Polar blast across south-eastern states

Millions of people in eastern Australia are pulling on their woollies and hats today as a polar blast of cold weather sweeps across multiple states.

Sydney is forecast to record its coldest temperature in two years early today, with the mercury dipping below 5C, but a wind chill is making it feel more like a chilly 2C.

That figure puts it on track to be the city’s coldest morning in two years, beating the previous mark of 5.2 degrees, and the coldest June morning since 2010. But Sydney’s western suburbs will be a few degrees cooler and some places are likely to be cold enough for frost.

Meanwhile, early today in Melbourne, the mercury hit a low of 3 degrees, but it felt more like zero degrees for the city’s residents.

Even Queensland is feeling the impact of the cold blast, with Brisbane shivering at a maximum temperature of 8 degrees but the apparent temperature being more than 6 degrees.

The polar blast over the southeastern United States was caused by a cold, dry air mass interacting with clear skies and light winds beneath a narrow ridge of high pressure.

Narrow ridges are notorious for causing cold mornings in south-eastern Australia in winter. This is because the central region of these high-pressure ridges, where the weakest winds and clear skies favorable for nocturnal radiative cooling are located, arrive relatively quickly after the passage of a cold front.

Freezing weather this week saw temperatures drop below -7C in Tasmania and Victoria, while parts of New South Wales shivered to near -9C.

Minimum temperatures in Sydney are forecast to start rising from tomorrow – when it is Australia’s winter solstice, marking the shortest day and longest night of the year – as wind, cloud and moisture increase as troughs pass through low pressure.

But minimum temperatures in Sydney and Melbourne will remain low over the weekend into next week.