Rain forecast positive, but variability persists

Rain forecast positive, but variability persists | The Outlook


By later in the weekend or early next week, an easterly ridge is favoured to redevelop across the western Pacific.


THE deep low in the Tasman Sea last week has acted as a blocking mechanism and as a result, a period of stable weather over the inland parts of eastern Australia is favoured to persist for a few more days to come.

Such synoptic "hiccups" can occasionally go against the trends indicated by the developing climate models but things will return to normal shortly.

With a developing Pacific La Nina such a "normal" will result in the potential for moisture to start feeding into eastern Australia from the tropical South Pacific but this is more likely to be in eastern Queensland initially.

By later in the weekend or early next week, an easterly ridge is favoured to redevelop across the western Pacific and this will extend a broad easterly flow across the Coral Sea, helping to push moisture into eastern Australia.

To result in any worthwhile rain, this increase in moisture will have to be timed to coincide with the next front/upper trough developing from the west.

In fact these types of developments will become a feature of the weather in late winter and spring if the Pacific La Nina continues to develop as is currently favoured.

As has been the case in recent weeks, the Indian Ocean Dipole and the Southern Annular Mode to the south are both still neutral, although the SAM continues to fluctuate a little. (It was briefly negative earlier this week, but not long enough to have an effect.)

Nevertheless, it is still keeping active Southern Ocean fronts a little further south than would normally be the case in mid-winter and this is unlikely to change before it becomes more negative for a longer period, which is unlikely in the foreseeable future.

The IOD is still favoured to stay in the neutral range for some months.

Two major models (the Australian and European) believe it might be slightly positive, while most of the other international models believe it could swing into the negative.

This would be preferable for those looking for a boost to south-east Australian rainfall but its variability is making any prediction less confident than usual.

Sea surface temperatures remain up on normal around most of continental Australia except in the Great Australian Bight.

This will help maintain temperatures near to or slightly up on normal into spring.

It will also help a little as far as rainfall is concerned as any onshore winds will find it easier to pick up moisture, so as noted in previous reports, the current situation favours a slightly positive rainfall outlook but variability is likely to remain a feature.

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