Some smoke upstairs, but good on the ground floor…

Western Washington has fared pretty much so far this year when it comes to bushfire smoke. We can thank the constant flow of clean air from the Pacific Ocean, save for a short visit from this couple we all try to forget, a particular thermal dome that probably deserves its name. But I’ll save that for another time.

In any case, this constant flow of clean air can’t hold up all summer, and it looks like it’s going to change on Fridays, Saturdays, and even Sundays. The HRRR model shows a decent plume reaching western Washington late Friday afternoon, with another wave trending overnight and into Saturday. Here are more details:

To date, the Pacific Northwest mostly gets clean marine air that flows from west to east. But a ripple in pressure patterns sent smoke from northern California and Oregon into the northwest, which is fine for us. This is expected to arrive late Friday afternoon. (See the first figure, which shows total smoke at all levels, such as looking down from a satellite.) The pressure gradient will shift in central and eastern Washington, and further east, on Friday and Saturday and start sending smoke back to us, too. Late Saturday afternoon, you will receive another wave of smoke from central and eastern Washington and British Columbia.

But what does this mean for air quality in western Washington? …seems to be a classic upstairs downstairs setting that most of us would likely avoid in the lowlands of Puget Sound and Western Washington, while smoke billows in the sky.

While two waves of smoke are expected to reach our sky, they will be two kilometers or higher (see Figure II), and the situation on the surface should be completely different. Over the weekend, there will still be a surface pressure gradient from the coast to the west side of the Cascades Series. Therefore, the clean navy should at least continue to rush into the hills. Although the smoke upstairs and the marine air downstairs generally keeps to itself, there is a chance that a few upstairs visitors will flock to the basement and push us into a moderate air quality.

To add to the mix, warmer temperatures lead to higher ozone (smog) conditions. The atmosphere cooks the ozone layer off emissions from cars, trucks, industry, and even plants. In the summer, when temperatures soar into the 80s and 90s, ozone can rise to levels considered unhealthy for sensitive groups. Because urban emissions take time to “cook” and the winds during these hot spells blow to the east, high ozone levels often occur in the foothills of the Cascade Range rather than in the heart of the city. Today (Friday) we are likely to see highs of around 90, which means ozone could reach an unhealthy level for sensitive groups. Saturday will still be hot, but it will have some clouds, so it won’t be ‘cooking’ that fast, so we should stay in the moderate air quality category, for ozone, so overall…assuming no smoke seeps in from upstairs.

If expectations hold, Puget Sound should continue to have good to moderate air quality downstairs, although upstairs will look hazy. And hopefully, we don’t get a lot of lightning in the Cascades series.

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