Sydney, Melbourne, Adelaide and Canberra were all under severe weather warnings for damaging winds on Monday morning as a vigorous ‘double’ jet stream passed over southeastern Australia.

A powerful subtropical jet and a meandering polar jet are both passing over Australia’s southeastern states on Monday. These jet streams, which are bands of howling upper-level winds, are causing an outbreak of cold and blustery weather in several states and territories.

Image: Jet stream winds (300 hPa) at 8am AEST on Monday, November 21, according to the ECMWF-HRES model.

As of 10am AEDT on Monday, severe weather warnings were in place for damaging winds in parts of SA, Vic, NSW and the ACT. This included Adelaide, Melbourne, Sydney and Canberra, which means roughly 12 million Australians were under warnings for damaging winds on the same day.

In addition to the overhead jet streams, Monday’s blustery weather is being driven by a complex low pressure system passing to the south of Tasmania. This low and an associated cold front have already caused wind gusts above 100 km/h on Saturday and Sunday, although Monday will be the peak day of wind for many areas in Australia’s southeast.

Image: Speckled clouds passing over southeastern Australia on Monday morning, which is a clear sign of a cold air mass.

This powerful weather system is also driving unseasonably cold air across southeastern Australia.

More than 15cm of snow has already fallen in the mainland Alps and snow is expected to reach about 500 metres elevation in Tasmania, 700 metres in Victoria and 900 metres in southern NSW during Monday.

Amid this cold and windy weather, Melbourne’s temperature only felt like 3.4ºC at 9:40am on Monday. Just over an hour later, Canberra’s feels like temperature plunged to -2.9ºC as the mean wind speed reached 52 km/h.

Wind will gradually moderate over southeastern Australia during the next couple of days. However, damaging gusts will remain a threat in some areas throughout Monday and into Tuesday.

Check the latest warnings for the most up-to-date information on this system.