20 September 2023
By: Alani Janeke
As the next cold front reaches South Africa, causing rain over parts of the Western Cape, weather models indicate they may occur regularly until the third week of October.
This September has been colder than normal over southern parts of South Africa. Frequent cold fronts over the past few weeks have contributed to very low temperatures and frost damage which have particularly affected winter grains and fruits, especially in the lower Orange River region.
Johan van den Berg, an independent agricultural meteorologist, says the reason for the damage is that the cold winter has so far delayed the growth and development of winter wheat and grapes, with vineyards already starting to bud. The worst damage was in lower-lying areas.
Several districts in the Western Cape also experienced frost last week and snow fell in mountainous parts of the province.
How cold is it really?
Van den Berg compared minimum temperatures for the first 17 days of the month to average minimums for the period in several towns to determine how much colder this September has been.
For Prieska in the Northern Cape, the average daily minimum temperature for the first 17 days of this month was 0.98°C, compared to a long-term average of 4.36°C. The area’s high temperatures for this period were also slightly lower, with an average maximum of 23.28°C compared to a long-term average of 24.48°C.
In Ceres, Western Cape, the average minimum temperature for the first 17 days of this month was 1.4°C compared to an average of 4.25°C from 2018 to 2022. Maximum temperatures averaged 12.34°C compared to 16.28°C since 2018.
In Groblersdal, Limpopo, the average minimum temperature for the first 17 days of this month, 9.95°C, was higher than the four-year average of 7.74°C. The area recorded the highest average maximum temperature of 30.77°C this month, compared to an average of 29.55°C over the past four years.
So, it has been significantly colder in the south than further north so far in September.
El Niño’s impact
“These lower recorded values in September (but also in July and August) over the central to southern parts of South Africa are consistent with the trend of the past decade or longer, that especially August, September and October minimum temperatures show a declining tendency,” says Van den Berg.
“Furthermore, there are often indications that cold fronts occur more frequently, more intensely and also further north along the West Coast and adjacent inland areas during El Niño events, as is currently the case.”
Van den Berg says it is interesting that snow fell more frequently this winter over southwestern parts of Namibia. “On the other hand, the northeastern parts of South Africa were more subject to the influence of a high-pressure system, with descending air and warmer conditions. This also caused very little rain to date over the eastern parts, which traditionally receive the first rains during the spring.
“There is a very high risk of further cold conditions occurring over the southern and central parts in the coming weeks.”
Short-term forecasts indicate further cold fronts from September 19 to 23, September 25 to 26, September 28 to 29, October 4 to 5, and in the third week of October.
“While predictions of exact dates of cold front occurrences are often not accurate, it is still an indication that prediction models continue to forecast further frontal systems,” says Van den Berg.
“During the strong El Niño system of the 2015-16 and the 2018-19 seasons, Bloemhof in North West, among others, regularly recorded sharp temperature drops to below 5°C deep into November.
“Taking into account that frost damage to crops can occur when 5°C is measured at a weather station, the risk due to the occurrence of low temperatures late in the season can be seen.”
