Oolamoo, tumblebones are comparable to the eddies on the fringes and on the inside of a jet stream. The turbulence they create is due to how strong the jet stream is. The jet stream usually blows anywhere between 80-140 mph (sometimes, in excess of 200 mph). Usually, these eddies are quite strong, probably strong enough to warrant the name "tumblebones", since any owl that happens to end up in one is surely dead if they aren't a good flier and/or make a fast exit. Oh, and that windstorm on page 92 in The War of The Ember; I am pretty sure that is a really strong mid-latitude cyclone (low pressure system that you see in weather maps). Reading about the position of the River of Wind, it sounds like the perfect set of conditions for bomogenesis. The setup sounds like a cut-off low from the jet stream, and the jet stream causes air to funnel up and out of it very quickly (lows rotate counter-clockwise, and air spirals inward and up) causing large pressure falls (24mb/hr, Bomogenisis). Basically, the storm itself rapidly strengthens in wind speed. Since mid-latitude lows usually take a few days to spin down, I bet it stuck around a while (Don't take my word for it, haven't read Book 15 in a while).
Sorry about the delay, I was slammed last semester of high school, and I felt that I was not confident enough yet to answer your question, so I waited until the end of my Meteorology class this semester at college