UPDATE, Monday, 1.25pm:
Warrnambool and the south-west has had one of its driest five-month stretches on recent record.
A Bureau of Meteorology spokesperson said rainfall was up to 40 per cent below the long term average.
She said rainfall in Victoria's south-west since December last year was 20 per cent to 40 per cent below the 1961-1990 average.
"During December to April much of the south-west coast, including the Warrnambool area, has had rainfall that is in the driest 10 per cent of all years since 1900, meeting the Bureau's criteria for serious rainfall deficiencies," she said.
"The dry conditions in recent months affecting south-west Victoria have been caused by persistent anti-cyclones ("blocking highs") in the Australian Bight and South Tasman Sea, which have diverted cold fronts and moist tropical air away from the region.
"A persistent positive phase of the Southern Annular Mode (SAM) in the Southern Hemisphere, and the La Nia event have contributed to these weather patterns.
"Indian Ocean Dipole (IOD) outlooks indicate an increased chance of a negative IOD developing in the coming months.
"However, historical outlook accuracy for the IOD is low for outlooks made during autumn.
"A negative IOD increases the chances of above average winter-spring rainfall for central and southern Australia."
The Bureau's State of the Climate 2020 reported that April to October rainfall for south-eastern Australia has declined around 12 per cent since 2000, when compared with 1900-1999 rainfall.
"This is due to a shift in the weather patterns as a known response to global climate change," the spokesperson said.
Earlier: Today looks fine and clear across the south-west but Warrnambool is expecting rain for the next six days.
We're going to get a partly cloudy day today, with winds north-westerly 15 to 20 km/h becoming lighter in the late afternoon with just a 20 per cent chance of a shower.
Warrnambool is tipped to reach 21 degrees, Hamilton and Colac 20, Mortlake 21, Portland 19 and Port Fairy 21.
But, from here on the week gets a bit rough.
Tuesday there's an 80 per cent chance of rain (between 2-4mm) with a top of 21 degrees, before the rest of the week turns chilly.
Wednesday's top is expected to be just 15 with a 95 per cent chance of rain (between 10-15mm) and races holiday Thursday gets worse, with a top of just 14 and a 95 per cent chance of between 10-20mm.
Friday we're looking at a top of 15 and a 90 per cent chance of between 6-10mm with Saturday's maximum likely to be just 16 with a 90 per cent chance of rain (between 3-6mm).
A high pressure system over New South Wales will weaken and move into the Tasman Sea today as a cold front develops south of the Bight.
The front is forecast to approach the far south-west on Tuesday before crossing Victoria on Wednesday and introducing a cold and unstable southwesterly airstream across the state.
These conditions will continue on Thursday as a low pressure system develops east of Tasmania and a large high moves south of WA.
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