Melbourne's beating Sydney and Canberra at summer (maybe)
Image: Winds and maximum near-surface temperature in the 24 hour period prior on Wednesday 21st December, 2022, according to the EC model.
Both Sydney and Canberra have yet to record a 30-degree day this warm season. Melbourne passed the big three oh on the 3rd and 4th of December (reaching 31.0ºC and 34.5ºC, respectively) so, you could say, it won at summer. But, given it then plummeted below 20ºC for 9 days out the following 13, including only reaching 15.8ºC on Wednesday the 14th (the coldest day this late in the season in 16 years), such an assertion would be a stretch. None of the southeast capitals are doing very well at summer.
Melbourne is having its coldest start to December since 2001 (as mentioned here). Canberra loses by this measure too, ploughing through its coldest start to December since 1992. On average, December in the national capital sees more than seven days exceeding 30ºC. With none so far this year and the next week forecast to be another coolish one, it's safe to say that the number of days greater than 30ºC will be much less for 2022.
Sydney, meanwhile, is having its second cold start to summer in a row. Average maximum temperature is sticking firmly below 25ºC as it did for the same period of December in 2021. Prior to 2021, it hadn't been this cold in the first half of December since 2011. Last Monday's 29.6ºC was the closest Sydney has managed to a summer's day so far for 2022.
Image: Temperature anomalies over Australia during the past week.
The enlarged polar vortex and persistent southerly wind pattern responsible for the cold over southeast Australia will briefly give way mid-week, at least for Melbourne and Adelaide. Here, heat will encroach from the north ahead of another trough and cool change. The 30ºC heat is unlikely to push as far east as the NSW/ACT capitals, though it will certainly be warmer in Sydney and Canberra during this time, with outer western suburbs of Sydney possibly reaching 30 degrees during the two to three days before Christmas.
After a cool-to-mild Christmas for most centres except perhaps Adelaide (see here) warm northerly winds look to affect the eastern parts of the southeast, including Sydney and Canberra, between Christmas and New Year. Maybe, finally, bringing summer.