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.
A very cold airmass coupled with vigorous a low pressure system caused snow to fall to low levels in Tasmania last night and into this morning, leading to road delays and closures.
Shoalhaven oyster farmers face hundreds of thousands of dollars in losses as floods wash away salinity
Oyster farms flooded in this week's downpour at Greenwell Point on the New South Wales south coast could lose hundreds of thousands of dollars' worth of oysters.
Snow has affected some roads in Tasmania's south, prompting police to warn drivers to use extreme caution after a number of motorists were left stranded on Friday night.