Why are hot berg winds followed by cold weather?

In Knysna, Helen and I say that we don’t have seasons, we just have weather.

By that we mean that it can be 29 degrees in the middle of winter and 15 degrees in the middle of summer.

The hot winter days are caused by berg winds, and then a day or two later the temperature plummets from, say 28 to 14 degrees along with rain, rain, rain.

Now what is this all about? Here’s the big picture –

Weather all over the world tends to travel from West to East (because the globe is spinning from West to East and drags the air with it).

Down here in Knysna, the same applies. Now, when an atmospheric low (anticyclone) approaches from the West, along with its clockwise blowing winds, the wind starts blowing from inland towards the sea. We just happen to have two mountain ranges inland. As the wind blows over the mountains and down to us, it gets compressed because of the higher atmospheric pressure (we all know that eggs take longer to boil in Johannesburg than at the coast because of the low atmospheric pressure).

When air is compressed, it heats up and can also hold a lot more moisture. So our temperature climbs and the clouds evaporate. A beautiful day in Knysna!

But then the anticyclone moves on towards Port Elizabeth (now called Gqeberha) and we get its back end. The wind now blows in from the Antarctic (which is a very cold place to blow from). When it starts climbing the mountains, it cools even more and the air can’t hold as much moisture. The moisture condenses into cloud and then it rains. A cold, wet day in Knysna!

Of course, we’re not the only place in the world that experiences this berg wind phenomenon. I even learned about it in Geography at school in the UK.


    1. Hi Liam,
      I guess you already knew this stuff as you live in George? However, it’s the sort of thing that interests me – I always want to know “Why?”

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