'Remarkable' high pressure shielding much of Australia from winter's wrath

'Remarkable' high pressure shielding much of Australia from winter's wrath


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Farmers and ski resort operators are watching synoptic charts with growing anxiety.

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Farmers and ski resort operators are watching synoptic charts with growing anxiety as some of the highest pressure readings in a decade reveal an autumn that is refusing to let go.

Dominant high-pressure systems have lately been the norm. Parts of Australia recorded readings of 1039 hectopascals at the start of the month, compared with typical pressure levels of about 1013 hPa.

"Values that high are quite remarkable [and are] at least a one-in-10-year event...for any time of the year," Andrew Watkins, head of climate prediction services at the Bureau of Meteorology, said.

A string of high-pressure systems in recent weeks have been further south than usual, pushing rain-bearing cold fronts further poleward.

Rainfall totals across the country are running below 20 per cent of a typical June with almost two-thirds of the month over, Dr Watkins said.

Brett Dutschke, a senior meteorologist with Weatherzone, said recent conditions had been unusually free of cold fronts, leaving cities from Perth to Hobart facing among their warmest and driest starts of winter on record.

Meteorologists noted cold fronts have been tracking closer to Antarctica, leaving high-pressure systems to dominate other parts of the southern hemisphere as well. (See bureau chart below from June 18.)

Snow watch

Andrew Haigh, a bureau duty forecaster, said the coming cold front would likely clip the south-east corner of the continent and would probably not produce "a great deal of snow: "I don't think it will be a particularly strong one".

Whether the pattern will be broken up is not clear, either. "We could just as likely get another high-pressure in, making it stable for a while" over southern Australia, Mr Haigh said

The alpine resorts have enjoyed excellent snow-making conditions with the frosty nights - just as well with school holidays approaching.

How well they come out of the coming weekend, though, will depend on how much natural snow falls but also whether warm rains fall ahead of the front's arrival, Dr Watkins said.

(See Mt Perisher image (below) from Monday morning, via Ski.com.au)

Sydney waterspouts and outlook

For Sydney, the dominant feature lately has been moist onshore winds bringing coastal showers and rain.
Temperatures have been a bit over a degree warmer than average for both days and nights, with rainfall already topping the June average of 133 millimetres.

The coming cold front will mean cooler days for the city but probably drier conditions unless an east coast low sets up offshore.

"There is the chance for the odd low and trough developing near the coast," Mr Dutschke said. The city is likely to see fewer rainy days but some of them "could be really wet".

Coastal residents were treated to a relatively unusual weather event on Monday with at least one waterspout forming off Narrabeen on the city's northern beaches. (See picture by Nick Moir below.)

The bureau's Mr Haigh said waterspouts are typically associated with an updraft of air offshore that combines with a windshear to create a rising rotation.

"They tend to be fairly shortlived and usually don't affect the land," Mr Haigh said. "They are a bit like a tornado but a weak version of one."

"You probably wouldn't want to be right underneath one if you're on a surfboard but generally they don't cause too much trouble," he said.

El Nino chance fades

While some commentators have pointed to southern Australia's mostly dry past six weeks or so as a sign of a coming El Nino event, the models in fact are backing off such an event for 2017.

Dr Watkins said none of the eight models the bureau uses to predict conditions in the Pacific now forecast an El Nino this year. Back in April, six of the eight did so.

The more likely culprit for the relatively dry spell is the Indian Ocean, where cooler waters near Western Australia have tended to suppress rainfall over the continent, he said.

The near-term outlook is for dry conditions over most of Australia to persist for a few days yet - adding to concerns for winter crops needing a decent soaking.

(See bureau chart below for rainfall predictions out to Thursday.)

Weatherzone is owned by Fairfax Media, publisher of this website.

Sydney Morning Herald.

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