  This paper describes LFRic: the new weather and climate modelling system
being developed by the UK Met Office to replace the existing Unified Model in
preparation for exascale computing in the 2020s. LFRic uses the GungHo
dynamical core and runs on a semi-structured cubed-sphere mesh. The design of
the supporting infrastructure follows object orientated principles to
facilitate modularity and the use of external libraries where possible. In
particular, a `separation of concerns' between the science code and parallel
code is imposed to promote performance portability. An application called
PSyclone, developed at the STFC Hartree centre, can generate the parallel code
enabling deployment of a single source science code onto different machine
architectures. This paper provides an overview of the scientific requirement,
the design of the software infrastructure, and examples of PSyclone usage.
Preliminary performance results show strong scaling and an indication that
hybrid MPI/OpenMP performs better than pure MPI.
