  We theoretically investigate light scattering from an array of atoms into the
guided modes of a waveguide. We show that the scattering of a plane wave laser
field into the waveguide modes is dramatically enhanced for angles that deviate
from the geometric Bragg angle. We derive a modified Bragg condition, and show
that it arises from the dispersive interactions between the guided light and
the atoms. Moreover, we identify various parameter regimes in which the
scattering rate features a qualitatively different dependence on the atom
number, such as linear, quadratic, oscillatory or constant behavior. We show
that our findings are robust against voids in the atomic array, facilitating
their experimental observation and potential applications. Our work sheds new
light on collective light scattering and the interplay between geometry and
interaction effects, with implications reaching beyond the optical domain.
