THE South African Weather Service in the Free State has called on residents and farmers to be aware of the first spring thunderstorms.
Senior Weather forecaster Michael Nethavhani said residents of the Free State, Gauteng and the North West eagerly awaited the development of the first thunderstorms of the season.
Nethavhani said these storms, however, were characterised by widespread reports of strong, damaging surface winds across the three provinces and very modest amounts of rainfall.
"Radar and satellite remote sensing data provided little or no indication of possible severity of storms. However, a feature which proved to be significant was that, given the very dry conditions at the surface, the convective cloud base of the thunderstorms was at an abnormally high altitude above the ground," he said.
"While this type of storm development can occur at any time of the year, early summer season storms are notorious in terms of frequently being associated with strong, damaging winds caused by dry microbursts. Moreover, such storms are not typically associated with delivering much rainfall, which explains the popular term dry thunderstorms."
ALSO READ: Mum: My son is crying from the grave
Nethavhani further indicates that the sinking air, also known as a downdraft within a thunderstorm, is usually less than or equal to four kilometres in diameter and can cause extensive damage upon reaching the Earth's surface, and in some instances, can be life-threatening.
According to the weather service, precipitation evaporates above within the downdraft, causing the downdraft air to become colder and denser, thus accelerating the cold air towards the ground under the influence of gravity.
"This phenomenon is typically associated with high cloud base thunderstorms, as on Tuesday. This weather phenomenon has the capability of uprooting trees as well as lifting off entire building roofs, as indicated in the photos. We observed wind speed exceeded 50 knots (114 km/h) over Harrismith, which is consistent with the typical strength of a dry microburst. Significant damage was reported over the eastern and the North-Eastern parts of the Free State," said Nethavhani.
