Dangerous fire conditions continue as dozens of wildfires devastate the West

Red flag warnings are persisting across parts of the West as dozens of large wildfires continue to scorch through homes and dry earth.

A cold front bringing gusty winds and the possibility of thunderstorms is expected to pass through parts of southern Montana and southern Wyoming Sunday afternoon. Wind gusts are expected to reach up to 50 mph in some regions, while humidity will remain low -- at just 12% to 18%, according to forecasts.

More than 100 large fires are currently burning in the West, with the majority located from Northern California to western Montana.

The Dixie Fire, now the second-largest fire in California history after it has been burning near the Feather River Canyon since July 13, had singed through more than 463,000 acres by Sunday morning and was just 21% contained.

Firefighters had previously made progress on containing the Dixie Fire, but the fire re-exploded after jumping containment lines last week amid dangerous fire conditions. It has now destroyed 404 buildings as well as 185 other minor structures, damaged 27 structures and is continuing to threaten 13,871 structures.

Well over 100 home sand businesses in the downtown area of Greenville, California, about 150 miles northeast of Sacramento were decimated after dry, gusty conditions fueled the flames even further on Wednesday night.

Four people in the vicinity of the Dixie Fire are missing, the Plumas County Sheriff's Office said in a statement Saturday. Four firefighters were injured Saturday night while battling the Dixie Fire after a tree branch fell and hit them, according to officials.

The River Fire, near Colfax, California, is now 56% contained after its explosion last week prompted evacuations.

The McFarland Fire in Wildwood, California, just north of the Mendocino National Forest, has blazed through more than 30,000 acres and is 21% contained.

Six firefighters were injured on Friday while battling the McFarland Fire in Shasta Trinity National Forest. The heat was so intense that some suffered from first and second-degree burns, officials said.

Places around the world like the Western U.S. have become a "tinderbox ready to burn with any spark," Kristina Dahl, senior climate scientist for the Union of Concerned Scientists, told George Stephanopoulos on "This Week" Sunday.

"Around the world what we’re seeing is that very hot conditions tend to worsen any drought conditions that places might be experiencing," Dahl said. "So you end up with severe drought, coupled out with the drying out of vegetation, and that vegetation then becomes fuel for fires to burn."

Michael Mann, director of Penn State's Earth System Science Center, told Stephanopoulos that "dangerous" climate change has already arrived.

"We can see the impacts of climate change playing out now in real time on our television screens and in our newspaper headlines," Mann said. "...at this point it’s a question of how bad we’re willing to let it get."

The effects of the fires are also being experienced up to 1,000 miles away as the smoke from the fires travels east with the jet stream. Air quality alerts have been issued for nine states.

On Saturday afternoon, Denver had the worst quality ranking in the world, according to IQ Air, a data tool that measures and ranks air quality in cities around the world. Denver remained in the second spot on Sunday afternoon.

Air quality was also dangerous in Utah near Salt Lake City, prompting the National Weather Service to warn residents to remain indoors as much as possible.

Closer to the fires, white ash from the Dixie Fire was falling in the Lake Tahoe Basin, SF Gate reported.

Residents in Sacramento reported seeing hazy skies as a result of the smoke as the weekend rolled in, The Sacramento Bee reported.

Air quality alerts have also been issued in Southern California. The San Joaquin Valley Air Pollution Control District a health alert Saturday stating that the changing weather pattern would affect air quality in the area through Monday afternoon.

Experts advised residents in the Bay Area that they could expect smoky skies and bad air quality for decades to come.

"I think residents of the Western US are just going to have to get used to smoky skies and bad air quality as we go through the next few decades," Craig Clements, director of San Jose State University's Wildfire Interdisciplinary Research Center, told ABC San Francisco station KGO. "These fires are burning hotter, they're burning more intensely and so, they are creating a lot of smoke and it could really impact communities. So, we have to get used to that unfortunately."

ABC News' Brittany Borer and Jenna Harrison contributed to this report.