Corridor
Out here two separate things decide your air: what arrives, and whether the ground you live on lets it leave.
The sources are everywhere and they overlap. The Cascade crest, eastern Washington, central and southern Oregon, northern California, central Idaho and the Idaho panhandle, western Montana, and interior British Columbia all feed this corridor, and on the worst setups several of them feed it at once. British Columbia is the one people consistently underestimate: a bad BC season puts smoke over Spokane and the Flathead repeatedly without a single acre burning in the United States.
Then the terrain takes over. Missoula, Whitefish, Bozeman, Jackson, Spokane, and Boise all sit in valleys or basins that pool cold air overnight, cap themselves, and hold smoke at ground level long after the flow upwind has shifted. This is why bad air in the Rockies routinely outlasts the fire behaviour that caused it, and why a clear forecast upwind is not the same thing as a clear morning at home. Bend, on the dry east side of the Cascades, does the same trick with high-desert nights.
The coastal cities fail differently. Seattle takes smoke from two directions that behave nothing alike. Cascade and eastern Washington fires push it west through the passes on easterly flow, which arrives fast and clears fast, while Oregon, California, and BC smoke arrives aloft and settles into the Puget Sound basin for a week, because the marine geography that keeps the city mild also keeps its air from moving. Portland’s wrinkle is the Columbia River Gorge: east winds funnel smoke straight down it into the metro, fast, concentrated, and hard to forecast more than a day out.
September 2020 is the shared marker on the west side of this corridor. East winds drove the Riverside, Beachie Creek, and Holiday Farm fires toward the Willamette Valley and gave Portland the worst air quality on earth for several days with ash falling in the city, and Seattle sat under Oregon and California smoke with a flat orange-grey sky for the better part of two weeks. Inland, 2017, 2020, and 2021 are the seasons people name.
The visibility scale is at its most useful here, because the targets are mountains. A city page in this corridor tells you which peak goes at which level, and the peaks are far enough out that the top of the scale has somewhere to go: Rainier at roughly sixty miles from Seattle, Mount Hood at fifty from Portland, the Sierra-scale distances that a skyline city simply cannot offer.
Listed in the order the smoke reaches them, not alphabetically. Each level here is read when this page loads and carries the time it was read. Open a city for its clear time and the rest of the forecast. Each page also carries that city's own distances and its own named sightlines, so you can check a level against what you can actually see from there.
Smokeshow is for informational and educational purposes only. It is not health, medical, or safety advice. Forecasts are model estimates and can be wrong, sometimes by a lot. Descriptions of what you might smell, see, or feel are generalizations, not predictions about your body. For decisions about your health, outdoor activity, or air quality safety, rely on official sources like AirNow.gov, the National Weather Service, and your local health authorities, and talk to a medical professional about your own situation.