Overview of Sydney weather during the Forecast Demonstration Project

The Forecast Demonstration Project (FDP) took place from early September to late November, 2000. The goal of this paper is to document and show examples of the various types of weather events in order to provide insight into the forecasting issues. The experimental period marks the transition from early to late spring and the onset of the "severe weather" season with a dramatic increase in the probability of severe thunderstorms including large hail and tornadoes.

Sydney is a city of 5 million people and lies in a topographically complex area. This is seen by the bowing out of the seabreeze along the Sydney basin and numerous and varied topographically forced convergence lines. The higher terrain to the west is responsible for triggering much of the thunderstorm activity. Storms often die as they move off the mountains or across the sea breeze boundary. However, on occasion the storms may interact with the sea breeze and produce long lasting cells with severe weather elements, such as occurred on the November 3 tornado case discussed in detail in another paper. Other examples of significant weather include topographic modification of fronts producing a "southerly surge" up the coast, and widespread precipitation and rainbands associated with the passage of troughs. Intense "east coast cyclones" are another significant hazard, but none were experienced during the FDP.

Other issues relating to the detection of weather events will also be briefly discussed. This includes the occurrence of significant ground clutter, particularly over the higher terrain and ubiquitous sea clutter.