PREDICTING THE MOVEMENT OF MESOSCALE CONVECTIVE COMPLEXES

A procedure for operationally predicting the movement of the mesobeta- scale convective elements responsible for the heavy rain in mesoscale convective complexes is presented. The procedure is based on the well- known concepts that the motion of convective systems can be considered the sum of an advective component, given by the mean motion of the ce lls composing the system, and a propagation component, defined by the rate and location of new cell formation relative to existing cells. Th ese concepts and the forecast procedure are examined using 103 mesosca le convective systems, 99 of which are mesoscale convective complexes. It is found that the advective component of the convective systems is well correlated to the mean flow in the cloud layer. Similarly, the p ropagation component is shown to be directly proportional (but opposit e in sign) and well correlated to the speed and direction of the low-l evel jet. Correlation coefficients between forecast and observed value s for the speed and direction of the mesobeta-scale convective element s are 0.80 and 0.78, respectively. Mean absolute errors of the speed a nd direction are 2.0 m s(-1) and 17 degrees. These errors are sufficie ntly small so that the forecast path of the centroid of the mesobeta-s cale elements would be well within the heavy rain swath of the typical mesoscale convective complex.