The Distinction between Large-Scale and Mesoscale Contribution to Severe Convection: A Case Study Example

Using a case study of a relatively modest severe weather event as an example, a framework for understanding the large-scale-mesoscale interaction is developed and discussed. Large-scale processes are limited, by definition, to those which are quasi-geostrophic. Mesoscale processes are defined to be those which are linked in essence to processes occurring on both larger and smaller scales. It is proposed that convective systems depend primarily on large-scale processes for developing a suitable thermodynamic structure, while mesoscale processes act mainly to initiate convection. The case study is presented not as a “typical” event in its particulars, but rather to suggest the complex ways in which large-scale and mesoscale processes can interact. Implications for forecasting are an essential part of the discussion, since mesoscale systems are so difficult to predict with the present knowledge and technology available in operations.