SOI remains in "Near Zero Phase" for third month in row. Dave McRae, Qld Climate Change Centre of Excellence, 31/08/09.
Based on the shift in the monthly value of the SOI from plus 2.0 for July to minus 3.9 for August, the SOI is in a "Consistently Near Zero" phase.
An analysis of a Consistently Near Zero SOI phase at the end of August indicates a 30 to 50% chance of getting above the long term median rainfall throughout northern, central and western Queensland during September to November. Throughout the south east quarter of the state, the chance of getting above the long term median rainfall for the same period is marginally higher at 50 to 60%.
Based on these probabilities, this forecast would not be regarded as indicating a high chance of getting well above average rain during September to November. It's also worth remembering that we are still in our "traditional dry season" of August and September.
These months have the lowest median monthly rainfall totals for most locations in Queensland. For example median rainfall for August and September at Blackall is 9 mm and 6 mm, at Emerald is 11 mm and 9 mm, at Goondiwindi is 26 mm and 34 mm, at Toowoomba is 33 mm and 41 mm and Mareeba is 2 mm and 2 mm.
For those interested in following historical patterns more closely, some of the years that have had the same SOI pattern at the end of August include 2004, 2003, 2001, 1999, 1995, 1992, 1990, 1984, 1980, 1978, 1969, 1968, 1963, 1961, 1959 and 1952.
It can be useful to find out what rainfall and farming conditions where like in your area for September to November in those years. Information on what rainfall patterns where like in those years is available at www.longpaddock.qld.gov.au or in Rainman StreamFlow.
It will be interesting to see what the SOI does over the next few weeks. If it remains in a "Near Zero" phase through to the end of the September there is an increase in the likelihood or chance of severe storm activity across the southern half of Queensland and northern New South Wales.
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%.
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