Are Thunderstorms Possible in Still Airmasses?

SU27JY08 SW London.

The MWF precipitation chart for today, shows a big green spot over Central and South England, high expectation of rain.
I have been watching the sky develop.
At ground it is dead calm, and the clouds are not moving.
The pics show the cloud condition at 1631, 1744, 1857, 1925, 2035.
It is clearly humid up there, and the cumulus are growing visibly.
Its warm, moist, and energetic.

But can thunderstorms develop in these conditions with still air?

What happened here?
Did a thundercloud nearly form in the fourth pic?
Would one have formed had there been more energy or moisture or time?

There is no wind in the lower atmosphere to form an anvil, nor to start the air rolling along.
So nothing to start the process of updraughts and downdraughts.
Can up and down airflows start automatically, possibly triggered by some instability?
..

Attached Thumbnails

         

To answer your question TS can start in still airmasses. Its the convection that will be the trigger, which in itself will produce "internal" movement causing updrafts and downdrafts, rather than moving west to east for instance.

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You got me on this one .
A video recording might be good

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