Probability of Precipitation Exceeding a Specified Threshold
During a Sequence of 6-Hour Forecast Periods
We estimate the probability of precipitation at any given latitude
and longitude as the fraction of the ensemble forecasts
for which precipitation exceeds the specified threshold
for that location.
Tests indicate that the ensemble has a tendency to be too wet for small amounts
of precipitation, so probabilities of precipitation tend to be overestimated
for small thresholds. On the other hand, probabilities of precipitation
tend to be underestimated for large amounts of precipitation.