Federally regulated nuclear power plants and large dams are designed to withstand extreme floods produced by extreme precipitation events. Deterministic methods, such as the probable maximum precipitation (PMP), have historically been used in the computation of the probable maximum flood (PMF) for design/evaluation of protective works and hydraulic structures at these facilities. More recently, some federal agencies (i.e., Bureau of Reclamation and Nuclear Regulatory Commission) are utilizing or considering a risk-informed decision-making (RIDM) process for the evaluation of hydrologic risk for extreme floods. An important element in assessing hydrologic risk is the calculation of the likelihood of extreme floods, where the likelihood of extreme precipitation is a key contributing factor. Probabilistic methods provide a means to assess the annual exceedance probability (AEP) of extreme storms and PMP to provide insight into the level of conservatism (i.e., the resultant combination of rare probabilities of factors contributing to an extreme event) of the design-basis PMF that has been used for assessing the safety of critical facilities. The primary objectives of this probabilistic assessment study included: (i) describing the conservatism of the site-specific PMP and evaluation of the probability of the PMP using the L-moments regional precipitation frequency approach (see figure); (ii) assessment of the return period of the site-specific PMP relative to the observed storm climatology; (iii) construction of uncertainty bounds for precipitation frequency estimates; and (iv) comparison of the results with the estimates of the PMP and discuss the relevance to the PMF. This project was a collaborative effort between Leonard Rice Engineers and two Extreme Precipitation Group members, MetStat® and MGS Engineering.