The MetCoOp Ensemble Prediction System for Nordic Weather Conditions

We present the joint development, implementation and operational usage of a convection-allowing ensemble weather prediction model system for the Nordic region (see Figure). The Meteorological Cooperation on Operational Numerical Weather Prediction (MetCoOp) is unique in having three national weather services - Finland, Norway and Sweden - sharing operational model simulation, 24/7 surveillance, infrastructure (including computing resources), expertise, resources, and model development. MetCoOp strongly supports our national services in enhancing safety and securing life and property for the citizens, and is an essential part of the daily weather production. MetCoOp also facilitates closer collaboration in other areas of common interest, and the data and products are extensively used. The MetCoOp collaboration serves as a good example for future more extensive operational NWP cooperation in Europe.

In March 2014, the regional-scale AROME-MetCoOp model was put into operation by a cooperative effort of the Norwegian Meteorological Institute (MET Norway) and Swedish Meteorological and Hydrological Institute (SMHI). In January 2017 the collaboration was extended with the Finnish Meteorological Institute (FMI). AROME-MetCoOp is a branch of the shared ALADIN-HIRLAM NWP system, which is jointly developed within the framework of the two major European modelling consortia (ALADIN and HIRLAM), a research cooperation of 26 meteorological institutes. The ALADIN-HIRLAM consortia collaborate on long-term research and development of the model, as well as its code and system development. MetCoOp delivers an operational NWP system through short-term research focusing on aspects of the model system which need some extra push to become operational and/or are somewhat unique to the Nordic geographical domain. A close two-way coupling between research and operations is a main pillar in the organization of MetCoOp: It efficiently transfers results from research to operations, creating a lasting legacy in our weather prediction capacities; and the day-to-day operational weather forecasting pushes the model development.

Weather forecasting over the Nordic region spans a wide range of phenomena and scales and includes continental, maritime, and polar conditions. During summer, convective systems are common (in particular in the southeast), while polar processes, including severe polar lows, are frequently observed during winter (in the northern parts). Finland, Norway and Sweden have varying topography, complex coastlines, and gradients in land use, which imply local variations in weather. Thus, many aspects of weather forecasting in the Nordic region benefit from a local and probabilistic description of small-scale phenomena and forcing.

This presentation introduces and evaluates the AROME-MetCoOp model and collaboration after four years’ of operation. Specific modifications and updates that have been made to improve the forecast quality over the Nordics are described: Improved treatment of sea ice, a dedicated lake model and better representation of the mixture of open land and forest are some examples important for a realistic modelling of surface processes; the initial state has continuously been improved by not only including more non-conventional observations such as RADAR and GNSS and several satellite instruments but also by more refined methods to calculate the structure functions used in 3DVAR; and the performance of the ensemble system launched in late 2016 have been improved by a perturbation scheme for surface variables.