- Published Date
- John Olszewski
- Hits: 539
The progression of winter was delayed yet again by another secondary vortex development. Behind the well-marked Atlantic trough, the system weakened, splitting the cold front into two sections by Wednesday. The active sector, closest to the vortex moving well south of the Cape, held track with its cloud band moving at some speed and keeping south of the sub-continent. This is by no means unusual. This season it has happened more than once in the past few weeks. The northern sector of the cold front’s upper trough faded. The remains separated from the vortex circulation pattern and within less than a day became a thing of the past. The result was pleasant days for almost the entire week.
There were two dynamics at work. The first is geographic indicating the role of the landmass in collapsing the frontal system while the second pertains to the turbulent air behind the cold front which tend to create secondary vortices. Both aspects contribute to neutralise the winter effect of the cold front.
As weather events unfolded, it only demonstrated the inability of forecasts to anticipate local conditions. With such rapid arrival and departure of entire systems, a dependable view covers at most six hours. Weather patterns are known but their capabilities and their ability to change their predicted paths is a consistent aspect.
The most dominant feature of southern African climate is the shift in the latitude of the sub-tropical high pressure belt. High pressure cores follow each other with regular monotony as they circle the southern hemisphere. They are the driving engines transporting cold air from the south pole northwards, and reversing this flow once they have past, bringing warm tropical air southward. This is the source of the so-called trade winds.
But over the last decade, the track of the high pressure belt has shifted about 15 degrees further south. And this shift seems to have become permanent. What happens now is that much colder air is conveyed to the north resulting in short but intensely cold spells which we often experience in winter.
While their surface tracks keep to the 40oS line, their upper-air cones, the core of the sub-tropical high pressure belt, persist with their expected 25oS track or so. This pattern is interpreted as the evidence of effects induced by the change of climate.
Across these past few years, ranging to and fro from El Nino to La Nina as recorded in the equatorial Pacific, this pattern is taken as proof of the resultant departure from the accustomed normal range.
Friday sees the arrival of a steep trough, its precursor cloud band building from Wednesday; it develops further and rainy conditions develop in the south. The whole pattern moves quite quickly and is driven well inland so that by Monday warmer temperatures return. There are 3 cold mornings ahead - Saturday, Sunday and Monday. The arrival of the cold air in the northern half of the country is delayed by a day (Sunday). Widespread frost should be expected. By Tuesday, warmer daytimes return, but this is winter come to call: cold nights persist for the week.
As the cold front passes the Cape, it swing up the east coast, curls back overland and the signature early morning cold wind from the east returns. This happens by Tuesday morning. This easterly airflow naturally leads to “Oosweer” at the coast. Coastal conditions from Tuesday through Friday are expected to be warm.
- Articles In This Category
- Weekly Rainfall - 07 December 2012 (210 hits)WeatherWeatherWhat happened? While the southern hemisphere has experienced astonishing downpours, in Namibia we had good reason to query our prospects. The...WeatherWhat happened? The gradual approach of the fringes of the tropical airmass has proceeded despite an unfavourable upper air pattern dominating the...WeatherWhat happened? Following the off-on-off rainfall pattern of the past few weeks, this week saw a triple-barrelled pattern take position in our skies....WeatherWhat happened? Consistent daytime heat is an expected feature at this time of year, providing for daily development of a broad heat-inspired low...WeatherEl Nino and its driving force, the Southern Oscillation, are back in the news. Not because of their presence, but because of a possible resurgence....WeatherWhat happened? Yet again the previous weekend brought an active vortex pattern with a marked northerly extension. A low pressure trough with a cold...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? The disparate scene which has been hovering for some while is back in the weather saddle. While winter reigns across the Southern...WeatherWhat happened? Weather headlines feature the northern hemisphere’s abnormal events while our southern world escapes such headlines and their...
- Related Articles
- Understanding Weather - not predicting - (2317 hits)WeatherWhat happened? This past week an unusual synoptic pattern has held sway across the southern hemisphere. A major anticyclone with core pressures well...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....
- Latest Articles
- Spanish navy ship “Rayo” visits Lüderitz (187 hits)General NewsThe Spanish Navy Ship “Rayo” paid a visit to Luderitz this week. This is the first time this brand new ship, an ocean patrol vessel, entered...Conference in the North launched (438 hits)HeadlinesIts official, the Economist Businesswomen Club this week launched the 14th edition of its annual Businesswomen Conference in the North when...Govt urged to restructure energy (425 hits)HeadlinesThe business community has called for the restructuring of the local energy sector to allow for more players in the sector in order to guarantee...Trade with UK falls 28% (387 hits)HeadlinesThe decision by the world’s leading diamond company De Beers to move its diamond sorting operations from London to Botswana has seen a 28% drop in...The winter of our energy discontent (75 hits)Editors DeskWith the first portent of another winter arriving during the week, energy is again on everybody’s mind. And it is not only the dreaded fear of an...