SOI in Positive Phase for 6th month in row. Dave McRae, Qld Climate Change Centre of Excellence, 03/03/09.

The monthly value of the SOI for January was plus 8.2 and for February was plus 15.2. This places the SOI in a Consistently Positive phase for the 6th month in a row.

Based on historical rainfall records and a Consistently Positive SOI phase at the end of February, there is a reasonable 50 to 70% chance of getting above median rainfall during March through to the end of May across most of Queensland.

For example Nambour has an 70% chance of getting above its March to May median rainfall of 485mm, Prairie has a 70% chance of getting above its March to May median rainfall of 76mm, Alpha has a 65% chance of getting above its March to May median rainfall of 98mm, Barcaldine has a 65% chance of getting above its March to May median rainfall of 98mm, Dalby has a 60% chance of getting above its March to May median rainfall of 120mm, Longreach has a 60% chance of getting above its March to May median rainfall of 77mm, Roma has a 55% chance of getting above its March to May median rainfall of 118mm and Macalister has a 50% chance of getting above its March to May median rainfall of 130mm.

For more information on historical rainfall data for your region try Rainman Streamflow or www.bom.gov.au

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.

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 March to May in the following years since 1950 that have had a Consistently Positive SOI phase at the end of February; 1951, 1956, 1963, 1967, 1972, 1974, 1976, 1989, 1999, 2001 and 2008. Find out your average rainfall for March to May and see how many times rainfall was well below, well above or close to average during March to May in the listed years.

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%.

As autumn is a key time for the establishment of climate phenomena such as El Nino and La Nina QCCCE climate staff will continue to closely monitor what happens over the next few months. The 30 day average of the SOI as of 2 March is plus 13.3. 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.