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The left half of the plot, left of the horizontal dotted line indicating the forecast start, is the antecedent condition section. This part includes black dots (connected by black line), which shows show the average weekly (sub-seasonal) or monthly (seasonal) discharge from the so-called water balance, the proxi observations, which are produced as a LISFLOOD simulation forced with either gridded meteorological observations in EFAS, or ERA5 meteorological reanalysis fields in GloFAS. This represents the simulated reality, as close as it can go to reality in EFAS and GloFAS. It always includes 6 lead time periods of the past on the hydrographs, either the 6 calendar weeks before the first week of the forecast in the sub-seasonal, or 6 calendar months before the first month of the forecast in the seasonal (as in Figure 4a). The black dots are added to the hydrographs retrospectively, after each week (in sub-seasonal) or month (in seasonal) passes and the weekly or monthly mean proxi-observed river discharge values become available. For the seasonal forecast hydrograph, the water balance is known for all 6 past months at the time of the forecast hydrographs are prodced, run, produced, while for the sub-seasonal the last week of the antecedent section will not have a water balance black dot, as that is not available yet at the time of the production. The users are encouraged to go back and check previous forecasts to see how well the earlier forecasts predicted the anomalies.
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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).
The right half of the plot covers the forecast horizon, The right half of the plot covers the forecast part, in the displayed example in Figure 4 this means 7 lead times of 7 calendar months from August to February (next year) (see Figure 4a). The forecast distribution is indicated by box-and-whiskers, displaying the , while for the sub-seasonal it will be either 5 weeks or 6 weeks, depending on the forecast run date. The forecast distribution is indicated by box-and-whiskers, displaying the minimum and maximum values in the ensemble forecasts of all the 51 members and the lower and upper quartiles (25th and 75th percentiles) and the median (the 50th percentile).
The colour-shaded background in the hydrograph is the model climatology (see Figure 4b). The climatology is generated using reforecasts over a 20-year period. From the climatology, the 5 anomaly categories are coloured, the below 10th percentile zone ('Extreme low' with red), the 10th to 25th percentile zone ('Low' with orange), the 25th to 75th percentile zone (extended 'Near normal' with grey), the 75th to 90th percentile zone ('High' with cyan) and the above 90th percentile ('Extreme high' with blue). Further information on the climatologies and their generation is given on: Placeholder CEMS-flood sub-seasonal and seasonal forecast signal generation methodology.
In the forecast half, for each forecast period the equivalent climatology is plotted with that specific 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 roughly every 4 days (1, 5, 9, 13, 17, 21, 25, 29 of the months). So, for the forecasts, the 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, 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 in December.
In the antecedent half the hydrograph, the climatology with the shortest possible lead time will always be shown. For the seasonal, this will be the month-1 lead time, 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 lead time that can covers the actual Monday-Sunday calendar week periods from the most recent cliamate set. In the above example of the sub-seasonal run on the 14th of December 2024, which was a Saturday, 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. Thus, the first water balance antecedent period will be the Monday-Sunday before the week-1 forecast, which will be 9-15 December. So, at the time of the generation of the forecast for the 14 December, the water balance for this week will still not be known.
from lead time 1, so first week (always as days 1-7) or first month (whichever month of the year it is), as that is the closest equivalent to the proxi-observation-based climatology. While in the forecast half, for each forecast period the equivalent climatology is plotted with that specific lead time.
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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).
The coloured background behind the forecast box-and-whiskers plot The coloured background is the model climatology (see Figure 4b). This The climatology is generated using reforecasts over a 20-year period. Further information on the climatologies and their generation is given on: Placeholder CEMS-flood sub-seasonal and seasonal forecast signal generation methodology. The past past half of the hydrograph (left from the forecast run date vertical dotted line) includes 6 lead time period, either the 6 calendar weeks before the first week of the forecast in the sub-seasonal, or 6 calendar months period before the first month of the forecast. climatology forecast side of the climatology is always from lead time 1, so first week (always as days 1-7) or first month (whichever month of the year it is), as that is the closest equivalent to the proxi-observation-based climatology. While in the forecast half, for each forecast period the equivalent climatology is plotted with that specific lead time. From the climatology, the 5 anomaly categories are coloured, below the 10th the 'Extreme low' with red, above the 90th percentile the 'Extreme high' with blue, the 10th to 25th percentiles zone as 'Low' with orange, the 75th to 90th percentiles as 'High' with cyan and finally the remaining 25th to 75th percentile as 'Near normal' with grey. This 'Near normal' category is the extended one by merging the original 25-40, 40-60 and 60-75 percentile categories, including the narrower 'Near normal', the 'Bit low' and 'Bit high' categories.
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Unfortunately, this feature of contrasting the climatological behaviour at shorter and longer lead times, does not work for the sub-seasonal, as there is no 52+1 weeks available in the hydrograph (it would not be physically possible), which would be necessary to see the same week appearing as a week-1 climatology of the past period and as a week-6 climatology of the forecast.
The past past half of the hydrograph (left from the forecast run date vertical dotted line) includes 6 lead time period, either the 6 calendar weeks before the first week of the forecast in the sub-seasonal, or 6 calendar months period before the first month of the forecast.
Probability evolution table
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