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Understanding Weather..Not predicting |
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Written by John Olszewski
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Page 1 of 2
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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