«Previous efforts have focused on tornado reports, but the connection with changes in large - scale conditions hadn't been made,» he said. (sciencedaily.com)
While one study found that the number of tornadoes reported in the United States has increased by around 14 per year over the past 50 years, the trend may have more to do with how tornadoes are tracked and reported rather than how many are actually forming. (ucsusa.org)
Lastly, we note that Professor Muller's simple analysis of tornado reports does not address possible changes in the seasonality and / or regionality of tornado occurrence. (dotearth.blogs.nytimes.com)