A case-study of a Severe Thunderstorm Warning event in Sydney, Australia: combining forecaster input with automated nowcast guidance

The Severe Thunderstorm Warning service in Sydney, Australia, employs an innovative warning preparation system known as TIFS (Thunderstorm Interactive Forecasting System). TIFS uses TITAN to diagnose thunderstorm locations and tracks, allows the forecaster to graphically edit the automated detections, then automatically produces a warning graphic and a matching warning text for dissemination.

While TIFS would allow Severe Thunderstorm Warnings to be prepared with minimal forecaster input, experience has shown that human input remains important for an effective warning service. By combining close analysis of radar data with conceptual models of severe thunderstorms, forecasters can often significantly enhance the Severe Thunderstorm Warning product. TITAN cells, being based on reflectivity, usually depict well the potential extent of severe hail or rain, but may need to be adjusted to best represent the extent of storm-related severe winds. Forecasters can also enhance the warning product by anticipating thunderstorm intensification and new cell development, and can on occasion improve the TITAN-derived thunderstorm velocities. This paper will outline the current use of TIFS in Sydney, the value added by the human, and will provide suggestions for a more streamlined approach to the warning service, optimally combining the forecaster and the machine.

The preparation of a particular Severe Thunderstorm Warning for the greater Sydney area is described, including an assessment of the radar reflectivity and velocity data, the preparation of the warning using TIFS, and the eventual interpretation and application of the warning by emergency response personnel.