Four-dimensional Coupled Data Assimilation System (CDAS) using a forward full-physics model in which the precipitation and clouds are an optimized combination of observed and forecast fields has been developed at the Forecast Systems Laboratory. This system, based on the Rapid Update Cycle, can provide refinements for cycling surface fields such as soil moisture and snow water equivalent because errors in both observations and model precipitation forecasts are accounted for. Observed precipitation and cloud fields are updated hourly using both GOES cloud-top pressure and NEXRAD radar reflectivity. The assimilation techniques are the extension of the the hydrometeor analysis techniques developed by Kim and Benjamin (2000), and are presented by Dongsoo Kim at this conference. The resolution of the RUC CDAS is 20 km, with high-resolution fixed surface fields from USGS (land-use) and STATSGO soil types. The preliminary results from validation of CDAS surface fields and comparison to the LDAS surface fields and RUC fields without radar reflectivity assimilation will be presented at the meeting.