White frost visible on MSG RGB composites
Two frost events were identified with Meteosat-9 imagery during 2009's austral winter.
04 May 2023
17 June 2015
By Edwin Thema (South African Weather Service)
Between 15-17 June, a relatively strong cold front, associated with a cut-off low system, brushed the southern parts of South Africa bringing wet, cold and windy conditions.
This system moved through quickly, leaving behind an advection of polar dry air as far as Angola and Zambia. Snow was observed over the southern and eastern escarpment.
The Meteosat-10 Dust RGB (Figure 1) shows a large pink area indicating dry conditions over most of Southern Africa, with the first moisture boundary forming over northern Angola.
Figure 2 (source: EUMeTrain ) shows the same RGB product two hours later, with the Total Precipitable Water (TPW) from the ECMWF model overlaid. By this time the dry air of polar origin has been pushed far to the north into Angola, Zambia and even southern parts of the Democratic Republic of the Congo (DRC).
Due to these dry conditions temperatures dropped below zero degrees into the following morning.
The cold temperatures can be clearly seen on the colour enhanced IR image (Figure 3), showing temperatures below zero stretched from eastern and central South Africa to Botswana, Namibia and some spots over southern Angola and Zambia.
It was not only a very cold morning, but there was also widespread white frost visible after sunrise over the central parts of South Africa, which appeared as cyan on the Natural Colour RGB image (Figure 4) — this shows further evidence that temperatures were below zero in that area.
Observations from airport stations on the morning of 18 June, showed the low air and dew-point temperatures.