Comparison of 2 hour forecasts based on persistence and a cross-correlation technique

The NCAR Weather Support to Deicing Decision Making System (WSDDM) uses a cross-correlation technique to produce radar echo motion vectors. These vectors are then used to forecast snow water equivalent precipitation based on future echo positions with the focus on airports. It has been shown that WSDDM 30 min forecasts have large skill compared to persistence forecasts (a persistence forecast assumes that the current state will continue). This paper carries this type of comparative analysis out to two hours. Data from winter storms in the upper Midwest are evaluated and point forecasts near Chicago and Minneapolis are determined for both methods. Various echo configurations are used for the tests and include rain/snow bands, echoes from different sectors of synoptic cyclones and echoes with various reflectivity intensities.