Multi-sensor synthesis of the mesoscale structure of a cold-air comma cloud system

Sub-synoptic scale troughs and cyclones which form on the cold-air side of the main polar front are often responsible for adverse weather. Some of the more vigorous systems contain convective rainbands that can produce locally severe weather, including thunderstorms, with strong wind gusts and small tornadoes. There has, however, been relatively little research into the mesoscale organisation of these convective features and how they relate to the larger-scale dynamics of the overall comma-cloud system. The rainbands (but not the embedded convection) occur on a scale that is just about resolvable by the finest scale operational numerical weather prediction (NWP) models. With further improvements in model resolution, as well as in model physics and data assimilation, there may be an opportunity to make very-short-range forecasts of such events more site-specific and therefore more economically beneficial than at present. In order to determine the best way forward, it is helpful to obtain a deeper understanding of the mesoscale sub-structure and processes in these weather systems. This provides the practical motivation for the present study in which we use multiple data sources to carry out a multiscale description of a vigorous cold-air comma cloud that affected the British Isles on 26 January 1999. We also make use of the mesoscale version (12 km grid) of the UK Met. Office’s Unified Model and find out just how much of the observed mesoscale structure it was capable of reproducing in its present (1999) operational form.