COSMO-E comprises an ensemble of 21 slightly differing, but equally probable forecasts, calculated twice a day per 2.2 km horizontal grid box for the entire Alpine region. On the basis of these forecasts, the probability of particular weather events can be deduced, as can the most probable weather developments for the coming days. This method improves the quality of short to medium range forecasts for extreme and highly localised weather events, and allows the reliability of the forecasts to be estimated.
COSMO-E – probabilistic forecasts for the Alpine region
COSMO-E: Probabilistic forecasts for the Alpine region
The COSMO-E system, which is based on the COSMO ensemble-forecasting model, covers the entire Alpine region, with Switzerland at the centre of the model domain, and a horizontal grid box size of 2.2 km and 582 x 390 grid points. The corner coordinates for the forecast products are as follows: NW corner 49.52° N, 0.16° E; NE corner 49.73° N, 16.75° E; SW corner 42.67° N, 1.33° E; SE corner 42.85° N, 15.94° E. COSMO-E covers over 60 vertical layers.
Minor inaccuracies in the recording of the current atmospheric conditions can have a major impact on the reliability of weather forecasts. The objective of ensemble or probability forecasts is to take account of the existing uncertainty in respect of current conditions by calculating several forecasts with slightly varying initial and lateral boundary conditions. This spread of equally probable forecasts can then be used as a basis for calculating the probability of a certain event occurring. The ensemble also provides an assessment of the predictability of the weather conditions, allowing the reliability of the forecast to be quantified.
In contrast to IFS-HRES, the European Centre for Medium-Term Weather Forecast’s (ECMWF) low-resolution global model (with a grid box size of c. 20 km), the higher resolution of COSMO-E enables more sophisticated weather forecasts to be produced for Switzerland, particularly for extreme events such as storms or heavy precipitation.
COSMO-E for an individual location
The 21 different weather forecasts for the coming days at a particular location generated by COSMO-E can aggregated, in order to arrive at an assessment of the uncertainty of the forecast for that location.
COSMO-E probability maps
COSMO-E ensemble forecasts can also be used to produce probability maps, e.g. for precipitation. Such maps indicate the probability of a specific event occurring. The information on the probability that an event will occur can help users to make decisions.
Obtaining COSMO-E forecasts in real time
The forecasts generated with COSMO-E are available in real time and can be found under Services & publication.