SEATTLE -- Forecasters said a Pacific storm has aimed a huge wave of moisture at Washington that has sparked a flood watch for most rivers, could bring up to 15 inches of precipitation in the mountains and 3 to 8 inches of rain to the lowlands, could greatly increase the risk of mudslides and could bring extreme avalanche dangers in the mountains.

The storm is also forecast to bring wind to the greater Seattle area, and a wind advisory is in effect until 10 a.m. Wednesday.

"We have a lot of water headed in our direction," said Ted Buehner of the National Weather Service. "It doesn't look good at this point."

Soil moisture is already moderate after rainfall over the past two weeks, and the multiple inches of rain expected by Thursday will put extra pressure on landslide-prone areas.

KIRO 7 Eyewitness News meteorologist Rick VanCise said a combination of heavy rain and higher snow levels of 7,000 to 8,000 feet in the mountains will create rapid rises in rivers and small streams across Western Washington and bring danger of flooding.

A flood watch is in effect until Friday for most of Western Washington and there is extreme avalanche danger in the Olympics and Cascades into Wednesday night.

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"The avalanche danger is as high as it gets," said Buehner.

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Forecasters said that in areas outside of Seattle, total rainfall from the storm could be 3 to 8 inches in the lowlands and 10 to 15 inches in the mountains.

Asked about the flooding possibilities for the Chehalis-Centralia area, Buehner said, "I-5 may go under water for a period of time."

The Weather Service said the landslide threat will extend into the weekend.

VanCise said the rain will turn heavier by this evening.

The potential for river and small stream flooding will increase Tuesday night and Wednesday.

The Weather Service also warned of the load hazard on roofs brought by heavy rain falling on top of structures already covered with snow.

The heavy rainfall is expected to end on Thursday.