In what could end up being the coldest night in almost five years, Ballarat dropped to an icy -3.2.

But it was the 'feels like' temperature that gave an even lower reading just before sunrise.

At 6.30am, it felt like just -6.5 degrees outside, at a time when the actual temperature was sitting at -3.

Severe frosts hit the region and the black ice warning lights were flashing.

READ MORE: Ballarat's worst black ice spots, as identified by you

However, the freezing morning is expected to clear to become a pleasant winter's day.

It is forecast to be mostly sunny in Ballarat today, with a maximum temperature of 11 degrees.

And, remarkably, eight of the next nine days are expected to reach the same top temperature of 12 degrees.

What is the "feels-like" temperature and how is it calculated?

According to the Bureau of Meteorology, wind chill can make conditions feel far frostier than their instruments can read, particularly in Alpine areas.

The bureau measures temperatures across the country using thermometers sheltered from the sun and wind.

Gone are the days of the dutiful forecaster bending to check the reading at 9am and 3pm. In 2019, the bureau is fed rolling updates from 700 weather stations across Australia.

An equation then estimates what that temperature feels like relative to wind speed and humidity.

It's a mathematical model designed to measure the comfort of an "appropriately dressed" adult walking outside in the shade - based off how people gain or lose heat.

Meteorologists warn results may vary if your clothes are wet or you're in the sun but urged people to check the apparent temperature before heading outside - either to consider heat stress or how many (dozen) puffer jackets to cram on.

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