Occurrences of extreme rainfall in the United States between 2002 and 2011 were identified using NCEP Stage IV precipitation analyses. The precipitation amounts were compared against the thresholds set for the 1-, 6-, and 24-hour durations for both the 50-year and 100-year recurrence intervals. Points were placed where the precipitation exceeded the threshold, and the points associated with the same weather system were combined into events.

Spatial distributions of points across the central and eastern United States became more uniformly dispersed as the timescale increased. The number of events did not produce an apparent upward or downward interannual trend. The average number of events in a given year increases from the 1-hour to 6-hour timescale; however, the average number of 24-hour events is lower. In general, there are more extreme rainfall points per event in 24-hour cases than in the other two timescales. Monthly peaks in the number of points and events vary from region to region. The maximum usually occurs during the summer months and the minimum during the winter months; however, the 24-hour total points increase from tropical systems in September. Over the entire area studied, the most active time of day was found to be at 03 UTC and the least active at 15 UTC; however, prominent times vary by region. From this database of information, the magnitude of exceptional events could be expressed quantitatively in relation to other events.