The Influence of Cell Mergers on Supercell Characteristics and Tornado Evolution on 27-28 April 2011

Numerous questions remain regarding the influence of environmental inhomogeneities on supercell evolu-tion. Motivated by this topic, this study associates cell-merger occurrence with supercell evolution and tornado production during the prolific 27-28 April 2011 outbreak in the U.S. Southeast. This event included 29 discrete supercells that pro-duced 102 tornadoes and featured 300 cell mergers. Cell-merger frequency increased for supercells that initiated farthest east, possibly owing to changes in overall convective coverage over time. There is some signal for stronger mesocyclones to be associated with more mergers in the primary supercell's forward flank. There is also a slight tendency for supercells that encounter more cell mergers to produce tornadoes more quickly, especially for those that formed away from a significant zonal boundary. However, there is a slight tendency for supercells spawning the longest-lived tornadoes (especially those with durations over 60 min) to be associated with fewer cell mergers during the 15-min window preceding tornadogenesis. Of particular importance, a significant inverse relationship exists between premerger mesocyclone strength and the subsequent change in mesocyclone strength during the merger (i.e., weaker mesocyclones tended to strengthen as a result of the merger, and vice versa). These findings highlight the influence that cell mergers can have on supercell evolution and tornado production-even within an incredibly volatile environment-and motivate future work exploring the physi-cal processes involved and ways to translate these findings into experimental techniques or guidance for operational forecasters.