Atmospheric River Ahead for Western Washington

 FastCast—Thursday, Jan. 11 to Saturday, Jan. 14:

An atmospheric river is ahead for Western Washington, with rain expected through Friday, turning to showers on Saturday. In the lowlands, expect 0.5-1.5 inches, with higher amounts of up to 2 inches in the foothills. The coast will receive 2-3 inches, and with snow levels near 6,000-7,000 feet, the mountains will receive 3-7 inches of rain. Eastern Washington will receive 0.2-0.5 inches of rain, with higher amounts near the Cascades. Winds will be breezy at times through Friday, especially easterly winds near the Cascade Foothills. Gusts of 30-40 mph are possible, especially from Enumclaw to North Bend. Winds gusting 25-40 mph are possible area-wide on Friday. Due to high soil moisture and successive rainfall, there is an increased threat of landslides in Western Washington. This threat will be highest in the mountains and foothills, but use caution around prone hillsides. Additionally, rivers will rise, but the only river that will flood is the Skokomish River on the SW Olympic Peninsula.

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Continue reading the full blog below!

An atmospheric river (narrow current of significant, deep moisture) is ahead for Western Washington from early Thursday to late Friday. In the UW forecast below, the narrow current of moisture is seen paralleling the coastline and moving inland, at around 10 AM Thursday.

This is an interesting path for an atmospheric river, and the highest precipitation will be found (again) over Central/Northern California and Southern Oregon. 

However, the rain will definitely be noticeable in Western Washington. Below is the European model forecast showing rain through Friday night.

The European model shows 0.8-1.5 inches of rain for the lowlands, except 0.4-0.6 inches in the NE Olympics Rainshadow. The coast will get 2-3 inches and the mountains will get 3-5 inches. Eastern Washington will pick up 0.2-1 inch in this forecast, with the most near the Cascades.

Let’s take a look at some higher-resolution forecasts, starting with the NAM model, showing rain through 11 PM Friday.

The NAM forecast shows 0.9-1.25 inches in the lowlands, 2-4 inches on the Kitsap Peninsula, 1.5-3 inches on the coast, and 4-10 inches in the mountains. This shows less for Eastern Washington, at 0.2-0.5 inches.

Finally, the NWS NBM forecast, through 10 PM Friday.

The NWS NBM forecast agrees with the NAM and European, showing 0.75-1.25 inches of rain for the lowlands with the exception of the rainshadow. The coast and Kitsap Peninsula get 1.5-3 inches, and the mountains get 3-6 inches. Eastern Washington will pick up 0.1-0.5 inches, with more possible in the North Cascades.

Stay tuned! More active weather is ahead in the coming days.