I have never knowingly 'penetrated' a storm. Some storm cells lie next to each other, but I've always found a way between them. Sometimes you can penetrate the fuzzy tops where they are not so clearly defined, and it can get quite rough. If it looks bad enough, you go around them. It is common to be 30 miles off track in avoiding them. Still better than trying to get through them (as in 'into' them, which is a no-no). Going 'through' them is taken to mean going 'between' them, in the wider gaps, when it is unavoidable.