Has the weather gone totally mad?

Here's an American tourist at Bondi Beach on Wednesday as the temperature nudged the mid 20s. She'll get an awful shock Friday or Saturday when that bitterly cold southerly hits. Pic. Phil Hillyard. Source: News Corp Australia

THE cold front has just hit Melbourne. Tullamarine Airport just plummeted from 18 degrees to 7.7 in a matter of minutes, while the Yarra river is bursting its banks.

The Yarra is not overflowing because of rain, but due to a surge caused by incredibly strong winds which have buffeted much of south east Australia today.

FROM EARLIER TODAY...

THEY call it the hairdryer.

It's a gale-force westerly wind that heats up the south east of Australia in late winter, tearing the snow off the ski slopes like paint stripper and giving east-coast residents an early, teasing taste of spring.

Then it slams the door in your face, mocking your T-shirt and shorts with an Antarctic blast that sends you scurrying for your winter woollies.

Storm chaser Hannah took this from her balcony in Docklands just as the cold front hit Melbourne this afternoon. Picture credit: Hannah Weddell Source: News Corp Australia

When we first saw this image of Melburnians on Middle Park beach, we thought the black thing was an upside down labrador which had blown off its chain. We now realise it's apparently just a jacket. Either way, it illustrates wild weather. Picture: Nicole Garmston. Source: News Corp Australia

No, the weather hasn't gone mad. It's just gotten a little extreme.

It's also gotten extremely scary in some parts of the country. Launceston Police said a person had died as a result of injuries sustained when a tree fell in high winds about 12.30pm today. Strong-to-gale-fore winds will increase across much of south east Australia in the coming 24 hours.

So what's going on?

This is actually a classic setup for the second half of winter, and we're going to borrow a few weather charts from the Bureau of Meteorology website to explain all that.

This first chart shows the current weather situation right about now.

Lunchtime Thursday July 31. Source: NewsComAu

See the big low pressure system below Tasmania? The first thing to understand is that air circulates clockwise around a low.

The wavy lines, called isobars, help show you which way the air is flowing. So as you can see, right now there's a bunch of air flowing across NSW and Victoria which has more or less come from central Australia. As you'd imagine, that air is pretty warm.

You should also know that the closer the isboars are together, the windier it is. And those isobars are really close together. Thredbo in the NSW Snowy Mountains has had gusts in excess of 100 km/h for each of the last three days. In the last hour or so before this story was published, wind speeds touched 124 km/h. Mt Hotham in Victoria just hit 113 km/h. Eek.

As mentioned, all that wind plus warmish temperatures create a real hairdryer effect. That's why the snow in the Aussie Alps has gone from this...

The Aussie snowfields a couple of weeks back Source: NewsComAu

To this...

The same scene after three days of hairdryer. Source: NewsComAu

But the cold is about to return with a vengeance. Have a look at the projcted weather map for Friday.

See what we mean? Source: NewsComAu

See how the cold front will have crossed the south east by late Friday morning? The front is the line with the black "shark fins" on it. Now the air impacting south east Australia is coming from a cold place way down in the Southern Ocean. That means good snow for the Alps, plus snowfalls to fairly low levels in NSW and Victoria. The suburbs of Hobart and Canberra may even see a few flakes Friday.

It also means your taste of spring is over. For now.

In summary, the weather has not gone mad. Cold outbreaks like this with big surges of warm air ahead of them are really common this time of year. The strong winds are common too. Be careful out there, people.

Got a wild weather pic? Tweet us at @newscomauHQ or @antsharwood and we'll upload the best ones into this story!

Gigantic waves crash into Mornington Harbour on July 31, 2014 in Melbourne, Australia. Temperatures dropped and strong winds of over 100mk/h hit Melbourne this afternoon, bringing rain and hail across the state. (Photo by Michael Dodge/Getty Images) Source: Getty Images