Western Washington has mostly lucked out so far this year when it comes to wildfire smoke. We can thank a steady flow of clean air from the Pacific Ocean, except for a short visit from that in-law we’re all trying to forget, a certain heat-dome that probably deserves its own name. But I’ll save that for another time.
Anyway, that steady flow of clean air can’t hold up all summer, and indeed it seems to be changing on Friday, Saturday, and into Sunday. The HRRR model shows a decent plume arriving in western Washington late Friday afternoon, with another wave heading in overnight and into Saturday. Here’s some more details:
So far, the Pacific Northwest has mostly been getting clean marine air flowing west to east . But a ripple in the pressure patterns has sent smoke from Northern California and Oregon to the northwest, and right for us. This is forecast to arrive late Friday afternoon. (See the first figure, which shows the sum of smoke at all levels, like looking down from a satellite) The pressure gradient in central and eastern Washington, and further east, will also shift on Friday and Saturday and start sending smoke to us, too. Saturday late afternoon, we’ll get another wave of smoke from central and eastern Washington and British Columbia.
But what does this mean for Western Washington air quality? … it looks to be a classic upstairs-downstairs situation, in which most of us in the lowlands of Puget Sound and Western Washington will likely be spared, while smoke passes overhead.
While two waves of smoke are expected to reach our skies, they’ll be at 2 km or higher (see the second figure), and the situation at surface should be very different. Over the weekend, there will still be a pressure gradient at the surface from the coast to the western side of the Cascades. So, clean marine should continue to push in, to at least the foothills. Although the upstairs smoke and the downstairs marine air generally keep to themselves, there’s a chance that a few of the upstairs visitors might trickle downstairs and push us to MODERATE air quality.