35 Ill. Adm. Code 501.390
25-Year, 24-Hour Precipitation Event
Section 501.390Â 25-Year, 24-Hour Precipitation Event
The maximum 24-hour precipitation event with a probable
recurrence interval of once in 25 years, as defined by NOAA Atlas 14;
Precipitation Frequency Atlas of the United States, incorporated by reference
in Section 501.200.