Frequency Distributions of Heavy Precipitation in Illinois: Spatio-Temporal Analyses (Revised)

This document is a companion report to “Frequency Distributions of Heavy Precipitation in Illinois: Updated Bulletin 70” by Angel and Markus, published in March 2019. As stated in the Angel and Markus report, “Additional research results on precipitation relationships will be shared in a second report to be published in 2019. That report will revisit the distribution of precipitation within the storm, also known as Huff curves, along with the relationship between point and areal precipitation patterns out to 400 square miles.” Accordingly, this report shows results of the distribution of precipitation within a storm, presented in Section 1, and relations between point and areal precipitation amounts (areal reduction factor), shown in Section 2. Modified Huff curves were adopted based on new rich datasets. This study also recommended the use of the existing areal reduction factors, as the new analyses resulted in large uncertainties.