SOI in Rising Phase Dave McRae, Qld Climate Change Centre of Excellence, 2nd July 2007
Based on the rise in monthly SOI value from minus 2.5 for May to plus 5.4 for June the SOI is now in a 'Rapidly Rising' phase. With the rise in value of the SOI most of Queensland has a 50 to 70% chance of getting median rainfall for July through to the end of September.
For example Roma has a 70% chance of getting above its July to September median rainfall of 75 mm, Miles and Emerald have a 65% chance of getting above their July to September median rainfall of 85 mm and 55 mm respectively and Gympie has a 65% chance of getting above its July to September median rainfall of 115 mm.
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%.
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 July to September in the following years since 1920; 1920, 1922, 1929, 1934, 1945, 1947, 1950, 1951, 1953, 1957, 1958, 1966, 1967, 1970, 1973, 1986, 1996, 1998, 2001 and 2005. Find out your average rainfall for July to September and see how many times rainfall was well below, well above or close to average during July to September in the listed years.
It will be very interesting to see if the recent upward trend of the SOI is maintained over coming weeks or if it is just a short-term fluctuation. As stated regularly, for there to be an overall widespread and maintained improvement in conditions across the state, it would help if the SOI went into positive values for a couple of months at least. The last time the SOI was in a "Consistently Positive" phase for more than one month was from September 2000 to March 2001. Daily updates on the SOI are available on (07) 46881439 or at www.longpaddock.qld.gov.au and rainfall probability maps for Queensland, Australia and the world are at www.dpi.qld.gov.au/climate