Towards a deeper understanding of the scale interactions between cold fronts and convection during the European warm-season

While convection commonly initiates along synoptic-scale cold fronts during the European warm-season, rarely does convection initiate along the entirety of the boundary. This indicates smaller-scale processes, e.g., solar heating, outflow boundaries and topography, are likely responsible for the spatial and temporal onset of convective initiation. Interactions between the frontal circulation and such smaller-scale processes are not currently well-understood. Our cold-frontal convective cell climatology highlighted convective cells are most frequent marginally ahead of the surface front. On the other hand, pre-surface-frontal cells have the largest fraction associated with mesocyclones, intense convective cores and lightning. Pre-surface-frontal convergence lines, which have been observed to be linked to the western edge of elevated mixed layer plumes, could play a role in these larger cell intensity fractions.

Here we train a logistic regression model for cold-frontal convective cells based on thermodynamic and dynamic variables derived from ERA5 and assess its performance based on the area under the ROC curve (AUC). The logistic regression model exhibits high skill (AUC~0.90) but the model performance is not consistent across the cold-frontal environment. The highest model skill is for cells in the drier and cooler post-frontal airmass, whereas the lowest is for cells near the surface front. This highlights the complexity of smaller-scale processes favouring the development of convective cells near to the surface front. To further understand the underlying processes and multi-scale interactions responsible for convection initiation and cell evolution in cold-frontal environments we analyse case studies of interest in the Central European domain. We will also use these case studies to study up-scale feedbacks on the frontal structure caused by convective cells. This is an important step towards a more comprehensive understanding of scale interactions between cold fronts and convection.