* WHAT...Decreased air quality is likely to develop Friday morning. This is due to an inversion and stagnant air conditions near the surface that will trap pollutants within the valleys in Douglas, Josephine and Jackson Counties. * WHERE...Valleys in Douglas, Josephine, and Jackson counties. * WHEN...From 10 AM Friday to 10 AM PST Sunday. * IMPACTS...Poor air quality may cause issues for people with respiratory problems. Most outdoor burning will likely be prohibited as poor ventilation develops. * ADDITIONAL DETAILS...A strong area of high pressure will build in through Saturday, then weaken slightly on Sunday. This will lead to poor mixing of the atmosphere and the trapping of pollutants. The high is likely to strengthen again early next week.