Seasonal Climate Outlook Message for March to June 2004

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SOI in "Rapidly Rising" Phase 02/03/04

Based on its shift in value from minus 12.8 at the end of January to plus 9 at the end of February, the SOI is now classified as being in a "Rapidly Rising" phase. A rapidly rising SOI phase at this time of year creates a rather mixed seasonal outlook across Queensland. Generally speaking, for much of the northern half of the state there is a reasonable 60-80% chance of getting the long term March to May median rainfall.

This differs to south east Queensland where there is only a 30-40% chance of getting the long term March to May median rainfall. For the rest of the state though there is no strong signal towards either wetter or drier than normal conditions with a 50/50 chance of getting median rainfall.

An analysis of synoptic climatology associated with this SOI pattern, suggests an increase in the incidence of tropical depressions in the Coral Sea might be responsible for the increased rainfall probabilities that can be found along the north tropical coast.

A patchy seasonal outlook exists across the rest of Australia for March to May. The lowest rainfall probabilities (30-40% of getting the long term March to May median rainfall) can be found in central Western Australia and the northern half of NSW.

Higher rainfall probabilities (60-70% of getting the long term March to May median rainfall) can be found in the Northern Territory, the northern half of Western Australia and for scattered parts of South Australia. Generally speaking for the rest of Australia though there is no strong signal towards either wetter or drier than normal conditions with an approximate 50/50 chance of getting median rainfall.

When using probabilities or a percentage chance of something occurring (eg amounts of rain in a 3 months or winning the lotto), it is important to consider the opposing view. For example, while Charters Towers has close to a 75% chance of getting at least its long term March to May median rainfall of 138mm this also means that there is a 25% chance of not getting at least 138mm.

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, Charters Towers has received at least 138mm for March to May. Therefore in 2 to 3 years out of 10 (or one quater), Charters Towers has gotten less than 138mm for this period. Many people like to follow the historical SOI/rainfall patterns in more detail for their locations. For those interested, discovering what rainfall and farming conditions where like in your area for March to May in 2002, 2000, 1997, 1985, 1984, 1979, 1977, 1975, 1971, 1968, 1965, 1961, 1955, 1950, 1949, 1946, 1944 and 1933 could be useful.

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

The early February rain in many parts of Queensland was due, at least in part, to the Madden Julian Oscillation (MJO). This system passed across Queensland in the first ten days of February. It last impacted on our climate system between Christmas and New Year. It was next expected to affect our climate and weather systems in mid March. However it appears Cyclone Monty (currently impacting WA) is affecting its development and therefore the next MJO isn't expected to affect us until late March.

Interestingly at this time of year the MJO can intensify the monsoon season as well as help trigger cyclones if there are any existing low-pressure systems in the Coral Sea. There is also the potential for it to create westerly wind bursts in the central Pacific after it has passed over Australia. At this time of year (through to late winter) westerly wind bursts in the Pacific can help trigger El Nino events.

According to the Bureau of Met National Climate Centre (NCC) February update www.bom.gov.au/climate the Pacific Ocean has remained in a neutral sea surface temperature (SST) pattern.

While SST are slightly warmer than normal and there was some weakening of the south east trade winds, the Bureau do not believe there is a strong likelihood of an El Nino developing in the short term. The Bureau also state that the recent Kelvin Wave of sub surface warming should have only a minor impact on SST in the eastern Pacific when the wave reaches the South American coast in the next two to four weeks.

This differs from the comments made by the United States Climate Prediction Centre (CPC) www.cpc.ncep.noaa.gov/ in their February update where they placed a lot more emphasis on the December MJO passage and the effect it had on producing a Kelvin Wave.

During autumn and winter Kelvin Waves can be considered to be somewhat of a pre-cursor or early indicator that the risk of an El Nino developing is increasing. So it will be interesting to see what impact, if any, this Kelvin Wave will have and if any other Kelvin Waves or strong westerly wind bursts develop over the coming months. Key times to watch for this in terms of El Nino development will be during March to June.

Ocean and coupled ocean/atmosphere forecast models can be used to show likely SST development out to 9 months. Of 11 models that forecast out to June, 6 indicate the continuation of a neutral SST pattern while 5 suggest the potential development of an El Nino (or warm) SST pattern.

While it is positive that around half of these models highlight a continuing neutral SST pattern (rather than an El Nino), given current conditions our policy remains to recommend caution when considering the longer term outlook. It's also worth remembering that over autumn and early winter most models fall away in their forecasting skill.

So unless there is a very strong event coming as in 1997 (but which had limited effect here on rainfall) then some models do not tend to show an El Nino event until mid winter, by which time it is too late for us.

It may therefore be useful for businesses that are adversely affected by El Nino events to consider now what risk management strategies they could use if the likelihood of an event increases. More details on these models can be found at the Bureau of Meteorology internet site www.bom.gov.au/climate/ahead/ENSO-summary.shtml

When incorporating climate forecasts into management decisions, it could be worthwhile to consider some of the following general rules of thumb developed from feedback from climate users.

§ The first point is to be sure of your source of information and what it is actually suggesting. Do not take a quick grab of information from any source including radio or TV and assume what you heard applies to your location.

§ Try to access local information or at least be aware of the long term median for your location so you can correctly interpret the forecast.

§ It has also been shown to be useful to do a cost benefit analysis of any decision with a climate risk factor eg What will I gain if I get the desired outcome from this decision? What will I lose if I don't get the desired outcome from this decision? What other cost neutral options do I have if any?

§ Do not to take a forecast for a specific period (eg September to November) and expand it out (eg late summer).

An interesting site http://www.cvap.gov.au/mastersoftheclimate/> from the 'Climate Variability In Agriculture' (CVAP) research and development program is well worth looking at. It highlights some case studies on how producers and businesses have used (to varying levels of success) climate and weather information in their decision making processes.