Bay Area reservoirs yet to ‘panic’ over January’s last expected storm

The last storm expected until at least Groundhog Day rolled into Northern California on Wednesday afternoon, bringing moderate rainfall to the Bay Area and heavy snowfall to the Sierra.

Weather wonks welcomed the deluge, with some of the region’s reservoirs falling far short of normal levels and the state’s recent five-year drought still top of mind.

Brian Mejia, a meteorologist with the National Weather Service in Monterey, said the heaviest rains were likely to subside by Wednesday night, but showers likely would linger through Thursday and Friday morning. San Francisco was expected to receive a third to two-thirds of an inch of rain Wednesday, while the North Bay could get 1 to 2 inches, Mejia said.

San Francisco should see heavy rain on Wednesday, according to the National Weather Service. San Francisco should see heavy rain on Wednesday, according to the National Weather Service. Photo: Lea Suzuki, The Chronicle Buy photo Photo: Lea Suzuki, The Chronicle Image 1 of / 48 Caption Close Bay Area reservoirs yet to ‘panic’ over January’s last expected storm 1 / 48 Back to Gallery

The extended forecast, however, doesn’t feature any rainfall until next month.

“This will be the last storm for a while, at least as far as the next 10 days are concerned,” Mejia said. “We are entering a sort of dry period as far as our forecast period. Dry and mild weather will return to the region.”

That could spell trouble for reservoirs in the South Bay, which sit at just 52 percent of the average, according to the Santa Clara Valley Water District.

“This isn’t good, so hopefully we’ll get some storms,” spokesman Marty Grimes said, noting that the agency in charge of flood protection and drinking water for 1.9 million people has yet to go into “panic mode” because groundwater levels remain high.

San Francisco’s total reservoir system currently sits at 72 percent, not too far below its normal level of 79.4 percent, said Betsy Lauppe Rhodes, a spokeswoman for the San Francisco Public Utilities Commission. That number is skewed a bit by Cherry Reservoir, which was recently drained to just 7.4 percent of capacity as part of a valve replacement project, Rhodes said.

“We’re not in the deluge area, but we’re not in the dry area,” Rhodes said. “Our water managers are cautious but by no means panicked.”

In the East Bay, water storage levels are average, but rainfall has been lower than normal.

“As of (Tuesday) we were at 77 percent of average for precipitation levels,” said Andrea Pook, a spokeswoman for the East Bay Municipal Utility District. “Certainly, December was unproductive and we’re not quite at normal yet, but a couple good storms could change that pretty quickly.”

Meanwhile, the Sierra snowpack sits at an anemic level for January. As of Tuesday, it measured just 26 percent of the annual average.

“That’s not good for the third week in January,” said Scott McGuire, a meteorologist for the National Weather Service in Reno.

The snowpack has particularly suffered at lower elevations, he added, as many of the early season storms have been relatively warm. The weather system that moved on the Bay Area this week has been colder, though, which should help fortify the base.

“We’re looking at snow accumulation of 8 to 16 inches, from Lake Tahoe level up,” McGuire said. “This is a cold and quick-hitting system with pretty high snowfall rates.”

The highest peaks could get between 2 and 3 feet of snow, he said, which would make for a good weekend of skiing and snowboarding at some of the region’s resorts.

“Snow levels are looking phenomenal,” said Sam Kieckhefer, a spokesman for Squaw Valley-Alpine Meadows Resort, which is 7 miles northwest of Lake Tahoe. “We should see between a foot and two feet toward the top.”

A spokesman for Heavenly Mountain Resort, located in South Lake Tahoe, said the resort expects 7 inches of snow.

“This should hopefully bump (the snowpack) up a bit,” McGuire said.

While the first few weeks of January brought plenty of rain to San Francisco — 4.71 inches, compared with an average of 3.32 inches — the progress in restoring Northern California’s reservoirs and snowpack has been tempered by an incredibly dry few months. Rainfall between Oct. 1 and Jan. 23 was just 66 percent of the average for that time period.

A winter weather advisory remains in effect for the Sierra Nevada until 4 p.m. Friday, as the region prepares for cold, gusty winds blowing off the peaks.

The National Weather Service predicted there could be squalls up to 100 mph and urged drivers to exercise caution in the face of limited visibility and possible whiteout conditions. Travel delays are likely in the area.

As the first official month of winter came to a close this week, meteorologists are turning their attention to the weeks ahead.

“February is typically wet,” Mejia said. “So we should probably see a couple of storms then.”

Sophie Haigney is a San Francisco Chronicle staff writer. Email: sophie.haigney@sfchronicle.com Twitter: @SophieHaigney