Weather
Understanding Weather - Not Predicting - 17 Feb 2012
- Weather
- Published Date
- John Olszewski
- Hits: 95
What 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. The predictability of thunderstorms held sway above the north-eastern parts, cloudiness appeared across a broad range covering northern, eastern and across the central high ground.
Such a weather base provides for light convective showers, at least. But for those areas away to the coast and across the south, the heat of summer prevailed.
In arid Namibia, the outsider can query this: at least there was some cloud and some rain.
In our case, the view from inside, February is a key month on our weather calendar. With a range of weeks where the rainfall prospects have been at best intermittent and with limited intensities being recorded more often than not, there is much doubt about the rest of the rainfall season
Read more: Understanding Weather - Not Predicting - 17 Feb 2012
Understanding Weather - Not Predicting - 10 February 2012
- Weather
- Published Date
- John Olszewski
- Hits: 143
What happened?
The New Year’s greeting was accompanied by the percussion of thunder, the flash of lightning and the steady beat of myriad rain-drops upon the roof. The seemingly slow build up created by the heat of mid and late December across much of the south and western country was ripened to fruition as the prevailing area of activity, in effect the Inter Tropical Convergence Zone, extended its influence south and westward across Namibia. This development was assisted by a bend in the upper air isobars around a seemingly weak trough which formed west of the Cape during the last days of December.
This pattern did not appear with much exuberance on the various maps and charts but there was sufficient influence to bring about a broad flow of Congo air as well as a reasonable surface flow from the east to ensure active cloud-building and convection. There was very little influence to thwart this combination of airflows. Although intensities took some days to really have effect, enough reports indicate heavy falls to emphasize the tropical air impact which this combination would be expected to fulfil.
Read more: Understanding Weather - Not Predicting - 10 February 2012
Understanding Weather - Not Predicting - 27 January 2012
- Weather
- Published Date
- John Olszewski
- Hits: 319
What happened?
For yet another week the Inter-Tropical Convergence Zone, the so-called ITCZ, remained visible on synoptic charts covering the southern hemisphere. The western end of this inter tropical front showed a weak but persistent vortex just to the west of the Kunene estuary, extending across northern Namibia as it became most actively identifiable as the intense tropical cyclone “Funso” in the Mozambique Channel.
Thence it stretches across the Indian Ocean (spawning another tropical vortex) into northern Australia (2 more equatorial lows) thence to the Pacific, close to New Zealand. There it faded with two north-south troughs the only evidence of its mid-Pacific activity.
Over the central Pacific it disappeared emphasizing the still-evident La Nina providing adequate Trade Wind flows to control the weather across the tropical Pacific. This broad synoptic view was well reflected in the weather patterns presents in our skies.
Read more: Understanding Weather - Not Predicting - 27 January 2012
Understanding Weather - Not Predicting - 02 Feb 2012
- Weather
- Published Date
- John Olszewski
- Hits: 235
What happened?
Within the range of the sub-Tropical High Pressure Belt, good weather has much to do with rainfall.
In the season when rain us expected (summer to autumn) and with an overall weather pattern leaning towards La Nina, there is much optimism for the rainfall expectations of the next three months.
January 2012, in the realm of southern Africa, was beset with unusual activity in the way of Tropical Cyclones. These vortex patterns also have an effect of disturbing upper air flows and, hence, disturbing expected weather patterns. The consequence was a January with rainfall generally much less than expected.
As the disturbing influence has waned so also has the upper air gradually returned to a more regular pattern. Our southern African geography is conducive to weather patterns and resultant airflows which are fed on the lower levels with maritime air being advected towards the heated interior and also tapping the fringes, at least, of the Congo airmass. So when an alien element is dissipated, the return to normal is on the cards. This last week has seen the departure of the old and the return of the normal. This is not only our own position, it is in keeping with weather around the hemisphere.
Read more: Understanding Weather - Not Predicting - 02 Feb 2012
Understanding Weather - Not Predicting - 19 January 2012
- Weather
- Published Date
- John Olszewski
- Hits: 323
What happened?
The severe heat of the previous three weeks was finally broken this week. The northerly flow attracted by the lower pressure, caused widespread rains over the central, eastern, northwestern, northern and northeastern parts. But except for Owambo, falls were generally lacking in intensity.
An equatorial low which would usually be found above Zambia became more evident in Angolan skies and, rather in keeping with the sequence of the past 4 years came much closer to our northern borders. The resultant vortex, more visible with its cloud patterns, steered an equally visible cloud band south across Namibia. Cloud bands of this nature invite thunderstorm development.
Cyclonic activity tended to fade and depart in the Mozambique Channel, but not for long, by Sunday a new vortex was deepening and attracting inflow from the ridge lying east of Durban, much of this moisture would normally have been fed in to the interior to feed, in the lower layers, the heat low. This was left to survive on what the equatorial vortex could attract and supply. But, as was becoming apparent, this equatorial low was still very much part of the ITCZ which became apparent, quite consistently, across southern Zambia, northern Mozambique and thence across the Indian Ocean to western Australia. Although this stretch covers the zone where one would expect to find it, its identity on both synoptic charts and satellite image was clearly obvious.
Read more: Understanding Weather - Not Predicting - 19 January 2012
