An upper-air trough will be responsible for most of the action, and while not as intense as the system of the previous few days, it may still generate cool, cloudy periods with widespread showers or thundershowers during the long weekend across the central to eastern interior.
Yet another cold front will move over the southern parts of the country early in the period and with a fairly strong flow of colder air from the south, light frost is possible again over the southern high-lying interior and possibly in isolated pockets further north. Certain areas may receive cumulative totals in excess of 50 mm of rain during the weekend, especially over the central to eastern North West, southern Limpopo, Gauteng, southern and western Mpumalanga as well as the northern Free State. Following earlier wet weather, these may lead to water-logged conditions. Given the expected weather patterns of the next few days, there is no imminent threat of widespread significant frost according to current short to medium-term outlooks. The following is a summary of weather conditions during the next few days:
• General:
o Temperatures will on average be below normal over the central and eastern parts, but above normal in the west.
o Rainfall should be above normal for this time of the year over the central to northe astern parts and Garden Route, but below normal over the western parts of the country.
o The western to northern parts of the winter rainfall region are expected to be dry except for possible light showers initially.
o Showers are expected on several days along the Garden Route.
o A cold front will result in cooler conditions over the southern parts from Thursday to Saturday, with possible light frost over the high-lying southern interior.
o Widespread showers and thundershowers will occur over the central to eastern parts from Friday until Sunday. o The rainy conditions over the interior should clear on Monday, with drier conditions setting in from the west. o Much of the summer grain production region will be cool during the cloudy conditions from Friday afternoon to Sunday.
o Fresh to strong south easterlies are expected in the southwest most of the time.
o Temperatures over the summer-grain production area are expected to be in the below-normal category for this time of the year, associated with the increased cloud cover and rain during the weekend: ▪ Maximum temperatures over the eastern maize-production areas will be in the order of 12 – 25°C, with lowest temperatures expected during the weekend when it will be cloudy to overcast for the most part.
Minimums will be in the order of 6 – 14°C. ▪
Maximum temperatures over the western maize-production region will range between 16 and 26°C, with the higher temperatures earlier in the period and cool, cloudy conditions during the weekend.
Minimums will be in the order of 9 – 15°C.
Overview of expected conditions over the main agricultural production areas Another rain-producing system is expected to develop during the next few days, with partly cloudy to cloudy and cool conditions at times with scattered to widespread showers and thundershowers expected over the central to north eastern parts, mostly during the weekend.
The system (an upper-air trough over the western to southern parts) will be associated with a cold front in the south and a strong Atlantic Ocean High-pressure system ridging south and around the country. As the cold front moves over the southern parts, there will be another period of possible frost, mainly over the southern, high[1]lying parts of the country. The strong ridging action by the high to the south will also result in strong south-easterlies in the southwest. The high ridging around the country will feed in ample amounts of moisture from the east, supporting cloudy, cooler conditions over the central to eastern and north eastern areas with scattered to widespread showers and thundershowers. As the trough moves out east, it will clear from the west, with mostly dry conditions by late Monday and Tuesday over the interior according to current forecasts.
At this stage, there is no indication of a repeat of the intensification of the system in the east, therefore there are no indications currently of similar heavy rain along the eastern seaboard as was experienced on Monday this week. Maize production region: Following a sunnier, warmer start, thundershowers will develop by Friday initially over the western parts of this region, moving eastwards to cover also Mpumalanga by early Saturday. Thundershowers may produce hail as is typical this time of the year due to the cooler atmosphere and associated with strong upper-air instability. Widespread showers or thundershowers during the long weekend will be associated with cloudy, cooler conditions. It will clear and start warming up again from Monday onwards. Given the mixed situation going forward, the next few days are expected to see near-normal to below-normal temperatures on average for this time of the year:
• Maximum temperatures over the eastern maize-production areas will be in the order of 12 – 25°C, with lowest temperatures expected during the weekend when it will be cloudy to overcast for the most part. Minimums will be in the order of 6 – 14°C.
• Maximum temperatures over the western maize-production region will range between 16 and 26°C, with the higher temperatures earlier in the period and cool, cloudy conditions over the weekend. Minimums will be in the order of 9 – 15°C. • Wednesday and Thursday (13th, 14th): Cool in the morning and evening in the east, otherwise sunny to partly cloudy and mild to warm.
• Friday (15th): Partly cloudy and mild to warm, becoming cloudy and windy with scattered thundershowers over the western to central parts, spreading eastwards during the evening.
• Saturday to Sunday (16th to 17 th): Partly cloudy to cloudy and mild to cool with widespread showers and thundershowers, becoming less widespread on Sunday. • Monday (18th): Partly cloudy and mild with isolated thundershowers over the central to eastern parts, clearing.
• Tuesday (12th): Partly cloudy and mild. Cape Wine Lands and Ruens: A cold front will result in inclement conditions initially, mostly on Thursday until early Friday. The West Coast, Swartland and western parts of the Karoo should be sunny and warm for the entire period except for the initial windy and cooler conditions with possible light showers in places until Friday. Strong southeasterly to easterly winds will occur in the south and southwest most of the time. With the persistent southerly to easterly winds, showers are possible along the Garden Route, clearing by Saturday. The easterly flow over the interior will result in warming along the West Coast and Swartland, where it may become hot early next week. The entire region should be predominantly dry from late Saturday onwards, with mild conditions in the south and east while warming and becoming hot over the western to northwestern parts.
Possible extreme conditions - relevant to agriculture The South African Weather Service issues warnings for any severe weather that may develop, based on much more information (and in near-real time) than the output of one single weather model (GFS atmospheric model - Center for Ocean[1]Land-Atmosphere Studies (COLA) and Institute of Global Environment and Society (IGES) – http://Wxmaps.org) considered here in the beginning of a week-long (starting 13 April) period.
It is therefore advised to keep track of warnings that may be issued by the SAWS (www.weathersa.co.za) as the week progresses. According to current model projections (GFS model) of weather conditions during the coming week, the following may be deduced:
• Cool to cold, windy conditions over the high-lying southern parts on Friday and Saturday morning (15th, 16th) may adversely affect small stock.
• It will be hot: o Over the Lowveld on Wednesday and Thursday (13th , 14th). o Over the West Coast and adjacent interior and southwards into the Swartland from Monday (18th) to Tuesday (19 th).
• Significant rainfall totals may lead to waterlogged conditions and possibly flash flooding in isolated areas. Total rainfall exceeding 50 mm may occur: o Over the central to northern and eastern North West, Gauteng, southern Limpopo and southern to western Mpumalanga from Friday (15th ) to Saturday (16 th). • Some thundershowers may become severe: o North West, Gauteng and northern Free State, western Mpumalanga and southern to western Limpopo on Friday and Saturday (15th and 16th).
• Strong south-easterlies over the southwestern parts from Wednesday (13th) to Tuesday (19 th) may be conducive to the spread of wild fires where vegetation is dry.
• Cloudy to overcast, cool and possibly waterlogged conditions may adversely affect agricultural activities over the central to eastern parts from late Friday (15th) to early Monday (18 th).
