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Tuesday, 23 August 2011

Berg Winds

Since Sunday we have experienced Berg wind conditions here in KwaZuluNatal. Berg winds are mountain winds, know as Fohn-, or Foehn winds in Europe and Chinook in North America. These winds are caused by a high pressure system lying over the interior of South Africa, this forces the air over the escarpment and down the lee of the Drakensberg.


As the air descends it heats up, so called adiabatic heating, the temperature increases one degree Centigrade for every 100 metres decent, or ten degrees for every 1000 metres. Temperatures can rise by as much as thirty degrees Centigrade in a few hours. These winds can have a velocity varying from 10km per hour to over 100km per hour and can be very destructive. Sunday the wind was very strong, but yesterday and today just a breeze, but the temperatures here in our district rose from the mid teens last week to the high twenties yesterday and today.


This time of the year is also known as the fire season in KZN, these hot, dry winds are very conducive to fires. A fire driven by a 100km an hour Berg wind is unstop able. No farmer dare leave his farm during this time, as a fire could wipe out a lifetimes work.


Berg winds eventually put every ones nerves on edge, it's a hot debilitating wind that wears you down. Research done by Universities in Germany have shown that suicide, (known as Fohnkrankheidt, Fohn disease), increases by 10% during the Fohn wind season in Europe. 


A cold front has moved in again across the country and by 6pm the weather had turned decidedly chilly. According to the weather forecasters this should last until about Saturday. Tomorrows temperature will drop to a minimum of about 4 degrees Centigrade to a high of 17.


The sunset made up for it all.




Reflected sunset.


4 comments:

Kay L. Davies said...

Wow. Very scary, Phillip.
We get Chinook winds here in southeastern Alberta, but I never knew much about them. I was just impressed with watching the outside temperature rise so quickly. That's terrible about the fires, and the suicides, etc.
Meanwhile, to change the subject completely, I'm glad you are enjoying Dad's books. Sending a gift to someone I've never met can be tricky, but I really felt you and my dad had much in common.
All the best — K

Kay, Alberta, Canada
An Unfittie's Guide to Adventurous Travel

Desiree said...

Beautiful, beautiful photograph! Not good...those fires and suicides!

Joyful said...

It is too bad about the Berg winds. I grew up in northern Canada and we welcomed Chinook winds. They always warmed things up from a very cold winter and the winds themselves were never strong, irritating or exhausting. They were like a refreshing respite from the harsh winter. During Chinook winds people would become happier. I no longer live in the north country and the winters are no longer as cold so I'm not sure about the Chinook experiences nowadays.

Pumice said...

We never stop learning. I had never heard the term "adiabatic heating" before although I have obviously been experiencing it all my life. I looked it up and read a short article. Since my mind runs to sermon illustrations I may get around to using the term.

Keep teaching.

Grace and peace.