A win for Western Washington—but one that comes at a cost east of the Cascades.
A win for western Washington—but one that comes at a cost east of the Cascades.
The win? Clearing out the wildfire smoke that's been trapped in the Puget Sound Basin.
That process has already begun.
Winds above about 5,000 feet have shifted, steering much of the incoming smoke from the north-central Washington fires away from western Washington.
Near the surface, though, the smoke remains trapped in the Puget Sound "bowl," where light winds and a stable atmosphere have allowed it to linger.
Now it's the low-level and surface winds' turn.
High pressure offshore has shifted south, and its clockwise circulation is strengthening the onshore flow through the Strait of Juan de Fuca, the Strait of Georgia, and the Chehalis Gap.
Cooler, cleaner marine air will gradually spread inland through these corridors, slowly replacing the smoky air over the Puget Sound Basin. This won't happen all at once—it will be a day-by-day improvement through the weekend.
The reason? The thermal trough has shifted east of the Cascades. As intense inland heating lowered pressure over eastern Washington, the pressure difference between the Pacific high and the inland trough reversed.
That stronger west-to-east pressure gradient will accelerate the marine push into western Washington while also funneling stronger winds through the Cascade gaps and down the east slopes.
That's where the downside begins.
As western Washington cools, eastern Washington stays hot. That increasing temperature and pressure contrast will strengthen westerly winds Friday and Saturday east of the Cascades.
Gusts could exceed 40 mph in some locations, fanning the flames of existing wildfires, increasing the risk of rapid fire growth, and likely prompting another Red Flag Warning.
The good news is that much of the additional smoke should be carried farther east rather than back into western Washington.
So while the marine push brings cooler temperatures and cleaner air west of the Cascades, it also creates more dangerous fire weather to the east.
That's the price of clearing out western Washington.
