Folks,
Quite a long time ago, the RAF Publication "Elementary Meteorology for Aircrew" has the interesting assertion (in part) : "------- thunderstorms can be safely penetrated ----".
This has been comprehensively disproved, the hard way; are not the degrees of severity of the turbulence rather moot, when even the "lesser" has the capability to cause severe damage or loss of the aircraft.
I well recall an interesting bar conversation, too many moons ago.
A graduate of the RAF of the era of the above mentioned publication, by now working for a very well known international airline, an F/O on B707-320, inquired of the Fleet Manager Standards of said airline, a very experienced and highly respected pilot, in a very unctuous and ingratiating tone and manner: "Captain XXXXX, when, in your immense experience, would you consider it safe to penetrate a Cb.
The answer had the rest of us falling about laughing.
The answer: "Listen, son, if you never go in one, you'll never have a fxxxxg accident in one!!".
Those were the exact words, I can remember the scene like it was yesterday, and it wasn't.
Tootle pip!!