| Understanding Weather -not predicting- |
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| Written by John Olszewski | ||||
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The weather over the interior this week was indicative of large scale disturbances. Successive cold fronts brought stormy weather on their southern and eastern sides as they, and particularly the second one, moved across the Northern Cape. Namibia being on the northern and western side of these mobile systems, lay beneath the advecting air drawn from the north towards the vortex core.
Monday morning saw cloud of alto-cumulus formation produce rain which
is produced by the turbulence within the cloud but, falling through
bone dry air, is quickly evaporated. For a while, as I was fortunate
enough to see, this precipitation was icy, more likely very small
hailstones rather than snow, but still being absorbed by the dry air
beneath. One can tell the difference between rain (water) and hail/snow
(ice) by the very white appearance rather than the usual grey of the
virga clouds. The interesting feature is that the cloud-base appeared
to be of the order of some 7000 to 8000 feet above the surface which
means that the freezing level would have been some hundreds of feet
below that cloud-base. Quite low down for our latitude! There is a marked difference between this kind of weather and the many cold mornings of winter when frosty temperatures occur at ground level. The smoke plumes from Van Eck power station can tell us why. On cold mornings we can see the heat of the smoke being convected, almost like a column, to some 1000 feet above, then being carried away by what ever wind there is at and above that level. |
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