I do not know these answers offhand, but the timing of the latest winter storm is going to vary substantially based on the region of interest.  Regarding the 2011 tornado season, there probably were numerous factors, but there is a high probability that the La Nina in 2011 was a factor.  For more information on the relationship between ENSO and severe thunderstorm activity, please see this post: https://www.climate.gov/news-features/blogs/enso/enso-and-tornadoes