Feat evaluation

[Impartial_Euler]

Lumps of pitch black dark clouds surged over from far away, bringing a chilling and evil aura.

The dark clouds blocked the moonlight and casted a dense shadow. The shadow was like an evil beast, crossing across the crescent lake's surface and stopping at its center.

I was going to calculate this cloud KE feat when it started to elude me for some reason(over analysing maybe).

The lake's size is known, my question is which of the following descriptions most fits the clouds portrayal, cause that's all I have to work with:

1. Dwarfs it.
2. Is more or less equal to it.
3. At least half its size.
4. Less than half the size.

Secondly, which time frame fits best, (1 second/10 seconds/60 seconds)
Thirdly, what type of cloud is it likely to be among the clouds listed in cloud calculations page.