Prediction of lightning-producing convection over the UK using the 1.5 km resolution Operational Met Office Unified Model

Deep convective clouds which produce lightning, hail and turbulence are hazardous to aviation as well as those working outdoors. Although the UK experiences lower incidences of lightning than the continental interiors of the USA or Europe, when convective storms occur, it can be difficult to forecast whether the storms will actually produce lightning and hail.

Many traditional methods of forecasting lightning and hail occurrence, which are based on convective diagnostics, tend to significantly over-forecast the areas at risk of lightning. In order to improve these forecasts, we introduce a prognostic graupel species and a diagnostic lightning parametrization linked to graupel prediction into the operational 1.5 km Unified Model over the UK area. The lightning parametrization is evaluated over 40 case studies, equating to nearly a thousand hours of data. Results show that the model is able to give good guidance as to when and where lightning will occur. The model reproduces the observed increase in the lightning rate during the afternoon, but over-estimates the lightning flash rate when lightning does occur. In addition, the model is shown to produce accurate forecasts of lightning during the high-profile London 2012 Olympic Games.