What Influences Whether Convection will Cross the English Channel?

Oral Presentation

Severe convective events impacting the UK are often associated with convection that forms on or near the coastline of continental Europe, or over the continent itself, and is advected and/or propagates towards and across the UK. These events form a forecasting challenge throughout the summer with the operational community perceiving that convective-scale numerical weather prediction models have deficiencies in the representation of these events. Thus, it is beneficial to understand environmental factors which could help explain why “English Channel-crossing” convection occurs. 

An impactful case study is examined in three model configurations to identify the environmental factors that help determine whether convection will cross the English Channel. We show that, to a leading order, two factors help to influence whether convection will cross the English Channel: i) the presence of reservoirs of Convective Inhibition (CIN), and ii) the strength of the convection. These factors are independent of whether convection is parametrized and are consistent across all ensemble members. Therefore, combining the two factors could allow for a physically-based probabilistic perspective on whether convection will cross the English Channel. 

This probabilistic method would be based on whether there is sufficient lifting or vertical velocity within the convection or convective inflow environment to allow the CIN to be overcome during any stage of the convective lifecycle. The method presented exploits probabilistic forecasting in a process-based framework to ensure physical reasoning behind the probabilities and leads to improved forecasts for these hard to predict events and their associated impacts.