Summer Outlook Continues Optimistic
Rain and storms over the Christmas period have bought much needed relief rain to much of Queensland. While storm rains were are patchy, the continued positive summer outlook for Queensland, hopefully those areas that have missed out to date will get some rain.
The monsoon trough is now in place across northern Australia, bringing rain to northern centres. For example Charters Towers had over 100 mm in the last week of December. Tropical Cyclone "Melanie" and the Low pressure system to the east of Queensland are also associated with the monsoon trough, and with the recent passage of the MJO.
Currently (as at the 2nd January) the 30 day average of the SOI is plus 15.7
The 30 day average of the SOI remained positive through December, and was plus 13.3 for the month. The SOI Phase for December was 'Consistently Positive' (Phase 2). The outlook for January to March shows a 50 to 70 % chance of above median rainfall for much of Queensland.
Some regions including the coastal area from Mackay south to the Fraser Coast have a 70 to 80% chance of exceeding median rainfall. Some isolated regions in the west of the state only have a 40 to 50 % chance of exceeding their median rainfall. For more information 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. 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.
The Southern Oscillation Index (SOI) is simply 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. The phases are: Consistently Negative (SOI remains in negative values from one month to the next) Consistently Positive (SOI remains in positive values from one month to the next) Rapidly Falling (SOI significantly falls in value from one month to the next) Rapidly Rising (SOI significantly rises in value from one month to the next) Consistently Near Zero (SOI remains in a stable pattern near 0 from 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).