In this Wednesday, Sept. 27, 2017 photo, trees charred by a fire stand in the foreground in from of North Sister and Middle Sister in the background as seen from the drive into the Boy Scouts of America Oregon Trail Council's Camp Melakwa in the Willamette National Forest near McKenzie Bridge, Ore. (Andy Nelson/The Register-Guard via AP)

HELENA, Mont. - Cool, damp weather has brought relief from wildfires in the northwestern U.S., northern Idaho and western Montana, but the fall fire season is getting underway in Southern California, forecasters said Sunday.

The risk of big wildfires will be above average for Southern California through December, the National Interagency Fire Center said in its monthly forecast .

The risk is also elevated in central and northeastern Montana through the end of October because of a severe and prolonged drought.

The forecast calls for average risk of big wildfires over much of the nation through the end of the year, although parts of the Midwest and South could face elevated danger.

Wildfires have burned more than 13,200 square miles (34,000 square kilometres) nationwide this year, putting 2017 on pace to be one of the worst in a decade.

The U.S. Forest Service, the nation's primary wildfire-fighting agency, has spent more than $2 billion on fire suppression this year, a record.

The West has been vulnerable because a wet winter produced a dense crop of grass and small trees and a hot spring dried them out, fire managers said. Summer storms brought fire-starting lightning but little rain or even humidity.

By Sunday, 13 large fires were burning on 980 square miles (2,500 square kilometres). Oregon had seven large fires, California four, and Idaho and Montana had one each.

Southern California was unusually cool and humid in mid-September, which reduced the fire danger at a time when it's usually high, the National Interagency Fire Center said. But seasonal offshore winds could dry out the vegetation and raise the fire threat again.

The centre said two wet weather systems in mid-September dampened forests and grasslands in Idaho and western Montana.

"The recent precipitation coupled with prolonged cooling over the past 10 days has essentially ended the fire season over north Idaho and western Montana," the centre said.

But 40 per cent of Montana, mostly in the northeastern corner, remains under extreme or exceptional drought conditions, according to the U.S. Drought Monitor . Big wildfires could erupt there under warm, dry and windy weather, the fire centre said.

News from © The Associated Press, 2017