Hi Neupielot,
You'll notice a change in the ISA deviation as you fly across the frontal boundary between cold and warm sectors and often as you cross the jet stream. These areas are well forecast.
If you think you are going to fly into a warmer sector, then don't climb too close to Maximum Alt. All the data from the FMGC will still be there, although it may assume you'll descend again shortly to Maximum Alt (if you've inadvertantly exceeded it).
I don't recommend trying to outclimb the tops of CBs, you are better off using your WX radar to fly around them at Optimum Alt or even slightly lower to give yourself a bigger margin either side of your turbulence penetration speed.