A cell over far eastern Sioux County demonstrated rapid growth and a split in which the southern cell developed into a super cell (fig 1).  The split occurred around 1940Z which marked roughly the end in the increasing trend of flash-rate which showed a marked increase around 1915Z (fig 2). The flash rate served as SA for cell strengthening, the TOR was issued based on the development of a mid-level mesocyclone and a trend in increasing low-level velocity couplet at 0.5 degrees.

Fig 1: Spit with subsequent supercell formation at 1957Z.

Fig 2: Increasing flash rate between 1915-1940Z. Splitting cell occurred around 1940Z.