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.
Overnight, Melbourne experienced very warm temperatures under a blanket of cloud ahead of a cold front.
There are few things farmers enjoy talking about more than weather, even if it's bad news, but it's not just farmers who have a keen eye on the skies.
The weather bureau details the seasonal outlook for Tasmania and whether any extra rainfall is on the horizon
The weather bureau has released its latest seasonal outlook covering the three months of spring which says there are no strong indications for extra rainfall.