About 600 wildfires have burned a million acres in California in a week.

Hundreds of wildfires are burning in California, nearly one million acres have been torched in a week, and more critical fire weather conditions are being forecast for the region. Lightning may soon set even more blazes.

Since thousands of lightning strikes began hitting the state on Aug. 15, firefighters have responded to 585 wildfires, according to the state Department of Forestry and Fire Protection, known as Cal Fire. Two fire complexes have grown to be the second and third largest wildfires in California history.

The fires have torched nearly 700 homes and other structures; tens of thousands of people have evacuated; ancient redwood trees have been charred and the Giant Sequoia National Monument is located near one of the blazes.

California Gov. Gavin Newsom on Friday confirmed five deaths have associated with the fires. Separately, a Pacific Gas & Electric utility worker was found dead Wednesday in a vehicle in the Vacaville area.

More than 13,700 firefighters were on the scene, and many of the fires were continuing to grow Saturday, said Daniel Berlant, assistant deputy director for Cal Fire.

Newsom on Saturday announced that the White House had granted the state’s request for a Presidential Major Disaster Declaration – that’s despite President Donald Trump publicly chiding California over the wildfires earlier this week.

Many of the blazes were sparked by an unprecedented lightning siege of nearly 12,000 strikes over a three-day period.

The forecast for coming days has officials worried lightning may set even more fires.

Thunderstorm systems are expected to impact portions of Northern California starting early Sunday, prompting the National Weather Service to issue fire weather watches and red flag warnings, Cal Fire spokesman Daniel Berlant said Saturday afternoon.

Of particular concern: The storms could produce more dry lightning strikes, which occur without significant rainfall and often with high winds.

“The worst is not behind us,” Cal Fire Chief Thom Porter tweeted Saturday, referencing lightning activity that is expected across the state.

California fires: This is how a lightning storm can start a wildfire

Here’s what we know.

Map: How many fires are burning in California right now?

Hundreds of wildfires were burning as of Saturday, with three major fire complexes – encompassing dozens of fires – carving their way through forest, canyon country and rural areas in northern and central California.

A group of fires in Napa Valley, known as the L.N.U. Lightning Complex, was spreading through Napa, Sonoma, Lake, Yolo and Stanislaus counties. The fire has burned more than 490 square miles and is 15% contained, according to Cal Fire.

East of Silicon Valley, the S.C.U. Lightning Complex was burning in Santa Clara, Alameda, Contra Costa, San Joaquin and Stanislaus counties. The fire has burned more than 450 square miles and is 10% contained.

The L.N.U. and S.C.U. fire complexes grew to be the state’s second and third largest wildfires ever on Saturday, trailing the 2018 Mendocino Complex Fire, which burned more than 700 square miles, according to Cal Fire.

Farther west, a third complex – the C.Z.U. Lightning Complex in Santa Cruz and San Mateo counties – has burned about 100 square miles and is 5% contained.

“We have wildfires burning … the size of the state of Rhode Island. The size of the state of Rhode Island,” U.S. House Speaker Nancy Pelosi said Saturday. “It’s very, very sad. … All of us salute our firefighters.”

Hundreds of trees burn at Big Basin Redwoods State Park

California’s oldest state park, Big Basin Redwoods, has been damaged by the fires, which have charred hundreds of massive ancient coast redwoods – some more than 1,000 years old.

The fires have also damaged the park’s headquarters, historic core and campgrounds, according to the California Department of Parks and Recreation. All campers and staff had been evacuated.

Dozens of other state parks, beaches and nature reserves have also been closed.

Yosemite National Park remains open, but multiple park gateway communities are under wildfire evacuation orders.

A burned-out vehicle is seen along Highway 236 in Boulder Creek, Calif., outside of Big Basin State Park, Friday, Aug. 21, 2020, where the CZU August Lightning Complex has grown. (Shmuel Thler/The Santa Cruz Sentinel via AP)
Shmuel Thler, AP

Where will the West’s next deadly wildfire strike? The risks are everywhere

How lightning storms started California wildfires

Many of the fires were caused by a mass of lightning strikes last week – sparks that lit a tinder box of vegetation left dry and crunchy by months of persistent heat and low humidity. Read more about how those conditions evolved here.

“We’ve definitely had lightning complex fires before,” said Rick Carhart, Cal Fire public information officer for Butte County. “The scope of this one, just the fact it’s so many fires in such a large area of the state … is an anomaly.”

This particular surge of lightning-caused fires has been one of the most noteworthy in a decade, said Scott Rowe, a meteorologist with the National Weather Service.

A rare lightning storm crackles over Mitchell’s Cove in Santa Cruz, California around 3 a.m. Sunday morning August 16, 2020. The severe storm system rolled through the San Francisco and Monterey Bay areas early Sunday, packing a combination of dry lightning and high winds that triggered wildfires throughout the region. The National Weather Service on Sunday extended a red flag fire warning for the entire Bay Area until 11 a.m. Monday morning.
Shmuel Thaler, AP

Newsom on Friday attributed the phenomenon to climate change.

“These lightning strikes, this unprecedented heat dome, these world record temperatures, unprecedented in human history – we’re experiencing more and more of that because of climate change, and as a consequence, these fires are more ferocious, and they’re moving at much more rapid speeds,” Newsom said.

The fire season in California and across the West is starting earlier and ending later each year, and climate change is considered a key driver of this trend, according to Cal Fire.

“Warmer spring and summer temperatures, reduced snowpack, and earlier spring snowmelt create longer and more intense dry seasons that increase moisture stress on vegetation and make forests more susceptible to severe wildfire,” the departments says on its website.

These factors have lengthened the fire season by about 75 days across the Sierra Nevada, according to Cal Fire, which predicts that, in Northern California, “above-normal large fire potential” will persist through October. In Southern California, the department predicts there will be an above-normal large fire potential in October and November.

Wildfires in Colorado, across western states

Fires were also burning in Colorado, Utah, Montana, Oregon, Idaho, Nevada, Arizona, Texas, New Mexico and Wyoming, according to the National Wildfire Coordinating Group on Saturday.

“The heat dome that we experienced over the course of last week has not only impacted the state of California – it’s impacted the entire western United States,” Newsom said. “As a consequence of that, our mutual aid that goes outside the state of California has also been stretched.”

In Arizona, three lightning-caused wildfires forced the evacuation of multiple communities on Saturday. The Salt, Gin and Griffin fires burned a combined 50 square miles. The fires each remained uncontained.

In Colorado, Gov. Jared Polis on Friday, activated the Colorado National Guard to assist the State Emergency Operations Center and incident commanders fighting wildfires. Voluntary evacuations were underway in parts of the state.

What is the air quality and why don’t cloth face masks help?

Smoke from the fires is making the air quality in parts of California some of the worst in the world. A blanket of smoke – visible from satellite images – is covering parts of California, and the U.S. Environmental Protection Agency has listed air quality in areas across the state as “very unhealthy.”

And people in the area might not be able to smell the dangerous pollutants in the air.

Air quality experts measure the amount of fine particulate matter (PM 2.5) in the air. According to the EPA, those particles come from a variety of sources, including fires. Smoke from fires can send large amounts of PM 2.5 into the air and over large areas.

“Whenever things burn there’s a mixture of gases and particles,” said University of California, San Francisco pulmonologist Dr. John Balmes, an expert on the respiratory and cardiovascular effects of air pollutants. “When you smell smoke, you are smelling the gases in the air, not PM 2.5. … They go hand-in-hand near the fire source, but the particulates travel in the upper atmosphere.”

It’s possible to have bad air — air high in PM 2.5 — without smelling gases.

Your coronavirus mask may not protect you, unless you have a mask designed to filter PM 2.5, like an N-95. Those masks are scarce worldwide because of the pandemic. What residents really need are respirators.

Contributing: Doyle Rice, Elinor Aspegren, Wyatte Grantham-Philips, Joel Shannon, USA TODAY; Matt Brannon, Redding Record Searchlight; Brett McGinness and Amy Alonzo, Reno Gazette Journal; Kristin Scharkey, Palm Springs Desert Sun