  The measured transverse momentum spectra and HBT correlations of bulk (i.e.
low $p_T$) matter can be well explained by assuming that the soft sector of
particles produced in ultrarelativistic heavy-ion collisions is (approximately)
thermalized and undergoes collective accelerated expansion in both longitudinal
and transverse direction. However, this implies that bulk matter will have a
non-vanishing flow component transverse to the trajectory of a high $p_T$
partonic jets. In general, this will increase the energy loss experienced by
the jet parton and modify the shape of the jet cone. In this paper, we present
a systematic study of the magnitude of the additional energy loss induced by
flow under realistic assumptions for the medium evolution. We argue that a
perturbative QGP description may be sufficient for the measured $R_{AA}$ if
flow during the medium evolution is taken into account properly.
