During the first half of the simulation, a cold pool exists only in the elevated mixed layer at z = 2-4 km. After about 4 h, low θe air from mid-levels finally descends to the surface. At this time, strong diabatic cooling occurs in the 0-2 km layer, such that the cold pool extends downward, and now occupies the 0-4 km layer. Concurrently, the system develops a bow shape and produces severe winds at the surface. Passive tracers are used to diagnose the source of the strong system-generated horizontal winds. In this case, there is no evidence for an "up-down" trajectory, which has been discussed in previous studies (whereby it is hypothesized that near-surface parcels enter the system from the front and subsequently descend into the cold pool to create strong surface winds.) Rather, in this case, flow is accelerated into the back edge of the near-surface cold pool as it forms in the 0-2 km layer.