* WHAT...A persistent inversion with light and variable winds will lead to a period of stagnant air conditions. This scenario could result in the build up of air pollutants near the surface over time.

* WHERE...Foothills of the Northern and Central Oregon Cascades, North and Central Coast Range Valleys of Oregon, Lower Columbia River and Cowlitz River Valleys, Central Willamette Valley, Tualatin Valley, Willapa and Wahkiakum Lowlands, North Clark County Lowlands, and South Washington Cascade Foothills.

* WHEN...Until 4 PM PST Tuesday.

* IMPACTS...Deteriorating air quality may cause issues for people with respiratory problems.