The Next Generation Weather Radar (NEXRAD) system currently comprises 160 sites throughout the United States and select overseas locations. The NCEI archive includes the base data, called Level-II, and the derived products, called Level-III. Level-II data include the original three meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width, as well as the dual-polarization base data of differential reflectivity, correlation coefficient, and differential phase.
From the Level-II data, computer processing generates numerous meteorological analysis products known as Level-III data. All the National Weather Service (NWS) and several select continental U.S. Department of Defense NEXRAD sites record Level-II data. The majority of the sites record Level-III products. When NCEI receives the data, it is archived and disseminated.