The phrase "strongest tornadoes" refers to the most powerful and destructive tornadoes. These tornadoes have extremely strong winds and can cause severe damage to buildings and the environment. Full definition
The evidence for the overrating of earlier tornadoes includes the fact that environments and damage paths of many strong tornadoes in that retrospective era shared characteristics with weaker tornadoes from later years. (livescience.com)
Check this report that states, ``... there has been little trend in the frequency of stronger tornadoes over the past 55 years.» (parentpreviews.com)
Additional, more - selective analyses by Long and Stoy show that for some states in the region and for stronger tornadoes the season advances an average of 14 days compared to 1954. (sciencedaily.com)