The formation of jump-like features is explored in the context of impulsively accelerated stratified flow past two- and three-dimensional free-slip ridges. The analysis is aided by the consideration of numerical Helmholtz decompositions in which the rotational flow induced by the vorticity is explicity separated from the irrotational potential flow. Two-dimensional results suggest that for any finite mountain height the impulsively started initial-value problem inevitably evolves towards a singular jump-like feature in the lee of the obstacle. At large obstacle heights the singular feature shows a qualitative similarity to a shallow-water hydraulic jump; however, the jump-like feature is well-established long before the wave aloft has grown to the point of overturning and breaking. Consideration of the three-dimensional case shows that formation of the jump-like feature is closely associated with the formation of lee wakes and vortices.