The National Weather Service in Medford, Oregon, shared a terrifying video of a recent fire tornado forming over a Northern California wildfire near Mount Shasta, California.Firenados, or fire whirls, occur in extreme conditions when ground-level winds come into contact with a fire and whip it into the air, creating a tornado-shaped spiral of flames.The Tennant Fire ignited June 28 on the eastern side of the Klamath National Forest near Highway 97 in Siskiyou County and was 10,614 acres with 71% containment as of Wednesday. The footage captured by the U.S. Forest Service, which is managing the blaze, shows a whirl of smoke and flames on June 29.The weather service's office in Medford, Oregon, said meteorologists noticed the rotation on June 29 and shared a radar image as further proof of the incident."Our radar indicated anticyclonic rotation on the 29th as shown by the red outbound and green inbound winds in the radar image below," the weather service wrote on Twitter.Fire crews began to make significant gains in containing the blaze on July 3 and now the fire is mainly burning within the containment lines. Cooler temperatures on Wednesday are expected to help with the effort. Evacuations remain in place in the area.The cause of the fire is under investigation, the Forest Service said.