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If you were on Facebook or Twitter last night, chances are you saw one of the thousands of ‘UFOs over Table Mountain!’ photos or videos posted.
A number of stratocumulus standing lenticular clouds formed over our famous rock yesterday evening, offering a relatively rare photo opportunity for excited Capetonians.
Memories of District 9 immediately came to mind as I noticed the clouds form and slowly drift over the city; ominous and distinctly beautiful at the same time.
The explanation for these natural phenomenon is fascinating (although admittedly not as exciting as the extra-terrestrial version). Weatherman Derek van Dam explained it very succinctly on his Facebook fan page:
They form when conditions are just right. Air flows along the surface of the earth and reaches some sort of obstruction like a mountain or valley. Probably in this case, Table Mountain, Signal Hill or even the Overberg Mountains upstream from Cape Town.As if we needed another excuse to stare at Table Mountain?
The obstruction diverts the flow of the moving air which creates wind “eddies.” When this disrupted air flow has stable moist air within it, a series of large-scale standing waves can develop on the downwind side. Eventually the temperature at the peak of the wave drops to the dew point allowing for condensation and eventually your star-ship enterprise forms (i.e.-lenticular clouds) Once the moist air flows back down into the back side of the wave, the cloud will evaporate and disappear.