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page regenerated:
06 Apr 2004

The Bottom Line

The recent downward trend of the 30day average of the SOI has been generating much interest. As of the 6th of April it is minus 9 (down from plus 8 at the start of March). It will be very interesting to see if this fall in value is maintained or just a short term trend driven by recent cyclone/tropical low activity in the central Pacific.

If the 30day average of the SOI continues to 'fall' in value through to the end of this month, rainfall probabilities would also be expected to substantially drop in value in many areas of Queensland/northern NSW for the following 3 months.

As autumn is the key time of the year when climate conditions can change quickly, we continue to recommend keeping an eye on the SOI and sea surface temperature (SST) trends. For those who like to more closely follow the SOI, updates are available on (07) 46881439.

In the mean time there remains a reasonable 60-80% chance of getting at least the long-term median rainfall through to the end of June for parts of central Queensland as well as along the central and south east coastal strip of the state (refer to map).

Across the rest of the state there remains no strong signal towards wetter or drier than 'normal' conditions through to the end of June with a 40-60% chance of getting at least the long-term median rainfall.

The Full Story

Based on the SOI pattern over February and March, there is a reasonable 60-80% chance of getting at least the long-term median rainfall through to the end of June for a strip running from central Queensland down along the coastal strip to the NSW/Victorian boarder.

Reasonable rainfall probabilities (60-70% chance of getting at least the long-term median rainfall through to the end of June) can also be found in central SA, parts of the NT and the south west corner of WA.

There is a lower 20-40% chance of getting at least the long-term median rainfall through to the end of June for parts of central WA. Across the rest of Australia there remains no strong signal towards wetter or drier than 'normal' conditions through to the end of June with a 40-60% chance of getting at least the long-term median rainfall.

Interestingly this is the first time the SOI has been in a 'Consistently Positive' phase since March 2001. The big question therefore remains as to what the SOI will do over autumn as this is the key time of the year when climate conditions can change quickly.

The recent downward trend of the 30day average of the SOI has been generating much interest. As of the 6th of April it is minus 9 (down from plus 8 at the start of March). It will be very interesting to see if this fall in value is maintained or just a short term trend driven by recent cyclone/tropical low activity in the central Pacific.

If the 30day average of the SOI continues to 'fall' in value through to the end of this month, rainfall probabilities would also be expected to substantially drop in value in many areas of Queensland/northern NSW for the following 3 months.

As autumn is the key time of the year when climate conditions can change quickly, we continue to recommend keeping an eye on the SOI and sea surface temperature (SST) trends. For those who like to more closely follow the SOI, updates are available on (07) 46881439.

Cloud along the equator made the last passage of the MJO (40day wave) difficult to predict. When it did pass over Australia in mid-March, it coincided with development of an active monsoon and several tropical cyclones, including Fay, Grace and Oscar.

Information from the Qld Dept of Primary Industries and Fisheries and the Bureau of Meteorology www.bom.gov.au suggests the timing of next MJO passage should occur between the 22nd to the 30th April.

The MJO is simply 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 across much of Queensland.

As many areas of the state are in need of more rain before winter starts, hopefully the MJO may help trigger some widespread relief rain. However, big falls of rain in April across Queensland are not all that common.

While late April is also usually considered to be past the 'normal' monsoon season it is possible that this MJO passage could trigger a late season cyclone.

Many people like to follow the historical SOI/rainfall patterns in more detail for their area. Finding out what conditions where like in your area for April to June in 2001, 2000, 1999, 1989, 1976, 1975, 1974, 1971, 1967, 1956, 1950, 1945 and 1943 and comparing it to your 'normal' rainfall for April to June could be useful.

Information on what rainfall patterns where like for April to June in those years can be found at www.longpaddock.qld.gov.au or in Australian Rainman.

As always when using probabilities or a percentage chance of something occurring, it is important to consider the opposite view. For example, currently Nambour has a 75% chance of getting at least its long term April to June median rainfall of 330mm. This also means that there is a 25% chance of not getting at least 330mm.

Another way of looking at this is that in 7 to 8 years out of 10 (or around three quarters of years) with the current SOI pattern, Nambour has received at least 330mm for April to June. Therefore in 2 to 3 years out of 10 (or one quater), Nambour has gotten less than 330mm for this period.

As rainfall probabilities and median rainfall levels vary between locations, we recommend referring to AUSTRALIAN RAINMAN for more specific rainfall data. For more information try www.dpi.qld.gov.au/climate or call me through the DPI Call Centre on 13 25 23.

what is: "Seasonal Climate Outlook" ?

The term "Seasonal Climate" refers to what the weather was, is, is-likely-to-be for a particular season. The "Outlook" is based on the Southern Oscillation Index (SOI), Sea-Surface Temperature (SST) patterns in the Pacific Ocean are also important in driving climate variability and are useful guides to potential climate patterns in Australia (and other parts of the world too). The Queensland Centre for Climate Applications (QCCA) provides rainfall probability information using its "SOI Phase System" and the current "Outlook Message" gives commentary on the seasonal outlook. You will also find the "Winter Crop Outlook" on the Department of Primary Industries web site.