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10 October 2011

Tornadoes in the Western Cape?

The SAWDIS received the following two Twitter messages:

1. RT @OJTTL: @SAWDIS I wonder if worcester ever had tornados in the past. Cant find any info online.

2. RT @OJTTL: @SAWDIS I wonder if worcester ever had tornados in the past. Cant find any info online.

The SAWDIS answered: RT @OJTTL: Tornadoes in Worcester? Western Cape more known for microbursts caused by downdraught winds or air that falls out of a thunderstorm system. (Manenburg - August 1999)

Further research revealed the following map of tornado events over the eastern parts of South Africa in the period 1905 - 1997. (Goliger et al. 1997)

Image: Goliger et al. 1997

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; 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.

The prediction, detection and monitoring of severe thunderstorms and tornadoes are of the utmost importance. Throughout the world the timely issue of warnings for severe weather and tornadoes is critical to the protection of life and property. Nevertheless, timely warnings remain very difficult. Timely warnings of tornadoes can only be made if real-time observations and free radar data are available to the public of South Africa. It is therefor imperative that SAWDIS Observers and members of the public provide real time storm + weather observations to the SAWDIS. Without real time observations it is literally impossible to timely warn people of an approaching tornado or severe thunderstorm.