Operational, short-term prediction of rainfall using a cycled Markov chain method

The existing operational Markov technique, used by the National Meteorological Centre in Melbourne for the short-term prediction of rainfall at the eight Australian capital cities, is extended to include cycling throughout the day. In place of the current once-daily forecasts issued for the period 0600-1800, 12-hour probability of precipitation forecasts can now be issued around the clock at three-hour intervals. This ensures that forecasts have maximum timeliness and diminishes logistical problems of forecast distribution for the Regional Offices. Cycled forecasting also enables the predictions to incorporate the diurnal variations in rainfall distribution existing in some of the capital cities. A trial of the cycled system was carried out over the two-year period from January 1988to December 1989 inclusive. Results of the trial (presented as half-Brier scores and reliability diagrams) confirm the skill displayed by the method in the original non-cycled operational forecasts issued only at 0600.