For all types of squall lines, line motion is a result of both the advection of individual cells within the line and discrete propagation due to the triggering of new cells.

For squall lines composed of ordinary cells, each cell will tend to move with the 0-6 km mean wind. New cells will be triggered downshear in the direction of the low-level (0-3 km) vertical wind shear vector, along the leading edge of the spreading cold pool. For squall lines also composed of supercells, the supercells will be relatively long-lived and will have an additional component of motion perpendicular to the mean 0-6 km vertical wind shear vector.

For very long squall lines (greater than 200 km [110 nm] in length), individual cells may move at an angle to the line, but the net motion of the line is constrained to be perpendicular to its initial orientation, independent of the direction of the mean wind or mean wind shear vector.