| Southward burst mesoscale convective systems (MCSs) observed to have a component of motion in the upstream direction occurred over the southern Plains states on 11 and 12 May 1982. These MCSs are studied using observations and numerical simulations from the Penn State/National Center for Atmospheric Research mesoscale model. The large-scale flow creates a broad region of potential buoyant energy but, owing to weak large-scale forcing for upward motion and a restraining inversion, convection only is initiated where lifting associated with mesoscale features is able to eliminate the inversion. A series of eastward moving MCSs develop sequentially and propagate across the moist tongue. Each system produces an outflow of cold downdraft air that spreads progressively farther south than that from the preceding system. This conceptual model of the development and evolution of convection is very different from traditional models wherein convection develops and propagates more or less in phase with traveling upper-level disturbances.; Two 12-h simulations are conducted, beginning at 1200 UTC 11 May and 0000 UTC 12 May, respectively, to evaluate the ability of the mesoscale model to reproduce this complex evolution of events. The model reproduces the timing of initial convective development very well, while it errs in regard to propagation rates and amount of convection. This is attributed to the model parameterization schemes having a greater influence on the evolution of convection when the large-scale forcing is weak. Thus, any inaccuracies in these schemes can easily lead to divergences of the simulation from the observations.; The simulations also show that initial conditions created using only the large-scale observations are not sufficient to reproduce the events accurately. These initial conditions are modified to include mesoscale features, such as convective outflows, indicated in the surface and satellite data, but not well sampled by the upper-air observations. The improved initial conditions produce a much more reasonable simulation of the events, illustrating the importance of incorporating mesoscale features in model initial conditions when the large-scale forcing is weak. Including mesoscale features in model initial conditions is an unexplored aspect of present initialization schemes. |
