An “atmospheric river” containing lots of tropical moisture is aimed at western Washington over the Thanksgiving holiday period. The National Weather Service in Seattle expects very heavy rain over the region through Sunday, especially in the Cascades and Olympics. In addition, a strong warm front will cause temperatures to rise sharply, melting snow in the mountain ranges. This could lead to flooding on area rivers, including the Tolt, Snoqualmie, and Skykomish rivers in King County. A Flood Watch is in effect through Thursday afternoon.
Soil moisture across the region is high. With additional heavy rain expected, there could be landslides in areas with steeper slopes. The Washington Department of Natural Resources maintains a landslide hazard outlook map.
Stay tuned to local media and websites for the latest forecasts, and check the King County Flood Services page for alerts and warnings.
UPDATE 11/22/17 5:30am
The Snoqualmie River is now at Flood Phase 3, indicating moderate flooding across the entire valley. Take caution when driving in the area, and never drive through a flooded road.
In addition, the South Fork Skykomish River and the Tolt River are both at Flood Phase 2, indicating minor flooding along those waterways. Check www.kingcounty.gov/flood for the latest on flood conditions across King County.