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29 June 2017

How Antarctica is messing with our cold season

A positive Antarctic Oscillation, or Southern Annular Mode, has seen cold fronts that could bring moisture move closer to the pole and away from Australia. Picture: Bureau of Meteorology

THIS weekend much of the country’s east coast is set to shiver through one of the coldest snaps of the year.

“Extreme winter weather” is forecast with overnight lows in inland areas far below freezing.

So it will come as no surprise to learn that Antarctica is having an effect on our weather. But perversely, meteorologists have said that a weather system circulating around the polar region is not leading to colder, but warmer conditions.

The Bureau of Meteorology (BOM) released its climate outlook for July to September on Thursday and the forecast is for an overall mild rest of winter leading to a balmy spring.

It comes as we are about to head out of one the driest June months ever.

Victoria is set to record its driest June since record keeping began, breaking a record that was set in WWII.

June has seen some of the lowest rainfall on record. Picture: Bureau of Meteorology

June has seen some of the lowest rainfall on record. Picture: Bureau of MeteorologySource:Supplied

The BOM on Thursday said the driest June was in 1944, with 22mm of rain falling in those 30 days. This June is sitting at just 11mm of rain, with only 2mm more expected in the final 36 hours before July begins.

Senior Hydrologist with the Bureau, Paul Feikema, said a high pressure system was dominating much of the southern hemisphere pushing temperatures up and keeping the rain away.

“Outlooks suggest dry and warm conditions are likely to extend into early spring.”

The cause is due to the interaction, or lack of interaction to be more accurate, between three of Australia’s main climate drivers — El Nino, the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM).

This what the next three months will look like. Picture: Bureau of Meteorology

This what the next three months will look like. Picture: Bureau of MeteorologySource:Supplied

El Nino hasn’t really happened in the Pacific lately. On the other side of the continent, the IOD has also failed to muster much gusto either.

This has cleared the decks for a weather system around the South Pole, the SAM — also known as the Antarctic Oscillation, to have its wicked way with our weather. But far from this system from the icy south bringing cold temperatures, the opposite is happening.

“The unusual high pressure over Australia is due in part to the SAM. When SAM is positive, a belt of high pressure around the globe expands pushing cold fronts and moisture to the south away from Australia,” said Mr Feikema.

A positive Antarctic Oscillation, or Southern Annular Mode, has seen cold fronts that could bring moisture move closer to the pole and away from Australia. Picture: Bureau of Meteorology

A positive Antarctic Oscillation, or Southern Annular Mode, has seen cold fronts that could bring moisture move closer to the pole and away from Australia. Picture: Bureau of MeteorologySource:Supplied

With those cold fronts held at bay, it means daytime and evening temperatures are higher than usual, particularly in the south western and south eastern parts of the country.

But if you’re wondering how that marries up with the “unbelievably severe frost” and chilly nights forecast for this weekend, well that’s partly SAM’s fault too.

High pressure often leads to clear skies and that means what heat has accumulated during the short winter days can escape rapidly after dark leading the mercury to plummet on some days.

The prospect of an El Nino developing in 2017 has lessened.

“El Nino is very unlikely for this year but rainfall is likely to be below average for parts of southern Australia,” he said.

Oi mate, stop messing with Australia’s weather. Picture: istock

Oi mate, stop messing with Australia’s weather. Picture: istockSource:Supplied

In March, the BOM predicted a 50 per cent chance of an El Nino forming by July following changes in the Pacific Ocean and the atmosphere.

However, the chances have since dropped, partly because of a cooling in the waters of the Pacific Ocean off Peru during May and June.

While the IOD remains neutral, there’s a 50/50 chance it will crank up to positive mode which could increase the chances of a warm and dry spring in the east even more.

So enjoy this weekend’s chilly temperatures because they may be the exception in the coming months — not the rule.

— with AAP.

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