Figure 6 . 1951 UTC 7 June 1997. One plausible explanation for the longevity and strength of this boundary may be that the westward moving outflow, analogous to a density current, encountered little resistance, and in fact was most likely propelled by the momentum from east to northeast synoptic scale flow in the low levels. This high resolution data revealed that there were actually two boundaries propagating across southern Minnesota. Location of boundaries indicated by bold sawtooth contour.
Wind barbs are in knots.
Cloud cover is coded in the center of station model with none being clear, a single line few too scattered, and two lines broken. Shaded topographic relief map of a region. Higher terrain indicated by shades of red and lower terrain in yellow. Although the first boundary is hard to distinguish from surrounding convective rolls on the reflectivity image, the velocity data marks the leading edge of the boundary more clearly with stronger inbound winds over southwest Minnesota. Westward propagation of the boundaries was consistent with trailing easterly wind velocities resulting in weak system-relative convergence.