EASTERN Australia faces potentially significant delays to harvest due to a massive low pressure system set to dump substantial rainfall across virtually all of the cropping zone in New South Wales and Victoria and much of eastern South Australia.
The rain was crossing the Victorian / South Australia border as of Wednesday morning and was then due to push across to the north-east into central NSW.
Senior forecaster with the extreme weather team at the Bureau of Meteorology (BOM) Scott Williams said the system was a broad low pressure trough tapping into extensive moisture over central Australia at present.
“Earlier in the week there were extensive thunderstorms across the southern part of the Northern Territory and northern South Australia,” Mr Williams said.
He said the heaviest rain will occur in a square east from Adelaide, across to Melbourne, down to the coast and as far north as Broken Hill in NSW.
“It is likely the low will deepen through western Victoria during Wednesday and into Thursday,” he said.
From there, he said further rain would push up into central NSW, where harvest is in full swing.
In terms of damage, Mr Williams said while general rainfall is likely to only be between 15-40mm, an amount all crops would cope with even if mature, the danger came in localised heavy falls from thunderstorms embedded in the trough.
“We think we will see some tallies of 75mm or more recorded over a 24 hour period, it could happen anywhere in that vulnerable square, even in the Mallee where it has been dry.”
When the system moves through NSW, Mr Williams said there would be a greater chance of hail than in Victoria and SA due to the instability.
“We expect total rain tallies to be lower through central NSW, but the risk of hail is more pronounced.”
GrainCorp has already reported weather delays due to storms through much of NSW and added that the chickpea harvest had been slow in northern NSW due to the moist conditions.
Tottenham, west of Dubbo, farmer Terry Fishpool, said after a drought impacted harvest, he welcomed any rain.
“We harvested about 35 tonnes off 1500 acres (600ha), there was around 12mm of rain from March to the start of October, you just can’t grow a crop on that,” he said.
“However, since then we have had some good falls, around 70mm, and if we can get another good drop then there will be grass growing.”
“Most people in this area are mixed farmers so having some summer feed for livestock will be fantastic.”
In Victoria and South Australia, the rain will be of concern to Mallee farmers, where harvest is well and truly underway, however further south in areas like the Wimmera and SA’s south-east there is still green in the crop, so it will not cause damage.
Pulse producers are even hoping that with good rainfall that frosted chickpeas and lentils may reflower, compensating for some of the yield lost to frost.
Mr Williams said this week’s rain may not be the end of damp conditions for November.
“The moisture does not really push out, it will weaken, but there will be moist air over Victoria until the weekend.”
“Further out, there is another trough coming in from Western Australia sometime early next week, it is too early to say whether it will deliver substantial rain, but there is the potential it could.”
Mr Williams said the weather patterns were looking like those associated with a La Niña climate event.
“We are seeing all this tropical moisture pushing down regularly.
“You’ll often get one even like this in November, but it is more associated with the tail end of the spring weather pattern, this is more like the summer rain you can see with a La Niña.”
The BOM currently has a La Niña watch in place, saying a late season La Niña is a 50pc chance, around double that of normal.
A La Niña forming this late in the season is rare but not unknown.
The most recent modeling suggests that should a La Niña form it is likely to be short-lived and weak, unlike the mega La Niña that was a driver behind the flooding rain of the summer of 2010-11.
All international climate models suggest further cooling of the tropical Pacific is likely, with most models reaching La Niña thresholds in late 2017.
Six of eight models suggest that these levels will persist long enough to be considered an event.
In its rainfall outlook for summer, the BOM has not forecast the above average rainfall linked to a La Niña.
It also said weak summer La Niña events could increase the chance of prolonged heatwaves in south-eastern Australia.