This tabular data set represents 30 year annual average (1961-1990) number of days of measurable precipitation 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 annual average (1961-1990) number of days of measurable precipitation was originally PRISM-based data, with some further enhancements by ClimateSource.com and then provided to the USGS by the Environmental Protection Agency (Wet_Days_Annual.zip provided by Ryan Hill, EPA, written commun., 2012). Units are days per year. It should also be noted that Climatesource.com no longer exists, however the data is free to distribute and the USGS assumes no liability with its use. It is included with this data set. 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, 2016).