The strongest atmospheric river to hit California in months is expected to dump rain and snow across the northern half of the state this week — also bringing high winds and possible flooding — before eventually making its way south, say forecasters.

“This will be the first major storm of the season,” said Dial Hoang, a meteorologist with the National Weather Service in Monterey. The low-pressure system off the Pacific Northwest coast that is powering this storm will quickly strengthen on Tuesday, reaching the threshold of a bomb cyclone – which will dramatically increase its moisture content and strength.

Parts of Northwestern California will experience flooding and high winds starting Tuesday, when persistent rain is expected to begin, falling 4 to 8 inches over several days. Wind gusts of up to 120 km per hour can occur on some ridges.

“A strong storm system will bring heavy mountain snow, rain and high winds to the Pacific Northwest and Northern California through the week,” the National Weather Service Weather Prediction Center warned. “Numerous flash floods, hazardous travel, power outages and tree damage can be expected as the storm reaches maximum intensity” on Wednesday.

But after the initial peak, the system is expected to persist into the weekend, with a second wave of rain extending further south across most of the Bay Area, reaching the Central Coast and possibly reaching parts of Southern California.

The North Bay is forecast to receive 1 to 3 inches of rain Wednesday through Sunday, while some areas could see up to 11 inches of rain, according to the National Weather Service forecast discussion. Officials are hopeful the region will experience only minor flooding as few areas have seen real rainfall this season, so soils should be able to absorb significant rainfall.

But some parts of the North Bay “will likely become saturated very quickly,” Dalton Behringer, a National Weather Service meterologist, wrote in the daily forecast. “Even if we don’t see too much flooding on Wednesday, I wouldn’t be surprised if the flooding gets worse with the second wave on Friday, even if less rain is expected at that time.”

Some light rain could reach Southern California by the weekend, but it likely won’t be enough to eliminate the threat of wildfires by year’s end.

“It won’t be what Northern California will be, but every little bit helps,” said Bryan Lewis, a meteorologist with the National Weather Service in Oxnard. “It’s probably not enough to get us completely out of the woods yet (in terms of fire issues).”

A winter storm watch has been issued for the Northern Sierra and other Northern California mountains above 3,500 feet, where four to six inches of snow is possible Tuesday and Wednesday.

This storm marks the start of what appears to be a period of wet weather across the state, with above-average precipitation expected to continue until at least Thanksgiving, according to the National Weather Service’s Climate Prediction Center.

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This story originally appeared in the Los Angeles Times.