Heavy smoke continued to rise from the Middle Fork fire Monday, although warm, dry weather didn't bring as severe a challenge to fire crews as was initially feared, officials said.

Heavy smoke continued to rise from the Middle Fork fire Monday, although warm, dry weather didn't bring as severe a challenge to fire crews as was initially feared, officials said.

The National Weather Service office in Medford had issued a red-flag warning for Monday, cautioning that heat, wind and lightning could heighten fire danger in the Southern Oregon Cascades, including the areas where the Rattle, Middle Fork and Double Day fires have burned.

"The weather was less severe than expected," said Ken Malgren, a spokesman for the Lonesome Complex of fires. The Middle Fork fire is the only active fire in the group of several fires that were sparked by lightning in mid-August.

The blaze has burned 20,034 acres across the Rogue River-Siskiyou National Forest, Sky Lakes Wilderness, Crater Lake National Park and the Fremont-Winema National Forest. It was only 42 percent contained and 787 people were working to contain it, Monday's fire update on InciWeb.org said.

Smoke from the fire will continue to plague the Rogue Valley, Malgren said.

Cool, nighttime air drifts down from the mountains into the valley and pushes the smoke into low-lying areas far from the fire. During the day, the sun heats the surface of the earth, causing warm air to rise and creating upslope winds. These winds can push smoke out of some areas, but also can fan flames inside the fire lines.

"That's going to be routine until the smoke abates," Malgren said.

Department of Environmental Quality monitoring stations reported "moderate" air quality in Medford and Shady Cove Monday. Shady Cove hasn't seen a daily rating of "good" since Sept. 22. Medford's air quality has hovered in the moderate range since Saturday.

Fire crews now hope to have the Middle Fork fire contained by Oct. 15. Substantial rain could help them contain the fire sooner.

The 18,390-acre Rattle fire in the Umpqua National Forest is 65 percent contained, although crews found a spot fire north of a road they had hoped to use as a fire line, officials reported on InciWeb.org Monday. The fire is moving north and west through steep terrain.

The Double Day fire near Butte Falls is 100 percent contained and all remaining hot spots are deep within the fire lines, said Tyler McCarty, protection supervisor with the Oregon Department of Forestry. Two 20-person crews, five fire engines and an incident commander remained at the fire Monday mopping up hot spots inside the line and keeping an eye out for wind-driven spot fires outside the lines.

McCarty said crews had been called in to work overtime to keep an eye out for lightning strikes across Southern Oregon, and an additional helicopter was put on standby to tackle any new fires quickly. However, by early Monday evening, no lightning fires had been reported.

A batch of moist, unstable air was expected to roll in from Reno Monday afternoon, bringing a chance of thunderstorms, especially east of the Cascades, National Weather Service meteorologist Sven Nelaimischkies said.

Temperatures today will remain in the 90s, but won't approach the record of 98 degrees for Sept. 30, set in 1988.

A storm system headed into the region Wednesday night opens the door for a string of systems that could bring cool and wet fall weather through the weekend, Nelaimischkies said.