i agree with alex on all that he has mentioned above. also like to add that with total time going upto more that 16000 hrs on the flight deck [collective] and having engines producing great amount of thrust , i would not even think about taking on a cb from below. the distance as mentioned in the books is from 10 to 25 nm avoidance range from an active cb and 5000ft over it, though i know it is not always possible but the key is avoidance. if you enter try for the shortest route out, a huge turn can perhaps put lot of stress on the wing surface etc.keep a tab on the time for eg if your plane does 4nm per min and the cell is 20nm wide then you will take about 5 min to get through[this is if you have entered one].you got to judge if you can last that long .
if your radar fails in flight and you are in the middle of nowhere then remember the following
1.white lightning.................the cb is close apprx within 60 nm
2.cream lightning................60 - 120nm
3.pink lightning...................120-180nm