How's this year's autumn break shaping up?

How's the autumn breaking shaping up?

Weather
Victorian year to date rainfall deciles January 1, 2019 to March 31, 2019. Image: BOM

Victorian year to date rainfall deciles January 1, 2019 to March 31, 2019. Image: BOM

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In recent decades, the autumn break has been arriving later than normal for many parts of the state.

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April is the time when many farmers look to the heavens for the promised autumn break - that first 25 millimetre rain event that often marks the start of the winter crop and pasture growing season.

The autumn break typically arrives over eastern and southern Victoria during March and April, and typically hits the northwest during May.

In recent decades, it has been arriving later than normal for many parts of the state.

For example, the autumn break at Rutherglen is now a fortnight later than a century ago.

Likewise, autumn has been getting drier - 24 of the last 29 March to May periods in southeast Australia have seen below average rainfall.

The reason has been the steady increase in the number of high pressure systems over Victoria during autumn since the mid-1900s.

These highs not only prevent clouds forming, but also keep cold fronts to the south.

So what about this year?

The rainfall outlook for April indicates parts of the northwest are likely to be drier than average, but for the rest of Victoria the chances of wetter or drier than average month are roughly equal.

This indicates the autumn break is likely to arrive either close to its normal time or later than usual.

After Victoria's warmest summer on record, and a warm start to autumn, temperatures look set to remain higher than usual in the months ahead.

Higher than usual temperatures can result in an increase in evaporation, reducing soil moisture.

Root zone soil moisture, April 4, 2019.

Root zone soil moisture, April 4, 2019.

In much of Gippsland, central and western Victoria, record summer temperatures and low rainfall mean soil moisture is below average approaching mid-autumn.

For most of Gippsland, 12-month rainfall deficiencies are severe (<5th percentile), and 24-month rainfall deficiencies are the lowest on record for much of the West and South Gippsland district.

Above average rainfall during March in East Gippsland and the northeast means these areas have fared a little better more recently, and have arguably had their autumn break already, but overall the state remains dry.

The Victorian state average rainfall since the start of the year is 63 millimetres, which is 50 millimetres below normal.

For more information and to keep up to date with the current weather forecasts across the state, visit www.bom.gov.au/climate 

- Climatologist with the Bureau of Meteorology, Jonathan Pollock.

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