One-off rain events the best we can hope for

One-off rain events the best we can hope for | The Outlook


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Some months ago, this column indicated the most likely scenario for winter was for slightly above average temperatures.

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Some months ago, this column indicated the most likely scenario for winter was for slightly above average temperatures overall, but with the occasional, brief but significant cold outbreak.

In the past week most of south-east Australia experienced a significant cold spell - the third so for this season and there is potential for at least one other variation in temperature before the season has finished.

Into spring, such aberrations in the dominant synoptic patterns are more likely to result in a so-called one-off rain event and it is such occurrences that provide the only slightly opimistic outcomes in an otherwise pessimistic scenario.

However, as mentioned previously such events are likely to be only patchy rather than general.

The medium term climatic indicators have shown minimal change in recent weeks. In the Pacific basin, the sea surface temperatures now reflect a neutral situation, while the 30-day running mean of the Southern Oscillation Index is around -1 - back near the middle of the neutral range after being below -7 for the previous two months.

Other atmospheric indicators such as the strength of the south-eastern trades in the tropical western Pacific and the cloudiness near the international date line remain well within what would be expected in a neutral situation.

Over in the Indian Ocean, the Indian Ocean Dipole is positive, as it has been for some weeks now, and it is favoured to remain positive well into spring, which is not good news for those looking for rain events in pre-frontal situations for the rest of winter and the first half of spring. (Remember a positive IOD has a negative impact on winter rain in the south-east and eastern states but its influence decreases rapidly from mid spring.)

So what all these means is that we are still in relatively 'uncharted waters', especially as sea surface temperatures across the Tasman remain up on normal.

This will help in those rare one-off events, especially in coastal eastern Australia.

So the prognosis for a continuation of slightly below average rainfall for the coming months remains unchanged with the proviso that the occasional one-off event could be a useful boost to rainfall in limited areas.

Further into spring and early summer, rainfall is likely to be near normal - better than in recent years but unlikely to be sufficient to overcome the major deficiencies established by the drier years of recent times.

Temperatures are likely to average out warmer than average as we head into summer, as has been the case for many years now.

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