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The CEMS-Flood sub-seasonal products cover calendar week periods (i.e. always Monday-Sunday), while the CEMS-Flood seasonal products are valid for whole calendar month periods. The forecast signal is derived from the relationship between the calendar weekly or monthly averaged river discharge and the climatological distribution of the same historical weekly- or monthly-averaged values. While this consistency checks naturally works for the calendar months, the fixed calendar weekly lead times in the sub-seasonal allow the users to directly compare forecasts from different forecast runs, as the verification period is fixed onto the calendar weeks. This way, the evolution of the subsequent daily sub-seasonal forecast runs (always at 00 UTC) can be monitored by looking at the exact same verification period.
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Further details of the real time forecasts, reforecasts and the related generation of the climatologies are available here: Placeholder Description of the real time forecasts, reforecasts and climatologies as components of the CEMS-flood sub-seasonal and seasonal forecasts. |
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In order to display the information content of these 51 ensemble rank values, we use a simplified anomaly representation. For this, 7 anomaly categories were defined by the 10th, 25th, 40th, 60th, 75th and 90th percentiles, representing 7 categories from 'Extreme low' to 'Extreme high'. NaturallyIn the forecast, each of these 7 categories will have a probability value, depending on how many of the 51 ensemble members they contain.
The overall anomaly of the forecast is defined by the mean of the 51 ensemble member ranks (Rank-mean), which represents a robust anomaly value without any random jumpiness. In addition, the uncertainty about these anomalies is also defined by using the 51 ensemble ranks, namely by their standard deviation (Rank-std). Based on this rank standard deviation value, one of three uncertainty categories (low / medium / high) will be assigned to the forecast.
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