Variational assimilation of cloud fraction in the operational Met Office Unified Model

Short‐range forecasts of cloud cover are considered an important part of providing a public weather service in the UK. These require accurate initial conditions. Satellite imagery and surface cloud reports provide observations of cloud but using these to initialize forecast models is not easy. Cloud data are not well suited to variational analysis schemes. This paper describes how the Met Office variational analysis has been adapted to use such data. Results show that cloud observations can be usefully assimilated.