Biggest storm of 2019 to hit Bay Area, Sierra due to atmospheric river

The strongest storm of the year is expected to dump torrents of rain Wednesday and Thursday on the Bay Area and sheets of snow in the Sierra. A cold front will collide with an atmospheric river — a band of moisture that forms over the ocean — to squeeze out varying forms of precipitation as the system travels over land, officials said.

But after this week’s expected deluge, the weather will do what it does best. It will change.

Skies will likely be dry on Friday and Saturday, perhaps wet on Sunday, and then dry for a while after that. Ryan Walbrun, a National Weather Service meteorologist, said “a lot of the long-range indications show dry weather.”

He added, “I don’t want to say through the end of the month, but through at least late January.”

One forecaster is going even further, though, saying the Bay Area will dry out and stay dry up until the middle of next month.

Long-range predictions — anything beyond a few days to a week — are notoriously iffy, but climate scientist Daniel Swain, an assistant researcher at UCLA who publishes the California Weather Blog, said he expects “unususally warm, dry and quiescent weather” in Northern California for weeks, perhaps until mid-February.

“It does appear that California will rapidly dry out after this week’s storms and will enter a prolonged warm, dry period for the foreseeable future,” Swain said.

On Wednesday, residents in the North Bay can expect heavy rain to impact their morning and evening commutes.

“As we get into the Wednesday afternoon commute, we really expect heavy rain over the entire Bay Area,” Walbrun said. “I expect we’ll have reports of roadway flooding and small creeks and streams will rapidly rise and cause issues.”

A flash flood watch is in effect for most of the Bay Area from Wednesday afternoon to late Wednesday night, officials said.

Atmospheric rivers are a regular occurrence, but Walbrun said this week’s storm will be the strongest of the season. Forecasters expect 1 to 2 inches of rain to fall in a six-hour stretch Wednesday afternoon and evening in lower elevations, with higher areas seeing 2 to 4 inches.

The weather service issued a high wind watch for the region Wednesday afternoon through late in the night, and southerly winds could reach 30 to 40 mph with gusts up to 60 mph.

In the Sierra, ski resorts are gearing up for blizzard conditions and officials expect more than 2 feet of snow over the next few days. A winter storm advisory was issued for the area Tuesday and a winter storm watch goes into effect Wednesday night until Thursday night.

Cassie Leahy, a meteorologist with the National Weather Service in Reno, echoed transportation officials’ warnings against travel to Lake Tahoe and surrounding areas on those days.

“Heavy, wet snow with the winds can lower visibility pretty quickly, and that’s definitely not something people want to be driving in,” Leahy said. “If you do have to travel, prepare for much longer travel times than usual. But it’s definitely not recommended.”

Caltrans enacted chain controls along highways 4 and 108 on Tuesday and advised drivers to check road conditions before heading to the mountains.

Meanwhile, ski resort officials are looking forward to fresh powder going into the holiday weekend. Liesl Hepburn, a spokeswoman for Squaw Valley and Alpine Meadows, said the additional snow means the resorts are less reliant on snow-making machines.

The area has already received 65 inches so far this month, she said, and on average it receives 70 inches in January. This week’s storm could put the resorts above average snowfall for the month, Hepburn said.

“Because we stay open later than other resorts in Tahoe, this does indicate a strong season, so we’re prepared to be operating in May, June or even July,” she said.

Ashley McBride and Steve Rubenstein are San Francisco Chronicle staff writers. Email: ashley.mcbride@sfchronicle.com, srubenstein@sfchronicle.com Twitter: @ashleynmcb @SteveRubeSF

This post was originally posted at https://www.sfgate.com/bayarea/article/Biggest-storm-of-2019-to-hit-Bay-Area-Sierra-due-13536452.php.

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