The relative streams are calculated at two isentropic levels. The heights of these levels can be seen in the cross section image below, the location of cross section shown in the image above it. The lower isentropic level, 310K, represents the air flow within the cold frontal layer, whereas the upper isentropic level 318K represents the air flow above the frontal layer.

The relative streams at both levels show hardly any cold air moving from behind the Cold Front into the region of the Convergence Line at upper levels. The limiting streamline in the upper levels is well within the cold front cloud band. Thus, the cold air stream from behind the front cannot contribute significantly to the development of convection. The pre-frontal convergence, at least in this case, is not triggered by over-running cold air advection (as in the case of Kata Cold Fronts), but rather by processes in the warm air ahead of the Cold Front.