Thunder symbols

[Koen G]

As noted in another thread, Ellie Velinska noticed a similarity between the symbol for thunder in a 13th century Liber Scivias: You are not allowed to view links. Register or Login to view.

   

So I was thinking, if we assume that this star represents thunder, then what does that imply? Is this symbol-as-thunder unique to the Heidelberg MS? Or to Hildegard? Or has it been found in other manuscripts? 

I've been looking around a bit but haven't been able to find anything like this yet. Usually it looks like they draw a tempest, with clouds and stuff coming out of them.