During wintertime (October to April), helicopters flying in the North Sea have encountered lightning where it was not expected or forecast. It is thought that the presence of the helicopter triggers the majority of lightning strikes, since there is generally little or no natural lightning activity in the area in question around the time of the strike. Furthermore, strike rates are much higher than would be expected if due purely to chance. However, there has been little progress to date in both understanding this phenomenon and the ability to predict triggered lightning strike occurrence with NWP data.
Using forecast data from the Met Office Unified Model, an algorithm for triggered lightning risk has been produced. Evaluation against past helicopter strike cases has demonstrated that the new algorithm forecasts lightning risk for 80% of cases when triggered lightning occurred. The algorithm also correctly forecast 8/9 natural lightning strikes which were observed in the operating area during winter 20102011. This presentation will cover the details of the algorithm as well as our current research into the understanding of helicopter-triggered lightning.