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The first step is to set up a contingency table. Given criteria on time intervals to consider when matching thresholdsthreshold crossing events, the values of a , b , c and d in the table below can be filled in (where e.g. a is the number of matched observed and forecast thresholdsthreshold crossing events).
Once the contingency table has been filled, different skill scores can be established:
False Alarm Rate
Probability of Detection
Critical Success Index
Critical Reliability (checks if a forecast is available at least some time (but not too late) before the observed threshold crossing)
The First Forecast of Threshold (FFOT) is determined as the average time between the T~0~ of the forecast run in which a threshold crossing was detected and the time of the observed threshold crossing (i.e. the average lead time of the category a thresholds threshold crossing events in the contingency table).
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