WeatherViewer wrote: ↑Sat Jan 20, 2024 9:35 am
Hey gang,
Just a curious question about Summer this year here in Melbourne specifically.
I've been watching the charts this summer and anytime there is significant heat incoming and getting close to Melbourne, it seems to dissipate and head back North on the next ACCESS chart run for example.
I'm not asking for scorching heat, but years gone that heat would certainly push through and make it here, followed later with a cool southerly change.
It just doesn't seem to penetrate this far south this year. Are there any explanations?
It's been something of a pattern for the last few summers. I'd have to check but I think it has been a few years since Melbourne last had a 40+ day, certainly rarer at least. Heatwaves seem to have been less frequent too since 2020.
I'm not sure of all the possible factors, but we've been in a positive SAM this summer, with high pressure systems and cold fronts further south than usual. When they are further north, these tend to pull hot air down over Vic and Tas before cutting it off with a cool change a few days later, sometimes resulting in heatwaves. Might be that models are sometimes reflecting more normal conditions at first before adjusting to the current set up a few runs later.
Seems that in the past few years at least, our summers have tended more towards positive SAM, partly because this is more common during La Ninas, but even this year it has happened due to a strong polar vortex over Antartica which has pulled the belt of fronts further south.
The positive SAM has actually weakened a bit recently and models are suggesting it may switch slightly negative for a time as we head into Feb, so will see how things evolve during Feb.
Personally, I think a positive SAM summer is great. Easterlies, troughs, humidity, etc., all much better for storms, rainfall, and reducing bushfires. So far, this summer has been perfect, the best in a long time. A good amount of rain to maintain a green landscape and still enough warm and sunny days to feel like summer without those scorching northerly gales.