Image: Reitz Tornado - Hettie Steyn via Volksblad (Click on image for larger view.)
The SAWDOS received the following questions from our readers in view of this weekend's tornadoes. I would like to share my answers to these questions which might be of educational value to others.
1. Should South Africa be expecting any more tornadoes or any other disasters weather threats?
I am hesitant about making predictions about tornadoes, because — bar none — they are nature’s hardest weather event to predict.
That’s especially true of the most dangerous and destructive types of twisters, those classified as EF-5 and EF-4 on what meteorologists refer to as the five-point Enhanced Fujita Scale.
Tornadoes are essentially flukes of nature. Unlike other weather phenomena, they form spontaneously, are short-lived, and traverse a much smaller land mass by comparison.
Many atmospheric conditions need to converge at the right time for tornadoes to form. They need hot, humid air near the ground with a cool air mass above them. They also need strong wind velocity at higher altitudes, known as wind shear, to get them spinning
So I don't think every year is going to be as extreme and wild as this one. But I think the odds of those kind of years happening in the future will be steadily increasing.
Personally I am of the opinion that we can and will see some more tornadoes this coming storm season.
2. Why is it that people were not alerted of the tornadoes?
Throughout the world the timely issue of warnings for severe weather is critical to the protection of life and property, even more so for tornadoes. Nevertheless timely warnings remains very difficult. Severe weather events such as tornadoes can only be accurately predicted in situations where a storm or tornado already exists. Real time data such as radar, satellite, upper-air soundings and visual observations are of utmost importance once thunderstorm development has started.
Radar reflectivity values and the shape of the more intense cells can say much about the possibility for tornadoes to develop. Improved and timeous warnings of tornadoes can only be made if real-time observations and quality of radar data are available. This is where the SA Weather and Disaster Observation Service (SAWDOS) can play a very important roll in providing real-time observations to the general public. With an observer in the area of the storm valuable information can be gathered from real time observations to analyze the intensity and damage the storm caused.
The science of storm and tornado assessment relies on complex radar information and computer modeling, but witness accounts and painstaking inspections are equally important to create detailed maps of the path and extent of storms.
Tornadoes teach us humility. For all of the SA Weather Service scientific technology, they cannot issue tornado warnings. Without the help of the general public as severe weather observers there really isn't a thing they can do to warn those who are caught in a tornadoes path. The SAWDOS has nearly 300 real time observers out in the field that can send their observations to the SA Weather and Disaster Observation Service when severe weather or tornadoes occur providing that there is a weather observer in the area where the event occur. Tornadoes are conscienceless killers, coldly democratic in where and how they strike. The age of real time media has added a new and even more terrifying aspect: You can see the disaster forming then watch as it destroys.
3. Is climate change the reason behind the weather threats?
This is less clear: On the one hand, we would expect that a warmer climate would bring warmer temperatures and potentially warm moisture in the atmosphere, enhancing instability.
Instability is what happens when large masses of cold air in the atmosphere create updrafts, which can be up to 10 - 15 km high. These unstable conditions can lead to deadlier tornadoes. The jet stream plays a vital role. Climate change is expected to weaken the jet stream. And that's a key ingredient for making tornadoes. You need to have a really strong jet stream that changes velocity and speed with altitude in order to put a shearing force on those updrafts, to get them spinning, so that they become tornadoes. So it's unclear what's going to happen in the end.
In other words, the verdict is still not out on whether climate change will create more deadly tornadoes, and, at this time, there is no evidence that it will.
4. Are there any further weather threats that may effect further tornadoes in the Free State, Gauteng, Eastern Cape and Kwazulu Natal?
Severe weather and Tornadoes in South Africa can occur basically anywhere where a thunderstorm is possible. Tornadoes hit South Africa more than people would like to believe!! Analysis of tornadoes in South Africa reveal that the occurrence of tornadoes have been observed in Gauteng, Free State, Kwazulu Natal and parts of the Eastern Cape.
Most tornadoes events occur in mid-summer from November to January, although a large number of tornadoes have occurred in spring and early summer and in the late summer and autumn. Most tornado events occur in the late afternoon (16h00) or early evening.(19h00)
65% of South African tornadoes are classified as EF0 to EF1 (light damage) while more than 90% are classified as EF0, EF1 or EF2 (considerable damage) or less. A classified F4 tornado occurred near Mount Ayliff in the Eastern Cape on 18 January 1999. The tornado killed 21 people and injured 500 leaving hundreds homeless. The tornado had a track of 120 km long. The estimated wind speed of an EF4 tornado is between 350 - 400 km/h.
5. Natural disasters such as Tornadoes are not prone to South Africa, why is it that this occurred?
Tornadoes are small scale by-products of thunderstorms, with less then 1% of thunderstorms producing tornadoes. Until the middle of 1998 a general public perception prevailed that tornadoes do not occur in South Africa, but occur mostly in the USA. This perception seems to have changed during the 1998 - 1999 summer season when three damaging tornadoes occurred. These were named the Harrismith tornado (15/11/1998; F2 - F3), Mount Ayliff tornado (18/1/1999; F4) and the Umtata tornado. ( 15/12/1998; F2) Severe storms associated with extensive wind damage can, however, be erroneously reported as tornadic storms. An important point to remember is that a tornado's size is not necessarily an indication of its intensity. Large tornadoes can be weak and small tornadoes can be violent and vice versa. The life cycle of the tornado should also be taken into consideration. Damage varies from F0 to F5 with increasing numbers indicating increasing damage and therefor increasing intensity. The official estimate scale of a tornado is only made after the tornado has passed. The FP scale is, however, subjective and varies according to the degree of experience of the surveyor.
Tornadoes normally spawn from severe thunderstorms. Goliger et al. (1997) list the meteorological features necessary for tornado formation as, firstly, a deep layer of mid-atmospheric dry air above a moist surface; secondly, steep moisture and temperature gradients; thirdly, high surface temperature (not always a prerequisite as illustrated this weekend); fourthly, low-level convergence and upper-air divergence; fifthly, vertical wind shear; and lastly, atmospheric instability. Once you have the above conditions tornadoes can occur.
6. How many tornadoes formed this weekend in the Free State and what was the strength of the tornadoes that did touch down?
This is a million dollar question. I do not like to speculate, nor to make false statements. I will therefor just give my personal opinion after viewing nearly 100 photos and reading eye witness and media reports.
I would really be surprised if storms in the Reitz, Kestell, Bethlehem and Deneysville areas did not spawn tornadoes. I am of the opinion that there is enough "evidence" of a tornado in the Reitz area and I would allocate an EF2 strength to this specific tornado.
Unfortunately I do not have sufficient meteorological and other information at the time the severe weather developed and dissipated in the Kestell, Bethlehem and Deneysville areas. I cannot rule out the possibility that tornadoes moved through the Kestell and Deneysville areas. However the fact remain that severe thunderstorms (super-cells) did occur in these areas.
I trust that the above explain a bit more about tornadoes and that it might be of some educational value to our readers.
Regards
Johan Terblanche
Founder of the SA Weather and Disaster Observation Service (SAWDOS)
Mossel Bay
25 June 2012
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