* 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...Eastern Portland/Vancouver Metro, Portland West Hills and Chehalem Mountain, Inner Portland Metro, and Inner Vancouver Metro.

* WHEN...Until 4 PM PST Monday.

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