Chances of La Nina may mean a wet spring

Increased chance of La Nina in spring

Weather
WEATHER: Victoria's central districts have had a good start to the winter season, with pastures and crops getting away well on high soil moisture levels. But conditions in some other parts of the state remain challenging. Photo by J Powells.

WEATHER: Victoria's central districts have had a good start to the winter season, with pastures and crops getting away well on high soil moisture levels. But conditions in some other parts of the state remain challenging. Photo by J Powells.

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A look ahead to spring.

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Even though we are on track for a drier than average June, the wet start to 2020 means soil moisture is still very much above average in parts of the central district and around Melbourne.

But soil moisture in much of East Gippsland is very low, and is also below average in parts of the north west.

The Southern Annular Mode (SAM) is currently positive and, after a brief return to more neutral values, is forecast to remain positive for at least the next fortnight - with higher pressure likely over Australia.

In winter, a positive SAM typically means less rainfall for southern Victoria.

That is one of the reasons why July is showing increased chances of below average rainfall for parts of the south west.

The latest outlook for August shows no strong push towards a wetter or drier month for most of Victoria.

It has been an especially wet first five months of the year for much of central and north east Victoria.

That means streamflows are likely to be high at sites in central, eastern and north-eastern areas of the state during winter (June to August).

But low streamflow is likely at sites in the west.

Overall water storage in the Murray Darling Basin is at 41.1 per cent full, which is up 5.5 per cent compared to this time last year.

Daytime temperatures have actually been a bit warmer than usual during June so far for parts of Victoria. That will probably continue, with both maximum and minimum temperatures likely to be warmer than average during July and August.

Looking further ahead, the Bureau of Meteorology's ENSO Outlook has shifted to La Nina 'watch'.

Recent cooling in the tropical Pacific Ocean, combined with climate model outlooks, means the chance of a La Nina developing in 2020 is about 50 per cent - roughly double the average likelihood.

Some climate models suggest we could see a La Nina pattern become established by late winter or early spring. Half of the international climate models surveyed by the Bureau suggest a negative Indian Ocean Dipole may also form during winter or early spring.

La Nina favours above average rainfall for much of eastern, central and northern Australia.

A negative IOD typically brings above average rainfall to southern Australia.

The increased chance of a wet signal from either the Pacific or Indian Oceans, or both, is increasing the chance of above average rainfall for parts of Victoria following winter.

- Jonathan Pollock, BoM climatologist

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