Trend to La Nina is good news for farmers

Trend to La Nina is good news for farmers | The Outlook

Weather
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The best news for eastern Australian farmers and pastoralists at the moment is the continued gradual trend towards a La Nina pattern.

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THE best news for eastern Australian farmers and pastoralists at the moment is the continued gradual trend towards a La Nina pattern developing in the Pacific basin.

Although the El Nino-Southern Oscillation as well as the Indian Ocean Dipole remain neutral - as they have been for some time now - the cooling in the tropical Pacific Ocean has continued and as a result, most models now anticipate this cooling will be close to the threshold for La Nina by around the end of winter.

A La Nina event, more often than not, brings above average rainfall to much of eastern Australia in spring and early summer.

The last really strong La Nina in 2010-2012 brought Australia's wettest ever two-year period but before we get too carried away, the current developments are still pointing to a relatively weak event later this year. Nevertheless it remains a positive in the long-term outlook.

The patterns in the Indian Ocean were looking quite positive in early autumn, but an unexpected cooling of some waters in the north-east tropical Indian Ocean in April and early May meant that the IOD has remained slightly positive, which can restrict the development of north-west cloud bands that are so important for winter rainfall events in the south-east states.

These have been largely lacking in the past two months.

The big question remains what will now happen to the IOD as we approach mid-winter. Despite this recent but patchy cooling in the north-east Indian Ocean, half of the international models that analyse developments in the Indian Ocean indicate there is a good chance of a weakly negative IOD developing during late July and into early spring but there continues to be doubt about this prediction so the confidence level of any assessment based solely on the IOD is lower than normal at the moment.

If even a weak negative IOD developed then this, too, would increase the chances of prefrontal rain events in the second half of winter in the south-east states and southern Queensland.

However, it would also need to be accompanied by a change in the Southern Annular Mode to the south in the Southern Ocean.

The SAM is currently positive and has been that way in recent times.

This means Southern Ocean fronts have been weaker than if the SAM had been negative.

The ideal scenario would be the SAM to become negative at the same time the IOD does - thus increasing the chance of those north-west cloud/rain bands during August.

However, even if this does not happen, we still have the developing pattern in the Pacific to look forward to in spring.

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