Wet weather likely right up to Christmas

La Nina takes hold

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Graziers and croppers in northern and western parts of Victoria are likely to have a wet few months leading up to Christmas due to La Nina.

Graziers and croppers in northern and western parts of Victoria are likely to have a wet few months leading up to Christmas due to La Nina.

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BoM makes the call on a La Nina that will bring wet weather to eastern Australia this spring.

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It's official - the Bureau of Meteorology (BoM) has declared a La Nina pattern is established in the tropical Pacific.

And that is big news for weather in Australia.

Indicators in the Pacific Ocean and the atmosphere above it currently exceed La Nina thresholds.

Long-range forecasts show there is a high chance La Nina will last until at least January 2021.

La Nina typically means wetter weather for much of eastern Australia, so it is no surprise that much of the south eastern mainland, away from the coast, has high chances - of above 80 per cent - of a wetter than average October to December.

That includes parts of northern and western Victoria.

At the same time, days are likely to be warmer than average south of the Dividing Range and nights are very likely - with a greater than 80 per cent chance - to be warmer than average across the state, and most of Australia.

Adding to the wet signal for the months ahead is a higher than normal chance of a negative Indian Ocean Dipole (IOD).

A negative IOD is when warmer waters concentrate near Australia's north west, generating extra cloud and favouring weather patterns that can bring more rainfall to south eastern Australia.

While some of the climate models anticipate a negative IOD pattern will last for a couple of months, others show a return to more neutral conditions in November.

IOD events tend to break down when the monsoon arrives in the southern hemisphere around the end of spring.

Last year was a notable exception, when a strong positive IOD lasted until the last week of December.

This coincided with a late arrival of the monsoon over northern Australia, and a very dry October and December for Victoria (it was the eighth-driest and third-driest respectively).

This year is looking quite the opposite.

Looking back on the month of September, rainfall has been below average for most of the eastern half of Victoria and very much below average - in the bottom 10 per cent of records - for central and East Gippsland.

Most of Western Victoria has had near average rainfall, and parts of the south west even had above average monthly totals.

Despite snow down to low levels and a few very cold days in the past week, maximum temperatures were 6-8°C below average on September 25 in parts of the west and the north east.

Averaged over the month, days and nights have been warmer than usual across the state.

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