Sea fog shrouds SA on Saturday
Ben Domensino,
Monday July 30, 2018 - 12:13 AEST
Parts of South Australia were blanketed by a rare type of fog on the weekend, turning a sunny day grey in a matter of minutes.
Image: Glenelg Beach, SA by Sue Belperio
While fog is common in Australia during winter, it most commonly occurs early in the morning after the ground has cooled down during the night. This type of fog is called 'radiation fog' and it usually disappears shortly after sunrise.
However, there are a number of other types of fog that develop from time to time in Australia, including:
Advection fog, which is carried over a location by the wind
Upslope fog, which forms as moisture-laden air rises up the side of a mountain
Valley fog, which occurs when cold air pools inside a valley
Freezing fog, which develops when fog forms below zero degrees
After a sunny start to the day, some southern parts of South Australia were covered by a bank of fog on Saturday. The grey veil was a unique type of advection fog called 'sea fog'.
Image: Glenelg Beach, SA by Sue Belperio
As the name suggests, sea fog develops over water when relatively warm and moisture-laden air passes over a body of cooler water. This causes the air to cool down enough for water vapour it's carrying to condense into liquid droplets, forming fog. Sea fog sometimes remains anchored offshore, although it can also be carried over land by onshore winds.
On Saturday, the sea fog developed as warm, moist air passed over the relatively cool waters in the Spencer Gulf and Gulf St Vincent, where water temperatures are about 13-14 degrees. The fog then advected, or blew, over the beaches at Gleneg and numerous other places. Before long, the fog dissipated after it moved over warmer ground.
A similar case of sea fog also affected parts of South Australia on Wednesday morning last week.
- Weatherzone
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2018