Be sure to throw an extra blanket on the bed tonight if you’re in Sydney because the city is forecast to see its lowest temperature in two years early on Thursday morning.

Large areas of southeastern Australia have endured a string of bitterly cold mornings this week, with some places registering their lowest temperatures in years.

This spell of frosty overnight temperatures has been caused by a cold and dry air mass interacting with clear skies and light winds beneath a narrow high pressure ridge.

Narrow ridges are notorious for causing cold mornings in southeastern Australia during winter. This is because the central region of these high pressure ridges, where you find the lightest winds and clear skies that are conducive to nocturnal radiative cooling, arrives relatively quickly after the passage of a cold front. By contrast, larger high pressure systems take longer for the centre of the high to arrive following a front, which allows more time for the air mass to warm up.

This week’s frosty weather pattern has allowed temperatures to plummet below -7°C in Tas and Vic and close to -9°C in NSW.

Image: Modelled minimum temperature on Wednesday, June 19, according to the ECMWF-HRES model.

Some suburbs in Western Sydney saw frost on Wednesday morning, with Richmond chilling to -0.6°C shortly after 7am.

Sydney’s official weather station at Observatory Hill registered a low of 6.5°C early on Wednesday, which was its coldest start so far this year. However, it should get even colder tomorrow morning.

The temperature in Sydney’s CBD is forecast to drop to about 5°C early on Thursday morning. If it gets lower than 5.2°C it will be the city’s coldest morning in two years and its coldest June morning since 2010. Western suburbs will be several degrees colder and some places will likely be cold enough for frost.

Minimum temperatures will start to climb in Sydney from Friday as wind, cloud and moisture increase with the passage of a low pressure trough.