Beyond the geographical proximity of the two events there were a number of superficial similarities between the tornadic storms that took place in south west Missouri on 22nd May, 2011 and on 4th May 2003. In both cases a strong tornado caused significant damage and death after the rotating storm interacted with another supercell. However, the nature of the cell mergers differed between the two events. This work will examine and compare the atmospheric environment within which the two storms evolved, the development of the systems, and the rotation within them. Particular attention will be paid to the role that the supercell mergers played in the intensification or de-intensification of the convection and rotation of each storm.