PRISM is a set of monthly, yearly, and single-event gridded data products of mean temperature and precipitation, max/min temperatures, and dewpoints, primarily for the United States. In-situ point measurements are ingested into the PRISM (Parameter elevation Regression on Independent Slopes Model) statistical mapping system. The PRISM products use a weighted regression scheme to account for complex climate regimes associated with orography, rain shadows, temperature inversions, slope aspect, coastal proximity, and other factors. Climatologies (normals) are available at 30-arcsec (800 meters) and monthly data are available at 2.5 arcmin (4 km) resolution. PRISM is the USDA's official climatological data.
NCAR's Climate Data Guide (CDG) provides more information.