Hot‐wire velocity measurements in the free stream above turbulent spots generated in a laminar boundary layer on a flat plate show that the regions of largest positive and negative longitudinal potential flow disturbance occur at about 1.5 spot heights above the surface. These regions are located above the forward and rear primary foci previously identified as points of accumulation for particle paths and as extremal points for ensemble mean velocity and temperature perturbations. A three‐dimensional linearized quasisteady potential flow similarity solution for the flow field around a moving, growing bump on the wall, with a shape given by the measured unsteady boundary layer displacement thickness, exhibits the same main features as the measured potential flow field.