  Well-resolved numerical simulations are used to study
Rayleigh-B\'enard-Poiseuille flow over an evolving phase boundary for moderate
values of P\'eclet ($Pe \in \left[0, 50\right]$) and Rayleigh ($Ra \in
\left[2.15 \times 10^3, 10^6\right]$) numbers. The relative effects of mean
shear and buoyancy are quantified using a bulk Richardson number: $Ri_b = Ra
\cdot Pr/Pe^2 \in [8.6 \times 10^{-1}, 10^4]$, where $Pr$ is the Prandtl
number. For $Ri_b = \mathcal{O}(1)$, we find that the Poiseuille flow inhibits
convective motions, resulting in the heat transport being only due to
conduction; and, for $Ri_b \gg 1$ the flow properties and heat transport
closely correspond to the purely convective case. We also find that for certain
$Ra$ and $Pe$, such that $Ri_b \in \left[15,95\right]$, there is a pattern
competition for convection cells with a preferred aspect ratio. Furthermore, we
find travelling waves at the solid-liquid interface when $Pe \neq 0$, in
qualitative agreement with other sheared convective flows in the experiments of
Gilpin \emph{et al.} (\emph{J. Fluid Mech} {\bf 99}(3), pp. 619-640, 1980) and
the linear stability analysis of Toppaladoddi and Wettlaufer (\emph{J. Fluid
Mech.} {\bf 868}, pp. 648-665, 2019).
