Firefighters working on the colossal Rim fire in and around Yosemite National Park in California were optimistic after the fire’s pace slowed on Wednesday. The blaze has burned more than 300 square miles and destroyed at least 11 houses, and it was 30 percent contained as of Thursday morning. Firefighters have relied heavily on air support, including a DC-10 tanker and a Predator surveillance drone, to slow the spread of the flames in difficult, mountainous terrain. They expect to have the fire fully contained by Sept. 20:

The fire burned about 300 acres an hour on average during the 24-hour span ending Wednesday evening, down from 1,000 acres an hour the day before. It spread 10 times faster, burning more than 3,000 acres an hour, during its peak last week. . . .

“A lot of that has to do with the fact that the weather is cooperating a lot more with us,” said Cal Fire spokesman Daniel Berlant, noting temperatures have cooled and humidity has risen.

Berlant said the constant air drops and bulldozer-dug dirt lines around the perimeter of the fire have paid off.

“There’s a lot of work that’s been done over the past week and a half now to really put this fire to bed,” Berlant said. “We are hoping that we’ve turned the corner.”

San Jose Mercury News

It is not unusual for drones to be used in fighting wildfires, as they can stay aloft through the night and access more dangerous areas. Firefighters are using the drone over Yosemite to monitor where the flames are burning:

The plane, the size of a small Cessna, will remain over the burn zone for up to 22 hours at a time, allowing fire commanders to monitor fire activity, determine the fire’s direction of movement, the extent of containment and confirm new fires ignited by lightning or flying embers.

The drone is being flown by the 163rd Wing of the California National Guard at March Air Reserve Base in Riverside and is operating from Victorville Airport, both in Southern California. It generally flew over unpopulated areas on its 300-mile flight to the Rim Fire. Outside the fire area, it will be escorted by a manned aircraft.

Officials were careful to point out the images are being used only to aid in the effort to contain the fire.

In 2009 a NASA Predator equipped with an infrared imaging sensor helped the U.S. Forest Service assess damage from a fire in Angeles National Forest. In 2008, a drone capable of detecting hot spots helped firefighters assess movement of a series of wildfires stretching from Southern California’s Lake Arrowhead to San Diego.

Associated Press

The fire is large enough and intense enough to have created clouds. The Washington Post’s Amanda Morgenthal explains the phenomenon:

Also known as a “fire cloud,” a pyrocumulus cloud looks like a normal cumulus cloud, but is formed by intense heating of the surface below it by wildfire or a volcanic eruption rather than solar energy. This is obvious by the large tower of smoke leading up to the bottom of the cloud.

Many pyrocumulus clouds formed this summer with the intense wildfires in Colorado and New Mexico. NASA has an overhead image of the pyrocumulus cloud resulting from the New Mexico Silver fire, and The Weather Channel has an incredible ground view photo of the Patch Springs Wildfire’s pyrocumulus in Utah.

If the pyrocumulus occurs in an area where the atmosphere contains a lot of water vapor, the cloud can develop into a more dangerous storm cloud just like a regular cumulus cloud. It is then called a pyrocumulonimbus (The Weather Guys).

There was an incidence of pyrocumulonimbus on August 13th in Boise, ID from the Beaver Creek Fire that is still raging. Satellite imaging is available here.

Capital Weather Gang

Visit this page for time-lapse video of the fire. Find current official information on the fire here.