- Each point on the graph represents the likelihood that a precipitation value as high as that observed over the number of months indicated at the bottom would not be exceeded. This is very similiar to the percentile, or to the rank. (0 is lowest, 50 is the median, 100 is the highest.) For example, if 90% is shown for the 12 month period, then the likelihood of a lesser value occurring over any similiar 12-month period is 90% (or 9 out of 10 similiar periods will have lesser amounts.)