The CEMS-flood sub-seasonal and seasonal products are essentially the same across the two systems and similarly the same across EFAS and GloFAS. Below, the available products and their main features are introduced. The example snapshots below are from EFAS seasonal forecasts, but the styling is the same for the sub-seasonal and for GLoFAS GloFAS as well, other than the different forecast lead time periods and the domain.
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In the forecast half, for each forecast period the equivalent climatology is plotted with the appropriate lead time from one climatological set. For the seasonal, where the climatology is static and produced only once for each month of the year, the climatology with the same month is displayed. For example, for an August 2024 seasonal forecast run, all reforecasts with August run dates (from 20 years) are taken and the climatological percentiles for month1 (August), month2 (September) ..., month7 (February) of those reforecasts are generated and shown on the hydrographs. For the sub-seasonal, on the other hand, the climatologies are produced dynamically for every 4 days (fixed days as 1, 5, 9, 13, 17, 21, 25, 29 of the months). So, for the forecasts, the specific climatological set will be chosen which has the run date closest to the forecast run date. So, for example, for a sub-seasonal forecast of 14 December 2024, the climatology produced for 13 December will be chosen, which is the closest to the 14th from the available climate run dates of 1, 5, 9, 13, 17, 21, 25, 29 of of December. In addition, the week-1 forecast period (the first Mon-Sun period) will have the lead time of days3-9, week-2 is days10-16, week3 is days 17-23, week4 is days24-30, week5 is days31-37 and finally week6 is days 38-44.
In the antecedent half the hydrograph, the climatology with the shortest possible lead time will always be shown. For the seasonal, this will be month-1 for each of the 6 months. For the sub-seasonal, on the other hand, it is a bit more complicated and the climatology will be the shortest days1-7 climate lead time that can covers the actual Monday-Sunday calendar week period. In the above example of the sub-seasonal run on the 14th of December 2024, which was a Saturday run, the 6 water balance weekly periods will be . If one of the available climate dates coincides with the Monday of the water balance week, then that will be directly shown. While, if the Monday falls in between two climate dates, then we show the weighted average (by the distance in days from Monday) of those two climatologies. In the above example of the sub-seasonal run on the 14th of December 2024, which was a Saturday run, the 6 water balance weekly periods will be 4-10 Nov, 11-17 Nov, 18-24 Nov, 25 Nov - 1 Dec, 2-8 Dec and 9-15 Dec, all Monday-Sunday calendar weeks. The last of these 9-15 Dec, the one before the week-1 forecast, will not be known by the time the forecast signal is generated and will only be adde a bit added later retrospectively. For this 9-15 Dec week, the Monday of 15 Dec falls in between two climate dates of 13 and 17 Dec, so the plotted cliamate will be the average of the two with 50%-50% weights (as both 13 and 17 Dec are 2 days away from 15 Dec Monday).
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Figure 4. Example snapshot of the reporting point pop-up window product's hydrograph, with different interpretation schemes (a-b-c).
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