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Understanding Weather..Not predicting PDF Print
Written by John Olszewski   
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Understanding Weather..Not predicting
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What happened
Generally the dry, now drought-ridden conditions persisted across much of the country. Although favourable cloud patterns could develop on just about a daily basis, the ability to fulfill their individual early promise rarely occurred.

The main feature restricting this ability seems to focus on the broad zone of anticyclonic flow dominating the 500millibar (Pascale's level) across the western subcontinent, at least.
There has been some weakening of this dry air control as cloud movement which was slow but from a southerly direction has shown signs of movement from a westerly to northwesterly direction.
During the Easter weekend, clouds penetrated the south as far as the Keetmans Aus road. This development, accompanied with high temperatures, improved on Saturday eventually leading to widespread but brief showers over most of the south beyond Maltahoehe. On Easter Monday, similarly, cloud cover extended almost to the Orange River but the Namib remained hot and clear. There were some fantastic systems present over a 400km front in a line from Bullsport to Schlip to Duineveld and into the Kalahari.
Some good falls were registered. In the Karibib district a 30mm fall was measured, while Erundu   had a fall of 28.5mm. Other reported falls were in the 10 to 15mm range but far too many ranged from just 0.0 (drops) to a couple of millimetres or so.
It is in times like this past week that the value of the radiosonde ascent is emphasised. Radiosonde readings provide profiles of temperature, humidity, pressure levels, wind speed and direction throughout the air column from surface into the adjacent stratosphere. Placing the Windhoek ascent alongside the ascents from the South African stations, some 6 of them, gives a sound set of detail across the subcontinent. From the South African viewpoint, the Windhoek ascent provides the key to much of the subcontinent's weather. Since we no longer do radiosonde, unravelling weather patterns places an impossible burden on the forecasters at both national and international level. The quality of aviation forecasts is similarly degraded, hence aviation safety is at risk.


 
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DATE

Fri 28 Nov - Thu 04 Dec 2008
Volume 22 No.47