Federal Express driver Ramiro Saldana helps Gabrielle Dorsett with sandbags as she prepares to place them in front of her business, Wednesday Dec. 10, 2014 in Santa Rosa, Calif. Northern California residents are bracing for a powerful storm that could be the biggest in five years and which prompted the National Weather Service to issue a high wind and flash flood warning. The storm is expected to arrive Wednesday and pelt the region through Thursday. (AP Photo/The Press Democrat, Kent Porter)

SAN FRANCISCO - A storm predicted to bring torrential rains and hurricane force winds pushed across parts of Northern California early Thursday, after residents stocked up on supplies, schools cancelled classes, and communities prepared for possible emergencies.

Moderate rain and gusty winds began hitting the area north of San Francisco late Wednesday with heavier rain expected in coming hours across the across the region, the National Weather Service said.

As much as 8 inches of rain could fall on coastal mountains over a 24-hour period starting late Wednesday, the weather service said.

The storm is "slowing going to be advancing toward the south through the day today," weather service meteorologist Charles Bell said early Thursday.

"We're also seeing winds pick up," he said, noting gusts of up to 50 mph were hitting some buoys off the coast.

Bell predicted major elements of the storm would hit the San Francisco Bay area by late morning.

The storm is expected to be one of the windiest and rainiest in five years and could also cause debris slides, especially in areas affected by this year's intense and widespread wildfires. Big waves are expected along the coast.

"It's a short amount of time for that amount of water," weather service forecaster Diana Henderson said. "We are anticipating some localized flooding, maybe some downed trees and downed power lines. It could have an effect on a wide range of people."

Residents rushed to buy emergency supplies, with some stores running out of water, batteries and flashlights. Some cities announced on their Twitter accounts they had no sandbags or sand left by Wednesday evening.

"Sandbag locations in CH are closed. All bags and sand has been taken. All sand & bags were taken in 3hr period," the Citrus Heights Police Department tweeted Wednesday.

Ski resorts in the northern Sierra Nevada could get more than 2 feet of snow.

The storm is expected to later pound parts of Southern California, before a weakening system moves east through Nevada, Idaho, Arizona and New Mexico. Those states could get rain and snow, but nothing like what California is expected to experience, forecasters say.

In San Francisco, where as much as 4 inches of rain was forecast, crews cleared storm drains and removed loose rocks from a hillside to prevent them from crashing down. Residents were advised to sweep up leaves and debris in front of their properties to prevent them from clogging drains.

"We have crews working starting tonight in 12-hour shifts," said Rachel Gordon, a spokeswoman for San Francisco's public works agency. "It will be all hands on deck."

Public schools in several Bay Area cities, including San Francisco, Oakland and Berkeley, and some private schools were cancelling Thursday's classes.

Wind gusts of up to 70 mph were expected on mountain tops, creating possible blizzard conditions in the Sierra. Rain, pounding surf and gusty winds were forecast for Southern California starting Thursday evening.

The weather service issued a high-surf advisory from the Central Coast to Ventura County, saying "waves will over-top jetties and sea walls at times" and "will potentially wash into low-lying beach areas or parking lots."

In California's agricultural heartland, farmers were looking forward to the dousing after three consecutive dry years. Parts of the state have experienced above-average rainfall this year, but not enough to make much of a dent in the drought.

James McFarlane, a third-generation farmer in Fresno County, said workers would have to stop picking citrus crops during the storm, but rain this time of year makes fruit bigger, allowing it to fetch higher prices.

"If we're not getting some Mother-Nature-dictated time off out in the field, that probably means we're going to have a hard time finding surface water in the warmer months," he said.

The rain and the snow in the Sierra Nevada fills reservoirs that supply irrigation water during hot, dry months.

Farther north, a series of strong weather fronts with high winds and heavy rains could lead to flooding and landslides this week in western Washington state.

The weather service expects as much as 14 inches of rain between Monday and Thursday in the Olympic Mountains west of Seattle.

Saturated soils will bring the risk of mudslides, while winds could topple trees.

High winds were also forecast in Oregon.

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Associated Press writer Scott Smith in Fresno contributed to this report.

News from © The Associated Press, 2014