00:57 - Source: CNN
Strong atmospheric rivers impacting the Pacific Northwest with heavy rain and snow
CNN  — 

A second person has died in a swollen Oregon waterway after atmospheric rivers have pummeled the Pacific Northwest with two bouts of more than 9 inches of rain.

One man was found dead Tuesday in Bronson Creek in Washington County, Oregon, the Washington County Sheriff’s Office said. His body was found “entangled in tree branches within the creek,” the sheriff’s department said. The man’s identity and cause of death have not been released.

On Monday, Multnomah County sheriff’s deputies found the body of a man who was swept away in Johnson Creek in Portland. Investigators have been trying to determine how the man ended up in the fast-moving water.

Ken Lambert/The Seattle Times/AP
A man wades through water outside of his home after the nearby Stillaguamish River flooded several houses in the neighborhood in the Arlington area of Seattle, Washington.

And the danger isn’t over, even if it’s lessening. Flood watches remain through Wednesday evening in parts of Washington and Oregon. Another 2 to 4 inches of rain was expected through Wednesday in parts of Oregon.

Floodwater forced the closure of dozens of roadways Tuesday in Washington state, where officials repeated a familiar but often ignored mantra: “Turn around, don’t drown.”

A landslide during torrential rainfall Tuesday forced the abrupt cancelation of all Amtrak service between Seattle and Portland. Service between the two hubs is suspended until Thursday morning, according to Amtrak.

For residents caught in flood conditions, the weather service recommends staying indoors or seeking higher ground if shelter isn’t available.

By late Thursday and Friday, storm activity is forecast to taper off across much of the Northwest – though showers and some high-elevation snow are still possible.

But the break from soggy weather may be short-lived, as another atmospheric river could thrash the region by the early weekend.

The exact strength and overall impact of this potential event should become clearer once this week’s atmospheric river ends Wednesday.

Washington DOT
The side of a rural highway in Washington state collapsed Tuesday due to intense water flows both over and under the roadway from heavy rain from atmospheric rivers.

Soaked soils exacerbate flood threat

The sequence of back-to-back atmospheric rivers, called an AR family, began Saturday and did not leave much of a break period before Monday night’s system began. This lack of recovery time is a major factor in the increased risk of flooding.

The first atmospheric river moved into the region Saturday and Sunday, dumping 7 to 9 inches of rain in spots from Northern California to Washington.

The second atmospheric river was even more severe and reached a Level 5 out of 5 in the far northwestern part of Oregon Monday night into early Tuesday morning.

This atmospheric river also ushered in warmer temperatures, including a high temperature of 65 degrees in Portland, which ties with the city’s all-time high for the month of December last set in 1993.

These warm conditions helped melt snow across the Pacific Northwest, causing excessive runoff and rising creeks and streams.

Not all atmospheric river events are bad. In fact, AR event levels 1 and 2 are considered mostly beneficial rains and are much needed across the western US to build water supply levels. But AR event levels 4 and 5 are more hazardous than they are beneficial as the risk for flooding and travel dangers outweigh the benefits.

Correction: An earlier version of this article misstated when the Stillaguamish River reached a record high based on preliminary data. It was Tuesday.

CNN’s Andy Rose, Sara Smart, Allison Chinchar, Gene Norman and Sara Tonks contributed to this report.