Models all link up and suggest wet spring for the east

Models all link up and suggest wet spring for the east

Cropping
The BOM's spring outlook, from September to November is good viewing for farmers in eastern Australia.

The BOM's spring outlook, from September to November is good viewing for farmers in eastern Australia.

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There is unusually strong consensus from long term weather models suggesting a wet spring for eastern Australia - but farmers want evidence.

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A LONG time climate analyst said last week he had never seen such a strong push from forecasting models for a wetter than average spring for parts of eastern Australia.

Agriculture Victoria climate agronomist Dale Grey said the forecasting models were coming into agreement.

"It looks as though the odds for above average rainfall for spring are now very much above average in eastern Australia, especially in Queensland and NSW," Mr Grey said during a recent climate information webinar held by the Ag Vic climate monitoring service The Break.

"I've never seen the models come out with such a strong push in favour of wet conditions."

"The odds gradually decrease as you head south, so for the Riverina and even northern Victoria most models still forecast a wetter than average spring, but that decreases more towards neutral south of the Great Dividing Range," he said.

It is a similar story in South Australia, with northern areas more likely to exceed their median rainfall for the upcoming three months than the south.

The news is not so good for Western Australian croppers looking for rain to finish their season, with the likelihood of median rainfall hovering around neutral to slightly less likely than normal.

Part of the reason for the increased confidence of wetter conditions is a shift towards the likelihood of a La Nina weather event.

This week the BOM reported continued cooling of the tropical Pacific Ocean, changes in tropical weather patterns, and climate model outlooks shifting further towards La Nina, mean the Bureau's El Nino Southern Oscillation (ENSO) outlook has moved to a La Nina alert.

This means the chance of La Nina forming in 2020 is around 70 per cent or roughly three times the average likelihood.

ENSO indicators in the tropical Pacific Ocean are consistent with the early stages of La Nina development.

Surface waters are cooler than average, while sub-surface temperatures have cooled further over the past fortnight.

Three of the eight models used by BOM forecast drivers reaching La Nina thresholds in September, and two more in October.

On the other side of the continent the Indian Ocean Dipole (IOD) is currently neutral, despite the index dropping sharply in the past week.

Half the six BOM surveyed models indicate negative IOD thresholds could be met or exceeded during spring, with an IOD negative correlated with higher rainfall than normal in Australia.

In terms of the likelihood of forming Mr Grey said La Nina was the most probably of the events to form.

"La Nina is winning the race over the IOD negative at this stage."

The shift in the climate will be especially welcome by southern croppers, with Mr Grey saying there were very low soil moisture levels in many areas.

He said there were parts of western Victoria and South Australia that recorded their driest July on record.

However, he added there had been a welcome change in the weather pattern through the start of August.

"Most regions have seen at least some rain through August which has really helped, especially for croppers in northern parts of Victoria and into SA."

He said, however, that soil moisture reserves were relatively low, even in areas that have had good rainfall, such as the Riverina in NSW.

"There is still plenty of room for improvement and over into SA it is just plain dry, the state as a whole is between decile 1 and 3 (driest 10pc and driest 30pc) for stored moisture."

"Even in Victoria's dairy regions we saw soil moisture levels actually dropping for July which very rarely happens."

Mr Grey said in spite of the increasingly positive outlook, solid rain would be needed before those in the south became confident.

"There has been this wetter outlook out there for a while but the big high pressure systems stopped the rain from getting through so I think people will wait for some evidence before they truly believe."

Many farmers, especially in Victoria and South Australia are wary of reports after it was suggested in autumn that winter was markedly more likely to be wet than dry.

Following that there was actually a much drier than average winter for many.

In the short-term the BOM forecasts the fortnight 17 to 30 August is likely to see above average rainfall across most of mainland Australia, with south-west WA the only major agricultural region likely to be drier than average.

While the spring rainfall is welcome, there is perhaps an unwelcome hitch.

If the wet period continues too long it will run into harvest and potentially caused weather damage issues, and with a potential harvester shortage looming due to COVID-19 restrictions, farmers will be hoping for a dry harvest to ensure no price discounts for weather damaged grain.

The story Models all link up and suggest wet spring for the east first appeared on Farm Online.

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