Collective noun for lightning(s) / thunderbolts

Solution 1:

Lightning is the generic term for this weather phenomenon. In normal, non-technical English an individual instance is a lightning flash, a bolt of lightning or a lightning strike. There is no collective noun for them.

However, you could refer to a set of lightning flashes, bolts or strikes by one of the nouns used to describe a group of objects or phenomena. I would suggest something like a succession of lightning flashes. Besides electrical storm, the term lightning storm also exists as a way of implying or describing multiple lightning flashes.

Other suggestions in a non-exhaustive list of possibilities: barrage, volley, parade, procession, sequence and display, depending on which aspect or characteristic of the irruption of flashes seems most salient for the context in which you are describing them.

Because discharges of lightning are ephemeral, and do all not occur simultaneously even during a violent electrical storm, they do not exist as groups in the same sense as a group of children exists, say -- which would be one reason for the lack of a collective noun.

Solution 2:

You can call it a cascade of thunderbolts/lightning.

Merriam-Webster defines the noun form of cascade as:

a large amount of something that flows or hangs down

a large number of things that happen quickly in a series

You can also use cascade as a verb. Merriam-Webster defines the verb form of cascade as:

to fall, pour, or rush in or as if in a cascade

An example using cascade as a verb: Lightning cascaded across the sky over the valleys of the Grand Canyon.

Also, Wiktionary says that lightnings as a plural form of lightning is archaic.