Recent severe weather events have prompted the European scientific community to assess the current understanding of convective processes with a view to more detailed and accurate forecasting. The initial development of convective cells remains one of the least understood aspects and one in which limited research has taken place. The important processes can be split into three main areas: boundary-layer forcing, upper-level forcing and secondary generation. This paper is a review of the mechanisms responsible for the initiation of precipitating convection in the United Kingdom; i.e. why convective clouds form and develop into precipitating clouds in a particular location.
The topography of the United Kingdom has a large influence on the initiation of convection. Boundary-layer forcings determine the specific location where convection is triggered within larger regions of potential instability. These latter regions are created by mesoscale or synoptic-scale features at a higher level such as dry intrusions and mesoscale vortices. Second-generation cells are those formed by the interaction of outflow from convective clouds with the surrounding environmental air. Large, long-lived thunderstorm complexes can develop when new cells are repeatedly triggered on one side of the system. Current and future field campaigns along with the development of high-resolution modelling will enable these processes to be investigated in more detail than has previously been achieved. © Royal Meteorological Society, 2006. Contributions by P. A. Clark and M. E. B. Gray are Crown Copyright.