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Author: Weatherman

Overview for the week and 5-day outlook to Wednesday 21 February 2018

Visual: Synoptic map of southern Africa on Friday 16 February 2018 at midday. Source: South African Weather Service http://www.weathersa.co.za/observations/synoptic-charts What Happened The mid-level trough of last week lingered over Namibia for the first part of this week. It also formed the tail-end of a rainbearing system that develop far to the west and well below the escarpment. The result was widespread rain over the northern half of the country, and scattered rainfall over the southern half with the exception of the southern Namib. By Wednesday evening this system has departed to the east with the only substantial rain for...

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Overview for the week and 5-day outlook to Wednesday 14 February 2018

Visual: Satellite image of southern Africa at 06:00 on Wednesday 07 February and synoptic map of southern Africa on Thursday 08 February 2018. Source: First image: Space Science & Engineering Center, RealEarth Imagery, University of Wisconsin – Madison http://realearth.ssec.wisc.edu/ Second image: South African Weather Service What Happened Two major shifts have occurred in the local weather scene, both present and visible for the duration of the week. With a very active Inter-Tropical Convergence Zone situated almost on Namibia’s northern borders, conditions were just right for a tropical low pressure system to develop somewhere in the southern extremity of the...

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Overview for the week and 5-day outlook to Wednesday 07 February 2018

Visuals: Satellite image of southern Africa at 11:00 on Friday 02 February 2018 Source: Space Science & Engineering Center, RealEarth Imagery, University of Wisconsin – Madison http://realearth.ssec.wisc.edu/ What Happened This week’s progressive weather development offered a treat for physics geeks as it demonstrated in very practical terms the so-called Coriolis Effect. Amplified by the inputs from both high pressure cells that normally lie east and west of southern Africa, it is this phenomenon that causes the general air circulation over the mainland to be anti-cyclonic. Southern Africa’s anti-cyclonic circulation can vary quite a lot in intensity, but it is...

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Overview for the week and 5-day outlook to Wednesday 31 January 2018

Visual: Synoptic Map of southern Africa at 06:00 on Friday 26 January 2018 Source: http://www.weathersa.co.za/observations/synoptic-charts What Happened Extensive cloud cover over large swathes of southern Africa was the most visible weather feature of the week. However, the cloud layers, although complex in a few local spots, suffered from one universal drawback – a lack of height. The local scene was dominated by a fairly high cloud base between 12,000 and 16,000 feet depending on the strength of the South Atlantic high pressure cell. As can be seen on the synoptic may above, the high’s core has shifted south by...

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Overview for the week and 5-day outlook to Wednesday 24 January 2018

Visual: Forecast map of the 500 mB surface on Sunday 21 January Source: GrADS/Cola – George Mason University http://www.wxmaps.org/fcst.php What Happened The most notable and obvious local feature of this week was the persistent mid-level trough from the Kunene through Namibia, into southern Botswana and further into the South African interior. The rainfall results were however very poor with only unconfirmed records of substantial falls in the Bushmanland area. Over the interior there were several reports of very light rain from Tsumeb further south over large areas of the interior above the escarpment but these all failed to produce...

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Overview for the week and 5-day outlook to Wednesday 17 January 2018

Visual: Synoptic Map as at Friday 12 January 2018 Source: South African Weather Service http://www.1stweather.com/maps_fx.php What Happened The El Nino Southern Oscillation index of the Australian Bureau of Meteorology has turned starkly negative over the first two weeks of 2018. This is not a good sign unless it bounces back within the next two weeks. At the middle of December it was still a healthy 12.5 index points but it started plummeting shortly thereafter reaching zero between Christmas and New Year, and it has kept going down since. By the end of this week, it read -4.5 . The...

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The Week’s Weather up to Friday 22 December. Seasonal outlook for January 2018

Graph: 30-day Southern Oscillation Index maintained by the Australian Bureau of Meteorology. Source: http://poama.bom.gov.au/climate/enso/#tabs=SOI   This week saw a local weather pattern very similar to the previous week with the big exception that the active system in the convergence zone developed considerably further west than expected a week ago. Although widespread showers occurred from Omusati in the north-west across the interior and deep into the south-east, the downpours were still more isolated than widespread. Heavy falls were reported from farms north of Okahandja, from Tsumeb, from Windhoek, from a farm near Witvlei, and further south along the Botswana border....

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The Week’s Weather up to Friday 15 December. Five-day outlook to Wednesday 20 December 2017

Map: Expected accumulated rainfall for southern Africa from 15 to 22 December. Source: COLA/George Mason University, http://www.wxmaps.org/fcst.php The forecast rainfall map for the next week shows a close correlation to the updated seasonal rainfall expectations prepared by the SADC Climate Services Centre for the three-month season from January to end of March 2018. Although the featured map is for one week only, it shows a remarkably similar distribution to the three-month forecast maps. The reason is the current strength and locality of the South Atlantic High pressure cell indicating that the seasonal outlook bargains on the fact that the...

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