QuickTake:

The weather service says there is the possibility of minor flooding in some low-lying areas and along waterways. Rain is expected to begin Monday and persist in waves through Thursday.

A strong atmospheric river will bring widespread rain and wind this week, prompting National Weather Service forecasters to issue flood warnings for the southern Willamette Valley.

Consecutive waves of heavy rain are expected Monday through Wednesday, with 1.5 to 2.5 inches forecast across the southern Willamette Valley and 2 to 4 inches along the coast from Florence to Newport. The Coast Range could see 6 to 12 inches of rain. Lighter but steady rain is likely to continue into Thursday, keeping soil saturated and waterways rising.

The prolonged rain will push the Willamette River higher in Eugene and Springfield. Forecasters warn the river can keep rising for hours or even days after the heaviest rain ends, because it takes longer for all the runoff to reach it.

A 72-hour precipitation forecast, published the morning of Dec. 8, 2025. Credit: National Weather Service,

Several nearby streams and smaller rivers that flow into the Willamette River have a 40% to 60% chance of rising high enough to spill onto banks and low-lying areas — what forecasters call minor flooding. Urban flooding is also a concern in low areas of Eugene and Springfield, as creeks swell and storm drains clog with debris.

Tributaries and waterways that have flooded in similar conditions include the McKenzie River near Glenwood, Amazon Creek and the Delta Ponds.

“The chances for urban and small stream flooding in the Eugene area [are] is on the lower side as the heaviest rain associated with the main band of moisture with this event is forecast to be north of Eugene,” said meteorologist Hannah Chandler-Cooley.

“However, if the main band of moisture ends up shifting farther south than anticipated, persistent rain rates could increase and lead to a higher chance of urban and small stream flooding,” she said.

A flood watch remains in effect through 4 p.m. Friday. Landslides are possible on steep hillsides because soaked ground can start to give way.

What is an atmospheric river?

An atmospheric river is a long band of concentrated moisture that moves through the air like a river in the sky. These systems often help end the wildfire season and replenish the region’s water supply, but they can also trigger power outages and flooding. 

Eugene and Springfield have already seen several atmospheric rivers this fall.

While this storm isn’t cited as direct evidence of climate change, peer-reviewed research shows that as the atmosphere warms, it holds more moisture. When strong winds push that moisture inland, it can produce heavier, faster rainfall — like a sponge being wrung out.

Oregon State climatologist Larry O’Neill said winter storms with heavy rain are becoming more likely. The most intense of those events almost always arrive as atmospheric rivers. 

Still, O’Neill noted that these large storms are needed to rebuild reservoir levels and help prevent another drought in 2026.

“This storm coming in this week will be a great start,” he said. “But we’re going to need a couple others like it.”

Ashli Blow brings 12 years of experience in journalism and science writing, focusing on the intersection of issues that impact everyone connected to the land — whether private or public, developed or forested.