Air quality across Southern Oregon continues to worsen as forest fires burn to the north, and hot, smoky days will linger through the weekend.

Air quality across Southern Oregon continues to worsen as forest fires burn to the north, and hot, smoky days will linger through the weekend.

Air quality is listed as "moderate" in Medford but has dropped to "unhealthy" in Shady Cove and to "very unhealthy" in Klamath Falls. The air quality at Crater Lake remains "unhealthy."

The Klamath County health department posted a warning on its Web site recommending everyone avoid outdoor activity. People with breathing problems should stay indoors where air is recirculated and filtered.

John Becker, regional air quality manager at the Medford office of the Department of Environmental Quality, pointed out that smoke includes many of the smallest particles that can be inhaled deep into the lungs and that the body has little defense against.

The smoke will linger across the region through the weekend, as will unseasonably warm temperatures, the National Weather Service office in Medford reported. Valley temperatures will be well into the 90s this weekend, 10 to 15 degrees above average for the season, a special weather statement this morning said.

When the weather changes Monday, it will quickly plunge daytime highs to unseasonably cold temperatures, the statement said. Tuesday and Wednesday, high temperatures will be in the 50s and 60s across the region. Overnight freezing is expected to the east of the Cascades, and snow levels will drop to between 5,000 and 6,000 feet in the mountains. Rain showers are possible in the valleys.

— Anita Burke