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Low cloud steals Melbourne's chill

Max Gonzalez, Thursday August 21, 2014 - 13:49 EST

Overnight all the weather parameters were primed to bring a very cold morning to Australia's unofficial cultural capital.

A high just to the east of Tasmania was extending a ridge of high pressure over the Garden State, bringing mostly clear skies and light winds. These are the two main factors that lead to cold nights.

As such, temperatures were forecast to drop to about four degrees in the city and near freezing across its suburbs. This would have certainly been a shock to residents in the city after three mornings in a row only dipping to 10 degrees overnight.

However, the weather gods had other intentions and added an extra factor: low cloud. This allowed Melburnians in the city to wake up to a relatively balmy eight degrees. Melbourne's "four seasons in one day" is known to most, with Melbourne weather as varied as its population.

Cloud overnight acts as a blanket trapping the daylight heat closer to the ground, just as our beloved doonas trap the body heat just over the mattress. Without this, heat would escape up into the upper atmosphere as cold air (which is heavier than warm air) sinks and warm air rises.

Overnight, low cloud at about 1.5km above the ground trapped this heat around Melbourne CBD and surroundings extending from about the Brisbane Ranges in the west to Yarra Valley in the east and from the Dandenongs in the South to about Seymour in the north.

Under the cloud, Melbourne CBD only dipped to 8.4 degrees with Melbourne Park dipping to 7.5 degrees and Essendon Airport to 6 degrees. To the south, clear skies allowed Avalon to drop to 2.5 degrees while Geelong Racecourse dropped to 3.7 degrees.

On the western edge of the cloud Sheoaks dropped to 0.3 degrees. Similarly, Ferny Creek on the eastern edge dropped to 4.1 degrees while Coldstream further afield dropped to 0.6 degrees.

The chaotic nature of the atmosphere makes weather prediction extremely difficult sometimes. The cloud, was not uniform in thickness and extension and some areas like Frankston which was surrounded by clear skies only dipped to 7.4 degrees overnight, while Laverton (less than 20km away from the CBD) dropped to 3.4 degrees early in the night under a thinner patch of cloud. At the end of the day, the thicker the doona the more heat you trap.

Having been spared from the morning chill, Melburnians can now look forward to a gradual warming trend in the morning temperatures, only dipping to about 10 degrees on Sunday.

- Weatherzone

© Weatherzone 2014

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