High-resolution ensemble prediction of the Australian East Coast Low of April 2015

Abstract

An analysis of the East Coast Low (ECL) that affected the eastern coast of Australia between 20 and 23 April 2015 is presented, to get a better understanding of the dynamics of the storm as well as its predictability. For this, an ensemble consisting of 24 high-resolution simulations conducted using the ACCESS model is used. The simulated ensemble-mean forecast rainfall is in good agreement with the observed rainfall and identifies Dungog as the area of highest risk of extreme rainfall. A subset of ensemble members shows very little rain in the Dungog area; instead the high rainfall is located further south or east, indicating that a larger part of the coast was at some risk of significant rain. Ensemble member comparisons show that the strongest surface winds and highest rainfall occur to the south of the main surface low, while the strengthening of an upper-troposphere north-westerly jet and the associated cut-off low occur west of the surface low. However, small synoptic-scale differences between members produce large differences in the location and strength of near-surface extreme winds and highest rainfall, which develop in response to the same dynamic processes in each member. The analysis also showed that the thermal advection rainfall diagnostic is applicable to high-resolution data and could be used for analysing ECL development.