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The anomaly and uncertainty signals are determined by comparing the real time forecast ensemble members to the model climatology (see the middle-right section in Figure 1). This identifies how extreme the ensemble members of the forecast are in the context of the climatological behaviour, which is represented by the 99 percentiles and the corresponding 100 equally likely bins of the climatological range. Each ensemble member gets a rank from 1 to 100, after sorting them into one of the 100 climatological bins. The real time ensemble forecasts then will have has 51 rank values from 1 to 100.
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