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Southern Oscillation Index

location
Aus

period
Weekly
Monthly

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 Niña.

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 Niño.

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.

Southern Oscillation Index

Nino3.4 Index

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Wintry blast on the way

16:44 AEST The mild autumnal weather that southeastern Australia has been basking in this week is about to come to an abrupt and chilly end, with snow possible down to 600 metres in Tas. A strong cold front will cause the huge contrast in temperatures and is expected to sweep across southeastern Australia on Friday and into the weekend. The cold front will drag a frigid airmass over the region late this week, dropping temperatures to 3-5°C below average and bringing subzero overnight temperatures to some areas.