Severe storm at Klerksdorp, South Africa.
21 October 2020
12 November 2006
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 Afica 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 500 hPa 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 > 51 DBZ) developed by 09:10 UTC (11:10 SAST) southwest of Klerksdorp. The storm intensified while moving northeastward and reached a maximum of 60 DBZ 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 61.2 mm from 09:40 to 10:40 UTC with 15.2 mm the highest 10-minute value at 10:10 UTC. Weather radar estimates reached values as high as 19.0 mm 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 19.1 m/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 98.4 mm.
See an IR video clip of the severe storms from 05:00 to 12:00 UTC under 'See also'.
Met-8 RGB Composite Images
Animation IR10.8 (05:00–12:00 UTC)
Severe weather over South Africa and Botswana (6 November 2005)
Severe thunderstorm development over KwaZulu-Natal (3 January 2005)
Hailstorm in Potchefstroom area (27 October 2004)
Combined Radar and Lightning Image
13 November 2006, 09:50 UTC
Radar and lightning composite image
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