Warm Autumn, Cold June, Rain Welcome Dave McRae 10th July 2007
The rainfall that was recorded during mid June coincided with the last passage of the MJO. Based on its current timing it would be reasonable to next expect the MJO in early August. The MJO is a band of low air pressure originating off the east coast of central Africa travelling eastward across the Indian Ocean and northern Australia roughly every 30 to 60 days. Research has shown the MJO to be a useful indicator of the timing of potential rainfall events (but not amounts). For more information try www.apsru.gov.au/mjo/
Based on historical rainfall data and a 'Rapidly Rising' phase at the end of June, 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. The exception is for parts of the central north where there is a lower 40 to 50% chance of getting median rainfall.
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%.
The 30day average of the SOI continues to fluctuate and as of the 10th July has dropped rapidly to minus 5.9. While disconcerting this drop in value will have little impact if SOI values trend upwards before the end of the month. However if the SOI remains in negative values rainfall probabilities for coming months will drop.
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 or you can receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service call (07) 46881459.
In the latest El Nino wrap-up available at www.bom.gov.au the Bureau of Meteorology state that there remains an increased chance of a La Niña sea surface temperature pattern developing over the next 1 to 3 months (although at this stage it has not occurred). Given the continued fluctuations in SOI values and that it is starting to get late in the year for the development of a La Nina, at this stage sea surface temperatures are more likely to remain in a neutral climate pattern. The positive news is that is there is only a low risk of a return to El Niño conditions in 2007.