Air quality in valleys over much of Oregon will be worsening through the week and into the weekend, officials say.

According to the National Weather Service, a strong inversion will persist over the state, while the mountains will be sunny with above normal temperatures. In addition, freezing fog will occur during the overnight hours in valleys.

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air quality index for information about air quality conditions in your area.

The air stagnation advisory is in effect through Sunday for the Portland metro area, the Willamette Valley, and portions of Douglas, Jackson, Klamath and Lakeview Counties, according to the DEQ. S

Oregon earlier this week and are expected to improve as early as Friday in Gilliam, Morrow, Sherman, Umatilla and Wasco counties. This advisory is based on the latest information from the

.

Due to a persistent temperature inversion over much of the Northwest and light winds, air quality in portions of the affected area are already as bad or worse than during last August's forest fires, and all outdoor activity should be limited for all people in the affected areas. Air quality is expected to deteriorate during the weekend in many areas and pollutants may reach "unhealthful" levels.

Among other steps, DEQ asks that residents halt open burning, voluntarily limit wood heating and limit driving and idling.

Young children, pregnant women, asthma sufferers, those with lung or heart conditions and adults age 65 and older should limit vigorous outdoor activity, the state said. Pollution is highest in the morning and evening.

– The Oregonian