Large wildfires ignited in California, Montana, Oklahoma, Oregon and Texas on Sunday, bringing the total number burning across the U.S. to 53, according to firefighting agency data.

The big picture: A report from the National Interagency Fire Center (NIFC) Sunday indicates the worst may be yet to come, with the "potential for lightning followed by a heat wave across the northern half of the West." This "could increase the potential for significant fire activity," per the NIFC.

• "Hot and dry conditions with very little rain will continue across the Plains, Texas, Southeast and Midwest," the agency notes.

Threat level: Red flag warnings were in effect Monday for parts of Montana and California — which have both been hit by four large fires, per the NIFC.

• There were also red flag warnings for portions of Idaho, where three large fires were burning, and Oregon, which has reported one massive blaze.
• Hawaii was also under a red flag warning as officials announced that a wildfire on the island of Maui that's razed over 370 acres and forced road closures was fully contained late Sunday, Hawaii News Now reports.

Zoom in: In California, the McKinney Fire, near the border with Oregon is the state's largest wildfire so far this year. Gov. Gavin Newsom has declared a state of emergency in response and evacuation orders remain in place in Siskiyou County.

• Among the blazes in Montana is the Elmo Fire fire in Lake County, which has razed nearly 11,000 and was 0% contained Sunday, according to Inciweb.
• In Idaho, the Moose Fire in the Salmon-Challis National Forest that ignited July 17 has destroyed nearly 49,000 acres and was 21% contained, per Inciweb.

By the numbers: Elsewhere in the U.S., NIFC data shows are were four large fires in Arizona and another three in Nevada.

• Oklahoma and New Mexico, which has experienced a series of destructive wildfires since early in the season, have each reported two large fires.
• Firefighters in Utah, Texas and Wyoming are each battling one large fire.

Meanwhile, Alaska is facing a devastating wildfire season with 27 large fires burning across more than a million acres, according to the NIFC.

What to watch: The deadly Pacific Northwest heat wave is forecast to expand east this week and envelop much of the Plains and Lower 48 states.

Context: Scientific research shows human-caused climate change is a key factor in wildfire risk.

• Much of the U.S. West is in the grip of a climate change-driven drought, which is exacerbating fire risk, per Axios' Andrew Freedman.

Go deeper: Wildfire risk will jump 30% by 2050, UN says

Editor's note: This article has been updated with new details throughout.