The weather pattern that is forecast to bring excessive heat to the Pacific Northwest for much of this week may also bring wildfire smoke into the region from fires burning in California’s Sierra Nevada mountains. As of Monday morning, the largest smoke maker out of these is the Oak Fire burning near Yosemite National Park.
Smoke from this region was already making it into Southwest Oregon by 09:00 Monday and is expected to spread northward to add a haze to most Western Oregon and parts of Western Washington south of Seattle by sunrise on Wednesday. As the ridge axis slowly moves eastward, westerly winds may bring some of this into Eastern Washington and Eastern Oregon later into the week.
The smoke is not likely to be thick, and it is not likely to cause major impacts to air quality on the ground. Much of the smoke that comes into Washington and Oregon from California will be carried by mid- and upper-level winds and is not expected to mix down to the surface. A milky haze is probably the biggest impact most folks in the region see. The exception to this is Central Oregon and the adjacent Cascades, which may have minor amounts of smoke at the surface.
There is a chance that the smoke may be thick enough to moderate temperatures, especially in Western Washington and Oregon on Tuesday, but if so I expect this to only be by a degree or two. This will not be like the 2020 Labor Day fire event. Beyond Wednesday morning, limitations in predictability make it hard to say just how much impact the smoke will have but in the very least haze is expected to continue and spread eastward. At the surface, pollution from human activities is likely to develop and add to the haze, moderately impacting air qualities especially near medium and large cities.
This forecast only includes smoke from currently existing fires. Dr. Cliff Mass at the University of Washington pointed out in a blog post on Sunday that fire danger will increase in Eastern Washington and Oregon during the second half of the week. As temperatures cool west of the Cascades relative to areas east on Wednesday, winds will ramp up during the evening hours. The model graphic above highlights areas with higher fire danger due to a combination of wind, temperatures, and relative humidity. This pattern is forecast to continue for several days.
The greatest fire threat will come during the late afternoon hours in typical windy spots like the eastern Columbia River Gorge, Kittitas Valley, and parts of Oregon south and east of La Grande. Relative humidities during the hottest time of the day may be below 20% with temperatures well above 100°. Winds approaching 20 mph at times, while not significantly strong, will be enough to help any fires that start to move quickly.
You can check out what models are thinking about for wind, heat, and humidity by heading over to my Forecast Map page.
