The air quality level is expected to reach into unhealthy for sensitive groups.
Changes in wind direction have brought over more smoke to the area from wildfires around northern and central Washington, as well as from British Columbia.
The main concern today is areas of widespread smoke continuing to affect air quality and the visibility across the state.
Thick smoke blanketing British Columbia communities far from any flames - including Vancouver where the haze Monday obscured the city's mountain views - could be particularly harmful for children and seniors but anyone with poor health should take precautions, says a senior scientist.
As of 1:00 p.m. Sunday, air quality monitors in Yakima, Toppenish, Sunnyside and White Swan reported air quality as "very unhealthy", with each site reporting dangerously high levels of ultrafine "PM 2.5" particulate pollution.
It's the second time in a week smoke from wildfires has pushed the state's air quality into risky level.
Officials recommend staying inside with windows closed and air conditioners set to recirculate.
The National Weather Service in Seattle has issued an Air Quality Alert for Western Washington, as wildfire smoke returns to the Puget Sound. "It's substantial. Air quality definitely has an impact on public health". Air quality was improving in eastern Montana.
If you're anxious about the air quality in your home and don't already own an air purifier, you can build one for less than $20 if you have a box fan.
Fire information officer Chris Wyatt said Monday unsettled weather is expected for the next few days with the possibility wind gusts of up to 35 miles per hour on mountain ridges.
The air quality was so bad that everyone, regardless of physical condition or age, will likely be affected, according to the Spokane Regional Clean Air Agency.
Those who have to venture outside for extended periods of time and have considered wearing a mask should ensure they purchase the right one.