...
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 historical weekly- or monthly-averaged values. While calendar month naturally allow consistency checks, the fixed-calendar weekly lead-times in the sub-seasonal were introduced to similarly allow allow users to directly compare forecasts from different forecast runs, as the verification periods will be is fixed onto the calendar weeks, with different corresponding lead times from the forecast, depending on the day of the week the forecast did run.
...