  The Rayleigh scattering of cosmic microwave background (CMB) photons off the
neutral hydrogen produced during recombination effectively creates an
additional scattering surface after recombination that encodes new cosmological
information, including the expansion and ionization history of the universe. A
first detection of Rayleigh scattering is a tantalizing target for
next-generation CMB experiments. We have developed a Rayleigh scattering
forecasting pipeline that includes instrumental effects, atmospheric noise, and
astrophysical foregrounds (e.g., Galactic dust, cosmic infrared background, or
CIB, and the thermal Sunyaev-Zel'dovich effect). We forecast the Rayleigh
scattering detection significance for several upcoming ground-based
experiments, including SPT-3G+, Simons Observatory, CCAT-prime, and CMB-S4, and
examine the limitations from atmospheric and astrophysical foregrounds as well
as potential mitigation strategies. When combined with Planck data, we estimate
that the ground-based experiments will detect Rayleigh scattering with a
significance between 1.6 and 3.7, primarily limited by atmospheric noise and
the CIB.
