Seasonal Climate Outlook Message for April to July 2008

The bottom line

Winter Outlook

Despite some fluctuations of the SOI value during April the 30 day average is set to remain positive throughout April and was plus 4.8 as of 29 April. The SOI Phase for April looks to remain 'Consistently Positive' (Phase 2). Based on this SOI and historical rainfall records the outlook for April to June indicates a 30 to 60 % chance of above median rainfall for much of Queensland. This represents a slight shift in the odds towards drier conditions, however winter is our dry season.

Some regions in the about the Gulf and Cape have a higher chance (50 to 80%) of exceeding their median rainfall, however during the dry season only relatively low falls are need to exceed the average. For more information try www.longpaddock.qld.gov.au .

Further analysis indicates rainfall for much Queensland is more likely to be close to the long term average (or middle third) rather than well below or well above the wintertime average.

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 May to July in the following years; 1950, 1956, 1959, 1960, 1963, 1971, 1974, 1975, 2000 and 2006. Look at your long term average rainfall for May to July and see how many times rainfall was well below, well above or close to average.

The MJO signal has remained generally incoherent over the past few weeks. This often happens in autumn (and spring) as the heat equator shifts to the northern hemisphere. This rambling MJO signal is expected to continue over the next couple of weeks, and no significant impact on Australian rainfall could be expected.

During winter the south eastern Australian grain regions can expect MJO related rainfall events particularly in Phase 5, but also Phases 4 and 6. There is less direct impact of the passage of the MJO on tropical Australian rainfall during winter months compared with summer.

The MJO is a tropical 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. While the MJO is restricted to the tropics it affects areas well out of the tropics via teleconnections. This means that systems like the MJO interact with other weather and climate systems.

The MJO influences and is influenced by these other factors. Research has shown the MJO to be a useful indicator of the timing and amount of potential rainfall events in Australia. For more information try www.apsru.gov.au/mjo/ and http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/RMM/composites/ind ex.htm .