A data set of global monthly precipitation is being constructed on a 2.5 degree latitude/longitude grid for a 50-year period from 1950 to the present.

Over global land areas, the gridded field of monthly precipitation is defined by interpolating gauge observations at over 15,000 stations collected from the version 2 data set of the Global Historical Climatology Network (GHCN) of NOAA/NCDC and the Climate Anamaly Monitoring System (CAMS) of NOAA/CPC using the optimum interpolation (OI) algorithm. The gauge-based land precipitation analysis has been completed and the data set is available through anonymous ftp at ftp.cpc.ncep.noaa.gov.

Over global oceanic areas, the analysis is defined by projecting the historical observations (e.g. gauges, COADS present weather reports) onto EOF patterns determined from satellite-based precipitation estimates for a 20-year period from 1979 to 1998, As of August 2000, the construction of the oceanic monthly precipitation analysis is still in process.