Significant tornado events associated with cell mergers

All significant tornado events (EF2+) occurring between 2006 through 2010 over the CONUS were analyzed using archived WSR-88D radar data to determine whether a merger with an ancillary cell occurred nearly coincident with the reported start time of a tornado. Further classification of events based on convective mode was conducted in order to isolate discrete tornado-producing storms from other mode types where cell merger identification is more difficult.

The large sample size of 669 cases used in this study is sufficient for some inferences about diurnal, seasonal, and geographic trends in tornado-cell merger climatology to be made. Standard environmental parameters that are commonly used in operational severe weather forecasting, such as CAPE and effective shear, were examined in an attempt to identify whether tornadic cell mergers are predictable beyond the time-scale of the convective storm life cycle. Other storm-scale characteristics, including the storm-relative position of the merger and geometric characteristics of the ancillary cells, were also examined.