IOD has negative influence on winter rain

IOD has negative influence on winter rain | The Outlook

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The surface synoptic weather patterns have started to return to a more typical mid-winter pattern with westerlies and colder weather starting to dominate in recent days in the south.

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AS IS often the case in mid-winter, there has been little change in the majority of the long-term climate indicators in recent weeks.

The surface synoptic weather patterns have started to return to a more typical mid-winter pattern with westerlies and colder weather starting to dominate in recent days in the south.

This development will progress further in coming days.

The sub-tropical high pressure belts will strengthen and therefore, over northern and central Australia and along the east coast, mostly stable weather will become a feature into the foreseeable future.

Those areas of the south-eastern states that normally receive a little rainfall from a westerly air stream will get some rain but it will be mainly light.

North-west cloud bands which are needed to bring widespread, useful falls in pre-frontal situations, remain largely absent and with the Indian Ocean Dipole (IOD) likely to remain positive, these cloud band are less likely than in a neutral year.

The IOD will continue to have a negative influence on south-eastern Australian rainfall for much of winter.

The situation in the Pacific remains trending towards neutrality and the previously expected El Nino development is now increasing unlikely.

As noted previously that is one positive in an otherwise slightly pessimistic outlook.

However, the Southern Oscillation Index (SOI) continues to languish in the El Nino range - the 30-day running mean is still sitting around -9, where it has been for some weeks and the forecast of the El Nino not developing is based on the other features normally associated with it.

So, the SOI is a little worrying and there is no indication it is going to change in the immediate future.

In spring, the influence of the IOD will start to decrease, as is usual at that time and the situation in the Pacific will become more important.

A neutral pattern in the Pacific will help in the occasional development of those one off rain events which will become more important after a relatively dry winter.

With sea surface temperatures off the east coast remaining up on normal, this is another encouragement for those one off events but it will also encourages the early onset of spring warmth with above average temperatures favoured from mid spring and into early to mid-summer at least.

Despite this, the longer term assessment remains a little unclear.

Next summer may see some worthwhile rain developing in single events but the chance of any significant drought breaking rains in the next six months remains fairly low.

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