First storm of week brings rain to the Bay Area, treacherous travel conditions in the Sierra Nevada

Travelers hoping to get a few runs at a Lake Tahoe ski resort this weekend may want to get their driving done before Wednesday night, according to the National Weather Service.

The first in a string of storms was expected to continue to bring showers to the Bay Area and dump several feet of snow on the Sierra Nevada, making mountain travel precarious with significant delays and possible white-out conditions.

The storms began Tuesday after a low-pressure system from British Columbia moved south over the Pacific Ocean and off the coast of the Oregon-California border, according the weather service. The wet pattern continued into Wednesday morning; a lull in the rain was expected in the afternoon and evening. The rain should pick back up Wednesday night into Thursday morning before tapering off again in the afternoon, forecasters said.

A second weather system will travel into the Bay Area Friday night into Saturday, bringing another round of rain expected to last until at least Tuesday.

“It looks like there’s a big weather storm — a trough that’s offshore — and it’s just kind of stuck there,” said NWS forecaster Sean Miller. “Unless we get a big pattern change, we’ll be in the scenario where we have daily rain chances. We’re going to stay in this wet pattern at least into the foreseeable future.”

Throughout the week, lower elevations in the Bay Area, including in the East Bay, South Bay and the interior San Francisco Bay, could see 1 to 3 inches of rain. Coastal ranges, including the Santa Cruz mountains and the North Bay mountains, are expected to receive up to 5 to 6 inches of rain and the North Bay valleys will get between 2 to 3.5 inches of rain.

As of 8:55 a.m. Wednesday, 24-hour precipitation totals included: nearly one inch at Ben Lomond, 0.85 inches at Middle Peak at Mount Tamalpais, 1.02 inches at Kentfield, 0.74 inches in Redwood City, 0.67 inches in downtown San Francisco, 0.58 inches at Oakland International Airport, 0.16 inches at San Jose airport and 1.17 inches at Mt. Diablo.

Temperatures were expected to reach highs in the 50s and 60s and lows in the 40s — a warmer trend after the Bay Area saw overnight freezing temperatures in the past few weeks.

The “breeziest” period was expected to be on Friday night, with higher hills expected to see gusts up to 30 to 40 miles per hour.

Several inches of snow had already fallen in the Lake Tahoe region by Wednesday morning. The storms this week were forecast to dump 48 to 60 inches of snow on Echo Pass, 24 to 36 inches on Tioga Pass and 80 to 100 inches on Donner Pass, Carson Pass, Ebbetts Pass and Sonora Pass.

Several feet of mountain snow are possible between this afternoon and Monday. Expect chain controls and holiday travel delays. Hazardous travel conditions are expected, and mountain travel is highly discouraged over the weekend. #CAwx pic.twitter.com/CjFfY9IvtH

— NWS Sacramento (@NWSSacramento) December 21, 2021

Snow levels will hover between 5,500 to 6,500 feet on Wednesday before dipping to around 2,500 to 3,500 feet on Thursday.

Dangerous road conditions, especially on Interstate 80 and Highway 50, could make mountain travel treacherous this weekend, according to the weather service. The storms could result in slick roads, significant delays, reductions in visibility and the possibility of white-out conditions, especially with wind gusts on Thursday expected to blow snow around the highways.

The weather service said the best time for mountain travel would be before Wednesday night and “highly discouraged” travel after that through the weekend.

The storms come after a long dry spell in November and an atmospheric river storm earlier this month, when torrential downpour and strong wind gusts prompted evacuations, flash flood watches and drenched downtown Oakland and San Francisco in 3.55 and 2.67 inches of rain, respectively.

“We had a blocking pattern which kept weather systems from moving into our area in November but now it’s changed … (allowing) weather systems to keep bringing us chances of rain,” Miller said. “Until that pattern changes, we’re going to stay in this weather regime we’re in right now.”

There will be less potential for debris flows and mudslides than in previous storms for the burn scar areas from wildfires, Miller said, since these storms will bring persistent rain over a long period of time, instead of a one-shot atmospheric river storm that drenches the region in one go.

“It’s happening over a longer period that works in our favor,” Miller said. “We’re not expecting any big widespread issues but there could be local issues in areas with poor drainage where you could see water on roadways and smaller, shallow mudflows in hilly spots. It’s more of the nuisance variety. Of course, if you’re where that happens, it’s not going to feel like much of a nuisance to you.”