NMC DERF II (Reduced Version) is digital data set DSI-6125, archived at the National Climatic Data Center (NCDC). The NMC (National Meteorological Center) DERF II data set is an efficient, one-level, primitive-equation spectral model, and is NMCs 1988 Research version of the NMC medium range forecast model. DERF II is the second phase of the Dynamical Extended Range Forecast (DERF) data produced ... by the National Meteorological Center/Climate Analysis Center (now the National Centers for Environmental Prediction, NCEP) and the University of Marylands Center of Ocean, Land, and Atmosphere (COLA). DERF had been developed in response to a recommendation from the first Experimental Climate Forecast Center (ECFC) workshop held at Goddard Space Flight Center in 1987. The data set described in this document is a reduced version of DERF II and consists of 108 thirty-day forecasts starting at 00Z each day beginning 12/14/86 using the research version of the operational forecast model. The reduction was accomplished through a combination of reducing the spatial resolution and choosing a subset of fields most valuable to the immediate users. The fields selected from the original data for inclusion in this data set are the global post-processed mandatory pressure level data in the form of spherical harmonic coefficients at a resolution of rhomboidal 30 (R30). These fields are: ln (surface pressure), geopotential height, UCOSO, VCOSO, temperature, vertical velocity, and relative humidity. Global surface data are provided on a gaussian grid with 102 points in the north-south direction and 128 points in the east-west direction. The surface gridded fields are: surface temperature, soil moisture, snow depth, total rainfall, convective rainfall, surface sensible heat flux, surface latent heat flux, surface u-stress, and surface v-stress. The upper level elements were kept at 1000, 850, 700, 500, 400, 300, 250, 200, 150, and 50 mb. The exceptions are vertical velocity which was kept up to 100 mb and relative humidity which was kept up to 300 mb.