The La Nina sea surface temperature pattern that has persisted in the Pacific over summer has become less intense over the last few weeks. As the pattern breaks down over autumn, some areas of Queensland remain drought affected. Just as El Nino does not always equal a drought, La Nina's do not always bring above average rain and floods to all of eastern Australia.
As at 22nd of April the 30 day average of the SOI was plus 5.0. The average SOI for March was plus 10.2. This follows on a Consistently Positive SOI phase during February and March. Based on this Consistently Positive SOI phase and historical rainfall data there is a 50 to 70% chance of getting above average rainfall for April to June throughout most of Queensland. The main exception is for a few parts of northern and western Queensland where there is a slightly lower 40 to 50% chance of getting above median rainfall for this period.
In general terms this indicates a reasonable outlook for the start of the winter cropping season. For example Emerald has a 75% chance of getting at least 60mm while Dalby has an 80% chance of getting at least 60mm for April to June.
The SOI looks like it will remain consistently posiitve (Phase 2) for the remainder of April. This SOI and historical rainfall records indicate a 30 to 60 % chance of exceeding median rainfall from May to July. For Queensland, winter is the dry season, and it appears this dry season will be about average rainfall for most fo the state.
For those interested daily updates on the SOI are available on (07) 46881439 or at www.longpaddock.qld.gov.au http://www.longpaddock.qld.gov.au/> You can also receive a text message with the latest SOI values sent to your mobile phone. To subscribe to this free service call (07) 46881459.
While the SOI has remained positive the La Nina sea surface temperature has begun to weaken. Sea surface temperature patterns (La Nina/El Nino) usually break down during autumn and then re-establish by about June. At this stage there is no indication of a developing El Nino. The most likely scenario is for a neutral sea surface temperature pattern. For more information on La Nina/El Nino development have a look at www.bom.gov.au/climate http://www.bom.gov.au/climate>
The northern wet season (October to April) has been a somewhat mixed season for Queensland with the far west recording well below average rainfall. The south east recorded average to below average rainfall with average to well above rainfall recorded throughout the rest of the state.
For those looking for rain the next MJO event the signal is incoherent at present. Suring autumn and spring the RMM Phase system and other measures of the MJO often demonstrate this incoherence, or poor signal quality. This is because MJO convective activity is related to the warm ocean surface. After the autumn and spring equinoxes the warm areas of tropical sea surface shift towards the summer hemisphere. So, at the moment in our autumn the heat is dissipating in the southern hemisphere and building in the northern (summer) hemisphere. As convection strongly impacts the MJO signal and our ability to 'see' the MJO, this signal is most often incoherent in the transitional autumn and spring months.
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 www.apsru.gov.au/mjo/ http://www.apsru.gov.au/mjo/>