Although the southern portion of the United States does have a second severe storm season in October and November, in most of the country, the summer storm season is winding down. As of this writing, 850 tornadoes have been reported in the United States so far this year, whereas in 2008, 1691 tornadoes developed.
This has been a significant drop over not only last year, but the past several years when the seasonal average has been around 1300. The overall cool spring and summer seasons over the eastern half of the United States were not as conducive to severe weather this year as it is in a more average year. Although you can never blame one factor for changes in weather, the transition from the La Nina conditions in the Pacific Ocean the past few years to our current weak El Nino probably played at least a small role in the quieter storm season experienced this year.