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Weekend weather forecast: Cold conditions over Eastern Cape, snow over Drakensberg

JULY 22, 2016
Weekend weather forecast: Cold conditions over Eastern Cape, snow over Drakensberg

During the next few days, the South African Weather Service confidently expects an extreme, late winter weather system to develop, affecting mostly the southern and eastern parts of the country.

Areas likely to be particularly affected include the higher elevation and mountainous regions of the Eastern Cape, KwaZulu-Natal as well as eastern and north-eastern Lesotho. Significant, deep accumulation of snow can be expected between Sunday the 24th and Tuesday the 26th July 2016.

In southern Africa, the late winter season is well-known for delivering winter weather systems, often of an extreme nature. Such winter weather systems, often characterised by snow, bitter cold and strong winds, have the distinct potential to be hazardous to the public, with possibly fatal consequences for human life as well as livestock, when facing the elements for extended periods without adequate shelter. The winter weather developing over the next few days is likely to be no exception. 

What are the main weather systems involved? 

A well-defined, upper-air trough approaches the country from the ocean region south-west of the country on Saturday (23 July) and develops into a cut-off low pressure system, situated over the south-western interior of the country on Sunday the 24th.  A surface high pressure system ridges over the eastern parts of the country on Saturday and Sunday, introducing cold, moist conditions to these regions, as the cut-off low pressure system develops further. The surface ridging high allows cold, moist air to flow against the Drakensberg.

mountains, providing a mechanism for large-scale uplift and destabilisation of the air. The upper-air cut-off low additionally enhances vertical motion, whilst the markedly colder upper-air conditions promote further instability as well as favouring snowfall due (in part) to the low freezing level. It is, therefore, primarily the interaction of two weather systems, notably the surface high and the upper-air cut-off low, which are the major role players expected to contribute to the expected extreme weather. 

Figure 1. Daily diagrams indicating a 30% (yellow), 60% (green) and 80% (purple) likelihood of rain for the period Saturday, 23 July to Tuesday, 26 July 2016. Regions favoured for snowfall are indicated by small blue asterisks. By Wednesday, 27 July 2016, the system is expected to have weakened significantly, with only light showers in the south and east of the country. Showers and thundershowers can be expected over the northern provinces, especially on Monday, 25 July.

What weather phenomena can be expected? (and when?)

With reference to Figure 1, it will be noted that the cold front will most likely be positioned over the Highveld and northern KwaZulu-Natal by Saturday (23 July), with daytime temperatures likely to have fallen significantly over the bulk of the interior. The southern parts of the Cape provinces are likely to be bitterly cold on Saturday, together with showers and a light dusting of snowfalls over the mountainous regions in the south. Very cold conditions will spread to the Karoo and interior of the Eastern Cape on Sunday (24 July), while more widespread, persistent snowfalls can be anticipated for the mountains of the Eastern Cape, Lesotho and KwaZulu-Natal, with snowdrifts expected to become progressively deeper and more disruptive as the day progresses into the evening hours. Isolated to scattered showers can be expected over the eastern third of the country on Sunday.

The upper trough continues to deform over the western interior on Monday (25 July), situated over the Northern Cape, with the upper-air cold pool eventually cutting off from the parent trough. Scattered showers and even thundershowers can be expected over the eastern half of the country, becoming more widespread over north-east Free State, KwaZulu-Natal, Lesotho and the Transkei region of Eastern Cape, accompanied by bitterly cold conditions. Strong onshore flow along the KwaZulu-Natal coast and adjacent interior is likely to support heavier falls, with occurrences of localised flooding possible, especially over the southern and central parts. Heavy snowfalls are likely to result in significant disruption to infrastructure and transport over the mountains and high-lying terrain of Eastern Cape, Lesotho, north-east Free State and KwaZulu-Natal on this day.

The cold core of the cut-off low system is expected to begin migrating south-eastwards over the south-eastern part of the country on Tuesday (26 July), as a prelude to sliding away into the southern Indian Ocean region. Showers can still be expected over most provinces, with the possible exception of Northern Cape. Further snowfalls are indicated over the mountains of KwaZulu-Natal, although not likely to be as extreme as the previous day. Significant rainfall can still be expected over the south-eastern coast and adjacent interior of the country with indications of heavy rainfall here and there.  Very cold temperatures are expected to continue to affect the southern interior while the rest of the country is likely to remain cold to cool. Strong to gale force winds are a distinct possibility for the southern and south-eastern coastlines of the country.

By Wednesday (27 July)SAWS’ numerical weather prediction model suggests that the upper-air cut-off low should have moved off the country completely. A surface low, collocated with the upper-air system, is likely to drive strong coastal and marine winds at places along the south-eastern coast. Sea conditions may well deteriorate, in association with the strong winds. Whilst some residual showers may occur over the Eastern Cape and KwaZulu-Natal on this day, they are, however, expected to be of a light and isolated nature.

What can a responsible person do in order to remain safe during this event?  

Farmersin the Eastern Cape, Eastern Free State, KwaZulu-Natal and Lesotho are strongly urged to lead their animals down from the hills and mountains as early as possible, preferably well before the weekend and to shelter them at lower altitude. Small stock, such as sheep and goats are particularly susceptible to hypothermia, especially when conditions are cold, wet and windy.

Owners and guests at high-altitude hotels and ski lodges at localities such as (but not limited to) Barkly East, Rhodes, Tiffindell, Sani Pass, Giant’s Castle, Champagne Castle, Royal Natal National Park and the Phuthaditjaba area should take note that onset of snowfall is expected from Saturday night onwards, peaking Sunday night and into Monday and persisting on Tuesday. Snowfall is expected to be particularly heavy and disruptive along the border region of KwaZulu-Natal and Lesotho as well as over the Van Reenen’s Pass region on the N3 highway. The public is therefore urged not to venture into such regions unless absolutely necessary. It is recommended to seek shelter at lower altitude as early as possible, before Sunday afternoon. Alternatively, remain in the relative safety of an established lodge or hotel. However, in the latter case, please be mindful that, given deep snowdrifts, guests and lodge personnel may well need to plan for an extended stay of a few days (often with limited food and water supplies) until mountain passes are sufficiently snow-free.  

Due to the extreme and persistent nature of this event, the general public is strongly urged not to venture into snowy areas on sightseeing, leisure trips. There is a distinct risk of becoming trapped in one’s vehicle and facing the danger of hypothermia. At the very least, snowy, icy conditions dramatically raise the risk of serious vehicle accidents. It is quite likely that Van Reenen’s Pass (on the N3) may be closed for at least a day, in the period between Monday and Tuesday. Furthermore, the Mooi River area on the N3 is also likely to be affected to some degree by snow, icy roads, or both. Outdoor hiking or climbing in the above-mentioned snow-affected regions should not be undertaken under any circumstances, even if one is experienced.

The South African Weather Service will continue to monitor further developments during this period and will issue subsequent updates as required. Furthermore, the public is urged to regularly follow weather forecasts on television and radio. Updated information may also be accessed on www.weathersa.co.za as well as via the SA Weather Service twitter account @SAWeatherServic

 Report compiled by: Victoria Nurse and Kevin Rae at the SA Weather Services