Firefighters respond to a structure fire along Riverdale Boulevard as the fire line creeps up on Highway 9 during the CZU Lightning complex fire on Sunday, August 23, 2020 in Boulder Creek, California. 

Wildfires that have burned hundreds of thousands of acres in Northern California have also dimmed skies in much of Eastern Oregon with smoke.

After a reprieve on Saturday when northwest winds in the wake of a weak cold front shunted much of the smoke eastward, the pall returned Sunday.

And with no major changes in high-altitude winds for much of this week, the gray skies are likely to persist, according to the National Weather Service.

The Oregon Department of Environmental Quality on Monday added Baker County to an air quality advisory, although the agency noted that smoke issues in Baker County could be intermittent.

On Monday afternoon the air quality index, measured by a sensor on the roof of the David J. Wheeler Federal Building, 1550 Dewey Ave., in Baker City, was 74. That’s near the midpoint of the “moderate” category — 51 to 100.

Smoke is more dense — and the air quality comparatively worse — in many areas south and west of Baker County.

The air quality index Monday afternoon in both Burns and Lakeview, for instance, was 152. That’s in the “unhealthy” category. The index in Klamath Falls was 156, also in the “unhealthy” category.

Air quality is rated on a six-level numerical scale:

• 50 or below — “good”

• 51 to 100 — “moderate”

• 101 to 150 — “unhealthy for sensitive groups” (people suffering from asthma, for instance)

• 151 to 200 — “unhealthy”

• 201 to 300 — “very unhealthy”

• 300 and above — “hazardous”

After staying at 30 or below for most of Saturday, the air quality index in Baker City crept into the “moderate” category — at 52 — at 5 p.m. on Sunday. The index was at 80 at 2 p.m. on Monday.

The culprit — besides the wildfires, of course — is a persistent pattern of upper level winds from the southwest, according to the National Weather Service.

That directs smoke from California into Eastern Oregon, and in particular the southern half of the region.

This stagnant situation is forecast to change this weekend when a storm pushes into the Pacific Northwest from the Pacific Ocean.

The strongest part of the storm will likely stay north of Baker County, but the storm should shift winds to the west and northwest and potentially bring rain showers that would further help to clear out the smoke, according to the National Weather Service.

The storm will also bring cooler air, with high temperatures dipping into the 70s by Sunday.

Local fires are no longer contributing much to the smoke supply.

The area’s biggest blaze, the Indian Creek fire in Malheur County about 70 miles south of Baker City, was holding Monday at about 49,000 acres. The fire’s last major growth, of about 23,000 acres, was on Friday.

Forest Service fire crews quickly doused a blaze reported Sunday afternoon about a mile northeast of Anthony Lake. The fire burned about one-third of an acre. Crews were aided by a forest-thinning project in the past couple of years, said Travis Mason-Bushman, a spokesman for the Wallowa-Whitman National Forest.