Seasonal Climate Outlook Message for January to April 2005

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Climate Watch (Dated 06/01/05)

Based on the value of the SOI at the end of December (minus 10.0) there is a 20 to 40% chance of getting normal rainfall for January through to the end of March across much of Queensland. This does not mean there will be no rainfall at all for the 3-month period. For example, it will interesting to see what effect the current (first week of January) passage of the MJO will have on trigging rainfall events and intensifying the monsoon season across northern Australia. What it does means though, is that rainfall recorded for January to the end of March in the affected areas will, more likely than not, be below normal for this time of year.

In contrast, for parts of the Darling Downs, southern border region and the far south-west of the state, the chance of getting normal rainfall for this time of year is a little higher at 40 to 50%.

And in what would by now be a fairly familiar comment, for there to be an overall improvement in the climate outlook it would help if the SOI rose to a "Consistently Positive" phase for a couple of months at least.

As of the 6th January, the 30-day average of the SOI has risen marginally since the start of the month to minus 4.9. Daily updates on the SOI are available on (07) 46881439.

Similar to Queenslands climate outlook, there is a 20 to 40% chance of getting normal January to March rainfall across most of the Northern Territory, the north east quarter and southern border regions of NSW, the north east quarter of Victoria, central Tasmania and the eastern half of South Australia. A higher (60 to 70%) chance of getting normal January to March rainfall though can be found mainly in Western Australia.

The latest rainfall probability maps for Queensland, Australia and the world are at www.dpi.qld.gov.au/climate or www.longpaddock.qld.gov.au

As with any probability based forecast system it is important to consider the opposite aspect. For example, Bundaberg has around a 35% chance of getting above its normal January to March rainfall of 465 mm. This also means that there is a 65% chance of NOT getting the 465 mm over January to March.

Another way of looking at this is that in around 3 to 4 years out of 10 historically (or around one third) with the current SOI pattern, Bundaberg has received at least 465 mm over January to March. Therefore in 6 to 7 years out of 10 historically (or around two thirds), Bundaberg has gotten less than its normal 465 mm over January to March.

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 average chance 3. Probabilities below 40% highlight a below average chance 4. Probabilities below 20% have a low chance

As expected the MJO has enhanced rainfall conditions in Queensland in early January. It will interesting to see what effect it will have on trigging rainfall events and intensifying the monsoon season across northern Australia this week. Based on its current timing it would therefore be next expected in mid-February.

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.

Given the growing interest in the MJO, and with funding from the DPI&F, GRDC and CRDC we have developed a site www.apsru.gov.au/mjo that will allow anyone interested to track its passage.

At present, sea surface temperatures (SST) in the Pacific are not in a classic El Niño pattern such as occurred from mid 2002 to mid 2003. However, from a risk management view point, the fact that SST in the central Pacific from the international dateline running east are warmer than normal (+0.5 to 1.5oC) is cause for concern.

Research has shown that it is the central part of the Pacific Ocean that has a major impact of our seasonal outlook. When SST in this region are warmer than normal, there is an increased risk that our rainfall and water supply across eastern Australia will be below average. We describe this pattern as a "border line El Niño" and typically, a decline in rainfall is especially noticeable across eastern Australia during winter, spring and early summer.

As far what happens with this border line El Niño SST pattern in 2005, the important question will be what happens in mid to late autumn as that is the time of year when conditions in the Pacific can change reasonably rapidly.

To find out more on conditions in the Pacific try the Bureau of Meteorology "El Niño wrap up" at www.bom.gov.au/climate/enso/ or the US Climate Prediction Centre at www.cpc.ncep.noaa.gov/ For the latest sea surface temperature maps have a look at www.cpc.ncep.noaa.gov/products/ or at www.longpaddock.qld.gov.au/ In a recent media release the Bureau of Meteorology www.bom.gov.au stated that based on the best available and most recent information the lengthy run of relatively quiet cyclone seasons was likely to continue for Queensland with the number of tropical cyclones in the Coral Sea this season having only an outside chance of exceeding 2 or 3, and not all will cross the coast.

In a reflection of the lack of cyclone activity the Bureau also state that the last 15 years have been relatively quiet in terms of both cyclone activity in the Coral Sea and the incidence of significant cyclone impacts along the Queensland coast with the past 3 cyclone seasons being particularly unusual in that only 1 cyclone has crossed the east Queensland coast ("Fritz" a low Category 1 in the far north last February).

For more information on cyclones try the Queensland Tropical Cyclone Warning Centre at www.bom.gov.au/weather/qld/cyclone

On a positive note, the early summer storm rain received across much of southern Queensland and northern NSW has provided a good start to the grain sorghum cropping season. However, there is some considerable variation in the Queensland sorghum yield outlook.

At the end of December, current soil water conditions and the seasonal rainfall outlook indicated a below average chance (30 to 40%) of bettering the long-term median grain sorghum yields in most areas of Central Queensland. This contrasts with parts of southern Queensland and northern NSW, which had mainly above average chances of bettering the long-term median grain sorghum yield.

At this stage of the growing season widespread rain is still needed to ensure good planting opportunities and to improve the current sorghum outlook across the entire cropping belt.

This sorghum yield outlook is based on a shire scale. It does not take into account crop area planted and is purely a yield forecast. Nor does not take into account individual property circumstances or the effects and damage from poor crop nutrition, pests, diseases, frosts, heat stress and distribution of planting rain within a shire. For more information on the sorghum crop yield outlook contact Andries Potgieter on (07) 46881417.

Many people like to follow the relationship between the SOI and rainfall patterns in more detail. To do that, have a look at what happened in your area over January to March in the following years; 1994, 1992, 1986, 1982, 1977, 1963, 1957, 1951, and 1941 and compare the rainfall recorded with your 'normal' rainfall for January to March.

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

What is ENSO?

I thought I'd give a brief summary of what ENSO or the El Niño/Southern Oscillation means and the influence it has on the climatic characteristics (rainfall, temperatures, wind and evaporation) of the whole of eastern Australia.

Changes in sea surface temperature (SST) patterns along the equator from the west coast of South America to around the International Dateline drive shifts in the global circulation patterns (eg Walker Circulation) that influence our local climate. The Southern Oscillation Index (SOI) is a useful way of measuring these changes. The SOI is simply a measure of the difference in barometric air pressure between Darwin and Tahiti. It typically ranges in value from plus 30 to minus 30.

A summary of ENSO follows:

El Niño SST pattern

Sea surface temperatures (SST) along the equator from the International Dateline running east towards the coast of South America become warmer (plus 1.0 to 2.0oC) than normal, with SST to the north of Australia usually becoming cooler than normal.

Negative values of the SOI (eg. average monthly values of the SOI below minus 5) are usually associated with an El Niño because barometric air pressures over northern Australia are higher relative to those in the central Pacific.

This may slow or stop the flow of the southeast trade winds that push atmospheric moisture from the Pacific Ocean across Australia as well as reduce the occurrence of rain depressions (and cyclones). Typically, a decline in rainfall is noticeable during winter, spring and early summer.

La Niña SST pattern

Sea surface temperatures (SST) along the equator from the International Dateline running east towards the coast of South America become cooler (minus 1.0 to 2.0oC) than normal with SST to the north of Australia becoming warmer than normal.

Positive values of the SOI (average monthly values of the SOI above plus 5) are usually associated with a La Niña because barometric air pressures over northern Australia are lower relative to those in the central Pacific. This may cause an increase in the intensity of the monsoon trough across northern Australia as well as increase the flow of the southeast trade winds across Australia. There may also be an increase in the occurrence of rain depressions (and cyclones).

Typically, there is an increase in rainfall in a La Niña SST pattern in winter, spring and early summer.

Neutral SST pattern

About half the time the Pacific Ocean is in a neutral SST pattern. When SST patterns are near normal, the SOI is usually associated with near zero (average monthly values between minus 5 and plus 5) values. More information on the SOI is available at www.longpaddock.qld.gov.au and www.dpi.qld.gov.au/climate