As the fire danger level clocks over to "extreme" for southwest Oregon, wildland firefighters are already working to snuff several blazes across the region.

Triple-digit high temperatures won't help.

"That's going to be the story for everyone: the heat," said Melissa Cano, Oregon Department of Forestry public information officer.

The National Weather Service has issued an "excessive heat warning" for a sizable chunk of the state, including Jackson and Josephine counties. The warning, in effect until 8 p.m. Thursday, comes with a forecast for daily high temperatures of 100 to 115 degrees in valley areas, and overnight lows that won't dip below 65 degrees. Across the mountains, daily highs could range from anywhere from 95 to 100 degrees, with overnight lows that won't drop below 70 degrees, the bulletin said.

The Oregon Health Authority has issued a public health warning statewide because of the heat, and are urging Oregonians to stay hydrated and limit exposure to the sun between 10 a.m. and 4 p.m., when ultraviolet rays are the strongest.

Loose-fitting, light clothing should be worn. Opening windows in the home, allowing fresh air to circulate — especially during morning and evening hours — can also help. Additional information on beating the heat and avoiding heat-related illness can be viewed online at www.oregon.gov/oha/ph/Preparedness/Prepare/Pages/PrepareForExtremeHeat.aspx.

Daily temperature records could be broken in Medford Tuesday, Wednesday and Thursday, Weather Service officials said. Tuesday's forecast of 109 degrees would dethrone the current record of 104, set in 2015.

Wednesday's high is expected to reach 114 degrees, which would beat the 105-degree record that's been in place since 1993.

A high of 111 degrees is forecast for Thursday, 5 degrees warmer than the 106-degree record set in 1987.

The all-time high temperature record for Medford — 115 degrees — set July 20, 1946, is expected to remain intact. But it'll be close.

"We haven't been above 109 since 1992," said meteorologist Dan Weygand.

The Weather Service has also issued a red-flag warning, in effect from noon to 9 p.m. Tuesday, because the heat and dry conditions have the terrain primed for new wildfires.

The heat is expected to feed several fires already burning in Jackson County's northeastern corner.

"(We're) expecting more intense fire behavior," said Karen Ripley, public information officer on the Blanket Creek fire, a lightning-sparked blaze burning nine miles northeast of Prospect in the Red Blanket drainage near the Cold Springs trailhead.

The fire was estimated at 931 acres Sunday night, and it is about 3 percent contained. The blaze is burning in a steep area on the north side of Blanket Creek, and crews are utilizing off-road vehicle trails and U.S. Forest Service Road No. 6205 as containment lines at the northern and southern ends of the fire.

About 550 personnel are assigned to the fire. Full containment is estimated by Wednesday, Aug. 9, according to the InciWeb Incident Information System website.

Crews have also responded to a new fire on Crater Lake National Park's western boundary, about 12 miles north of Blanket Creek. Dubbed the Spruce Lake fire, it has grown to about 94 acres.

The Oregon Department of Forestry has continued to work on the 31-acre Burnt Peak fire, 13 miles northeast of Shady Cove. More than 100 personnel are assigned to the fire, which is 30 percent contained.

"It's just going to be an extensive mop-up for the next few days," Cano said.

ODF crews have lined the Savage Creek fire, burning on a ridge up Savage Creek Road near Grants Pass. It was spotted Sunday night and grew to just over three acres before crews got a handle on it. It is 35 percent contained, and mop-up is underway.

About 80 firefighters are assigned to the 2,877-acre Chetco Bar fire, burning on steep slopes in the Kalmiopsis Wilderness Area. The fire is burning in areas of fire scar from the 2002 Biscuit fire and in islands of trees that were untouched by fire. The combination of old, dry fuels with a newly cured heavy grass crop make the terrain hazardous for firefighters, according to InciWeb. Tree torching is isolated. The fire is primarily burning in the understory.

No structures are threatened by any of the fires thus far. Smoke from the blazes has cast a haze on some of the hills surrounding the Rogue Valley, but air quality is still listed at "good," according to the Oregon Department of Environmental Quality Air Quality Index.

— Reach reporter Ryan Pfeil at 541-776-4468 or rpfeil@mailtribune.com. Follow him at www.twitter.com/ryanpfeil.