If you live in Northwest Oregon or Southwest Washington, you may want to clean your gutters and clear out your storm drains this weekend.
The National Weather Service says heavy rain will be arriving in the region starting Monday, and that could mean flooding.
The culprit: what experts call an atmospheric river.
“When you hear the term atmospheric river, it’s this long, narrow corridor of moisture, essentially in the atmosphere. Think of a river, but in the sky,” said Noah Alvis, a meteorologist with the National Weather Service in Portland. “Most of the time it brings beneficial rain, but sometimes, like in the case for next week, if it brings too much moisture for a long period of time, it could lead to impacts such as river flooding, or flooding in urban areas.”
Runners jog through thick fog on a rainy evening in Southwest Portland, Ore., on Dec. 4, 2025.
Eli Imadali / OPB
The weather service forecasts steady precipitation at the coast, in the Coast Range mountains and further inland through the weekend.
But the risk climbs Monday, when the atmospheric river arrives with a surge of heavier rain.
Heavy rain through next Wednesday could lead to moderate flooding from rivers in Southwest Washington and Northwest Oregon, according to the agency’s hydrologic outlook.
Though it’s relatively unlikely that rivers will see significant flooding, streams will likely rise, and there could be standing water on roads in urban areas.
This is a good moment to remember how to respond when the rain is heavy, Alvis said.
“If you see a flooded roadway, don’t drive through it. Turn around and find an alternative route,” he said. “If you know you live in a flood-prone area, make sure you have a plan ready in case you experience impacts next week.”
Precipitation levels in the region have been below normal this winter, and the coming atmospheric river could reverse that in the areas it affects.
Portland International Airport saw just over 4 1/2 inches of rain in November – an inch below normal.
But skiers and snowboarders won’t get the relief they’ve been hoping for.
Lifts and trails are still closed at Mt. Hood Meadows, Mt. Hood Skibowl and Timberline Lodge, as all three resorts await colder temperatures and snowfall.
“Typically, when we get an atmospheric river, it brings warmer temperatures,” Alvis said. “Snow levels are going to be rising above 8,000 feet in the Cascades, so we’re expecting mainly rainfall in the Cascades – especially through the passes and, unfortunately, also the ski resorts. The very tip of Mount Hood might get some snow, but we’re going to have to wait a little longer for better snow for skiing.”
