We cannot stop them when they have 30 mph to 70 mph winds behind them. In the lightning caused Canyon Creek Complex, south of John Day, Oregon, there were spot fires being caused be winds throwing burning branches 2 miles ahead of the fire front. I worked for the Forest Service in that area 50 years ago, and we had many lightning caused fires, but never had 50+ mph winds. When you get a steady wind at that speed, and a lighting fire, you cannot control it, especially in rough terrain. And that fire burned over 175 square miles of mostly wooded hillsides, and many homes in the area.