Spring’s wild mood swings: surprising but not unusual

The extreme highs and lows of temperatures have many people wondering about the cause

We have seen in the past few decades

that these kinds of low weather systems seem like they are keeping

moisture much longer. They are stronger, they’re more slow-moving

and are producing more rain

After a week of sweltering heat, with temperatures peaking well into the upper 30s in some provinces, the South African Weather Service (SAWS) warned – correctly – on Friday, 27 October that the country was in for a spell of rain and cold temperatures, and even snow in some parts.

And so, particularly on Monday and Tuesday, the last two days of October, widespread, tropically sourced rainfall duly set in over the central and eastern half of the country, with heavy falls in places.

SAWS, the only mandated regulatory body that can issue weather warnings in South Africa, noted that this weather would be accompanied by a dramatic drop in daytime maximum temperatures over the eastern provinces, including Gauteng.

“Much of the Highveld can expect maximum temperatures in the low teens on Monday and Tuesday, with Johannesburg likely to peak at only about 11 to 12°C. Some high-lying areas may even see single-digit maximum temperatures,” forecaster Kevin Rae said in that statement on Friday.

Along with damaging winds and severe thunderstorms, Monday saw a rare October spring snowfall in small towns in the Free State such as Harrismith, and in the northern areas of Kwazulu-natal and southern Mpumalanga.

SAWS also correctly predicted scattered to widespread showers and thundershowers over the central and northeastern areas on Tuesday, with cold to cool conditions remaining over the northeastern parts.

It issued Yellow Level 2 warnings for disruptive rain in places over Mpumalanga, severe thunderstorms in parts of North West and Gauteng, and disruptive snow in parts of Kwazulu-natal and the Free State.

Then, on 1 November, showers and thundershowers were expected only over the eastern areas, with most parts of the country otherwise expecting fine conditions and temperatures gradually warming.

Is this unprecedented?

Meteorologist Annette Botha from Vox Weather told Daily Maverick that during spring – the transition season – it is usual to get this type of extreme swing of temperatures and changing weather.

“That’s why we also do get a lot of severe storms during spring, because of the changes in the atmosphere from warm to hot – that’s one of the ingredients for severe weather,” said Botha.

Botha said last weekend’s high temperatures, as opposed to the cold that was felt on 30 and 31 October, marked “an extreme, steep drop in temperature”.

She added that she wouldn’t be surprised if a few lowest maximum temperature records were broken either on Monday or Tuesday for the month of October in South Africa “because this is something that, as a meteorologist, I’ve not ever seen for this time of the year”.

And though snow is quite common for the mountainous areas of the Cape, Lesotho or the Drakensberg during spring, Botha said it is unusual and rare to get ground snow in towns, as happened on Monday.

“It is definitely a very special system and it is rare for this time of the year.”

Botha added that saying it was rare didn’t mean it hadn’t happened before. Snow at this time of year has occurred in small towns before, mainly in the Eastern Cape and Kwazulu-natal.

Why is this happening?

“It’s actually two weather systems working together that’s responsible for the extreme drop in temperature and severe weather that we’ve had since 30 October,” said Botha, explaining that a high-pressure system that’s been sitting south of the country for a few days was bringing in cold air from the Antarctic, as well as a continuous onshore flow of moist tropical air.

This high-pressure system was basically feeding the cut-off low weather system that was sitting over the southern Cape, explained Botha, and it was also responsible for the cut-off low moving extremely slowly and not being able to exit quickly.

There’s a ‘but’ in there...

Asked whether this could this be attributed to climate change, Botha said: “I’m going to give the answer that all climatologists and meteorologists give – that you can’t blame one small weather system on climate change.

“But we have seen in the past few decades that these kinds of low weather systems seem like they are keeping moisture much longer. They are stronger, they’re more slow-moving and are producing more rain. And that’s where climate change plays a role – because it definitely plays a role.”

Francois Engelbrecht, a professor of climatology at the University of the Witwatersrand, previously told Daily Maverick: “Across the world, we are seeing an increase in the number of intense storm systems. This is very well documented.”

The Intergovernmental Panel on Climate Change’s Sixth Assessment, published in August 2021, found that “human influence is making extreme climate events, including heatwaves, heavy rainfall and droughts, more frequent and severe”.

The reason is simple, said Engelbrecht. “The warmer we make the atmosphere, the more water vapour it can hold, and therefore there’s more water available for storm systems to eventually cause precipitation… a direct consequence of a warmer world.

“This is a direct finding from a statistical analysis of the data that we have from satellites and weather stations – for the last five decades in the case of the weather stations and the last four decades in the case of the satellite data.”