Qld weather: Reason for long run of particularly cold temperatures

Winter has shredded Queensland’s history books this year, with a number of regions dropping to record low temperatures and recording their coldest July days in decades earlier this month. Here’s why the state has been hit so hard this year.

Winter has shredded Queensland’s history books this year – a number of regions across the state reached record low temperatures and recorded their coldest July days in decades earlier this month.

Monday, July 4, is thought to have been the coldest July day on record for many Queensland communities, including Emerald where it got to a maximum temperature of just 11.5C, Gladstone (11.9C), Moranbah (11.5C), Maryborough (12.9C) and Maroochydore (13.4C), while the Darling Downs continues to reach subzero temperatures most mornings.

Minimum temperatures have been consistently below freezing this winter too – the coldest minimum temperature this year was recorded on July 11, with -3.9C at Roma and-3.6C at Mitchell, while July 10 saw -3.5C at Applethorpe.

But why is this winter so cold?

The University of Southern Queensland’s Professor Roger Stone, who also serves on the UN World Meteorological Organisation, says that a major reason for the bone-rattling winter chill is the combination of a prolonged La Nina system and a weather driver known as the Southern Annular Mode – a combination bringing strong south-westerly bursts of cold Antarctic air to Queensland.

THE SOUTHERN ANNULAR MODE

Professor Stone said that a weather system known as the Southern Annular Mode was having a big impact on this year’s big freeze.

He described the SAM is a band of wind moving west around the Antarctic Circle that usually brings cold bursts of weather to southern areas of the country like Victoria and Tasmania during winter, but said that a suspected build-up of ice around Antarctica had made these winds colder and more far-reaching this year.

A frosty morning out at Stanthorpe last week. Photo: Diamondvale Cottages

“So those south westerly winds we’ve been having in Queensland are carrying that cold Antarctic air up to Queensland, and that is having an impact with those colder temperatures we’ve been seeing,” Professor Stone said.

“Every time we see those significant temperature drops, it’s usually because of that cold air – also called a cold front – being pushed north by south-westerly winds, and this system is what is driving those winds.”

He said that while some of the Southern Annular Mode winds make it to Queensland every year, the likely build-up of Antarctic ice was making the winds colder this year and was a major contributor to our lower temperatures.

The Southern Annular Mode can also increase rainfall over eastern Queensland and Northern New South Wales.

LA NINA

Professor Stone also said that while La Nina has officially ended, the characteristics of the phenomenon known to bring above average rainfall and cooler temperatures to Queensland were still present.

“First of all, La Nina hasn’t really gone away, that’s the key point here,” Professor Stone said.

“The Australian Bureau of Meteorology uses some different modelling and systems to interpret La Nina events so even though they’ve said that it ended a few weeks ago, most international systems say that it is still here but just a bit weaker.”

“La Nina tends to bring with it cooler and wetter conditions, so that is one reason why this winter has been a bit colder and wetter than the last few years.”

Professor Stone said that most modelling, including that of the BOM, forecast the La Nina system to return to full force in the Spring.

“A likely resurgence of the La Nina climate pattern in the eastern and central Pacific Ocean is likely to increase rainfall again,” he said.

“These systems tend to last from Autumn to Autumn, and all the modelling predicts the system reasserting itself again at the end of this year and then breaking in Autumn, 2023.”

Professor Stone said that “until then, we can certainly expect wet and cold conditions,” but after La Nina breaks, Queensland is likely headed for a drier and warmer winter next year.