Southern Oscillation Index
The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.
A strongly and consistently positive SOI pattern (e.g. consistently above about +6 over a two month period) is related to a high probability of above the long-term average (median) rainfall for many areas of Australia, especially areas of eastern Australia (including northern Tasmania) - La Niņa.
Conversely, a 'deep' and consistently negative SOI pattern (less than about minus 6 over a two month period, with little change over that period) is related to a high probability of below median rainfall for many areas of Australia at certain times of the year - El Niņo.
However, it is important to remember that the pattern of relationship between SOI and rainfall (and temperature) can vary depending on the particular season and region. Additionally, the change in SOI over a specified period can be as important in understanding relationships between SOI and rainfall as is the absolute value in SOI.
Bedgerabong in the central west of New South Wales has been isolated by flood waters.
Farmers across Western Australia's grain growing regions have been dealt a bitter blow, with their hopes of record crops dashed by frost just weeks before harvest.
Wet weather "on par" with a system that caused widespread flooding across Adelaide earlier this month has been forecast to hit the Mount Lofty Ranges on Wednesday and Thursday.