SOI in Rapidly Falling Phase Dave McRae Qld DPI&F 06/11/06
Based on the SOI and historical rainfall records the chance of getting median rainfall throughout southern Queensland varies between 30 to 50% for November through to the end of January. While this is not high it is an improvement when compared to most of the last 9 to 12 months. The chance of getting median rainfall throughout central and northern Queensland is generally lower and varies between 10 to 40%. The main exception is for the far north west of the state along the Northern Territory border where there is a 50 to 70% chance of getting above median rainfall for November to January.
For example Ayr has a low 18% chance of getting its November to January median rainfall of 360 mm, Winton has a 25% chance of getting its November to January median rainfall of 130 mm, Mackay has a 27% chance of getting its November to January median rainfall of 500 mm, Wyandra has a 45% chance of getting its November to January median rainfall of 100 mm and both Roma and Gatton have a 55% chance of getting their November to January median rainfall of 190 mm and 255 mm respectively.
It is worth noting that even for those areas with a low chance of getting median rainfall that as we are entering our spring/summer rainfall season there is a still a reasonable chance of getting some useful relief rain.
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 November to January in the following years that have had a 'Rapidly Falling' SOI phase at the end of October; 1915, 1920, 1925, 1931, 1941, 1944, 1947, 1963, 1978, 1981 and 1992. For example at Emerald, below average rainfall for November to January in those years was recorded 6 times, close to average rainfall was recorded 4 times with well above average rainfall recorded once. Therefore rainfall during November to January at Emerald is more likely to be below average to average than well above average. For more information refer to Rainman StreamFlow.
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 more information contact the DPI&F on 132523.