Cumulus report for March 2022
Wetter conditions are returning to the interior, while February turned out to be generally drier over many areas.
Precipitation was mainly in the form of thundershowers, sometimes severe, while the long cloudy and rainy spells of earlier this summer was largely absent during the month. While upper-air high-pressure systems dominated the circulation across the interior during most of February, a significant upperair trough is expected to develop over the western parts during the rest of the week, bringing much more favorable conditions for widespread rainfall and cloudy, cool spells over especially the central to southeastern parts.
The next few days will therefore see a return of somewhat more widespread rainfall to the interior, focusing on the central parts, with more abundant cloud cover. Scattered to widespread showers and thundershowers are expected over these parts until the weekend. Rainfall however should be largely absent over the northeastern parts, including the eastern parts of the maize production region, while the western production areas should see relatively high rainfall totals. The cloudy, cooler conditions will result in below-normal temperatures over the summer-grain production areas, but the northeastern and western parts of the country will be relatively warm. There will be some frontal activity initially over the southwestern parts, with showers especially towards the south.
Through the period, the southwestern interior should become warmer to hot, event though thundershowers may spread into the western interior during the weekend.
The following is a summary of weather conditions during the next few days:
- Temperatures will be normal to below normal over the central parts, including the western summer-grain production areas.
- Temperatures will on average be normal to above normal over the western and northeastern parts of the country, including the eastern summer-grain production areas in Mpumalanga.
- Rainfall will be above-normal over the central to southeastern and eastern parts of the country.
- Below-normal rainfall is expected over most of Limpopo and Mpumalanga.
- Below-normal rainfall is also expected over much of the western to the southwestern interior.
- Widespread showers and thundershowers are expected over the central to southeastern parts during the remainder of the current week, associated with cloudy and mild to cool spells.
- A cold front will bring some precipitation to the southern parts of the winter rainfall region initially.
- Current forecasts indicate drier conditions dominating from the west by early next week, with some thundershowers possible in the northeast.
- Strong to gale-force southeasterlies are expected in the southwest on most days from Friday (4th) onwards.
- Temperatures over the summer-grain production area will be somewhat lower than during late February, especially during day time:
Maximum temperatures over the eastern maize-production areas will be in the order of 24 – 31 °C. Minimums will be in the order of 10 – 18 °C.
Maximum temperatures over the western maize-production region will range between 20 and 32 °C, with coolest conditions during the rainy conditions on Friday and Saturday. Minimums will be in the order of 15 – 19 °C.
Overview of expected conditions over the main agricultural production areas With the upper-air trough over the western parts during the remainder of the week, a significant period will see cloudy and cooler conditions with scattered to widespread showers or thundershowers over the central to southeastern parts of the country. A frontal system, associated with the developing upper-air trough in the west, will initially make its presence felt over the winter rainfall region. It should clear from the west early next week, when anti-cyclonic circulation will once again start to dominate.
Maize production region: Cloudy spells with widespread showers and thundershowers will occur over the central to western parts until the weekend. The northeastern parts should be mild to warm with only isolated thundershowers.
It will clear from the west early next week when some thundershowers are possible in the northeast:
- Maximum temperatures over the eastern maize-production areas will be in the order of 24 – 31 °C. Minimums will be in the order of 10 – 18 °C.
- Maximum temperatures over the western maize-production region will range between 20 and 32 °C, with the coolest conditions during the rainy conditions on Friday and Saturday. Minimums will be in the order of 15 – 19 °C.
- Wednesday (3 rd): Partly cloudy and warm. Isolated thundershowers are expected over the central to eastern areas.
- Thursday – Saturday (3 rd – 5th): Partly cloudy to cloudy and mild with widespread showers and thundershowers over the central to western parts. The north-eastern parts will be partly cloudy to cloudy and mild to warm, with only isolated thundershowers expected.
- Sunday – Monday (6th – 7th): Partly cloudy with scattered thundershowers over the central to western parts. It will be sunny to partly cloudy and warm over the eastern parts with little to no rain according to current forecasts.
- Tuesday (8th): Dry in the west, but partly cloudy and warm with isolated thundershowers over the central to eastern parts.
Cape Wine Lands and Ruens
The period will start out relatively cool, with light showers on Wednesday (2nd) due to a cold front moving through.
A southerly on-shore flow will also result in light showers in the south along the Garden Route according to current forecasts by Friday (4th).
It will gradually become warmer over the region, with hot conditions dominating over most of the region from Saturday (5th) until Monday (7th) when it should become cooler in the south with light showers possible along the Garden route until Tuesday (8 th). Some thundershowers may move into the interior regions on Sunday (6th), especially the northeastern parts.
Except for westerly winds initially, strong south-easterlies are expected according to current forecasts on several days in the southwest
According to current model projections (GFS model) of weather conditions during the coming week, the following may be deduced:
It will be hot:
- Over the Lowveld most of the time. Over northeastern KZN Thursday (3rd) to Saturday (5th).
- Over the western Karoo and southwestern parts, especially the Swartland, Saturday and Sunday (5th and 6th).
- Over the southern parts, including the Karoo, Sunday (6th).
Thundershowers may become severe:
- Over the western to central parts of North West, central, southern and western Free State and northern to eastern parts of the Eastern Cape, including the southern Drakensberg, Thursday (3rd).
- Over the central to southern parts of the Northern Cape and northern parts of the Karoo on Sunday (6th).
Significant 24-hour rainfall totals are possible:
- Over the central to southern parts of North West and western to northern parts of the Free State, Friday (5th).
Dry and windy conditions over the southwestern parts on several days from Thursday (3 rd) until Tuesday (26th) may be conducive to the spread of wildfires where vegetation is dry.
Seasonal forecast
Because seasonal forecast systems consider Sea Surface Temperatures (SSTs) as a major factor to predict coming conditions, it is worthwhile to take note of current SST anomalies. In general, current patterns reflect anomalies usually associated with higher rainfall than the norm over southern Africa – and lower rainfall over Equatorial East Africa.
Most importantly, these include:
- Anomalously cool SSTs over the central to eastern equatorial parts of the Pacific Ocean. These are at La Niña thresholds and indicative of a weak La Niña in progress. Given the current SST anomaly patterns across the Globe, seasonal forecasts from most international institutions favour LaNiña-like rainfall patterns over sub-Saharan Africa. These include anomalously wet conditions expected over the summer rainfall region of South Africa for most of the summer, with the temperature outlook calling for normal to below-normal maximum temperatures, associated with the expected wetter conditions and more extensive cloud cover than normal.
More recently, seasonal forecasts for southern Africa for the remainder of summer have drifted towards a drier outlook.
The Australian Bureau of Meteorology points out that La Niña conditions are present. (Updated 1 March): The 2021-22 La Niña is past its peak, with outlooks indicating a return to neutral El Niño-Southern Oscillation (ENSO) levels – neither La Niña nor El Niño – during the southern hemisphere autumn. As La Niña weakens, it will continue to influence global weather and climate. Atmospheric and oceanic indicators over the Pacific remain at La Niña levels.
Eastern tropical Pacific sea surface temperatures remain cooler than average despite a slow warming of deeper waters. Warming below the surface of the Pacific Ocean typically foreshadows a breakdown in La Niña, and typically occurs in the southern autumn. In the atmosphere, several indicators remain at La Niña levels, including decreased cloudiness along the Date Line, strengthened trade winds in the western Pacific, and a positive Southern Oscillation Index (SOI).
CUMULUS seasonal outlook, based on decadal variability
This outlook is based on the typically observed rainfall patterns over the north-eastern half of the country (including most of the summer grain production region), as associated with the cyclic variability of the global climate system. Summers that are similar to 2021/22 more often experience a seasonal rainfall curve that compares to normal conditions as indicated in the bar graph below, with wetter conditions focussing on December and March while drier than normal conditions focus on October and February:
- Probabilistic forecast for rainfall over the summer rainfall region, based on the natural cyclic nature of the climate system as seen in decadal variability, per month for the period September 2021 – April 2022 (Forecast issued in 2021-09).
Typical patterns during similar summers, over the north-eastern half of the summer rainfall region, are:
- September – 20 October: Relatively dry conditions over the north-eastern half of the summer rainfall region
- 20 October – 20 November: Near-normal rainfall over the north-eastern half of the summer rainfall region
- 20 November – 15 January: Near-normal to above-normal rainfall over the north-eastern half of the summer rainfall region
- 15 January – late February: Below-normal rainfall over the north-eastern half of the summer rainfall region
- March – April: Above-normal rainfall over the north-eastern half of the summer rainfall region.
