A fascinating aspect of this case to be presented involves the early evolution, interaction and merger of cells that initiated along the dry trough just west of the Mississippi River in Missouri. Radar analysis of this evolving convection reveals a complex pattern of storm splits and mergers. Of more than a dozen initial cells along the dry trough, only 2 large long-lived supercells remained that tracked across central Illinois, spawning numerous tornadoes along their paths. It appears that differential motion due to the rotational character and phase of development of the storms led to the numerous mergers that produced the single 2 central Illinois supercells. Evidence exists that mergers may have influenced the intensification and increased the rotation of the primary supercells. Cell interactions also exist between storms that initiated on the warm front and those that approached from the dry trough to the southwest (especially those anticyclonically rotating storms resulting from storm splits). The connection between these merger events and tornadogenesis onset will be presented. A companion presentation by the authors (lead author Jewett) will present modeling results that address the role of the prominent boundaries on this day in terms of their local environment influence on storm intensity, structure and organization.
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