Probable Maximum Precipitation Study for Arkansas, Louisiana, Mississippi, and Oklahoma

Investigator(s): Bill Kappel, Barry Keim, Whitney Montague, Ed Knight, Devan Mahadevan, Zachery Hollandsworth
Research Dates: 2018 - 2019
Affiliate Organization(s): Applied Weather Associates LLC • Louisiana State University • Arkansas Natural Resources Commission • Louisiana Department of Transportation • Federal Energy Regulatory Commission • Oklahoma Water Resources Board
stakeholder(s): Louisiana • Mississippi • and Oklahoma; Federal Energy Regulatory Commission • Dam Safety Offices in Arkansas • Dam Owners in Arkansas • and Oklahoma

New estimates of Probable Maximum Precipitation (PMP) were developed for Oklahoma, Arkansas, Louisiana, and Mississippi. PMP is defined as the extreme upper capacity of the atmosphere to produce rainfall if every worst case variables came together to produce the worst storm possible. The estimates were derived for 1- to 120- hours and for area sizes of 1 square mile to 20,000 square miles. The findings led to lower PMP estimates for some parts of the region which will lead to increased water storage capacity during severe storms. The express use of this information is for the design of dams and the report serves as a guiding document recognized by the Federal Energy Regulatory Commission for the design of dams across the 4-state region. It is estimated that the economic impact of this study saved dam owners between $50-100 million in design and remediation costs in the first year of the study alone. The full report is available from the Oklahoma Water Resources Board at

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