Sydney 2000 Field Demonstration Project—Convective Storm Nowcasting

A primary goal of the Sydney 2000 Field Demonstration Project was to demonstrate the nowcasting of convective storms with state-of the-art nowcasting systems. For this purpose nowcasting is defined as time and place specific 0-6 hr forecasts that are heavily based on observations. This paper will summarize the scientific status of nowcasting convective storms and then describe the scientific technology used by each of the WWRP Sydney 2000 nowcasting systems. These systems make heavy use of radar echo extrapolation techniques. In addition several of the systems utilize data from satellite, radiosondes, mesonet, profiler, lightning and numerical weather prediction models. In addition to extrapolation of existing convective storms three of the systems forecast storm initiation, growth and dissipation.

Several convective storm cases from Sydney 2000 will be used to demonstrate how the different systems performed under varying situations. Although radar echo extrapolation has received considerable attention over the past 50 years significant error can be still traced to inaccurate extrapolation vectors. While large-scale synoptic conditions generally established favorable conditions for deep convection, triggering of the convection was often associated with local scale phenomena. Convection often formed and remained fixed to the mountains or along the coastline. The tendency was for storms to dissipate when moving from the mountains, and either from ocean to land or land to ocean. Typically the sea breeze moves inland without associated convection, however there are occasions where it appears to play a major role in generating severe weather. This was particularly evident during the November 3 tornado case to be discussed elsewhere in this session. As evident in previous nowcasting experiments, the lack of detailed stability conditions on the scale of a few kilometers is believed to be a major contributor to inaccurate forecasts. The use of detailed boundary layer wind fields as available from radar wind retrieval techniques (discussed in this session) shows significant promise as a means for improving convective storm nowcasts.