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Michelle Harrison and Bill Donnelly battle wind and rain as they enter city hall in San Jose, Calif. on Thursday, Feb. 6, 2014. A cold front arrived in the Bay Area bringing the first significant rainfall of the season. (Gary Reyes/Bay Area News Group)
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The Bay Area got a pretty heavy soaking Thursday morning -- and it's only the beginning, with another storm expected to hit Friday.

More than .80 inches of rain fell Thursday in some areas around the region, creating slippery roads and prompting a warning from the California Highway Patrol urging motorists to slow down and use caution.

Friday's storm off the California coast could bring several inches of rain, said Bob Benjamin, forecaster for the National Weather Service. The two storms are expected to double the amount of rainfall that the Bay Area has seen all season.

"We expect this next storm to really dump a lot on us," Benjamin said. "It's shaping up to be a very wet weekend."

Forecasters say a stronger system moving in Friday morning will dump as much as 6 inches of rain on Bay Area mountains and 2 feet of snow in the Sierra over the weekend.

More than an inch of rain fell Thursday in the higher elevations around the region, creating slippery roads and prompting a warning from the California Highway Patrol to slow down and use caution.

According to the weather service, Santa Rosa saw a total rainfall Thursday of .84 inches, the highest of any other Bay Area city by 4 p.m. when the service totals its rainfall for the day.

In Contra Costa County, .70 inches fell in Concord San Jose and Oakland were both soaked with .62 inches, though Fremont had the heaviest rain in Alameda County at just under an inch.. San Francisco received .74 inches, while Moffett Field, near Palo Alto, received .54 inches.

While the overdue wet weather is welcome, forecasters say California needs much more rain and snow to make up for one of the driest rainy seasons so far.

"I won't say the storm door is open, but maybe we'll get into more of a routine storm pattern now," Benjamin said.

The rain, coming on the heels of such a dry winter, made for difficult travel conditions.

The long period of drought made roads slicker than normal and, according to the CHP, created optimum conditions for hydroplaning. The wet conditions were blamed for a big-rig truck jackknifing across Interstate 80 near Richmond early Thursday, blocking three lanes of traffic in both the eastbound and westbound directions.

Drivers were reminded that turning on their lights is mandatory in the rain and were urged not to tailgate. In case of a skid, drivers should steer gently in the direction of the skid without braking heavily.

"People just need to use extreme caution and go slow," CHP Officer Ron Simmons said. "It's gonna be slick."

Air travel was also impacted. San Francisco Airport spokesman Doug Yakel said 47 arriving and department flights at SFO had to be canceled by 1 p.m., most of them flights up and down the West Coast. Other flights were leaving an average of 60 minutes late.

"The storm isn't that bad, but it's creating those visibility issues we sometimes have when we get these conditions out there," Yakel said.

Benjamin said the steady pace of the showers, coming on fairly dry land, will allow vegetation to absorb the rain without concerns of landslides or flash flooding.

"The second storm could bring what we call, 'nuisance flooding,'" Benjamin said. "You may see some ponds on the highways, and you might get some flooding with the smaller streams. But most of that will probably be in the North Bay more so than (in Santa Clara, Contra Costa and Alameda counties)."

Staff writer Julia Prodis Sulek contributed to this story. Contact Rick Hurd at 925-945-4789 and follow him at Twitter.com/3rdERH.