Toward an objective climatology of extreme rainfall in the United States

The NCEP Stage IV multi-sensor precipitation analyses are used to objectively identify instances of heavy precipitation in the United States during the years 2002--2011. The analyzed precipitation amounts are compared against recurrence interval thresholds representing a 1% and 2% probability of occurrence in a given year, for 1-hour, 6-hour, and 24-hour accumulations.

In general, the distributions of events are consistent with past research on heavy local rainfall, with maxima occurring in June, July and August. There is also a maximum in 24-hour extreme rainfall points in September that is associated with landfalling tropical cyclones. Hourly heavy rainfall occurs most often from the late evening through the night, and least often in the late morning and early afternoon. This method also emphasizes the relative magnitude of precipitation events in different parts of the country.

The atmospheric processes contributing to extreme precipitation will be discussed, including results distinguishing "extreme" from "nearly extreme" weather systems. Furthermore, information will be provided that shows how other interested researchers can access and use this database of heavy rainfall events. In total, we hope to contribute a resource for extreme precipitation that is analogous to the SPC's database of tornadoes, severe hail, and severe wind reports.