U.S. Daily Snow Cover Grids is digital data set DSI-9940, archived at the National Climatic Data Center (NCDC). SNOw Data AssimilationSystem (SNODAS) is a modeling and data assimilation system developed by the NOAA National Weather Services National Operational Hydrologic Remote Sensing Center (NOHRSC). Its purpose is to provide the best possible estimates of snow cover and associated variables to ... support hydrologic modeling and analysis. The aim of SNODAS is to provide a physically consistent framework to integrate snow data from satellite and airborne platforms, and ground stations with model estimates of snow cover. SNODAS includes procedures to ingest and downscale output form Numerical Weather Prediction (NWP) models; a physically based, spatially-distributed energy-and mass-balance snow model; and procedures to assimilate satellite-derived, airborne and ground-based observations of snow covered area and snow water equivalent. The snow model has high spatial (1 km) and temporal (1 hour) resolutions and is run for the conterminous United States. SNODAS is run each day, forced by downscaled output from the RUC2 NWP model. Each day, analysts decide whether or not to use remote sensing and ground based observations to update the snow water equivalent state in the model. Difference fields between model and observed snow water equivalent are generated. The model is then re-run for the last 6 hours of the hindcast step using scaled difference fields to 'nudge' model estimates of the snow water equivalent estimates. A 12 hour forecast of snow cover is then made using NWP output. The variables included in this archive are: Snow water equivalent, Snow depth, Snow melt runoff at the base of snow pack, Sublimation from the snow pack, Sublimation of blowing snow, Solid precipitation, Liquid precipitation, and Snow pack average temperature.