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What happened? 19 Oct 07 PDF Print
Written by John Olzsewski   

The prospect was for the core of the sub-tropical anticyclone to reign supreme and generally restrict convective cloud development. There was also the outside consideration though that, being more on the edge of this zone of descending air; some alto-level inflow of tropical air could appear. Interestingly, the one aspect faltered and the other became more prominent. Considering the overall dryness of the air, we did not do too badly.From Saturday onwards, isolated convective development has been visible both by sight and by satellite observation. Rainfall reports are certainly scant and, where recorded, have shown the limited precipitation activity

Although there has been some alto-level moisture, there is no input of surface moisture. The advent of our rainy season still lies ahead.
We should remember though, that at this time of the Southern Hemisphere season, the oceans, pressure patterns and resultant wind-flows would all be favoured by the emerging La Nina conditions.
Around the southern oceans, the eastern anticyclonic cells are tracking close to the 40oS latitude and showing values above the 1030 hPa mark.
f some interest, though, the breaking up of the warm water zone off the southwest Cape and the continued cooling of the west coast waters is evident.
What's coming?
The present pattern, which continues without visible interference, seems to favour the gradual inching in of rainfall favourable conditions. That there can be possible interference cannot be ignored, but the present assumption is that such interference would brief and limited.
There should be a fairly broad band of alto level moisture being fed southward and then south-eastward across the western subcontinent. The outlook is that this band can vary in how far west would it stretch and how far eastward could it retreat. From mid-week, a more positive move seems to develop.
With the daily heating, convection currents will be plenty. Occasional development can thrust such activity locally deep into the upper air: the resultant thundercloud will produce some rain. Local intensities could be surprising. But, as with this last week, many places will see rain falling. Usually a few drops can reach the ground and with a down-draught of air accompanying this rainfall attempt. A few places will, hopefully, have figures to record.
The present rainfall detail reflects the quite widespread range of the slight precipitation from the alto-levels, some 8 to 10000 above the surface, through the dry air beneath, at least.
This still October, the likelihood of heavier falls is scarce on the record, so while hope may spring a thermal, let rainy optimism bide its time.

 
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DATE

Fri 28 Nov - Thu 04 Dec 2008
Volume 22 No.47