‘Unmelted’ hail in Dinokeng game reserve explained

Hail still frozen in the north of Pretoria two weeks later has residents puzzled by how this could be in the heat of summer, Rekord North reports.

On Thursday, pictures of the hail at Dinokeng game reserve were shared with media.

Dawid Boshoff, manager at the reserve, said the thick layer of ice could be seen for 30 metres along a river bank.

“The ice was still solidly frozen and laid at least a metre thick on the ground,” Boshoff said.

“It hailed on 13 October and since then the ice had not melted on this relatively large area near the river.”

He said what was even stranger about the unmelted ice was that it lay covered in ash and soot from recent fires that had ravished the area.

Seeking a possible explanation for this occurrence, the meia, made an enquiry at SA weather service.

Elsa de Jager, manager of the national climate centre, said there could be several factors and possible explanations for this phenomenon.

“In general ice melts at different speeds based on a number of factors, including amongst others the size of the ice, the ambient temperature, and if the ice is exposed to direct sunlight,” she said.

De Jager explained that pellets of hail that accumulated at least one-metre deep could have the ability to protect the hail in the bottom of the heap – and it could, therefore, take much longer to melt.

“Furthermore, the fact that the hail at the bottom was not exposed to direct sunlight, would have been a contributing factor why it did not melt over a relatively long time.”

She said with the severe thunderstorms that occurred on 13 October, a substantial drop in temperature took place.

“As an example, the maximum temperature measured at the Pretoria University Proefplaas dropped from 33,8 °C on Friday, 12 October to 20,7 °C on Saturday – a drop of just more than 13 degrees.

“Temperatures dropped further on Sunday, 14 October, with the maximum temperature only reaching 18,3 °C at Proefplaas. Maximum temperatures recovered over the following days reaching the high twenties; however, it dropped again on Sunday, 21 October reaching 24,8 °C, while on Monday, 22 October the maximum temperature only reached 23,2 °C.”

De Jager said in order for ice to melt, it would need to absorb enough heat to raise its temperature above the level of 0 °C.

“Another factor that could have contributed in this case, was that the ground surface on which the hail was laying was also cold and wet after the severe thunderstorm, resulting in not enough heat available for the hail to absorb and reach melting point.”