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The generation of the sub-seasonal and seasonal forecast signal relies on few major steps, illustrated by a flowchart in Figure 1, with some further details described in Figure 2 and 3. The forecast anomaly and uncertainty signals are derived by comparing the real time forecast (top left section in Figure 1) to the 99-value percentile climatology (bottom left section in Figure 1). The real-time forecasts are based on the ECMWF sub-seasonal and SEAS5 seasonal meteorological forecasts (Figure 2), while the climatology is generated using reforecasts (from the same two systems) over a 20-year period, which provides range-dependent climate percentiles that change with the lead time (Figure 3).
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