  We introduce a second-order numerical scheme for compressible atmospheric
motions at small to planetary scales. The collocated finite volume method
treats the advection of mass, momentum, and mass-weighted potential temperature
in conservation form while relying on Exner pressure for the pressure gradient
term. It discretises the rotating compressible equations by evolving full
variables rather than perturbations around a background state, and operates
with time steps constrained by the advection speed only. Perturbation variables
are only used as auxiliary quantities in the formulation of the elliptic
problem. Borrowing ideas on forward-in-time differencing, the algorithm
reframes the authors' previously proposed schemes into a sequence of implicit
midpoint, advection, and implicit trapezoidal steps that allows for a time
integration unconstrained by the internal gravity wave speed. Compared with
existing approaches, results on a range of benchmarks of nonhydrostatic- and
hydrostatic-scale dynamics are competitive. The test suite includes a new
planetary-scale inertia-gravity wave test highlighting the properties of the
scheme and its large time step capabilities. In the hydrostatic-scale cases the
model is run in pseudo-incompressible and hydrostatic mode with simple
switching within a uniform discretization framework. The differences with the
compressible runs return expected relative magnitudes. By providing seamless
access to soundproof and hydrostatic dynamics, the developments represent a
necessary step towards an all-scale blended multimodel solver.
