Understanding Weather - not predicting -
- Weather
- Published Date
- John Olszewski
- Hits: 2273
What happened?
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.
What’s coming?
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
- WeatherWhat happened? Sadly Sandy took the weather headlines but gave two pertinent practical pointers regarding Namibia. As a source of energy, wind has...WeatherWhat happened? With the double-barrelled impact of global warming and the induced change of climate, much of our conventional knowledge of climate,...La Nina returns to the Pacific (1015 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 changing climate brings a range of varying aspects clustered under the same roof becomes more and more obvious, not only...WeatherWhat happened? With the gradual transition from autumn to winter in the southern hemisphere, a more typcial (expected) weather pattern is slowly...WeatherWhat happened? Every weather map has detail from which each and every observer tries to interpret just what factors are about to emerge for the area...WeatherWhat happened? ”Weather” this week caught the early bus to arrive one day early. While quite active weather persisted across the northern...WeatherWhat happened? The rumble of thunder across September skies offers an augury of contrasts for the now and the future. Historically disturbed weather...
- 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
- Mobilising BEE power in tourism (566 hits)HeadlinesEntrepreneurship is said to be the main driver for economic growth hence the need for promoting and training entrepreneurs especially those engaged...Houses by the thousands (557 hits)HeadlinesA massive housing development programme, which will see a major facelift of the country’s informal settlements, is in its final stages of...From ECB to Energy Regulator (560 hits)HeadlinesThe transformation of the Electricity Control Board to a broader Energy Regulator is well on track with the final industry adjustments taking place....How many billions can the mattress hold? (26 hits)Editors DeskMy views on the informal economy are regularly sought by policy makers and entrepreneurs alike. The reason is rather straightforward: by all...WeatherWhat happened? Major disparities are prevalent across the three dimensional atmospheric range as revealed by the synoptic charts for surface levels:...
