Hey Micheal, thanks for the reply.
I've been looking through
this gallery and the daytime images seem to show the volcano erupting into fairly clear skies. I would expect this type of electrical storm to kick off once the eruptive column punched through the bottom of the stratosphere.
Also, if you look at image 13 in the gallery above, you can see the green lightning bolt that I alluded to earlier...it may just be the same bolt from a different angle but the scene looks different. I can't remember seeing a green bolt of lightning before, would the colour of the bolt have any significance?
Cheers!