A brush fire in Mariposa County showed extreme behavior as it exploded in size to 1,600 acres Friday night, prompting authorities to expand evacuation zones.
Around 3:30 p.m., about an hour and a half after it started, the Oak fire was 60 acres and 0% contained, according to the California Department of Forestry and Fire Protection. An hour later, it had grown to 611 acres. By 5:38 p.m., the blaze was 1,300 acres and remained uncontained, Cal Fire said.
Shortly before 7 p.m., the blaze had grown to about 1,600 acres, according to a Mariposa County fire map.
Some evacuating residents and observers posted photos to Twitter of a pyrocumulus cloud ballooning into the atmosphere. The cloud top reached altitudes of 25,000 to 30,000 feet early Friday night, according to Andy Bollenbacher, a meteorologist with the National Weather Service in Hanford.
Conditions in the area helped drive the fire’s rapid growth, Bollenbacher said. Relative humidity was very low — about 7% to 8% — and temperatures hovered around 95 degrees. Winds came out of the northwest at 5 to 10 mph and gusted to about 20 mph, he said.
Lighter winds Saturday could bring limited relief and tamp down the extreme spotting behavior observed Friday, but temperatures and humidity will stay about the same, Bollenbacher said.
The fire showed rapid growth and extreme behavior as it tore through an area with extremely dry fuels near “subdivisions nestled in the foothills amid dense vegetation,” Daniel Swain, a climate scientist at the University of California, Los Angeles and a California climate fellow at the Nature Conservancy, said on Twitter.
The fire started around 2 p.m. in the area of Highway 140 and Carstens Road, near Midpines, Cal Fire said.
Authorities issued an evacuation order and closures for Carstens, Buckingham Mountain and Plumbar Creek roads and for Triangle Road to Highway 140, according to the Mariposa County Sheriff’s Office. Jerseydale and all side roads were later added to the evacuation and closure list.
Deputies have received reports of people trapped in the evacuation zone either without vehicles or otherwise not able to leave, said Kristie Mitchell, spokesperson for the sheriff’s office. Units were on the way to help them evacuate.
An evacuation center has been set up at the New Life Christian Fellowship at 5089 Cole Road, the sheriff’s office said. Those with large animals should go to the Mariposa Fairgrounds and Exposition Center at 5007 Fairgrounds Road.
