The apparent temperatures this morning were, mostly, far cooler that the ambient temperatures.

ON TUESDAY morning, many Sydneysiders could be forgiven for thinking their commute to work was freezing. Well, if not freezing, pretty chilly.

Yet, at 7am it was a fairly average 9.5C in Sydney’s CBD, not really that cold at all for winter. So why did it feel so brisk?

The answer is the apparent or ‘feels like’ temperature. In Sydney this morning it actually felt like a far more icy 3.6C.

It wasn’t just Sydney either; at 9am in Orange it was 5.6C but felt just 0.6C. At the same time, Melbourne’s Tullamarine Airport went from 8.1C to an apparent 3.5C, while up in the slopes of Thredbo an already freezing -4C plunged to a positively Siberian -14C.

Inner city Sydney felt a lot colder this morning than it actually was. Picture: Bureau of Meteorology appSource:Supplied

In Canberra it felt like it was below freezing when it was a couple degrees above. Picture: Bureau of Meteorology appSource:Supplied

Spare a thought for Canberrans, shivering through their coldest ever start to winter; they had to contend with temperatures that felt like they were way below freezing when they were actually a couple degrees above the zero mark.

How is it even possible to have an actual temperature and then an entirely different ‘feels like’ temperature?

Luckily the weather boffins at Sky News Weather are on the case. Tom Saunders, a meteorologist at the station explains the difference.

“The actual temperature is just the ambient temperature, or how much energy is in the air; the apparent temperature is how if feels like when you factor in humidity and wind.”

The actual temperature is recorded in something call a Stevenson screen, basically a box that protects a collection of meteorological instruments while allowing air to flow through.

A typical Stevenson screen, which is used to measure ambient — or actual — temperature. Picture: Kimberley Vlasic.Source:Supplied

Measurements are always taken in the box, which is in the shade, because otherwise the sun would heat up the outside of the thermometer providing a false reading.

To get the apparent temperature, the Bureau of Meteorology has a handy equation, and you can use it to. Here it is:

AT = Ta + 0.33×e − 0.70×ws − 4.00

The apparent temperature (AT) equals the actual temperature (Ta) with the humidity (e) and wind speed (ws) taken into account.

But, you’re right, it’s all a bit too scary to work out, so here is the theory explained in layman’s terms.

WHY IT FEELS WARMER THEN IT ACTUALLY IS

“The body cools by sweating but you only actually cool down when evaporation takes the heat away from your body,” said Mr Saunders.

“If it’s very humid, the air already has moisture in it so it won’t be able to absorb that evaporation as efficiently.”

This means the hot sweat sticks around on your skin for longer making everything feel warmer.

In contrast, on hot but dry days the sweat wicks away more efficiently cooling you down quicker.

These were the actual temperatures on Tuesday morning in NSW, the ACT and parts of Queensland and South Australia. Picture: Sky News Weather.Source:Supplied

The apparent temperatures this morning were, mostly, far cooler. Cooper Pedy went from 5.5C to -0.7C. Picture: Sky News Weather.Source:Supplied

WHY IT FEELS COLDER THAN IT ACTUALLY IS

This is down to wind and its interaction with a layer of warm air that emanates from and surrounds the body — a kind of toasty force field

“When it’s windy that layer of warm air gets blown away which means it feels colder,” said Mr Saunders.

“At hot temperatures that process doesn’t work. So if the body is 38C and the wind is also 38C, it’s not going to have an effect.”

On Tuesday morning in Sydney, a combination of winds and low humidity led to the apparent temperature to seem substantially cooler than the ambient temperature.

“In general, the windier it is and the lower the humidity the colder it feels; the lighter the winds and the higher the humidity the warmer it feels,” said Mr Saunders.

Although the actual temperature is the one often on the bulletins, he said it’s a good idea to seek out the ‘feels like’ temperature if you’re doing outdoor activities.

“If you’re going skiing and it’s 0C but it’s gale force winds, the apparent temperature could easily be 10C to 20C below.”

The Bureau of Meteorology include both the ambient and apparent temperatures on their app.

But if you’re going off just the actual temperature, it’s safe to assume that on chilly winter mornings, particularly when the wind is up, you should dress prepared for it to be a lot colder than it seems.