Mesoscale convective systems observed in the southern High Plains during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-central (PRE-STORM) field program were analyzed using radar and rawinsonde data. Although radar data indicate that no two systems are identical, basic recurring mesoscale structures are evident. Based on these recurrent features, the systems have been classified into three types of mesoscale convective patterns: linear mesoscale systems, occluding mesoscale systems, and chaotic mesoscale systems. Examples of all three types are discussed. High-density rawinsonde data collected in the regions ahead of the mesoscale systems have been averaged to produce composite soundings; the composites exhibit differences in both thermodynamic and wind structure between types.