This tabular data set represents PRISM 30-year average (1961-1990) relative humidity (percent) compiled for two spatial components of the NHDPlus version 2 data suite (NHDPlusv2) for the conterminous United States; 1) individual reach catchments and 2) reach catchments accumulated upstream through the river network. This dataset can be linked to the NHDPlus version 2 data suite by the unique identifier COMID. The source data for 30-year average (1961-1990) relative humidity (percent) was originally PRISM-based data, with some further enhancements by ClimateSource.com and then provided to the USGS by the Environmental Protection Agency (Ryan Hill, EPA, written commun., 2011). It should be noted this data set is discontinued and may be available only by contacting the PRISM Group at Oregon State University directly. Units are percent. Reach catchment information characterizes data at the local scale. Reach catchments accumulated upstream through the river network characterizes cumulative upstream conditions. Network-accumulated values are computed using two methods, 1) divergence-routed and 2) total cumulative drainage area. Both approaches use a modified routing database to navigate the NHDPlus reach network to aggregate (accumulate) the metrics derived from the reach catchment scale. (Schwarz and Wieczorek, 2018).