PORTLAND, Ore. — Much of Oregon and Washington saw worsened air quality and hazy skies on Friday. In many spots across the Northwest, air quality levels had decreased to "moderate" by the afternoon, with some smaller areas seeing "unhealthy" levels.
The reason behind it? The air aloft is warmer than the air on the surface, which traps all the particulate near the surface, causing decreased air quality, according to KGW meteorologist Chris McGinness.
"High presser lofts, stagnant air and not much to stir things up, and so what that leads to is occasionally moderate air quality," McGinness said.
The color-coded U.S. Air Quality Index (AQI) map shows much of Oregon and Washington in the yellow "moderate" range, meaning there may be some health risks for people who are sensitive to air pollution. Some places along Oregon's southern coast and in the Salem metro area reported air quality in the orange "unhealthy for sensitive groups" range, as well red "unhealthy" levels.
Pleasant fall weather, mild afternoon temperatures and sunshine with light wind are allowing pollutants to build up slightly.
"It's nice to see the sun, but that is also kind of helping to trap some of those pollutants in a little bit," McGinness said.
Adding to that, temperatures Friday morning were warmer at Timberline (6,000 feet elevation) on Mount Hood than they were in much of the Willamette Valley. Temperature inversions, like what the Northwest saw on Friday, takes longer to break during the fall and winter when there's less daylight, McGinness said. That can allow pollutants to build up over time.
McGinness expects the air quality to improve across western Oregon on Saturday. It'll be mostly cloudy, but dry until night time when a weak weather system will bring light rain. The forecast shows wet weather possibly at least through Thursday of next week.
AQI's interactive map below and here shows the current air quality levels. You can zoom in and out on the map, and search for addresses.