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. Some stations also report stream stage or tidal levels.

A meteorological observer, or weather observer, is a person authorized by a weather authority to make or record meteorological observations. They are technicians who are responsible for the accurate observation, rapid measurement, timely collection, recording, and timely submission of meteorological parameters and information and various atmospheric phenomena to the Meteorological Center. Surface, upper air, radar, and satellite are all forms of weather observations.