...AIR STAGNATION ADVISORY REMAINS IN EFFECT UNTIL 4 AM PST SATURDAY... ...DENSE FOG ADVISORY IN EFFECT UNTIL 11 AM PST FRIDAY... * WHAT...For the Air Stagnation Advisory, light winds and limited air movement will lead to a period of stagnant air conditions. This scenario could result in the build up of air pollutants over time. For the Dense Fog Advisory, visibility frequently below one quarter mile in dense fog and areas of freezing fog. * WHERE...South Willamette Valley. * WHEN...For the Air Stagnation Advisory, until 4 AM PST Saturday. For the Dense Fog Advisory, until 11 AM PST Friday. * IMPACTS...Poor air quality may cause issues for people with respiratory problems. Low visibility could make driving conditions hazardous. * ADDITIONAL DETAILS...Fog will reform and increase across the south Willamette Valley this evening. Overall, temperatures will hold at or just above freezing overnight. But, a few spots will drop back below ...