  We study scattering amplitudes in the shadow conformal primary basis, which
satisfies the same defining properties as the original conformal primary basis
and has many advantages over it. The shadow celestial amplitudes exhibit
locality manifestly on the celestial sphere, and behave like correlation
functions in conformal field theory under the operator product expansion (OPE)
limit. We study the OPE limits for three-point shadow celestial amplitude, and
general $2\to n-2$ shadow celestial amplitudes from a large class of Feynman
diagrams. In particular, we compute the conformal block expansion of the
$s$-channel four-point shadow celestial amplitude of massless scalars at
tree-level, and show that the expansion coefficients factorize as products of
OPE coefficients.
