Recent updates to the CASA nowcasting system

The Collaborative Adaptive Sensing of the Atmosphere (CASA) nowcasting system currently provides 0-30 min automated forecasts (nowcasts) of precipitation to National Weather Service forecasters, emergency managers, and researchers using composite X-band weather radar data. Nowcasting is accomplished in two steps. First, the Fourier-based Dynamic and Adaptive Radar Tracking of Storms (DARTS) technique computes a motion vector field representing precipitation pattern motion using a recently observed sequence of radar reflectivity fields. Then, future reflectivity fields are estimated by recursively advecting the latest observed or predicted field according to this motion vector field using a sine kernel-based method. This paper presents potential upgrades to the CASA nowcasting system. The performance of the current sine kernel-based advection method is compared to that of a backward mapping technique in terms of categorical (rain/no rain) assessments of accuracy. Because computational efficiency is an important concern given the high-resolution (0.5 km/1 min) nature of the CASA data, the respective computational efficiencies are also compared. A technique to perform temporal interpolation within the DARTS model with the potential application to data fusion is also presented and assessed.