Severe weather phenomena have significant impacts on society. To be able to best forecast and prepare for these phenomena, it is essential to understand the environments in which they develop. In light of potential future changes to these environments due to climate change, determining how just knowing the large-scale storm environment can provide useful guidance about severe weather events is especially important. This project investigates how severe thunderstorm environments, represented by 0-6 km vertical wind shear and maximum updraft speed parameters calculated from NCAR's 20th Century Reanalysis, Version 2, can discriminate between times with varying levels of tornado activity. These two convective parameters are examined for four regions in the United States -- northeast, southeast, north central and south central -- from 1871 until 2008. Discrimination is evaluated by looking at high and low tornado activity years since 1954 when tornado reports are reasonably reliable. It is found that the monthly averages of these extreme values can discriminate most strongly between high and low tornado activity in the south central region. The interannual variability of the parameters is considered by looking at the complete dataset. Future research should be conducted for other variables and in other regions of the world.