Multi-model ensembles for sea surface temperature (SST), sea surface salinity (SSS), sea surface currents (SSC), and water transports have been developed for the North Sea and the Baltic Sea using outputs from several operational ocean forecasting models provided by different institutes. The individual models differ in model code, resolution, boundary conditions, atmospheric forcing, and data assimilation. The ensembles are produced on a daily basis. Daily statistics are calculated for each parameter giving information about the spread of the forecasts with standard deviation, ensemble mean and median, and coefficient of variation. High forecast uncertainty, i.e., for SSS and SSC, was found in the Skagerrak, Kattegat (Transition Area between North Sea and Baltic Sea), and the Norwegian Channel. Based on the data collected, longer-term statistical analyses have been done, such as a comparison with satellite data for SST and evaluation of the deviation between forecasts in temporal and spatial scale. Regions of high forecast uncertainty for SSS and SSC have been detected in the Transition Area and the Norwegian Channel where a large spread between the models might evolve due to differences in simulating the frontal structures and their movements. A distinct seasonal pattern could be distinguished for SST with high uncertainty between the forecasts during summer. Forecasts with relatively high deviation from the multi-model ensemble (MME) products or the other individual forecasts were detected for each region and each parameter. The comparison with satellite data showed that the error of the MME products is lowest compared to those of the ensemble members.

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The Danish Maritime Safety Administration (DaMSA) provides forecast of elevations, currents, and other parameters to the maritime society. Accurate and reliable predictions are important to help navigate Danish waters in a safe manner, and the forecasts are routinely used by the Vessel Traffic Services in the Great Belt and the Sound. The DaMSA model setup includes three nested models, with coarse resolution in the North Atlantic and increasing to 600 m in the Belt Sea and South West Baltic. Observations of some special events in late 2009 drew attention to a possible relation between Atlantic-scale surge events and small-scale currents in the Danish Straits. During the special event with large-scale surge, the observed southward moving current in the Danish Straits was 0.5-2.0 m/s for several days, while the operational model showed a much smaller response. As a consequence, the entire DaMSA model complex was revised during 2010. Multi-annual reruns have showed that with the updated model, the explained variance of the current increases from 67% to 88%.