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The forecast signal is shown by colouring on the map product layers, either for individual river pixels or larger basins (see the further product details below in the subsequent sections). Each of these river pixels or basins are coloured by the expected anomaly category and the uncertainty sub-category defined for the actual forecast. There are altogether 7 anomaly categories (from 'Extreme low' to 'Extreme high') and 3 uncertainty sub-categories (from 'Low to 'High'), based on the extremity level of the 51 ensemble forecast members in the 100-value climatological distribution and the mean and standard deviation of these 51 rank values. The details of the computation methodology is described in: Placeholder CEMS-flood sub-seasonal and seasonal forecast anomaly and uncertainty computation methodology.
In total, there are 15 forecast signal categories coloured on the maps. Out of the possible combinations of the 7 anomalies and 3 uncertainties (7*3), 5*3=15 category combinations are represented by colours, after To help users to focus on the larger anomalies, a 5-anomaly categories colouring was implemented by merging the middle three anomaly categories ('Bit below', 'Normal' and 'Bit high') are merged into one 'Near normal' category. The choice of 5 anomaly categories for the colouring allows the users to focus on the larger anomalies, supplemented by the This also allows for 3-level uncertainty representation . The 7 base and 5 simplified anomaly categories, the 3 uncertainty categories and the related 15 colours are for each category. In total, there are 15 forecast signal categories coloured on the maps as shown in Figure 1.
Each of the 5 anomaly categories indicated on the maps have a distinct colour ranging from red ('Extreme low') to blue ('Extreme high'), with the 'Near normal' category indicated by the neutral grey colour, while the 3 uncertainty sub-categories are indicated by different intensities of the same colour, going from darker to lighter versions as the uncertainty increases.
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