CNN  — 

A wildfire in Northern California that exploded in size over the weekend has killed at least two people, forced thousands to evacuate and grown into the state’s largest wildfire this year, with lightning Monday threatening its further expansion.

The McKinney Fire broke out Friday afternoon in the Klamath National Forest near the California-Oregon border and has since ripped through more than 55,000 acres, advancing on homes and forcing nearly 2,000 residents to evacuate Saturday, authorities said.

The blaze has become California’s largest wildfire so far this year, Cal Fire Capt. Chris Bruno told CNN.

Two people were found dead Sunday morning inside a vehicle that burned in the path of the fire, the Siskiyou County Sheriff’s Office said. The two were found on a residential driveway along Doggett Creek Road near Highway 96, the sheriff’s office posted Monday morning on Facebook. Officials have not released any more information on them.

The McKinney Fire burns near Yreka, California, Saturday.

As the weekend ended, the blaze was 0% contained, and firefighters face a long battle ahead as lightning and thunderstorms complicated efforts while the flames raced through dry vegetation. Heavy smoke over the fire helped slow its growth Sunday but also kept firefighting aircraft grounded, the US Forest Service said in a Sunday night update.

Oregon state Rep. Dacia Grayber her husband, both firefighters, were camping near the California state line when they woke up Saturday to orange skies, hot wind gusts, lightning and blowing ash, she said on Twitter. They evacuated from the campground knowing one of them may return on deployment if the fire grows.

“In 22+ yrs of fire I’ve never experienced anything like this fire behavior at night. It felt absolutely surreal and not just a little apocalyptic,” Grayber tweeted.

The fire is just one symptom of the American West’s historic drought and the human-caused climate change crisis, which has caused more frequent and more severe wildfires. California’s persistent drought conditions have set the scene for rapid fire spread in the forest, with the fires burning extremely dry, receptive fuels, according to the forest service.

Sprinting through dry brush, grass and timber, the fire activity has been extreme, with the flames running uphill, and spotting further out, according to fire officials.

“Klamath National Forest is a big and beautiful forest, but it also has some steep and rugged terrain. And with that, coupled with the high temperatures, low humidity, they all come into play and make it a very extreme fire danger situation right now,” Tom Stokesberry of the US Forest Service told CNN affiliate KTVL.

Over 2 million under red flag warnings Monday

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The fire risk could intensify Monday.

“Abundant lightning” is expected through Monday, as well as scattered thunderstorms, which could spread the flames out further, according to the National Weather Service.

“These conditions can be extremely dangerous for firefighters, as winds can be erratic and extremely strong, causing fire to spread in any direction,” forest service officials said in a news release.

Dry thunderstorms like those occurring over the weekend happen when rainfall evaporates before ever hitting the ground, leaving only lightning strikes capable of sparking new fires and fueling existing ones, CNN meteorologist Robert Shackelford said.