Severe storm at Klerksdorp, South Africa

By Jan H. Vermeulen, Lee-ann Clark and Karel de Waal (South African Weather Service)

On 13 November 2006 Meteosat-8 satellite images helped the detection and monitoring of severe storms over Botswana and South Africa when convection activity lasted well into the evening. The satellite images indicated severe storms with overshooting tops over South Africa (see green circle) and eastern Botswana. The bright yellow signature of the convective storms indicates very cold cloud tops with small ice particles (strong updrafts, large overshooting tops).

As regards the synoptic situation, an intense upper air trough moved eastwards from the central interior region causing southwesterly winds at 500hPa over northwest and Freestate provinces of South Africa. The northeasterly surface flow that was very moist triggered convection early in the morning along the Vaal River. The cooler upper air increased the instability and a severe storm (radar reflectivity of > 51DBZ) developed by 09:10 UTC (11:10 SAST) southwest of Klerksdorp. The storm intensified while moving northeastward and reached a maximum of 60DBZ at 09:50 UTC over Klerksdorp (see combined radar lightning image below).

Tshepang hospital in the outskirts of Klerksdorp (KDP) experienced a deluge of hail causing its roof to collapse with subsequent flooding of buildings. This necessitated the evacuation of all patients to surrounding hospitals. SAWS's Automatic Weather Station (AWS), the green circle east of town, measured 61.2mm from 09:40 to 10:40 UTC with 15.2mm the highest 10-minute value at 10:10 UTC. Weather radar estimates reached values as high as 19.0mm in 10 minutes for an area of maximum reflectivity that passed west of AWS. The highest wind gust at the start of the storm was 19.1m/s with a direction of 188 degrees. The severe storm continued until 11:10 UTC when it was NNE of Klerksdorp and, thereafter, it weakened and headed for Ventersdorp. Daily rainfall at Klerksdorp was 98.4mm.

See an IR video clip of the severe storms from 05:00 to 12:00 UTC under additional content

Additional content

Animation IR10.8 (05:00–12:00 UTC)