Tornados are mentioned only once, and not in the main series, but rather in The Incomplete Book of Dragons.
|“||Wheeling by their side, slaloming sinuously through the jutting rocks of the islands, as neat as threading a needle, are the Tornados and the Rocket Rippers, and the odd rare glimpse of a diving Phantom||”|
|— The Incomplete Book of Dragons|
This passage is introducing the Sky Dragon class chapter in the book. Therefore the Tornado is a Riding Dragon in the Sky Dragon class, and must be rather sleek-looking.
Tornados are only mentioned once, at the beginning of the Sky Dragon Class chapter.