After 43 days of bone-dry weather, San Francisco was getting its first rain Thursday night, the start of a storm that's expected to drench Northern California and the Pacific Northwest into the middle of next week.
But the soaking won't do much to relieve California's historically parching drought, forecasters said Thursday.
Coastal and northern parts of the Bay Area could get as much as 6 inches of rain by Sunday, with isolated parts of the North Bay possible getting more than 9 inches, according to the National Weather Service, which issued flood watches and small watercraft advisories for the area through late Friday night.
Minor flooding was reported in Eureka, in Humboldt County in the northwest corner of the state. But the worst of it will come Friday, when heavy rain is expected to be accompanied by winds up to 30 mph with gusts above 40 mph.
"The highest potential for any flooding will be in the North Bay" on Sunday as a second round of rain falls on ground saturated by the rain Thursday night and Friday, said Jeff Ranieri, chief meteorologist for NBC Bay Area.
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Even heavier rain is expected north, along the Oregon and Washington coasts. The National Weather Service forecast as much as 10 inches in the Olympic Mountains of northwest Washington by the weekend, with totals through next Wednesday approaching 17 inches in higher elevations of Northern California and in Washington near the Canadian border.
"This is going to be a Thursday-through-Monday rain event," said Ari Sarsalari, a forecaster for The Weather Channel. "That entire time, it's pretty much going to rain," likely causing significant landslides, mudslides and flooding.
Meteorologists call the warm, wet system an "atmospheric river." NBC News' Al Roker described it as a "conveyor belt of the jet stream" pulling moisture to the north, causing "a parade of storm after storm after storm."
In the Santa Cruz Mountains along the San Francisco Peninsula, tree trimmers were booked solid paring branches that could knock out power lines or tumble onto homes in the high winds.
"They act as big sails," Ralph Miljanich, who lives in the area, told NBC Bay Area. "These branches catch the wind and the trees will move 20 feet from side to side."
At Healdsburg Vintage, an antiques store in Sonoma County, owner Constance Newton already had sandbags in place by mid-afternoon.
San Francisco, which got no precipitation at all in January for the first time in 165 years, is part of the 40 percent of California that's under "exceptional drought" conditions, according to a National Weather Service assessment released this week.
The storms might have a small impact on the crushing dry conditions, Sarsalari said, but "it's going to take a whole lot more than that for a long period of time to put a real dent in the drought."