The ECMWF Integrated Forecasting System: recent progress and performance in global medium-range weather forecasts

The European Centre for Medium-Range Weather Forecasts (ECMWF) is a world leader in the production of global weather forecasts, with a strong focus on the medium-range (up to two weeks ahead). ECMWF ensemble forecasts give a direct assessment of the range of possible future weather scenarios. This allows users to take a probabilistic approach and to assess the risk of specific events that may affect their activity. This is especially important for mitigating impacts of potential extreme weather events.

The presentation will provide an overview of the ECMWF Integrated Forecasting System (IFS), and discuss recent and upcoming developments with a focus on model improvements, new products and new evaluation measures.

Recent model upgrades have improved the overall performance of the forecasting system throughout the medium range. The vertical resolution of the model was increased, enhancing the representation of clouds and boundary layers. Upgrades of vertical diffusion and orographic drag alleviate systematic wind shear and wind-turning effects in the boundary layer. Verification of wind speed at tall tower observation sites in Europe has shown that the night time winds have improved in the height range from 50 to 200m, which is relevant for wind energy applications. A revised convection scheme has been introduced that improves the diurnal cycle of convection so that the peak cloudiness and rainfall occurs later in the afternoon than in previous cycles.

In spring 2015 a new IFS cycle will introduce a large number of changes affecting all components of the forecasting system. Significant changes to the model physics, assimilation, observation usage and the ensemble configuration have shown to deliver significant analysis and forecast benefit. The model changes include modifications to the cloud scheme and activation of a lake model (FLAKE). The improvements to the cloud and precipitation physics in the model reduce the occurrence of light precipitation (drizzle) in situations where stratiform rain dominates, and also increase the amount of precipitation in heavy events. A new precipitation type parameter will be introduced, which includes freezing rain. The new lake model will improve 2m temperature forecasts in the vicinity of the (sub-grid) lakes that are now represented in the model.

ECMWF runs a real-time re-forecast ensemble to enable calibration of the operational forecast products. The re-forecasts are updated each week, initialised from start dates over the previous 20 years. With the introduction of the new cycle, the re-forecasts will be run twice a week and the size of each re-forecast ensemble will be increased from 5 to 11 members. This will provide a substantial increase in the sample size for the model climates for the medium-range Extreme Forecast Index (EFI) and the extended-range (monthly) products.

Plans for future model upgrades including an increase in horizontal resolution will be briefly reviewed.