Northwest wildfire smoke to blanket Seattle, Portland

Smoke from a rash of Northwest wildfires is forecast to pour into western Washington and Oregon, leading to unhealthy air quality in Portland, Seattle and other cities.

The most numerous large wildfires right now are burning in the eastern two-thirds of Oregon and Washington.

Three of those burning in the Spokane, Washington, metro area destroyed hundreds of homes and businesses. Thirty large fires are burning in central and eastern Oregon.

Other large fires are burning in Idaho, Montana and Utah, among other western states.

Ground-level wildfire smoke over the past week or so has largely been confined to the interior Northwest closest to the fires. But that's changing.

The typical west-to-east onshore winds in the Pacific Northwest are turning around. Over the next couple of days, offshore winds will blow from the east or northeast.

Winds from that direction will pull increasing ground-level smoke into western Oregon and western Washington.

That includes the Interstate 5 corridor, including Seattle, Tacoma and Olympia, as well as Oregon's Willamette Valley, including Portland, Salem, Corvallis and Eugene.

Ground smoke will also continue in Boise, and could flow as far south as Salt Lake City, according to some computer models.

This smoke in western Washington and western Oregon may linger into Wednesday, before winds turn onshore and the smoke layer thins out Thursday.

If that wasn't enough, the same pattern that's drawing the wildfire smoke westward is also turning up the heat west of the Cascades.

Daytime highs may approach 90 degrees in Seattle and upper 90s in Portland, though if the smoke is dense enough, that could knock a few degrees off those daytime highs.

Those could flirt with daily record highs from Seattle to Eugene and Medford, Oregon.