Comparison of precipitation frequency distributions from National Weather Service Cooperative stations with surrounding CoCoRaHS stations

The Community Collaborative Rain, Hail and Snow network (CoCoRaHS) now has several years of data with large numbers of volunteer precipitation measurements in relatively high concentrations across the U.S. This study examines daily precipitation characteristics in five regions of the country: western Oregon, the Colorado Front Range, central Illinois, central New Jersey and the Tampa Bay area of Florida. Comparisons are made between the frequency distributions of daily precipitation from long-term National Weather Service Cooperative stations with over 100 years of data with similar frequency distributions developed from high concentrations of supplemental CoCoRaHS stations (several dozen) in the near vicinity of the COOP station with only short periods of record. The results show that most characteristics of the frequency distributions of daily events can be represented with just a few years of data from numerous nearby sites. Quantitative insight on extreme value statistics needed to estimate design rainfall and flooding for engineering and design applications, can also be derived from these short records but with more uncertainty. Results will also be presented to show how well a single data point (the NWS COOP station) represents the average regional precipitation (derived from many CoCoRaHS stations) over a period of months and years.