This is the best summary I could come up with:

Over the July 4 weekend, hundreds of fires sparked across California, feeding on the hot, dry conditions of an ongoing heat wave.

Overnight hours, when temperatures tend to go down and relative humidity, or the amount of water vapor in the air, goes up, can act as a barrier to fire.

In Siskiyou County in Northern California, the Shelly fire has grown to more than 8,200 acres since it was first sighted in the Klamath National Forest last Wednesday.

The area is under an excessive heat warning, with daytime temperatures in the triple digits, and more than 2,000 personnel are working to control the fire, which is 0 percent contained as of Wednesday morning.

Decades earlier, firefighters could rest and regroup at night, and fires required less personnel, said Kaitlyn Trudeau, a senior research associate at Climate Central who worked on the report.

Mr. Luo’s study found that while heat waves are a big contributor to extreme fire behavior, drought conditions could be the main driver.

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