Why is it so cold right now? And how long will it last? A climatologist explains


Anyone living in South East Australia will have noticed the cold that has set in over the past few days. After relatively mild conditions last week, an onset of winter has arrived.

These temperatures are well below average, even for mid-winter.

So why is it so cold? And how long will the cold last?

Read more: ‘One of the most extreme disasters in Australian colonial history’: Climate scientists talk about floods and our future risks

Temperatures fell below double digits across swathes of southeastern Australia on Monday.
meteorological office

An Antarctic explosion

Much of southeastern Australia is currently under a cold air mass from the south.

Indeed, a low pressure system that brought heavy rain, high winds and even a possible tornado to South Australia moved eastward.

Air moves clockwise around low pressure systems in the southern hemisphere, so low pressure over Tasmania and the Tasman Sea means we have strong southerly and southerly winds -west over Victoria and New South Wales.

This 4am weather map on May 31 shows low pressure southeast of Australia and cold fronts and troughs moving through the region.
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As the low pressure moves eastward, cold fronts and troughs moved through the region. This led to most of southeastern Australia experiencing rain or snow.

While an anticyclone briefly dominates our weather on Thursday, a new low once again brings cold and wet conditions throughout the weekend. Another cold front is expected to cross Tasmania, Victoria and southern New South Wales on Friday evening.

Read more: ‘A vigorous cold front’: Why it’s been so cold this week, with more on the way

How unusual is that?

For many Australians, this cold spell will have been an unpleasant shock to the system. But it’s not uncommon to have cold spells bringing wet and windy conditions to Tasmania, Victoria and New South Wales.

However, this outbreak of cold air arrived quite early and resulted in significant rainfall totals and persistent below average temperatures.

For example, Melbourne is expected to have nine days in a row where maximum temperatures are below long-term averages.

This includes five days where daytime highs are more than 3℃ cooler than normal.

Daily maximum temperature anomalies relative to 1900-2021 for the same calendar date. May 30 and 31 are based on observed data while June 1 and 7 are based on forecast data. Climatology 1900-2021 is calculated from observations from the Melbourne Regional Office (1900-2013) and Olympic Park (2014-) collected by the Bureau of Meteorology. Note that the Olympic Park site is slightly cooler on average than the regional office.
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Melbourne’s daytime temperatures are highly variable in summer – days above 30℃ as well as days below 20℃ are quite common.

But at this time of year and throughout winter our daytime temperatures are much less variable.

The cold temperatures we’re seeing right now are only a few degrees below normal, but five days of this cold snap are in the lower 10% of the daytime temperatures we’ve seen at this time of year. .

Cold weather is widespread in southeastern Australia and brings heavy snowfall in early winter to some ski resorts.

Is this a sign of a cold winter ahead?

Today is the first day of meteorological winter which covers the months of June, July and August. With cold weather already present and expected to persist in the coming days, does that mean we can expect a particularly cold winter?

The seasonal outlook from the Bureau of Meteorology suggests that cooler than normal conditions are likely in the interior of the continent.

This is noteworthy since the average conditions to which the seasonal outlook is compared relate to the period 1981-2018. Over the past few decades, Australia has warmed considerably, making cooler-than-average conditions more unusual.

Colder than average daytime temperatures are expected across much of the continent this winter.
meteorological office

Precipitation forecasts predict widespread wetter than average conditions this winter.

This continues the pattern of wet conditions we have seen in recent months which led to the devastating floods seen in February and March in south east Queensland and coastal New South Wales in particular.

The seasonal outlook also calls for a wet winter over most of Australia.
meteorological office

Read more: ‘One of the most extreme disasters in Australian colonial history’: Climate scientists talk about floods and our future risks

Australia’s climate is most strongly tied to the conditions of the Pacific and Indian Oceans in winter and spring.

This increases proficiency in the Bureau of Meteorology’s seasonal outlook in relation to warmer times of the year.

The cool and wet outlook is tied to the persistence of La Niña and the projected development of a negative Indian Ocean Dipole (a natural climate phenomenon that influences precipitation patterns around the Indian Ocean).

Both of these phenomena are associated with warmer ocean temperatures near Australia and are conducive to more humidity over the continent and stronger low pressure systems over southern Australia.

This in turn increases the likelihood of wetter than normal conditions and suppressed daytime temperatures.

Outbreaks of cold air like the ones we’re seeing right now in southeastern Australia are a big part of our cool season weather.

The outlook suggests that we could see more of these cold spells than normal in the winter of 2022.

Read more: Wet Winter, Soggy Spring: What is the Indian Ocean Negative Dipole, and why is it so important?

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