Storm rains welcome
Rain and storms over the Christmas - New Year period have bought much needed relief rain to much of Queensland. While storm rains were patchy, the continued positive summer outlook for Queensland, hopefully those areas that have missed out to date will get some rain.
Currently (as at 8 January) the 30 day average of the SOI is plus 20.3.
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. For more information try www.longpaddock.qld.gov.au http://www.longpaddock.qld.gov.au/> or contact me on 07 4688 1588.
Sea surface temperatures around the Australian coastline have increased to anomalously warm. This feature, especially combined with the La Nina, can enhance the flow of moist air across the continent. The La Nina is expected to break down during Autumn, but may have peaked in magnitude.
The MJO is now in Phase 6. During summer Phases 4 to 7 indicate enhanced probabilities of rainfall across northern Australia. The monsoon trough developed as the MJO travelled over Maritime Continent (Phases 4 to 5).
Northern Australia can expect MJO enhanced rainfall probabilities Phases 4 through 7 during summer. We usually expect to see a greater impact from the MJO on our (northern Australia) rainfall during our summer and autumn.
During summer the MJO is typically associated with Southern Hemisphere tropical storms, and cyclones in the Indian Ocean and western Pacific Ocean. At this time of year the MJO often initiates the onset of the Australian monsoon, and increased rainfall for northern Australian.
The MJO is a tropical band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. While the MJO is restricted to the tropics it affects areas well out of the tropics via teleconnections. This means that systems like the MJO interact with other weather and climate systems.
The MJO influences and is influenced by these other factors. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events in Australia. For more information try www.apsru.gov.au/mjo/
The Full Story
Lexie Donald, Qld Climate Change Centre of Excellence, 4th December 2007.
The seasonal outlook for Queensland is optimistic. Compared to this time for the past several years, there has been a moderate to strong shift of the probabilities towards a wetter outlook.
Based on a shift in monthly SOI values from plus 9.9 during November to plus to 13.3 in December the SOI is in a "Consistently Positive" phase. 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.
The chance of getting above median rainfall for much Queensland is a 50 to 70 % chance of exceeding median rainfall. As Queensland receives much of its rain during the summer period there is a very reasonable chance of getting some useful rainfall.
Some coastal regions, from Mackay to the Fraser Coast, have a higher 70 to 80 % chance of getting more than the median rainfall. Small isolated regions, predominantly in the west of the state, 40 to 50 % chance of above median rainfall. The very tip of Cape York has a lower 30-40 % chance of exceeding median rainfall, but the January - March median for this area is high compared to many areas of Queensland.
Probabilities will continue indicate median to above median rainfall if the SOI stays 'Consistently Positive' (say above plus 7.0) and remains there until autumn (March), when the existing ENSO pattern traditionally breaks down. The last time the SOI was in a "Consistently Positive" phase for more than one month was from September 2000 to March 2001.
The current outlook is an improvement on this time last year when much of the state had as low as a 10% to 30% chance of getting median rainfall.
Based on a "Consistently Positive" SOI phase at the end of December there is a 50 to 70% chance of getting median rainfall for January to March with higher rainfall probabilities (70 to 80%) along isolated coastal regions. The other exceptions are relatively scattered regions throughout the west and extreme north of the state where there is a lower 40 to 50% chance of getting median rainfall.
While these probabilities may still not be as high as some would like, there is a reasonable chance of getting useful rainfall. For example during December to February Kingaroy has a 82% chance of getting at least 200 mm, Jondaryan has a 71% chance of getting at least 180 mm, Roma has a 75% chance of getting at least 150 mm, Emerald has a 85% chance of getting at least 120 mm and St George has a 75% chance of getting at least 120 mm.
Interestingly a Near Zero SOI phase around September (like this year) is associated with an increased chance of hail and thunderstorm activity throughout northern NSW and southern Queensland. This is due to the increased instability of the middle atmosphere (600mb to 500mb) combined with cool air at those levels.
When using any probability based forecast you should remember that the probability or percent chance of something occurring is just that - a probability. If there is a 70% chance of recording more than 100 mm there is also a 30% chance of recording less than 100 mm i.e. 70-30; 30-70. It does not mean that you will get 70% more than 100 mm or 100 mm plus another 70%. For more on rainfall probabilities for your location refer to "Rainman StreamFlow".
To follow the relationship between the SOI and rainfall patterns in more detail have a look at what happened in your area during January to March in the following years: 1950, 1955, 1959, 1960, 1961, 1970, 1973, 1975, 1988, 1998, 1999, and 2000.
Find out your average rainfall for December to February and how many times rainfall was well below, well above or close to average during January to March during those years.
For those interested daily updates on the SOI are available on (07) 4688 1439 or at www.longpaddock.qld.gov.au You can also receive a text message with the latest SOI values sent to your mobile - just contact me on 4688 1588.
The MJO is currently in Phase 6 (8th January). As expected in a Nina year, the monsoon trough to developed in short order after the MJO reaches the Maritime Continent (Phase 4 -5). Northern Australia can expect MJO enhanced rainfall probabilities Phases 4 through to 7 during summer.
The next passage of the MJO (Phase 4) can now be expected in mid February. The past 2 MJO's have lingered in the western Pacific, after rapid progression eastward over the Indian Ocean basin. This is most likely due to the La Nina atmospheric signature in the western Pacific. The current MJO (Phase 6) might reasonably be expected to behave in a similar manner, and linger in the western Pacific for the next week to ten days.
At this time of year the MJO is typically associated with the Australian monsoon and increased rainfall over much of Northern Australian and also with features such as tropical cyclones. Several tropical cyclones and tropical lows have/are developing with this passage of the MJO through the tropics north of Australia.
As the summer progresses the passage of the MJO will typically be associated with Southern Hemisphere tropical storms, and also cyclones in the Indian Ocean and western Pacific Ocean. We usually expect to see a greater impact on our rainfall (northern Australia) during our summer and autumn.
The MJO is a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events. For more information try www.apsru.gov.au/mjo/
According to the Bureau of Meteorology in their "ENSO Wrap-up" available at www.bom.gov.au/climate/enso/ the La Nina is now firmly established.
For example, eastern equatorial Pacific Ocean temperatures have continued to cool and the SOI has remained weakly positive, rather than being strongly positive as during many La Nina events. However, south east trade winds have weakened with the passage of the MJO over the past week.
This La Nina developed late and was not established before the end of winter. Hence, we did not see rainy southern Australian winter-spring often associated with LA Nina conditions. The climate models used by the Bureau suggest that the La Nina event will persist until about March, before breaking down into a more neutral pattern.
Another factor influencing this 'less rainy' La Nina was Australian coastal sea temperatures, which were cooler than normal for a LA Nina event. For the general summer seasonal outlook, the chance of rain has improved as the ocean temperatures off the eastern Australian coastline have now become warmer than normal. This promotes cross-continental moisture flow.
Key points about how climate information is applied have been developed from client feedback. These include that management decisions should never be based entirely on one factor such as a climate or weather forecast. As always, everything that could impact of the outcome of a decision (soil moisture, pasture type/availability, crop and commodity prices, machinery, finance, costs etc) should be considered. For example, the level of soil moisture at planting is the major factor influencing crop yield or success.
A simple cost benefit analysis when making a major decision may also be useful. For example what will I gain if I get the desired outcome? What will I lose (sleep, money, family relationships) if I do not get the desired outcome and what other options (risk neutral) are there? A PART OF THIS PROCESS IS TO HELP MANAGERS TO BE CAREFUL NOT TO CHANGE FROM NORMAL RISK MANAGEMENT TO HIGH LEVEL RISK TAKING BASED ON A PIECE OF INFORMATION (SUCH AS A CLIMATE FORECAST).
The Climate Variability In Agriculture' (CVAP) program has an interesting site which highlights some case studies on how producers and businesses have used climate and weather information in their decision-making processes at http://www.managingclimate.gov.au/.