The exceptional rainfall is calculated by comparing the forecasted weekly rainfall to the percentiles of the long term total observed weekly rainfall for the same week.

Exceptional Rainfall Forecast f90

This indicates a forecast where the predicted rainfall amount has a 10% chance of being exceeded in a given week, based on the long-term climate record.

Exceptional Rainfall Forecast f95

This points to a more severe weather event. The f95 threshold signifies that the forecasted rainfall is expected to be of a magnitude that is historically met or exceeded only 5% of the time.

Exceptional Rainfall Forecast f99

This is a forecast for a very rare and potentially hazardous rainfall event. The f99 designation means the predicted rainfall accumulation falls within the top 1% of historical rainfall events.