, anywhere between one and three feet of snow will fall from Saturday to Monday, said Tony Fuentes, a National Weather Service meteorologist. Snow will also drop down to the lake level.

The atmospheric river sweeping into California will release rainstorms punctuated by weaker periods and several respites over at least 10 days. The snowstorm headed for the Sierra mountains will start out relatively warm but develop into a colder front by Saturday night.

"This could be that one-two punch that takes us over the top," said Kevin Cooper, a spokesman for Heavenly and Kirkwood resorts. "I would describe it as a miracle March."

The system, brewing in the north-central Pacific, is a welcome sign for skiers and state water officials alike.

Over the 10-day period starting Wednesday, the median inflow prediction for the state’s largest reservoir, Lake Shasta, is 475,000 acre feet of water, according to Peter Fickenscher, a hydrologist with California Nevada River Forecast Center. The second-largest, Lake Oroville, is expected to get 300,000 acre feet and Folsom Lake, near Sacramento, is looking at 250,000 acre feet. One acre foot is equal to about 325,900 gallons.

“There’s a lot of uncertainty. Storm patterns shift — they go north, they go south,” Fickenscher said. “But after a dry February, this is a very welcome change in the weather pattern.”

Inflows do not represent the total amount by which reservoirs will rise, since regulations from the U.S. Army Corps of Engineers require reservoir officials to release water if it reaches a designated threshold in order to avoid flooding. Folsom Lake, for instance, must stay 40 percent empty.

Major changes ahead! California could receive large amounts of rainfall these next 7 days. #cawx pic.twitter.com/s0mC6FVYL9 — NWS Sacramento (@NWSSacramento) March 2, 2016

In the last few weeks at Folsom, outflows needed to increase from 3,000 cubic feet per second to 7,200, according to Louis Moore, a spokesman for the U.S. Bureau of Reclamation, a federal agency that oversees water resource management.

The storm system is also expected to boost snowpack levels in the Sierra Nevada, but it’s too early to tell by how much, forecasters said Wednesday. The average water content of snow in the state on Wednesday fell to 82 percent of the historical average for this time of year — down from 114 percent one month ago.

Kimberly Veklerov is a San Francisco Chronicle staff writer. Email: kveklerov@sfchronicle.com Twitter: @kveklerov