This study presents an analysis of the synoptic scale influences on potential re-newable energy output for eastern Australia (the National Electricity Market (NEM) region). Common synoptic scale weather patterns are identified using a Self-Organising Map (SOM) of 1989-2009 ERA-Interim Mean Sea-Level Pres-sure (MSLP) for the Australian region. Using wind speed and surface shortwave radiation output from the Australian Community Climate and Earth-System Simulator (ACCESS) regional model (ACCESS-R) for 2010-2011, in tandem with a Genetic Algorithm, a cost-optimal placement of renewable resources for the NEM is derived. Moments of very low output from the combination of wind and solar are then analysed to show that a ridging high pressure system south of Perth and a summer continental heat low significantly co-occur with very low output. Another MSLP type represented by a cold front approaching South Aus-tralia was shown to never associate with very low output. An investigation into the 2010-2011 period when compared to the previous 21 years showed that the La Niña conditions during 2010-2011 period were more challenging than nor-mal for wind and solar for some areas. What the study also shows is that despite the large geographical area the NEM region cannot rely solely on non-dispatchable renewable electricity, without installing unrealistic amounts of over-capacity.