Sudden temperature changes in the Sydney Basin: Climatology and case studies during the Olympic months of September and October

The accurate prediction of sudden large changes in the maximum temperature from one day to the next remains one of the major challenges for operationa l forecasters. It is probably the meteorological parameter most commonly ve rified and used as a measure of the skill of a meteorological service and o ne that is immediately evident to the general public. Marked temperature ch anges over a short period of time have widespread social, economic, health and safety effects on the community. The first part of this paper describes a 40-year climatology for Sydney, Australia, of sudden temperature rises a nd falls, defined as maximum temperature changes of 5 degrees C or more fro m one day to the next, for the months of September and October. The nature of the forecasting challenge during the period of the Olympic and Paralympi c Games to be held in Sydney in the year 2000 will be described as a specia l application. The international importance of the accurate prediction of a ll types of significant weather phenomena during this period has been recog nized by the World Meteorological Organisation's Commission for Atmospheric Science. The first World Weather Research Program forecast demonstration p roject is to be established in the Sydney Office of the Bureau of Meteorolo gy over this period in order to test the ability of existing systems to pre dict such phenomena. The second part of this study investigates two case st udies from the Olympic months in which there were both abrupt temperature r ises and falls over a 4-day interval. Currently available high resolution n umerical weather prediction systems are found to have significant skill sev eral days ahead in predicting a large amount of the detail of these events, provided they are run at an appropriate resolution. The limitations of the se systems are also discussed, with areas requiring further development bei ng identified if the desired levels of accuracy of predictions are to be re liably delivered. Differences between the predictability of sudden temperat ure rises and sudden temperature falls are also explored. Copyright (C) 200 0 Royal Meteorological Society.