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'Olympic Wind Shadow' has Snohomish County wondering: Where's the wind?

A thunderstorm makes its way down the Strait of Juan de Fuca on Dec. 20, 2016. (Photo: The Responder News)

The Olympic Rain Shadow -- that local feature that keeps Sequim dry -- is pretty well known around here. But Tuesday morning the Olympics created a rather different effect around here -- what we'll call the "Olympic Wind Shadow".

A potent cold front swept through early Tuesday morning bringing a round of gusty west/southwest winds to much of the region. Here are some peak gusts in the storm:

  • Oak Harbor: 55 mph
  • Port Angeles Coast Guard Base: 50 mph
  • Seattle (Sea-Tac Airport): 41 mph
  • Port Angeles Airport: 40 mph
  • Friday Harbor: 40 mph
  • Forks: 40 mph
  • Shelton: 39 mph
  • Tacoma: 39 mph

And one wind gauge on Trial Island just off the coast of Victoria in the Strait of Juan de Fuca reported an amazing 76 mph gust! Puget Sound Energy reported 8,000 people without power during the peak of the storm and a run of the Port Townsend ferry had to be canceled due to high winds.

But in Snohomish County (and into parts of northern King County): The trees were barely rustling. Sure, it rained a bit, but wind? Nada.

Why? Those rascally Olympic Mountains.

This storm set up was a bit different than a typical wind event when a low pressure center makes landfall close to here, then sweeps inland just to our north, bringing a round of strong southeasterly winds first to the Northwest Interior before the storm hits, then a few hours of strong near-due southerly winds as the storm passes due north. The "Olympic Wind Shadow" effect isn't new -- just in our typical south-wind storms, the mountains protect areas directly to their north -- like Port Angeles and Sequim. Many times even when much of the region is under wind warnings or advisories, that central Strait area is left out.

But with this storm making landfall so far away, those southeast/south wind weren't really in play. Instead, we had a period of strong west-to-southwest winds that chase behind the storm's cold front. With that wind alignment, the strongest winds occur along and to the east of the Strait of Juan de Fuca, since the waterway is aligned west-east making it act as a wind tunnel. That's how Trial Island hit 76 mph and why some of our strongest wind gusts reported were in Port Angeles and Whidbey Island.

But with the west/southwest wind alignment, the Olympic Mountains stood as a big rock in the way, protecting areas to the east/northeast of the mountains -- in this case Snohomish County. The forecast models picked up on this very well and Snohomish County was exempt from the various wind warnings and advisories Tuesday morning:

I saw this myself driving into the office Tuesday. I live in southern Snohomish County and it was a calm morning, and driving through Shoreline it was dead calm. But get to Northgate and the wind began blowing, and by the time I'm crossing the Ship Canal Bridge in Seattle, cars were struggling to stay in their lane from the wind gusts.

About that time, Sea-Tac Airport reported its peak gust of 41 mph for the day. At the same time in Everett? A 6 mph wind... that would drop to 3 mph the next hour.

Don't worry, Snohomish County, you were likely going to get some extra rain Tuesday from that other Olympic Mountain weather-maker: The Puget Sound Convergence Zone. So don't feel too left out.

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