Heavy rainfall is expected to soak the region through at least Thursday night. Add melting snowfall, and there’s a heavy flood danger throughout Western Washington.

“It’s going to rain a lot,” Johnny Burg, a meteorologist with the National Weather Service in Seattle, said Tuesday.

The service issued a flood watch and a wind advisory for the South Sound, which will last through Thursday. About 3 inches of rain were expected in the lowland areas in Pierce County, with winds of 25 to 30 mph, gusting to 50. Damage began Tuesday afternoon with downed power lines and trees across area roads.

But more serious damage is expected in the mountains.

Some areas on the Pacific slope of the Olympic Mountains could get up to 20 inches of rain. The slopes in saturated areas are at a high risk for mudslides, and the runoff will surge and possibly cause flooding in lowland areas around rivers.

With more than a foot of rain in the forecast, Olympic National Park officials closed access to the Hoh and Queets river valleys Tuesday afternoon as a safety precaution, said chief ranger Kevin Hendricks. In addition, park staffers doing spotted owl surveys were called out of the backcountry because of avalanche danger.

The forecast Tuesday afternoon called for rainfall totals by tonight of 6 to 10 inches on the coast and up to 20 inches on the west-facing slopes of the Olympics.

The closures are necessary “so we can remove the public from areas that might be blocked by rising rivers and fallen trees,” Hendricks said.

The U.S. Geological Survey gauge on the Hoh River at U.S. 101 showed stream flows steadily rising Tuesday afternoon, reaching 4,230 cubic feet per second at 3:15 p.m.. Flows were as low as 1,670 cfs Sunday afternoon.

John Preston, a ranger based at the Hoh Rain Forest Visitor Center, said the storm is a dual threat. Not only is a lot of rain forecast, but also the accompanying warm temperatures will melt much of the snow that’s fallen in the last month.

“They’re calling for 12 inches of rain,” Preston said. “That would be a major flood event if that happens. So far, they’ve been spot on.”

A foot of rain would be comparable to the December 2007 storm that caused flooding in Chehalis and shut down Interstate 5.

“It’s going to be wild and woolly in the Hoh the next few days,” Preston said.

Mount Rainier National Park was expected to see much less rain, but officials were still watching the rainfall gauge and area streams and looking for any trees fallen over roadways.

Pierce County officials were preparing for flooding on the Puyallup, Nisqually and Carbon rivers, and anyone who lives in those areas should be prepared, said Sheri Badger, spokeswoman for Pierce County Emergency Management.

“Keep your ears and eyes peeled for what the rivers are going to do,” she said. “Prepare for flooding. Make sure you have an alternative place to go.”

The Pierce County Emergency Operations Center was to open today at 8 a.m., and officials have placed a sandbagging machine in Orting. Sandbags are available to the public at local fire stations.

The main concern for county officials are the Puyallup and Carbon rivers because of the population along the basins. There are shelters available and officials are prepared to notify residents when they need to evacuate, Badger said.

The King County Flood Warning Center opened Tuesday afternoon to keep an eye on the storm. In Thurston County, emergency manager Kathy Estes wants those who live in river basins to be prepared for evacuation.

“We don’t know how serious the flooding might become, but the projections show possible significant flooding along the Chehalis, Deschutes and Skookumchuk Rivers,” Estes said in a statement. “That means area residents should be prepared to leave their homes on short notice.”

Although heavy rains are typical this time of year, the strength of this storm front stands out.

“This is not exactly your typical thing to have happen this time of year,” Burg said. “There’s just not going to be very good weather for the next couple of days.”

Brian Everstine: 253-597-8374

Jeffrey P. Mayor: 253-597-8640