Why are temperature forecasts from the Australian Digital Forecast Database poorer on summer afternoons?

Abstract

Temperature forecast grids from the Australian Digital Forecast Database have been routinely verified since 2013. It was noted that forecast accuracy, deter-mined using root mean square error (RMSE), tends to be poorer for summer af-ternoon forecasts for each Australian state. Temperature forecast grids for Western Australia were examined to investigate possible reasons behind the re-duced accuracy. A suspected flaw in the verification process was confirmed and was found to slightly increase RMSE. Increases in summer afternoon forecast errors associated with coastal sea breezes and rainfall together with systematic bias were also identified as contributory factors to the increased RMSE. In view of these findings, a number of refinements to the verification process are pro-posed with the aim of improving future forecast accuracy.