Intraseasonal forecasting of the 2009 summer and winter Australian heat waves using POAMA

Abstract

Extreme heat waves occurred over much of southern and eastern Australia during the summer (27 January–8 February) and winter (14–31 August) of 2009. The summer heat wave resulted in many temperature records across southeastern Australia, as well as devastating bushfires in Victoria that caused losses of life and property. The winter heat wave primarily affected subtropical areas of eastern Australia and produced major disruptions to agricultural industries. In this study the ability of the Bureau of Meteorology’s dynamical seasonal prediction model, the Predictive Ocean Atmosphere Model for Australia (POAMA), to forecast fortnightly means for two periods corresponding to the heat waves (25 January–7 February and 15–28 August, respectively) is assessed. The forecasts are based on 10-member daily lagged-ensemble forecasts, initialized up to 30 days prior to the verification date. Ensemble mean and probabilistic forecasts are assessed. The paper forms part of a larger study investigating the use of POAMA for filling the current prediction capability gap between weather forecasts and seasonal outlooks for Australia. The most successful forecasts were initialized up to 2 weeks prior to the verification date, when POAMA demonstrated the ability to predict widespread warming over southeastern Australia for the summer event and over central and eastern Australia for the winter event. At these lead times, the ensemble mean forecast captured the midtropospheric subtropical anticyclonic anomaly over Australia that characterized both heat waves. The magnitude of the peak daytime warming in the ensemble mean forecast was, however, underpredicted, more so for the summer heat wave, and maximum warming occurred farther east than observed in both events. POAMA was able to predict temperature anomalies similar to those observed over the southeast in the ensemble initialized 0–9 days prior to the forecast verification date for the winter heat wave, thus being of potential benefit to the grain-producing regions of southeastern Australia.