This process is external to the storm, but can be intertwined with gust-front propagation. The Superior, NE, supercell of 22 June 2003 was affected by a boundary layer convergence feature. Note that storms don't always change direction upon interaction with a boundary (depends upon ambient shear, angle of interception, thermodynamics, UVV). Especially important with "high" BRN (weak shear vs. CAPE), and with storm motion somewhat parallel to the boundary layer convergence zone (next example)-"erratic" movement may occur.