South Africa Weather for Hang Gliding and Paragliding Pilots

by Ulf Arndt,  2008

This write-up is intended to give tips specific for South Africa to the thermal hunter.

Most  weather books available for Hang Gliding and Paragliding pilots in South Africa are written for the Northern Hemisphere.
And cover an area which is influenced by a mix of warm and cold fronts.
This type of weather we tend to get in South Africa only in the local winter mostly  in the Western Cape area.
Otherwise the flying weather is driven by the fact that the Karoo desert is the counterpart to the Sahara.
And the Gauteng area is subtropical, what corresponds to the area South of the Sahara.

The overseas books are still good to provide you with the basics. Like Dennis Pagen, Understanding the Sky. And there is one local written book, which is a bit over the top for most of us,  called  The Atmosphere and Weather of Southern Africa by Preston-Whyte and Tyson for anyone who wants to get  a good understanding on the local weather.

Summer and Winter  in South Africa

 Winter Weather

 Western Cape

----- Original Message -----

To: <>

Sent: Thursday, May 20, 2004 5:11 PM

Subject: [cahgc] Beware the FOG


> Just another winter notice.


> We had a bit of a incident the past weekend, when on saterday morning I arrived at Rondebossie it was nice and clear with fog on the coast.

> Winds where light and the paragliders where training so I sat around watching them and microlights and ultralights enjoying the morning air.


> Then suddenly the whole of the cape and the flats was covered in FOG, it happened at a astonishing rate, easily 5 minutes flat from great vis

> over the whole area to no ground in sight, this must have created havoc  for the microlight pilots as they where seen flying around circling the hill, I was already thinking of clearing the hill to make a landing spot for these guys.


> But the fog slowly started to burn of after about a hour, and these guys could land. I bet some of them where low on fuel by then!!!


> So beware, FOG can really mess up your flying...


> FOG - F**k Oll Ground.


> Have fun out there...




A high-pressure system moves northward bringing Westerly winds to the south-western and southern coasts of this region.

Cloudiness and rainfall are normally restricted to this region and south-eastern coasts, as a result of cyclonic or frontal type ,.


A separate cell of high pressure is situated over this area during winter. This result in clear skies and calm conditions. Snowfalls occur along the escarpment and more rarely, over the interior.
Interior snowfalls are usually associated with the presence of a strong high following closely behind a cold front (thus “pushing” the cold air into the interior from the east), as well as a strong upper air low which enables uplift, condensation and cloud formation to take place although orographic uplift (mountain lift) is important along the escarpment.

Summer Weather Conditions

Western Cape

The Atlantic and Indian high pressure systems have moved southwards. This causes the westerlies to blow well to the south of the continent.

The Atlantic high , which has its center near the west coast of South Africa, is a source of dry, subsiding air. Air from this high generally has a short sea track, carries little moisture and generally invades the country from the south-west. The general summer pattern consists of low rainfall and south-westerly winds.


The Indian high has its center well out to sea. The winds that originate from this high travel across the warm Indian Ocean picking up moisture as they go. This air influences the eastern parts of South Africa including the Highveld area.

Where the air from the Indian high meets the air from the Atlantic high a so-called moisture boundary (sometimes referred to a moisture front) occurs. The Atlantic air undercuts the Indian air, causing uplift, condensation and cloud formation.

The position of this boundary often effects the distribution of rainfall over the whole Highveld region. When it lies to the north, drought
conditions prevail, when to the south, widespread rains are possible. Easterly, north-easterly to northerly winds tend to prevail in this region.

Where do we find the weather we are looking for ...

The good flying in the Gauteng, Northern Cape area is determined by a mix of dry desert air from the high pressure system which causes the desert climate and the humid air that gets shuffled down from the equator.  The boundary between the humid and the dry air is called the trough.
In summertime the trough is somewhere over the South Africa. The good flying is located on the trough axis towards the humid area.
If we go too far to the humid area, then one gets too many thunderstorms.

Too far towards the dry air, and nothing works. Why ,  that air comes from the Atlantic Ocean, cooled down a bit on the bottom from the cold water current that runs up along the West coast of Africa.  Cold air at the bottom, still warm higher up, makes it a stable air mass.

One has to find the right mix between those two airmasses,  with some moisture to get the good thermals with the high cloud base.

The Netfor website indicate the trough axis on good days.
See also The Magic of the Trough Line

With the seasons the trough axis and the permanent high pressure zone fluctuates.
In the SA summer, the desert climate wanders more to Cape Town, and gives the Cape lots of sunny days, a Mediterranean climate. A the strong high pressure cell is supposed to keep away any cold fronts. While Gauteng and the Limpopo area get all the humid air shuffled down from the equator and indian ocean.
In winter the high pressure belt moves towards the equator and is located over Gauteng area.

To have all year good flying one has to follow the trough axis. In summer it can be located over the Porterville area. In Spring and autumn one can find it around Mafikeng , Gauteng area.
And in Winter someone will have to find it one day in the Limpopo Zimbabwe area. Up to now no one has been looking for there yet.

And the area which are normally too wet in summer, like the Lowfeld Ngodwana Barberton area can provide good flying in winter.

 Dusties, Whirlys and why is it so rough in spring in the Highveld ...

 June, July, August ,Winter in SA,  in the Highveld can be rather boring flying. Thermals start late, let's say 14.00 onwards and close down after 15.00
And then comes September and October and the conditions suddenly become rough, with dusties and whirlies lurking everywhere. And once the first rains set in the air becomes smooth and the thermals become softer. Why ...?
My explanation ..  Winter means that there has been no rain for a long time. The ground is dry.
The ground  still got time to cool down a lot over night with no clouds holding back any radiation over night.
In the morning we got a strong inversion, cooled down air close to the ground.
During the day the sun rays warm up the ground.
Typical whirly days have something like 6 degree Celsius in the morning and close to 30 or more degrees maximum temperature during the day.
And that warmed up air sticks to the ground for a while until it releases with a vengeance.
Once we get some rain, the ground got some humidity / water on the top. Now the sun's energy gets used up first to make vapor.
The dew droplets on the grass  in the morning "suck" up energy when they get converted to vapor.
The energy of the sun rays does not heat up the ground and the air close to the ground so much anymore. The droplets "steal" some of the energy.
Now vapor is H2O molecules which are lighter than N2 or O2 molecules.  H2O got a molecule weight of 10 ( 2x1 + 8) while N2 is 14 and O2 is 16.
The lighter H2O Vapor get pushed up by the heavier N2 and O2 mix ,  rise and start  releasing thermals easier.
as they go up they take some surrounding air with them that  got a bit warmed up.
The air does not get warmed up for so long anymore before it releases. The thermals pop more often and are less violent.
As a PG or HG pilot consider the time before the rains start in the Highveld as the most dangerous season to fly.
Or in layman terms...
If there is no dew on the grass in the morning in September or October in the Highveld, expect whirlys.

More on thermals see

Aware of 3 incidents where pilots got picked up from the ground by whirlies.

- Pilot was about to get into his harness at The Dam. When a whirly came through and lifted his canopy up. Pilot got dragged through the rocks. Hanging upside down , his feet caught in the harness, and his head ( with a helmet) bouncing through the rocks.

- Student pilot was ready to launch at Laudium when a whirly picked him up and dropped, dumped him some meters behind take off

- Pilot was ground handling his canopy on flat ground in Dunnottar. When a whirly cam through, lifted him 10m into the air. Dumped him into the parked vehicles and then dragged him through the adjacent mealie field.

Recommendation - put your helmet on before you climb into the harness.



 Use T-Phi Skew-T Diagrams

Sorry,.. what ???

 If you have no clue, what this is all about,  have a look at the    document.

Welcome to the world of internet and online information. To get good cross country flying is about being at the right spot at the right time.
Making the right decisions.
To make the best decisions you better have the right information.
And thanks to the world wide web we now got the information at hand early in the morning to see if this will be a great cross country flying day.
Only if you are lucky and live close to Irene or another weatherstation that does a sounding. Close is anything of 100 km to 300 km around that weatherstation.
Why that range? One can assume that the air does not change much over few 100 km . And if you are downwind of that weatherstation, then you get this air that they measured at night. For Irene, with a predominant NW wind, and they measure at 2.00 local time, and a windspeed of 10 km/h , then this air at 12.00 local time will be 100 km further, roughly around Dunnottar for example.

If you live in the Lowfeld, Kuruman, or PE, .. you can skip that paragraph. Or try a power pilot to do the sounding for you in the morning.
Gariep and Bitterwasser does it for example , using their own soundings with a power aircraft.

Or checkout   to analyze NOAA data.

 SA Weather on the web

Welcome back to those who worked their way through the T-Phi part.
There is another way to figure out if this will be the day of the year.
Use the   which will give you expected wind and thermal strength.
They seem to get it right for the central Karoo of the country. Like Kuruman and Prieska. And when you monitor their forecasts for a while then you will see that the good flying over summer is mainly in the Prieska to Beaufort West area.

Other links are for the SA Weatherbureau.
And for the flying forecasts. takes you to METARS which give you  regular updated  weatherstation readings from various airports.
       FARG 190600Z AUTO 05001KT //// // ////// 03/02 Q1024=
   FARG is Rustenburg ,  done on the 19th of the month,  at 06.00 Zulu time , what is 8.00 in the morning
  It was done by some automatic device,  with the wind 050 ( North East)  and 1 knot
  Temperature was 03 degree celcius, dew point was 02 ,   and the airpressure was 1024.

Very basic info from

Some crystal ball few days ahead guess from

Block format

  The Aviation website of the SA Weather bureau provides block weather forecast info.
One can use it to get an idea of the wind and lapse rate.

first of all one has to make sure it is valid for the time period that you plan to fly.
This one says Valid 20020804 12 UTC.  Means 14.00 local time.
When we plan to be up in the thermals. They get prepared in 6 hour intervals. The 6.00 UTC and the 18.00 I only use to see the trend in the wind speed and direction.
So what do these numbers mean?

First of all you have to figure out where you favorite flying site would be located on this map.
Map??? What you see there is Southern Africa.
And Gauteng, Dunottar, The Dam, Rustenburg,.. are between 25E and 30E and a bit below 25 S towards 30 S.

Let's have a look at the 25/25 intersection.

 First column is altitude in 1000's of feet.
 Next is the wind direction in degree , 0 is North, 90 would be east, 180 is south, 270 is west, and 360 is again North
 Then comes the wind strength in knots, double the value  -10 percent to get km/h
 And the last column is a guess on the temperature in degree Celsius.

  For our flying we only hover around between 7000 and 10000 feet.

So, only the 2 lowest rows are of interest.

  The lowest row means,  in 7000 feet  ( 2300m ASL) one can expect a Northerly wind , of 18 knots ( what is 33 km/h ) and 10 degree
  One higher up, at 10000 feet, ( 3300m ASL, thumbsuck normally cloudbase) , Northerly , same 18 knots , and 1 degree.

Ok, so your site is not exactly on one of those grid points. Then you have to interpolate in between. look at the grid points around your site, and average in between those values to get guesstimate of what might happen where you plan to fly.

To get an idea if it will be a good thermal day, have a look at the temperature difference between the 7000 feet and 10000 feet.
in this example it is 9, what is normal.. Dry adiabatic lapse rate is around 1  degree per 100 meters, Or 3 degree per 1000 feet. Or 9 for 3000 feet.
You can expect average, 2-3 m/s max thermals. If you get a 10 difference, then get excited, its going to be a very good day.
If you get 8,  stay at home.

Synoptic Chart

I use it to get a bit of an idea if we got any fronts approaching or what the wind will do.

Below is an example of a windy, blown out day.


You can see those curves, called isobars, are quite close together over the country. Means you are going to have lots of wind. Not a great flying day.

Here is an example of a day with not much wind  from the Aerosport website

And the same from the CSAG website

And this was a world record day in De Aar area. 400km PG flight from Vosburg. Notice the trough, the 2 low pressure systems over the area where the pilots flew.


Weather Radar

If it looks lousy where you are, does not mean it is the same some 200-300 km away.
Use the weather radar off the web to get an idea how big this cloud cover is.

Here you see a  front approaching from the south. Not a good idea to go out to fly  the south of Johannesburg.

It rains in Joburg,  but Welkom is clear

Spot Graphs 

Most popular site with the cross country pilots.
Gives you a quick overview for a certain area of what to expect during the day.
The Dam happens to be right close to one of those dots.

I tend not too rely too much on the thermal forecast. If it correlates with Soarcast and then I believe it.
But those  Spot Graphs diagrams seem to work very well for the Kuruman, Prieska , De Aar area.

The green color means wet, humid air.  Or cloud, fog, rain ....


From October until February we can expect daily thunderstorms in the Highveld Gauteng area.
See also the CAPE value in the Skew-T Diagram.
Stay clear of them, avoid them, get down when they start to develop around you.

How thunderstorms develop and what happens in there is explained at.

The local thunderstorm forecast on the web seem to get it quite right


Phoning the Met Office

So you are out in the bundu, and not telephone line or computer  to get onto the Internet?

You can phone the Met Office using 082 233 8800

State that you do Paragliding at whatever place.

 And you are interested in what the ground and and the winds up to 10 000 ft will be doing during the day at xyz.

  What is the wind doing at the moment?

  What will be the expected cloudbase and thermal activity?

   Any chance for thunderstorms?

   Any frontal systems on their way which will create gust fronts?

Weather Info via the Cell Phone

If you are a Vodacom subscriber then you send a SMS to 4000 with the following text:

weather Welkom (or)
weather JHB (or)
weather jhb tomorrow

 ICAO / WMO Cloud continuity scale

Used in the Metar code

· SKC - sky clear, no cloud.
· FEW - few clouds, one to two oktas.
· SCT - scattered, 3 - 4 oktas. Clear intervals between clouds predominate.
· BKN - broken, 5 - 7 oktas. Cloud masses predominate.
· OVC - overcast, 8 oktas. Continuous, no clear intervals.

References, URLs, Weather on the web

Remember "Weather forecasts are horoscopes with numbers."

More info at  and scroll down to the Weather section.


Some of the Pictures in this document have been copied from the following websites


Magic of the trough line

  Weather ABC in German  at


Prepared and maintained by Ulf Arndt, Copyright Ulf Arndt 2008
  For more info for Paraglider pilots in South Africa visit