Optimistic Autumn Outlook
Storms and rain have been welcome in drought affected and dry areas. However, Queensland remains a state of contrast with many cleaning up after floods and almost constant rain over late summer.
The 30 day average of the SOI remained positive through February, and was plus 21.0 for the month. The SOI Phase for February was 'Consistently Positive' (Phase 2). The outlook for March to May indicates a 50 to70 % chance of above median rainfall for most of Queensland.
Some scattered regions in the far west and south of the Queensland only have a 30 to 50%chance of exceeding median rainfall. For more information try www.longpaddock.qld.gov.au or contact me on 07 4688 1588.
Further analysis indicates rainfall for much Queensland is more likely to be close to or above the long term average (or middle third to upper third) rather than below or well below average.
Most of Queensland has received close to or above median rainfall during so far this summer. The exceptions are the far west of the state, and the south east corner, including the granite belt and eastern Darling Downs.
Currently (as at 4 March) the 30 day average of the SOI is plus 19.7.
Remember any probability forecast is just that - a probability. A 60 % chance of getting above median rainfall also means that there is still a 40 % chance of not receiving median rainfall.
For example, say your locality has a 60 % chance of exceeding the median rainfall. If your median for February is, for example, 100mm, then in other years with an SOI similar to this, 6 times out of 10 there was more than the median. In 4 out of the 10 years less than 100mm fell.
For more information on probabilities, or to explore median rainfall figures try Rainman Streamflow available from the DPI&F on 13 23 25.
The Southern Oscillation Index (SOI) is a measure of the difference in barometric air pressure between Darwin and Tahiti. It typically ranges in value from plus 30 to minus 30.
There are five different phases of monthly SOI and they are used to categorise shifts in value of the SOI from the end of one month to the next.
By using a statistical analysis of SOI phases and historical climate data (rainfall, frost, hail, temperature, etc), a forecast can be developed to indicate for example, whether the coming three months are likely to be wetter (above the median) or drier (below the median) than normal (the median).