The Australian National Thunderstorm Forecast Guidance System: Current Design, Verification and Future Plans

The Australian Bureau of Meteorology operationally runs a numerical model post-processing algorithm that produces a range of thunderstorm-related diagnostics such as the chance of surface-based thunderstorms or supercells. This algorithm, named the National Thunderstorm Forecast Guidance System (NTFGS), ingests model output four times a day and produces its diagnostics in 3-hourly timesteps out to 48 hours. Most of the diagnostics are currently dichotomous (yes/no) decisions which indicate that the occurrence of a convective hazard is either likely (“yes”) or not likely (“no”).

Each diagnostic is based on the exceedance of individual thresholds for the underlying ingredients. For example, for warm season surface-based thunderstorms to be diagnosed as “yes”, model-based values for the surface-based Lifted Index to 500 hPa, equilibrium level temperature, cloud depth above the freezing level, convective inhibition and vertical velocity between the surface and 850 hPa need to be exceeded simultaneously. A strength of the overall system is that an accompanying tailored graphical viewer can overlay each ingredient which highlights how the ingredients are physically coming together within the underlying model.

The NTFGS algorithm will be introduced, with the above features highlighted. Some verification results using an Australian lightning detection network will be shown, and ideas for further system development will be presented.