More accuracy with less precision

Abstract

Reducing the numerical precision of the forecast model of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF) from double to single precision results in significant computational savings without negatively affecting forecast accuracy. The computational savings allow to increase the vertical resolution of the operational ensemble forecasts from 91 to 137 levels earlier than anticipated and before the next upgrade of ECMWF's high-performance computing facility. This upgrade to 137 levels harmonises the vertical resolution of the medium-range deterministic forecasts and the medium-range and extended-range ensemble forecasts. Increasing the vertical resolution of the ensemble forecasts substantially improves forecast skill for all lead times as well as the mean of the model climate. ECMWF's ensemble and deterministic forecasts will run operationally at single precision from IFS model cycle 47R2 onwards.