A strong to extreme atmospheric river is forecast to bring widespread heavy rain and flooding risk to northwest Oregon and southwest Washington from Thursday, December 18 through Saturday, December 20, 2025. The greatest concern is for urban flooding Thursday and river flooding Thursday night into Friday as saturated soils and already elevated rivers respond to another intense round of moisture.

What is causing the threat

Meteorologists expect a focused corridor of deep Pacific moisture—an atmospheric river—to move over the region late this week, delivering several inches of rain in less than 48 hours. Because earlier storms in December have already soaked the ground and pushed many rivers near or above normal levels, additional heavy rain will more easily run off into streams, rivers, and low-lying areas instead of soaking into the soil.

Areas at greatest risk

The flood potential covers all of northwest Oregon and southwest Washington, including coastal communities, inland valleys, and foothill areas draining the Coast Range, Willapa Hills, and Cascades. Faster-responding rivers and creeks, along with small urban streams and poor-drainage neighborhoods, are expected to see the earliest impacts from rapid rises in water levels.

Expected impacts Thursday–Saturday

On Thursday, heavy rain may overwhelm storm drains, leading to ponding on roads, flooded intersections, and water in low-lying homes or businesses, especially in known trouble spots. As runoff moves downstream Thursday night into Friday, many rivers and creeks are forecast to reach at least minor flood stage, bringing the potential for flooded fields, road closures, and inundated floodplains. Landslides and debris flows are also possible in steep terrain and near recent burn scars where saturated soils lose stability.

Preparedness and safety actions

Residents in historically flood-prone or low-lying areas are urged to activate their flood plans now: move valuables to higher levels, clear nearby drains, and be ready to protect property with sandbags or barriers where feasible. During the event, never walk or drive through flood waters, since as little as six inches of moving water can knock a person down and a foot of water can sweep away a vehicle. Stay informed through local forecasts and alerts, and consider alternate routes in case your usual roads become inundated or blocked by high water or landslides.

Sources
Portland – National Weather Service https://forecast.weather.gov/product.php?site=PQR&issuedby=PQR&product=AFD&format=CI&version=1