Wildfire smoke is expected to return to the Hillsboro area by Thursday evening, Aug. 13, bringing a second round of poor air quality less than two weeks after the region's first major smoke event of the season.
The smoke should be less severe this time. KOIN meteorologist Josh Cozart reported Tuesday, Aug. 11, that this round is "not expected to be as impactful as early August's round of smoke" and should last a much shorter time, with northwesterly winds clearing the air by Friday afternoon, Aug. 15.
The mechanism is the same one that choked the metro area in early August: winds shifting from northwest to northeast will funnel smoke from eastern Oregon wildfires through the Columbia River Gorge and into the Portland metro, including Washington County. Forecasters expect moderate-to-unhealthy air quality Thursday evening through Friday morning before conditions improve.
No Oregon DEQ air quality advisory specific to Washington County had been issued as of Wednesday, Aug. 12. Existing advisories for eastern Oregon and Washington were set to expire at noon Thursday but could extend westward as smoke moves in.
Who is most at risk
Multnomah County health officials identified the most vulnerable populations during the early August event: pregnant people, children, older adults, people with heart or lung conditions and outdoor workers. Those groups should plan to limit time outside Thursday evening and Friday morning.
Air Quality Program Specialist Jonathan Cruz urged residents on Aug. 6, during the first smoke event, to "keep an eye on air quality levels before heading outdoors." That guidance applies again.
What residents can do
Health officials recommend staying indoors with windows closed, setting air conditioning to recirculate, running a portable HEPA air cleaner or a box fan fitted with a MERV-13 furnace filter, and wearing an N95 mask if outdoor activity is unavoidable.
An AQI above 100 is considered unhealthy for sensitive groups. Above 150, it's unhealthy for everyone. During the early August event, Hillsboro's AQI peaked at 163 and forced cancellation of the Tuesday Night Market. As of Aug. 11, Hillsboro's AQI had returned to 14, well within the "Good" range.
Residents can track local conditions in real time at AirNow.gov (search "Hillsboro, OR") and at the Oregon DEQ's air quality site, aqi.oregon.gov.
What's ahead
The City of Hillsboro maintains cooling and health resources on its website. Washington County opened severe weather shelters in Hillsboro and Tigard during the first smoke event; no announcement about shelters for Thursday's forecast had been made as of Wednesday.
Clear skies and warmer temperatures are expected to return to the Willamette Valley by the weekend, but the lack of rainfall and above-average heat will keep Oregon's wildfire threat elevated. The state has burned more than 2 million acres this year, a single-season record.
