Heat, wind and more lightning could add to fire danger in the Cascades, the National Weather Service warned today.

Heat, wind and more lightning could add to fire danger in the Cascades, the National Weather Service warned today.

The weather service's Medford office has issued a red flag warning that will be in effect until 11 p.m. across the Southern Oregon Cascades, including the areas where the Rattle, Middle Fork and Double Day fires are burning.

The warning cautions that strong winds, high temperatures and low relative humidity will create the potential for explosive fire growth.

This morning's cloud cover is expected to burn off, but another batch of moist, unstable air likely will roll in from Reno this afternoon and could bring thunderstorms, meteorologist Sven Nelaimischkies said.

"With this build up of thunderstorms, especially east of the Cascades, we could have extra fire starts," he said.

Isolated storms likely will arise on the west side of the Cascades, too, keeping fire crews hopping.

"Our fire folks should be able to handle things," Nelaimischkies said.

Tyler McCarty, protection supervisor with the Oregon Department of Forestry, said crews had been called in to work overtime to keep an eye out for lightning strikes, and an additional helicopter is standing by to tackle any new fires quickly.

The Double Day fire is 100 percent contained and all remaining hot spots are deep within the fire lines, McCarty said. Two 20-person crews, five fire engines and an incident commander remain on the scene of the fire outside Butte Falls.

The more than 20,000-acre Middle Fork fire is only 42 percent contained and still has 787 people working on its lines. This morning's fire update on InciWeb.org said crews expect increased fire activity in the face of heat, wind and dry conditions. Columns of smoke from the fire may be visible.

East winds are hitting the uncontained east flank of the fire and pushing it back on itself, the update said. Crews will continue mop-up and line reinforcement on the fire's northwest, west and southwest flanks.

As this morning's cloud cover burns off, temperatures in Medford could soar to the mid 90s, but probably won't top a record of 96 degrees set in 1987. Tuesday's temperatures should be slightly cooler, and a storm system headed this way Wednesday night opens the door for a string of systems that will bring cool and wet fall weather through the weekend.

— Anita Burke