Ventura County Fire Department officials shared a timelapse video on December 12 showing huge plumes of smoke from the Thomas Fire “collapsing,” creating conditions for rapid fire spread and change of wind direction on the ground.

It’s not yet clear when the video was shot.

In a reply to another Twitter user, the VCFD PIO explained why the collapse is dangerous: “As the plume collapses it creates a very dangerous wind shift on the ground from ‘downdraft’ winds. These winds have potential to spread fire in an outward circle from the point of collapse. Fiirefighter’s on the ground must remain aware of current and forecast weather forecasts.” Credit: Ventura County Fire Department via Storyful