At the current time it is not possible to anticipate the sign of any climate change in tornado occurrence or strength. (giss.nasa.gov)
Data like the number of tornadoes per day would typically be pictured as a line, from the number on day 0 (Jan. 1) to the number on day 365 (Dec. 31), with no relationship assumed between tornado occurrence on the start and end dates. (scientificamerican.com)
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)