NOAA has computed monthly total and normalized monthly total grids from daily 1-degree grids of highly reflective clouds (HRC) for January 1971 to December 1985. In addition to these grids, there are grids indicating the number of missing days in the monthly total grids, and long term means and standard deviations of normalized monthly total grids.

These data are based on once daily visible pictures from orbiting satellites. The pictures were manually inspected for highly reflective clouds. If a 1-degree lat-lon square was dominated by such clouds that were likely to be associated with precipitation, a "yes" was recorded for the square.