- Friday, 04 November 2011 12:54
- Published Date
- John Olszewski
- Hits: 3653
This past week an unusual synoptic pattern has held sway across the southern hemisphere. A major anticyclone with core pressures well above 1030hPa straddled the Date Line (180o) in the south Pacific while on our side, a complex low pressure pattern covered most of southern Africa and the southern oceans.
Both high and low pressure systems have been static for this period. Static in position but active within themselves: anticyclonic strength ensured a consistent flow to maintain La Nina’s, positive oscillation, and dominance of global weather.
The complexities of the vortex areas see one core deepen, drift somewhat eastward while in the cold, unstable polar air behind it a secondary vortex quickly forms, weakening the older core, then the same cycle is repeated. The effect of this pattern maintained a zonal flow throughout the troposphere (surface to 40000 feet) above southern Africa.
The unusual feature is that these differing systems have held their geographical placing while whatever else may be on the weather map either by-passes or collapses while these two major systems remain.
The other unusual feature is the global situation on either side of globe: the high and the low. Again, the effect saw a limited, if not absent, eastern Atlantic anticyclone, and similarly an absence of the western Indian Ocean anticyclone.
This departure from the norm means there is no lower level moisture input from the Indian Ocean, so with no push from the east, the heat-low pressure belt across southern Africa remains static ensuring that over Namibia there has been an advection of bone dry southerly air. This limits daytime temperatures but with no anticyclonic thrust it cannot undercut the heat-low. Without convergence, there is no cumulus cloud and no rain!
The thin layer of cloud visible has too little moisture but its presence offers hope for improvement as November wears on.
The vortex pattern persists. The weak South Atlantic anticyclone remains limited throughout the period and because there is little ability to ridge round the continent, any development of a cell away to the east is restricted. Any prospect of late Spring showers depends on the persistent heat-low generating an upward convective extension to tap the adjacent moister air mass gathering above much of Zambia, linking with the equally adjacent Congo air mass then to advect this combination into our Kavango area or further west.
Current outlooks show a mixed set of patterns across the northern mid-subcontinent. Much of the data available is based on satellite images showing cloud coverage and direction of movement. Other observational sources in that area are, largely, non-existent. This data provides the grist from which computer models are built. Otherwise, it is up to a weather observer to assess what is seen to be present and offer an outlook regarding what the current situation will be able to evolve. The heat factor is seen to be increasing and its effects, as outlined earlier, offer a prospect of showers into the new week. n the south west, temperatures will be considerably cooler with a fresh southwesterly wind as a result of the high ridging in from the south Atlantic.
- Articles In This Category
- 30 May 2014 (897 hits)WeatherWhat Happened? Conditions across the sub-continent have been under the influence of two complex low pressure systems, the first of which announced...Season Rainfall (1068 hits)WeatherWeatherWhat happened? What has become quite a recurrent feature in active weather patterns, is the ability for vortex circulations to develop on the...WeatherWhat happened? The week’s dry outlook was fulfilled, we had only the role of spectator while much of the world, let alone our hemisphere, chalked...14 February 2014 (1309 hits)WeatherWhat Happened? The week started with another prominent weather anomaly. A cyclic low pressure cell developed early in the week over the northern half...Weekly Rainfall - 14 December 2012 (361 hits)WeatherWeatherWhat happened? What do we believe: our eyes or our charts? For long years, centuries in fact, mankind’s navigators only had eyes, then came...La Nina returns to the Pacific (1353 hits)WeatherDuring November and December, atmospheric conditions over the equatorial Pacific changed from neutral to a weak La Nina, with current forecasts...WeatherWhat happened? That the weather patterns prevail to their own set of rules is a key reason why weather observations are performed so frequently in...Understanding Weather - not predicting - (3653 hits)WeatherWhat happened? This past week an unusual synoptic pattern has held sway across the southern hemisphere. A major anticyclone with core pressures well...
- Related Articles
- WeatherWhat happened? At an unusual time of the year we have seen, one way or the other, a departure from synoptic patterns prevalent across the southern...WeatherWhat happened? That the world’s weather patterns are at odds with themselves seems to be a common consensus. Primarily the cause is to be...WeatherWhat happened? We have seen an interesting hiatus in the development of weather patterns variously around the world as year 2011 progressed. Seasons...WeatherWhat happened? Summer begins with December. From one aspect at least, a start is made to summer as pressure patterns move toward a summery stance....WeatherWhat happened? This week was marked by a cut-off low over the Orange River in the south and a broad trough of tropical moisture moving in from Angola...
- Latest Articles
- Northern farmers grow for food security (13 hits)HeadlinesThree farmers from the North excelled this week Thursday at a Horticultural Day organised by the Namibian Agronomic Board to award the best farmers...Trustco HEPS shoot up 402% (13 hits)HeadlinesAfter Trustco released its interim trading statement for the six months ended 30 September 2014 on Wednesday this week, Trustco shareholders will in...HeadlinesThe Namibia Logistics Association Secretary General, Harald Schmidt said that the country is fast approaching a point where new road surfaces will...Property is ablaze but everybody loses (16 hits)Editors DeskThe runaway cost of land and housing is defeating all the growth and progress made over the past five years. Two significant events over the past...31 Oct 2014 (11 hits)WeatherWhat Happened? Conditions this week were fairly conventional for this transitional period between the seasons. At the beginning of the week, the...