Why is it so hot and then so cold? Is the weather broken? Is this a climate change thing?
If you live pretty much anywhere in Australia’s south-east, and especially in our two most populous cities Sydney and Melbourne, you’ve heard people asking these sort of questions all week, right?
Right. In fact you’ve probably been wondering about the wildly fluctuating weather yourself.
Example. In Sydney last week, temperatures hit 41 degrees on Friday. Then on the weekend it was a comparatively chilly 22 both days. Just when you’d put your jumpers away for good, you were back up the ladder to bring ’em back down the attic. What a drag.
Even Melbourne, which is famous for its four-seasons-in-one-day weather, has had wildly wavering weather this spring. Top temperatures on Thursday will be well and truly mired in the teens. It’s the third time this month that Melbourne has endured a solidly sub-20 degree day after a day well in excess of 30.
So what’s going on? Why can’t spring just gradually warm until it turns into summer? Why is there such a violent tug-of-war between seasons?
Blame it on three things. Firstly, we live in the temperate zone, which means the zone between the tropics and the polar regions. Here we are subject to weather systems influenced by both the colder zone to our south and the hot bits to the north.
In spring, these two zones both fling chunks of weather our way. That’s not a particularly meteorological turn of phrase, but you get the idea. And if you don’t, the weather map above illustrates it really clearly.
It’s the map from Wednesday afternoon. To read it like an absolute champion, you need just one factoid. Memorise this and be weather wise forever. Air moves anti-clockwise around a high pressure system. That’s it. That’s all you need to know.
So if you look at the big H in the ocean way west of Perth, and if you then trace your finger around it, you can see that the air approaching Adelaide has come from waaaay down south in Antarctic waters. That’s why Adelaide was 31 degrees at 9 in the morning on Wednesday with bushfires in the region, but had cooled to 21 degrees by 4pm -- which is usually the heat of the day.
The cold air reached Melbourne on Thursday after a day in the mid 30s Wednesday. It’s going to be so cold that there may even be a sprinkling of snow on the peaks of the Victorian Alps. Sydney will cop cold air on Friday after a scorching 38 degrees forecast for Thursday. But again, this is normal. It’s all part of the temperate zone dance.
As mentioned, however, there are two other reasons why spring weather in the southern half of Australia is so volatile.
The Huffington Post Australia contacted Dr Karl Braganza, climate monitoring manager at the Bureau of Meteorology, who in our opinion is definitely one of the top two Dr Karls in Australia. Here’s what he told us.
“Most of the Australian population centres are along the coast," he told HuffPost Australia.
"That means the prevailing wind can make a massive difference from one hour to the next."
And from one day to the next, as we all know.
And the final reason for huge day-to-day and even hour-to-hour discrepancies? It’s the incredibly rapid movement of weather systems across southern Australia, which happens because we don’t have much in the way of mountains to stall them.
“In North America for example, you have the Rocky Mountains to the west of the east coast, which means weather systems tend to stay for longer over one side of the country," Dr Karl explained.
"In Australia you don’t have the topography so they move through a little quicker and change a lot more.”
In summary, it’s boiling hot one day and bloody freezing the next because:
1. We live in the mid latitudes;
2. Our coastal cities have big weather fluctuations due to localized sea breezes;
3. There are no proper mountains in the way to slow weather systems down;
4. This is normal spring. Nothing to see here. The weather is not broken, even if it definitely feels that way;
5. We have no idea what you should wear tonight. But take a cardigan just in case. Who doesn't look good in a cardigan?