Two massive California wildfires have triggered new mandatory evacuation orders for thousands of people and destroyed homes and businesses in the state's north overnight.

Details: The Dixie Fire, California's biggest blaze, razed houses and businesses as it ripped through the Greenville area of Plumas County Wednesday night, per AP. The rapidly spreading River Fire burned "multiple" homes as it tore through Placer and Nevada counties, KOVR notes. Mandatory evacuation orders were in effect for both fires.

Threat level: Firefighters were facing the threat of extremely dry forests combined with Red Flag fire weather conditions overnight.

By the numbers: As of Wednesday evening, the River Fire had burned 1,400 acres and was 0% contained.

• The Dixie Fire had ravaged 278,227 acres and was 35% contained.

Context: Several, but not all, of the fires in northern California have been burning for some time.

• Illustrating the dangerous conditions in place, the River Fire exploded from a spark on Wednesday to well over 2,000 acres by dusk and growing quickly, threatening several small towns, and billowing smoke more than 30,000 feet into the sky.

Our thought bubble: The extremely dry conditions in northern California are the result of a severe drought, which is the worst the West has seen so far this century.

• Northern California as well as the neighboring states of Oregon and Washington have also experienced repetitive heat waves this summer that have dried out the forests even more, and shrunk lakes and reservoirs to record low levels.
• Human-caused climate change is driving an increase in the likelihood and severity of heat waves and droughts, and is behind a trend toward larger wildfires in much of the West in recent years, studies show.
• Last year was California's worst wildfire season on record. So far, this season is ahead of last year's pace, and the climatological peak of the season doesn't begin for several more weeks.

Editor's note: This a breaking news story. Please check back for updates.