The Bureau of Meteorology has been producing operational probabilistic calibrated thunderstorm guidance since October 2016. This first version of the Calibrated Thunder (CT) system sources its input from a 5-member lag ensemble of the regional and global versions of the ACCESS model (version 2) and produces output with lead times out to eight days.

Verification results have indicated that the thunder probabilities have unconditional skill for the shorter-range forecasts (to about three days), but the system skill gradually contracts to the afternoon and evening periods of the warm season as the forecast lead time is increased to eight days.

CT is now migrating to input from an 18-member global ensemble ACCESS-GE3. Apart from more than a threefold increase in membership, this new ensemble input also capitalises on ~five years of ACCESS model development, including an updated dynamical model core (ENDGame). Additionally, the calibration technique of the upgraded system will be ‘localised’ so that those parts of the model domain with low lightning predictability will no longer reduce the thunder probabilities in other parts where predictability is higher.

This presentation will introduce the planned CT upgrades in more detail, and present early verification results to show system improvements over the current operational lightning prediction guidance.