Key Takeaways:
- A strong atmospheric river is expected to bring heavy rain to northwest Oregon and western Washington between Monday and Wednesday.
- The region is under a flood watch, with some areas expected to receive four or more inches of rain.
- The heaviest rain is expected to fall north of Lane County, with widespread river, small stream, and urban flooding likely to occur.
- People living in areas prone to flooding should be prepared to take action should flooding develop.
- The National Weather Service has issued maps showing the probability of exceeding 4 and 6 inches of rainfall in different areas.
Introduction to Atmospheric Rivers
Monday started wet in parts of northwest Oregon and western Washington, and things were only expected to get wetter. A strong atmospheric river is expected to bring inches of rain to the area between Monday and Wednesday, with much of the region under a flood watch. An atmospheric river is essentially a band of water vapor moving through the sky. Unlike some atmospheric rivers earlier this fall, December’s event is expected to lead to some flooding, as it comes after several days of rain. This is a significant concern for the region, as the prolonged rainfall can cause widespread flooding, landslides, and debris flows.
Rainfall Predictions
A map from the National Weather Service shows which parts of the region could see four or more inches of rain over the next several days. The 72-hour probability to exceed 4 inches of rainfall through Thursday, December 11, 2025, in Oregon and Washington, indicates that some areas are more likely to experience heavy rainfall than others. Some areas could see even more rain, with another map from the National Weather Service showing that in the coast range near Tillamook, there’s a 74% chance of six or more inches of rain between 4 a.m. Monday and 4 a.m. Thursday. This is a significant amount of rainfall, and residents in these areas should be prepared for potential flooding and landslides.
Flooding and Landslide Risks
The National Weather Service has warned that the heaviest rain is expected to fall north of Lane County, with widespread river, small stream, and urban flooding likely to occur. People, structures, and roads located below steep slopes, in canyons, and near the mouths of canyons may be at serious risk from rapidly moving landslides or debris flows. This is a significant concern, as landslides and debris flows can be deadly and cause significant damage to property. The agency has advised those living in areas prone to flooding to be prepared to take action should flooding develop. This includes having a plan in place, staying informed about weather conditions, and being ready to evacuate if necessary.
Preparation and Safety Measures
The National Weather Service has issued several maps and warnings to help residents prepare for the heavy rainfall and potential flooding. These maps show the probability of exceeding 4 and 6 inches of rainfall in different areas, and residents can use this information to plan and prepare accordingly. Residents are advised to stay informed about weather conditions, sign up for emergency alerts, and have a plan in place in case of an emergency. This includes having a emergency kit with essential items such as food, water, and first aid supplies, and knowing the safest routes to take in case of an evacuation. By taking these precautions, residents can help keep themselves and their loved ones safe during the heavy rainfall and potential flooding.
Conclusion
In conclusion, a strong atmospheric river is expected to bring heavy rain to northwest Oregon and western Washington between Monday and Wednesday, with much of the region under a flood watch. The heaviest rain is expected to fall north of Lane County, with widespread river, small stream, and urban flooding likely to occur. Residents are advised to be prepared to take action should flooding develop, and to stay informed about weather conditions. By taking the necessary precautions and staying informed, residents can help keep themselves and their loved ones safe during the heavy rainfall and potential flooding. The National Weather Service will continue to monitor the situation and provide updates, and residents are advised to stay tuned to local news and weather reports for the latest information.