The Bureau of Meteorology has determined that 50-60 per cent of Victoria has experienced an autumn break already, but it will be difficult to determine when other regions will get significant rainfall.
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The bureau defines an autumn break in Victoria as the first three days of where rainfall is greater than 25 millimetres prior to sowing.
Bureau senior climatologist Zhi-Weng Chua said it will be a complex story for the northern and western areas of Victoria that haven't seen a break yet.
"If you think about the three day definition, they're a short term weather event, which is difficult for climate models to represent," he said.
"The climate models for May though [look as if] more likely than not rainfall will be below median for these parts of the state that haven't had the autumn break yet, which is mostly the Western and parts of Northern northern Victoria."
Mr Chua said while in May there is a possible 60-70pc chance that rainfall will be below median for those areas, it doesn't mean an autumn break won't happen over three days.
"It can be a bit tricky to determine these things... but for Western and Northern Victoria, below median rainfall would be the most likely outcome,"
"If you look at June, it seems it is a month where models are finding it hard to pick what will happen with a wide possibility of scenarios and not much certainty at that time."
Mr Chua said from historical records the Mallee median time for a break would be mid to late winter, while the Wimmera and northern country would see it from mid to late autumn
Far eastern and central Victoria, along with the majority of Gippsland and Alpine regions have all received an autumn break during expected times based on historical records.
The exception for this was central Victoria, which experienced a heavy rainfall event in early April that triggered the autumn break definition.
"I think the central Victorian rainfall was more like a weather variability or what they call weather noise where you get short-term weather events that are quite random," he said.
"We just happened to get this random event that happened over in early April that drove that earlier than usual onset of a break."
Agriculture Victoria seasonal agronomist Dale Grey said while there were very early signs of a La Nina forecast, it was far from a certainty.
The bureau is also being cautious about such a determination and encouraged farmers to see the spread of possible regional scenarios for a long range forecast on their website which Mr Chua said would be "helpful for people wanting more detail."
He said while there were some signs of a potential positive Indian Ocean Dipole (IOD), "it is hard to attribute the effect it would have in Victoria or southern Australia as a whole."
"There's quite a lot of different influences happening at the same time, so even though we can identify this potential possible positive IOD development, it's hard to tie it to a specific effect."
