Weather
Understanding Weather - not predicting - 30 November 2012
- Weather
- Published Date
- John Olszewski
- Hits: 162
What happened?
In daily weather terms, summer means an ability for moister air to penetrate into both upper air and lower level circulation, coupling with daytime heat to give convection and increased instability a chance to produce precipitation.
The result is bigger and better thunderstorms closest to the moist air mass while further away cloud development advanced the southern and western weather boundaries into the areas where upper air anticyclonic control has been present. The extension has seen both a weakening of the extent of this control and a thinning of its vertical extent, so giving the convection a more favourable airmass to thrust through.
Weather moves at a much slower pace than we mortals may desire, but the approach saw, variously, substantial (25mm or more) falls occur where, at this juncture in time they are to be expected. The Okavango catchment and adjacent countryside has benefited accordingly. In the more distant areas, the excessive heat formed cloud build-up, so limiting the insolation and its direct heat.
What we a re seeing, at this stage of the rainfall season 2013, is both the confirmation of the expected pattern coupled with an optimistic influence offering a more favourable aspect for the immediate future than these parts of Namibia would expect at this pre-Christmas period.
Read more: Understanding Weather - not predicting - 30 November 2012
Understanding Weather - not predicting - 23 November 2012
- Weather
- Published Date
- John Olszewski
- Hits: 182
What happened?
The gradual approach of the fringes of the tropical airmass has proceeded despite an unfavourable upper air pattern dominating the middle layers from 700hPa upward to above 400hPa, in measurable terms from 10000ft to above 25000. Yet there persisted a quite broad inflow of air moist enough to keep a reasonably turbulent, unstable, altocumulus cloud band and airflow present above the northern half of the country.
Personal observation noted the sedate nature of this drift. There was ample daytime heat to ensure active convection within the range of this upper air inflow, similarly the drift of these clouds was at seemingly a walking pace: anticyclonic cores and their adjacent wind patterns are identified by slack airflow. The clash of the favourable and the less favourable meant the resulting showers were of generally limited intensity. The most intense recorded fall was 53.8mm from the automatic weather station at Okaukuejo. Various measures from the Cuvelai delta passed the 10mm mark, but similar values were scant to non-existent elsewhere beneath the cloud band.
How did this match the broader picture and with what relevance to the local prospects?
Read more: Understanding Weather - not predicting - 23 November 2012
