Seasonal Climate Outlook Message for May to August 2002

The bottom line

No real Change In Overall Outlook (Dated 1st May)

Key point at present is the continuation of relatively low rainfall probabilities over most of Qld for May to July based on the recent pattern of the SOI over March/April.

The 30-50 day intra-seasonal oscillation is next expected in the first two weeks of May (keeping in mind that the timing of this phenomenon can alter occasionally). It is also important to remember that while it is a tropical phenomenon it also appears to influence the potential timing of rainfall events (rather than the actual amount of rain) across southern and central Queensland.

Due to the variability that exists in sea surface temperature patterns over the next few months we continue to strongly recommend closely monitoring information on SOI trends and sea surface temperature patterns. A sustained drop in SOI values between March and May would, for example, further substantiate the potential for reduced rainfall in many districts for the following 6-9 months.

The 30day average of the SOI as of the 1st May is -3.4

The full story

No real change in overall outlook (Dated 1st May)

Key point at present is the continuation of relatively low rainfall probabilities over most of Qld for May to July.

Currently there is only a 20-50% probability of receiving median rainfall for May to July for most of the south, south-east, west and north of the state. Across central Queensland the probability of receiving or getting the long term median rainfall for May to July varies between 40-70% depending on location.

The monthly value of the SOI at the end of March was -5.6 and at the end of April was -3.4. Based on this shift in the monthly value of the SOI over March/April, the SOI is now in a 'Consistently Near Zero' phase.

It is essential to remember that when dealing with probabilities to also consider the additional information that probabilities provide. For example, based on the recent pattern of the SOI there is a 39% chance of getting the long term May to July median rainfall of 100 mm at Talwood. Therefore there is a 61% chance of not getting the May to July median rainfall.

Another way of looking at this is that in approximately one third of years (approximately 3-4 years out of 10) with the current SOI pattern has Talwood received it long term median May to July rainfall.

Therefore in around two thirds of years (6-7 years out of 10) with the current SOI pattern below median rainfall has been recorded at Talwood for May to July.

For those who like to follow historical patterns more closely, the last 15 years that have had a 'Consistently Near Zero' SOI phase in March/April are 2001, 1996, 1988, 1986, 1982, 1979, 1978, 1973, 1972, 1970, 1968, 1964, 1962, 1958 and 1957.

What was the rainfall like for May/July in your area for those years? Details of the rainfall in those years can be found at the 'Long Paddock' internet site www.longpaddock.qld.gov.au or in the Australian Rainman CD.

The influence of the 30-50 day intra-seasonal oscillation was last apparent in early April. It is next expected in the first two weeks of May (keeping in mind that the timing of this phenomenon can alter occasionally). It is also important to remember that while it is a tropical phenomenon it also appears to influence the potential timing of rainfall events (rather than the actual amount of rain) across southern and central Queensland.

Due to the variability that exists in sea surface temperature patterns over the next few months we continue to strongly recommend closely monitoring information on SOI trends and sea surface temperature patterns.

A sustained drop in SOI values between March and May would, for example, further substantiate the potential for reduced rainfall in many districts for the following 6-9 months.

If anyone requires more climate related information contact the DPI Call Centre on 13 25 23. Alternatively try the DPI's climate web site www.dpi.qld.gov.au/climate on which the "Climate Note" can be found. The climate note contains more detailed information including rainfall probability maps, SST information etc. A recorded message with the 30day average of the SOI is also available on 46881439.