The tornado sequence happens in chapter 16 of the book. On the whole, Brian is not having a good day in chapter 16. It starts off easily enough, but by the end of the chapter Brian has been attacked by a moose, flung around by a tornado, and lost all of his supplies and tools except for his hatchet. Oh, and his shelter has been completely wiped out. The only good thing about the tornado was that it whipped up the lake water so much that it caused the tail of the plane to be poking out above the surface of the water. That allows Brian to gain access to the plane. He is able to salvage the emergency survival pack from the plane, which gives him some ready to go meals and a few tools.