Cooperative Observer Program

The NOAA Cooperative Observer Program (COOP) is a citizen weather observer network run by the U.S. National Weather Service (NWS) and National Centers for Environmental Information (NCEI). Over 8,700 volunteers from the fifty states and all territories report at least daily a variety of weather conditions such as daily maximum and minimum temperatures, 24-hour precipitation totals, including snowfall, and significant weather occurrences throughout a day that are recorded via remarks in observer logs.

Source: Wikipedia — Cooperative Observer Program (CC BY-SA 4.0)