Seasonal Climate Outlook Message for August to November 2006

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Climate Watch Dave McRae Qld DPI&F 01/08/06

Marginal improvement in seasonal outlook

Based on a Consistently Near Zero SOI phase at the end of July there is a 40 to 50% chance of getting above median rainfall throughout most of Queensland during August to October. This is a marginal improvement on the July to September seasonal outlook.

The exception is for the region running from the central Queensland coast to the peninsular where there is a lower 20 to 40% chance of getting above median rainfall.

It is worth noting that we are in our 'dry season' with August and September having 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, at Morven is 15 mm and 11 mm and Mareeba is 2 mm and 2 mm.

Daily updates on the SOI are available on (07) 46881439. Rainfall probability maps are available at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au For more information refer to Rainman StreamFlow or contact 132523 or (07) 3404 6999.

The full story

Marginal improvement in seasonal outlook 01/08/06

Based on a Consistently Near Zero SOI phase at the end of July there is a 40 to 50% chance of getting above median rainfall throughout most of Queensland during August to October. This is a marginal improvement on the August to October seasonal outlook. The exception is for the region running from the central Queensland coast to the peninsular where there is a lower 20 to 40% chance of getting above median rainfall.

It is worth noting that we are in our 'dry season' with August and September having 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, at Morven is 15 mm and 11 mm and Mareeba is 2 mm and 2 mm.

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 August to October in the following years since 1930 that have had a 'Near Zero' SOI phase at the end of July; 1930, 1932, 1935, 1942, 1944, 1953, 1957, 1958, 1959, 1961, 1962, 1966, 1967, 1969, 1971, 1980, 1983, 1991, 2000, 2001, 2002 and 2005.

For example at Dalby, below median rainfall for August to October in those years was recorded twice, close to median rainfall was recorded 15 times and above median rainfall was recorded 5 times. Therefore rainfall during August to October at Toowoomba is more likely to be close to median than well above or below median.

Based on a Near Zero SOI phase at the end of July there is a 30 to 50% chance of getting above median rainfall during August to October across most of the rest of Australia. The exception to this is for the north west of Australia which is seasonally dry at this time of year and for the coastal strip of NSW where there is a 40 to 60% chance of getting above median rainfall.

An interesting feature of recent synoptic weather charts is that the latitude of the sub-tropical ridge of high pressure is further south than normal for this time of year. This has the potential to increase shower activity for Queensland through increased flow of moist easterly winds especially across northern and coastal regions.

For those interested in cloud seeding there is an interesting report from CSIRO available at http://www.cmar.csiro.au/e-print/open/cloud.htm It is a better source of information to quote or believe than some of the recent media articles on this topic.

While there were MJO events over the Indian Ocean in April, May and June there was little or no rainfall impact across Australia and the MJO events were weak in amplitude and structure. If the recent timing of the MJO persists at around 30 days then the next passage north of Australia would be expected in late July. For those seeking rain for dry planted winter cereal crops, a synoptic feature such as a north-west cloud band or trough system is required in conjunction with the passage of the MJO in winter to result in rain. Over the past two weeks the passage of the MJO has triggered monsoonal activity in India and Indonesia.

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 http://www.apsru.gov.au/mjo/ or http://www.bom.gov.au/climate/tropnote/tropnote.shtml

The output from ocean/atmosphere forecast models continues to indicate a neutral sea surface temperature (SST) pattern in the central Pacific (rather than an El Nino or La Nina). However both surface and sub-surface ocean temperatures in the key regions of the central Pacific have warmed over the last 2 months. If this warming trend in the central Pacific continues it may adversely impact on our expected winter, spring and early summer rainfall. For more on conditions in the Pacific try the Bureau of Meteorology at http://www.bom.gov.au/climate/ahead/

As always with probabilities it is important to consider the opposite aspect. For example, Rockhampton currently has a 40% chance of getting its August to October median rainfall of 100 mm. This also means that there is a 60% chance of NOT getting its August to October median rainfall of 100 mm.

Another way of looking at this is that in 4 times out of 10 with the current SOI pattern, Rockhampton has received more than 100 mm during August to October. Therefore in 6 times out of 10 with the current SOI pattern Rockhampton has received less than 100 mm during August to October.

When looking at rainfall probabilities for your area it may make it easier to think of them in these terms: 1. Probabilities above 80% highlight a high chance 2. Probabilities above 60% highlight an above median chance 3. Probabilities below 40% highlight a below median chance 4. Probabilities below 20% have a low chance

When I'm asked about how climate information can be used I refer to a couple of key points developed from client feedback. Key points include that management decisions should never be based entirely on one factor such as a climate or weather forecast. As always, everything that could impact of the outcome of a decision (soil moisture, pasture type/availability, crop and commodity prices, machinery, finance, costs etc) should be considered. For example, the level of soil moisture at planting is the major factor influencing crop yield or success.

A simple cost benefit analysis when making a major decision may also be useful. For example what will I gain if I get the desired outcome? What will I lose (sleep, money, family relationships) if I do not get the desired outcome and what other options (risk neutral) are there? A PART OF THIS PROCESS IS TO HELP MANAGERS TO BE CAREFUL NOT TO CHANGE FROM NORMAL RISK MANAGEMENT TO HIGH LEVEL RISK TAKING BASED ON A PIECE OF INFORMATION (SUCH AS A CLIMATE FORECAST).

Forecasts as well do not always give a strong signal as to likely conditions for your location. In assessing climate forecasts as a management tool consider the level of signal for the key decision times in your location. Rainman StreamFlow is a useful tool for this. Daily updates on the SOI are available on (07) 46881439. Rainfall probability maps are available at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au For more information refer to Rainman StreamFlow or contact 132523 or (07) 3404 6999.