SOI in Consistently Positive Phase Dave McRae, Qld Climate Change Centre of Excellence, 01/06/10
Based on the monthly SOI values of plus 12.1 for April and plus 10.5 for May, the SOI is in a 'Consistently Positive' phase. The last time the SOI was in this phase was in February 2009.
An analysis of historical rainfall records and a consistently positive SOI phase at the end of May indicates a 40 to 60% chance of getting above median rainfall for June through to the end of August throughout most of Queensland. This is in comparison to last year when there was a lower 20 to 40% chance of getting median rainfall throughout the southern half of the state as well as along the central and northern coastal strip.
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 June to August in the following years since 1950 that have had a Consistently Positive SOI phase at the end of May: 1950, 1956, 1960, 1961, 1963, 1971, 1974, 1975, 1985, 1989 and 2000.
Find out your average rainfall for June to August and see how many times rainfall was well below, well above or close to average during June to August in the listed years. For more information on historical rainfall data for your region try Rainman Streamflow.
If the SOI remains in a consistently positive phase through to the end of the month, rainfall probabilities for the rest of winter and early spring would be expected to increase. And unlike this time last year when an El Niño climate pattern was developing, all the leading climate models surveyed by the Bureau of Meteorology indicate a neutral sea surface temperature pattern for winter. Interestingly five of the six climate models surveyed also indicate the potential development of a La Niña climate pattern by spring.
For more climate related information, updates on SOI values and the latest outlook map go to www.longpaddock.qld.gov.au To receive the latest SOI values sent to your mobile phone e-mail firstname.lastname@example.org.