Originally posted by cloughie
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Here's a beautiful timelapse of footage taken in London yesterday showing a procession of two cloudscapes. The first "bubble wrap" altocumulus, sweeping across from the SE, indicates instability already at around the 8-10,000 foot mark. At around 2 mins, note the sudden manifestation of surface convection in the form of cumulus at about 3,500 feet first appearing on the left of the screen and then more generally, building up and breaking through the inversion, or "cap", which would have been just beneath the level of the altocumulus seen earlier, to produce the heavy showers and thunderstorms which formed right across north London in the early afternoon, giving the day's heaviest national rainfall at Northwood. What is fascinating to see is the veering of the upper wind, with the cumulus moving northwards, away from the viewer, indicating the emergence of a surface low pressure to the left, instead of coming in from the right of the picture. Note, too, the subsequent lessening of convection as the lower air cools and stabilises, with the cumulus now building but evaporating before reaching shower strength.
Temperatures reached 25 C across London yesterday; this hot air was on the point of being displaced by colder air advancing from the north - which we now have - and undercutting the unstable overheated air at a convergence line, forcing the air upwards.
Nature is wonderful! Enjoy!
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