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ABC News

Perth weather surprise as city marks a year without reaching 40 degrees Celsius

Perth is more than half way through a summer that feels markedly different to last year, with the city officially reaching a full year without hitting 40 degrees Celsius.

While several days have come close, and some of the eastern suburbs have exceeded 40C, none have made it over the mark at the city's main gauge in Mt Lawley. 

In contrast, by February 5, 2022, the gauge had hit 40C 13 times — including a record number of consecutive days over that mark in mid-January.

Bureau of Meteorology (BOM) forecaster Jessica Lingard said the difference was due to heat-driving weather systems, such as the west coast trough and high pressure systems, moving from west to east at a faster pace.

"Last year, what happened was these west coast troughs were forming and then they were sitting off the coast and really lingering for days and days." she said.

"And so because they were sitting and lingering persistently, that allowed the heat to build along the west coast. 

"This year, they've been doing exactly what they're supposed to do.

"They form down the west coast, hang around for maybe a day, then a nice ridge of high pressure forms and pushes them eastwards."

Weather defies data

According BOM data, Perth would usually have hit 40C once or twice by February.

The city normally records three to four days over 40C each year — one every 10 years in November, one per year in December, one to two per year in January and one in February.

But it is not unprecedented to go a full summer without hitting the mark.

There have been three summers without a 40 degree day in the last 30 years, in 2017/18, 2001/2022 and 1998/1999.

However, looking back even further — with data dating back to 1876 — there have been dozens.

Still a chance for 40C day this summer

Ms Lingard said with most of February still to go, there was still a good chance Perth would see a 40C day this summer. 

"Usually, in February, we do see at least one 40 degree day and at least seven days above 35 degrees, which I think we've definitely achieved," she said.

"And February is, by 0.3 of a degree, our hottest month of the year.

"So we're not out of the woods yet."

Climate change making extreme heat more common 

Ms Lingard said the gentler summer weather, so far, may be one to savour.

Climate change is increasing the overall temperature and days of extreme heat across the country, in all months, according to the latest State of the Environment report.

"And it's not just on average, but also it's going to make the extremes of our summer more extreme," she said.

"We may see not just more 40 degree days, we may see more 45 degree days.

"I'm going to take any of these summers that we do get that are slightly cooler, and just really enjoy them, because I don't really want to go through another summer like last year."

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