"6000fpm is the low 30K's is quite possible in an A320, and does not need an "updraft"."
What would the g loading be at this ROC and would envelope protection not say computer says NO.
Likely cause of such ROC must be exceptionally powerfull updrafts in the storm cell.
The 'g' loading would be 1g (or strictly marginally less by COS(Climb Angle) and marginally more when pitching up).
What envelope protection would intervene? There is no "RoC Protection"? 6000'/m is easily achievable to low altitude, but not usually high up due reduced thrust. All my "scenario" involves is an increasing HW to substitute for the IAS loss. Put another way, the high RoC (increasing PE) is obtained by loss of KE (measured v GSpd) - the key is the
increasing HW (temporarily) maintains IAS = AP target.
It does not
need to be an updraft.