Wheat yields in Australia have been correlated with values of the Southern Oscillation Index (SOI), an index of a major climatic phenomenon known to affect Australian rainfall. The SOI provides the basis for the seasonal prediction of rainfall. Values of the SOI, routinely available before and near the sowing date, can provide skilful yield forecasts. These forecasts would be available several months before harvest starts, require little data, and are quick and easy to prepare. The best predictors appear to be trends in the SOI, i.e. the SOI values near planting minus the values in the previous year, rather than absolute values. Wheat yield is negatively correlated with the SOI of the year prior to planting and positively correlated with the SOI during the crop season. The skill levels of SOI vary from r2 = 36% for Queensland to r2 = 6% for South Australia.