Atmospheric River Set to Impact Pacific Northwest with Significant Flooding

A powerful atmospheric river, often referred to as the "Pineapple Express," is currently impacting the Pacific Northwest, particularly western Washington and parts of Oregon. This weather phenomenon, characterized by a strong influx of subtropical moisture, is expected to bring substantial rainfall starting Monday, December 8, 2025, and continuing through Wednesday, December 10, 2025. Forecasts indicate that some areas could receive between 10 to 15 inches of rain, particularly in the mountainous regions, while lower elevations may see totals ranging from 2 to 6 inches.

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The National Weather Service has issued flood watches across much of western Washington, warning of widespread river flooding, urban flash flooding, and increased landslide risks due to saturated soils. Major rivers, including the Snoqualmie, Puyallup, and Skagit, are forecasted to reach significant flood stages, with the Snoqualmie River near Carnation expected to experience prolonged major flooding over several days. The heaviest rainfall is anticipated on Tuesday and Wednesday, with river levels expected to peak during this period.

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Meteorologists have classified this atmospheric river as a Category 4 event on the scale used to assess their intensity, indicating a high potential for hazardous conditions. Cliff Mass, a professor of atmospheric sciences at the University of Washington, noted that this storm is one of the strongest atmospheric rivers to hit the region in recent years, although it is not a record-breaking event. The storm's warm nature means that most precipitation will fall as rain rather than snow, exacerbating runoff into rivers and increasing flood risks.

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The National Weather Service has emphasized the importance of preparedness for residents in flood-prone areas. They have advised individuals to secure loose outdoor items and to avoid driving through flooded roads. Local authorities are closely monitoring river levels and may issue evacuation orders if necessary. The weather service also highlighted that the combination of heavy rain and saturated soils creates ideal conditions for landslides, particularly in areas with steep terrain.

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While the atmospheric river is expected to provide much-needed moisture to alleviate drought conditions in the region, some experts caution that the rapid influx of rain could lead to severe flooding and infrastructure challenges. Concerns have been raised about the potential for urban flooding, where storm drains may become overwhelmed, and the risk of landslides in vulnerable areas.

MyNorthwest

As the atmospheric river progresses, residents are urged to stay informed through local news and National Weather Service updates. The storm is expected to taper off by Thursday, December 11, but the threat of flooding and landslides will likely persist for several days afterward. Continued monitoring of river levels and weather conditions will be crucial as the situation develops.

MyNorthwest

• “This is a very strong atmospheric river. When this moisture hits our mountains, it produces huge amounts of precipitation.” — Cliff Mass, Professor of Atmospheric Sciences, University of Washington

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• “The key thing is you don’t drive through water. Some people make the mistake of doing that (you can get into trouble that way). So don’t go into water.” — Cliff Mass

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• “Those living in areas prone to flooding should be prepared to take action should flooding develop,” — National Weather Service Bulletin

Atmospheric river to slam Pacific Northwest with days of heavy rain

This atmospheric river event underscores the need for vigilance and preparedness as the Pacific Northwest braces for significant weather impacts.

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