Update at 5:10 Tuesday:
The air stagnation advisory was extended Tuesday through 4 p.m. Friday.
Original story below:
An air stagnation advisory is in effect for most of western Oregon and southwest Washington through Wednesday afternoon.
A new dense fog advisory was also issued Sunday for the central and South Willamette Valley lasting through noon Monday. It's expected to cause poor visibility of one-quarter of a mile in areas of dense fog.
Air stagnation can cause respiratory problems for some residents and has led to the National Weather Service recommending no outdoor burning.
Meteorologist David Bishop with the NWS in Portland explained that stagnant air is caused by a persistent ridge of high pressure over the area, usually resulting in calm weather.
"If that ridge and calm weather decides to hang around for an extended period, the air also isn't moving around," he said.
According to the NWS advisory Sunday morning, stagnant air is expected in areas below 1,500 feet elevation, lasting through 4 p.m. Wednesday.
Bishop said there would be minimal air movement in the area, which could lead to some effects on health.
"Obviously if the air is not changing out, particulate matter can hang around, which could lead to an impact," he said.
The advisory states that the poor air quality could cause hazardous driving conditions with low visibility, and that air quality agencies "highly recommend" no outdoor burning occur and residential wood burning devices be "limited as much as possible."
The advisory also recommends drivers slow down, use headlights in poor visibility and leave plenty of space between vehicles.
It suggests people with respiratory illness to follow their doctor's advice for dealing with high levels of air pollution during stagnant air.
The Lane Regional Air Protection Agency issued a "Yellow Home Wood Heating" notice for Eugene, Springfield and Oakridge for Saturday through Wednesday. The notice recommends residents not use fireplaces and wood stoves to improve air quality.
"If you do light a fire, this is the weekend to check your smoke plume and assure it's creating as little smoke as possible," the notice states. "Efficient fires are small, hot and use dry, seasoned wood with open dampers."
LRAPA's air quality map showed both Eugene and Springfield at "good" air quality index ratings of 29 and 15, respectively at noon on Sunday. Salem was at a "good" rating of 41 a little after noon, according to the air quality website AirNow.gov.
The NWS advisory was initially issued for the south Willamette Valley, but then was expanded to all of western Oregon and southwest Washington aside from the coast a little after noon Sunday.
This article originally appeared on Register-Guard: Stagnant air advisory issued for Willamette Valley now through Friday