The prediction of two cases of severe convection: implications for forecast guidance

Summary Severe convection in the Sydney basin regularly produces destructive winds, heavy rain or flash flooding, and damage from large hail. Such convective activity is a major forecasting challenge for the Sydney basin, especially during the October to April warm season. There presently is a need to provide timely, accurate and reliable numerical guidance to supplement the current probabilistic convective outlooks, issued by the operational forecasters. Initial work has been carried out that examines two cases of severe convection in the Sydney basin. The performance of a very high resolution (2 km) numerical weather prediction (NWP) model is assessed in terms of how well it performed in providing guidance on heavy rainfall and hail, as well as other key mesoscale phenomena such as low level convergence lines. The model results discriminated well between severe convection that actually did occur in the first case (1 December, 2000) and the failure of severe convection to develop in the second case (8 December, 2000). The operational forecasters predicted severe convection to occur in both cases. It is now planned to take the next step of augmenting the quasi-subjective approach of the operational forecasters with the NWP guidance to provide an enhanced capacity to forecast severe convection in the Sydney basin. Received October 20, 2001 Revised December 28, 2001