Based on Hoerling et al. & Wolter et al. (2016), we utilize 987 meteorological stations in the contiguous US extracted from GHCN-D (Menne et al. 2012) with at least 100 years of non-missing daily observations during 1901–2014, as well as mostly complete data in 2015. The “RX1day” index (maximum 1-day precipitation), as defined by Sillmann et al. (2013), is computed at each station for all annual and bimonthly cases (base period 1901–80).

We applied the generalized extreme value (GEV) distribution, known as the block or annual maxima approach for analysis of 20-yr precipitation events, using the Matlab NEVA package (Cheng et al. 2014). The lower confidence bounds (2.5th percentile) of the GEV-estimated return level for 20-yr events are applied in order to include all cases that might be considered of that intensity. We validated these results against the empirical estimates of the 20-yr events by ranking the annual and seasonal maxima at each station.