Precipitation nowcasting using radar-derived atmospheric motion vectors

The method to predict precipitation for couple of hours in the future, deve loped at FMI, applies modified correlation-based atmospheric motion vector (AMV) system provided by EUMETSAT. PseudoCAPPI reflectivity fields with int erval of 5 minutes are used as the input to the AMV system. That provides a smooth vector field from which a trajectory field is calculated. Speed and direction inaccuracies along the trajectories gives us an "error ellipse" around each starting point of a trajectory. The reflectivities within the e llipse are then applied to calculate a set of forecast products for 0.5 4 h ours from the initial time. The verification results show that some convent ional quantities like POD and FAR are quite sensitive to the size of the pr ecipitating area. (C) 2000 Elsevier Science Ltd. All rights reserved.