Page History

...

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 those 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 forecast then will have 51 ranks rank values from 1 to 100.

In order to display the information content of these 51 ensemble rank values, a simplified anomaly representation was necessary. For this, 7 anomaly categories were defined by the 10^th, 25^th, 40^th, 60^th, 75^th and 90^th percentiles. These will span 7 categories from 'Extreme low' to 'Extreme high'. Naturally, each of these 7 categories have a probability value, depending on how many of the 51 ensemble members they contain.

...