Eastern Pacific SST's warm - SOI fluctuates in value Dave McRae, Qld Climate Change Centre of Excellence, 12/05/09
The monthly value of the SOI rose in value from minus 1.3 for March to plus 8.0 for April placing the SOI in a Rapidly Rising phase.
Based on historical rainfall records and a Rapidly Rising SOI phase at the end of April, there is a reasonable 60 to 80% chance of getting above median rainfall across parts of north-west, central, south and south-east Queensland during May to July. Across the rest of the state there is a 40 to 60% chance of getting above median rainfall for May through to the end of July.
For example Townsville has an 70% chance of getting above its May to July median rainfall of 50mm, Roma has a 65% chance of getting above its May to July median rainfall of 90mm, Pittsworth has a 60% chance of getting above its May to July median rainfall of 110mm, Longreach has a 60% chance of getting above its May to July median rainfall of 50mm and Emerald has a 60% chance of getting above its May to July median rainfall of 80mm.
When using a climate forecast you should remember that the probability or percent chance of something occurring is just that - a probability. For example 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%.
Since the start of the month the SOI has dropped in value. As of Monday 11 May the 30day average of the SOI had dropped to plus 0.1 (from plus 8.0 at the end of May).
While fluctuations in the value of the SOI are not unusual at this time of year (during the autumn predictability barrier) it will be interesting to see if this downward trend of the SOI is maintained over coming months. If the 30 day average of the SOI where to fall into strongly negative values and remain there, it would be a warning sign for a likely dry winter/spring.
You can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service, call me on (07) 4688 1459 or e-mail firstname.lastname@example.org
For those who like to follow the relationship between the SOI and rainfall patterns in more detail, have a look at what happened in your area during May to July in the following years since 1950 that have had a Rapidly Rising SOI phase at the end of April: 1954, 1961, 1984, 1985, 1989, 1990 and 1999.
Find out your average rainfall for May to July and see how many times rainfall was well below, well above or close to average during May to July in the listed years. For more information on historical rainfall data for your region try Rainman Streamflow or www.longpaddock.qld.gov.au
The Madden-Julian Oscillation or MJO last crossed northern Australia during the middle of April. The next active phase of the MJO is likely to cross northern Australia during the second half of May. It will be interesting to see if it co-incides with the development of the monsoon over the South China Sea.
The MJO is a band of low air pressure which originates off the east coast of central Africa. It travels eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Because of the timing of the MJO the phenomenon is also known as the forty day wave. It can be used as an indicator for the timing of potential rainfall events.
The impact of the MJO on rainfall varies between the different seasons and location. For example the MJO has a greater influence on rainfall throughout northern Australia during summer and southern Australia during winter. For more information on the MJO go to www.bom.gov.au
A neutral sea surface temperature (SST) and climate pattern can be found in the equatorial Pacific (key region running along the equator from the international dateline west towards South America). However SST's in this region though have warmed over the last couple of months. This is a trend away from the cooler La Nina like SST pattern that was a feature of the last 6 to 9 months.
It is also worth noting that a consistent and maintained warming of SST in this region throughout autumn and into winter would be viewed as a precursor for the development of an El Nino climate pattern. Therefore QCCCE staff will closely monitor what happens over the next few months especially as autumn is a key time for the establishment of climate phenomena such as El Nino and La Nina.
The majority of the surveyed global climate models are forecasting a neutral SST pattern through to at least July 2009 (ALTHOUGH WITH A WARMING SST PATTERN). Interestingly none are forecasting any potential return of La Nina or La Nina like conditions. Updates on the development of these climate patterns can be found at www.longpaddock.qld.gov.au or www.bom.gov.au/climate/enso or www.cpc.ncep.noaa.gov
SOI influence on climate varies across Australia (greatest skill is for eastern Australia) and between seasons (usually greatest skill is for winter, spring and early summer). Therefore users of the SOI and any other seasonal forecasts are urged to investigate skill level for their location by using such tools as Rainman StreamFlow.
When I'm asked about how climate information can be used I refer to a couple of key points developed from client feedback. Key points 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).
Forecasts as well do not always give a strong signal as to likely conditions for your location. In assessing climate forecasts as a management tool consider the level of signal for the key decision times in your location. Rainman StreamFlow is a useful tool for this.