The merger of a supercell and squall line in the Great Plains. 1: Initiation of the supercell

Multiple convergence bands associated with the heterogeneous LLJ were identified, and the timing and location of CI were governed by these bands. CI occurred when one of the convergence bands moved northward to a position beneath a divergence band at the entrance of the mid‐tropospheric jet. This overlapping pattern of convergence‐divergence persisted for over an hour, facilitating both the initiation and development of the supercell.

Additionally, we observed two other episodes of CI ahead of the squall line, each with different characteristics. The first, occurring earlier than the supercell initiation, was triggered by topographic convergence in a valley but quickly dissipated. Later, as the LLJ rotated clockwise, the most prominent convergence band shifted eastward, favoring the continuous development of forward‐building cells ahead of the squall line, resulting in a T‐shaped system.