Cloud and hydrometeor analysis using metar, radar, and satellite data within the RUC/Rapid-Refresh model

NOAA Forecast Systems Laboratory has developed a combined cloud/hydrometeor assimilation technique utilizing surface, radar and satellite data within the RUC model. Within this assimilation procedure, data from various observing systems are combined with fully cycled model cloud/hydrometeor fields to update an evolving a three-dimensional description of cloud/precipitation systems. Within the RUC, five species of cloud (water and ice) and precipitation (rain, snow, graupel) are cycled. GOES cloud-top pressure/temperature information is used to specify cloud top and areas of no cloudiness. METAR surface observations of broken/overcast cloud layers are used to define cloud base. In addition METAR visibility and current weather observations are used to modify near-surface hydrometeor fields and adjust cloud depths. Radar reflectivity data are used to modify rain water and snow mixing ratios obtained from the previous 1-h RUC forecast.

Work is underway to update the radar analysis module to make use of a three-dimensional radar reflectivity mosaic being produced by the National Severe Storms Laboratory (in place of the two-dimensional radar reflectivity product currently be used). Additional work is beginning to explore the use of experimental advanced GOES satellite products from NASA Langley. Finally, a parallel effort will begin this fall to build RUC cloud/hydrometeor analysis features into a modified version of the Global Statistical Interpolation (GSI) package. This modified GSI will be utilized by the Rapid Refresh modeling system, which is slated to replace the RUC at NCEP in 2007. The Rapid-Refresh will expand hourly cycled predictions to a domain covering all of North America, including Alaska and the Caribbean.