In this photo provided by Caltrans, smoke rises from the Head Fire in the Klamath National Forest in Northern California Tuesday.

As the Head Fire took hold Tuesday about 20 miles west of Yreka, California, a dangerous pyrocumulous cloud built up overhead.

“Early this evening, [the fire] experienced a weather event resulting in extreme fire behavior and a pyrocumulous building over the fire,” Rachel Smith, forest supervisor, wrote in a social media posting at 11 p.m. Tuesday.

Intense rising heat over a wildfire can combine with smoke and water vapor to form pyrocumulous clouds that suck in air from below, fanning flames and producing updrafts. The clouds can create downbursts and lightning, spreading fire across the landscape.

Janine Summy, a public affairs officer for the national forest, said the cloud over the Head Fire produced wind that spread flames.

“It created some winds that increased the spread of that fire,” she said.

The fire grew from a reported 20 acres at 5 p.m. Tuesday to 2,705 acres later that night. In addition to wind, the fire was driven by steep terrain, high temperatures and low humidity.

Smith on Wednesday described just how fast the fire moved.

“Just in a matter of a couple of minutes yesterday afternoon the fire grew from just 50 acres to nearly 1,500 acres,” she said. “This is the kind of growth that historically we have not experienced on our forest prior to the last couple of years.”

Overnight, the fire’s spread slowed, but another cloud built over it again Wednesday afternoon, according to video provided publicly by the University of California San Diego, in cooperation with Pacific Gas and Electric Co.

The Head Fire is burning at the confluence of the Klamath and Scott rivers, about 33 miles southwest of Ashland and about 17 miles from the California-Oregon border southeast of Applegate Lake. The fire was discovered Tuesday after lightning storms swept from east to west across a swath of forest land south of the border, sparking at least 19 other fires in the Klamath National Forest south of Jackson County and 23 fires on the Six Rivers National Forest to the west in California’s Coast Range.

Fire on the west side led to the closure of 15 miles of Highway 199 from Gasquet to Oregon Mountain Road, at 2 p.m. Wednesday, according to the California Department of Transportation. The highway is the main route from Grants Pass and Interstate 5 to the Brookings area and to Crescent City, California.

Continued heat and the threat of more lightning was forecast for late Wednesday in an area stretching from southwest of Yreka to Ashland and along the Cascade Range north to Crater Lake, according to the National Weather Service. The high temperature in Yreka was expected to reach 102 degrees Wednesday.

The Head Fire started north of the Klamath River and spread to the river’s south side, where it burned on both sides of the Scott River. Firefighters on the ground have been working to protect homes in the areas of Steelhead, Scott River Road and Highway 96, according to Summy.

“We’re very concerned for people’s well-being — their own well-being and the protection of responders,” she said. “If people don’t evacuate when they’re being asked to evacuate, the first responders potentially risk their lives [protecting those who stay behind].”

Fires burning Wednesday afternoon on the Klamath National Forest included the Ash Fire, which had burned 10-15 acres of timber and brush about 10 miles north of Yreka and three miles west of Interstate 5. Also, the Titus Fire burned about 15 acres in the Marble Mountain Wilderness south of Norcross Campground, where smokejumpers had arrived. In addition, the Scott Fire had burned about 10 acres near the Scott Bar Lookout.

In the Six Rivers National Forest, the Holiday Fire had burned 100 acres north of Patrick Creek near the Oregon-California border. And the Kelly Fire, no size listed, was burning about one mile south of Patrick Creek, with the fire visible from Highway 199.

The Lone Pine Fire, the largest fire on the Six Rivers National Forest, charred 352 acres and was burning into the Hoopa Reservation. The North Coast Interagency Type 3 Team is assigned to that fire.

The Siskiyou County Sheriff’s Office early Wednesday ordered evacuations for an area roughly 660 square miles located south of the Oregon-California border, including Seiad Valley. Highway 96 was closed from near Interstate 5 on the east nearly to Happy Camp on the west.

Specially trained hotshot crews and smokejumpers were in use on the fires Wednesday, according to Summy. Smokejumpers are firefighters who parachute into remote areas.

A Type 1 fire management team, Mueller’s Interagency Incident Command Management Team 5, was due to arrive Wednesday to manage resources combating the Head Fire.

Summy discouraged journalists from visiting the Head Fire area.

“It is extremely chaotic out there,” she said midday on Wednesday. “We are asking reporters to please stay out. We just don’t have the capacity to interface with the media out there and it’s already very congested.”

Shelters for fire evacuees have been set up in Yreka and Happy Camp, while animal shelters have been opened in Yreka. About 92 miles of the Pacific Crest Trail in Northern California was closed from the Mount Etna summit to the Oregon-California border.

Information about the Head Fire and other fires in the region can be obtained from the Klamath and Six Rivers national forests; sheriff’s departments in Siskiyou and Del Norte counties and emergency services departments in those counties.

The Associated Press contributed to this story.