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Contrasting start to summer expected for Australia’s west and southeast 

As we head into the beginning of December, the contrasting patterns in Australia’s weather can be summed up in one sentence; Melbourne could have its coldest opening day of summer on record, while Perth has its hottest. 

This may not be an exaggeration come tomorrow night. For December 1st, Perth’s highest temperature on record is 37.4°C in 1979, while Melbourne’s lowest is a wintry 15.5°C in 1987. Tomorrow’s forecasts for Perth and Melbourne are 38°C and 16°C respectively, although Melbourne could stay even chillier than its forecast with a soggy day expected.

Image: Forecast temperature and winds across southern Australia on December 1st 2pm WST using ECMWF. 

Let’s start with the west, where a typical summer setup is developing. A trough is beginning to extend down the west coast of Western Australia, drawing hot air from the interior towards the west coast. This setup is a regular feature of summers for west and southwest WA, with Perth exceeding 35°C an average of 27 times between October and April.  

Meanwhile, Melbourne—and in fact southeast Australia in general—has been subjected to an unusually chilly November, with multiple days of snow so far over the mainland Alps and the Tasmanian highlands. We wrote a few days ago that a cold front will likely bring snowfalls on the first day of summer, which you can read more about here. For Melbourne, this cold front will bring thick cloud cover and showers, making it feel much more like the first day of winter than the first day of summer.

Image: Forecast accumulated rainfall for the 48 hours to December 1st using ECMWF. Victoria's rainfall should be relatively evenly split between Sunday and Monday. 

You can see the differing patterns in the forecast synoptic chart for Monday below, with very warm to hot winds pushing through the west coast, and cool southwesterlies accompanying the expected rainfall across the southeast. While Melbourne’s official forecast is 16°C, these persistent showers could keep the day cooler than expected.Image: Forecast synoptic chart for Monday across Australia. 

Of course, these temperatures are a long way off reaching any all-time December records, and there is still a chance that each of these cities don’t even reach their respective December 1st records. However, the fact that we are talking about the possibility highlights the vastness of the country and the massive contrasts that can eventuate in our weather patterns.