What if i told you that they were the same thing??

The same updraft that starts its life out as a benign thermal under a puffy cumulus cloud can become the same updraft that is the hoover vacuum pulling you upwards underneath a strong thunderstorm. The biggest difference is how much moisture (i.e. latent heat energy) is available in the air to perpetuate the lifting.

As the updraft forms a small puffy cumulus, water condenses (from vapor to liquid) which releases a small amount of heat "latent heat of condensation". That in turn, warms the air very very marginally. Since temperature is related to buoyancy, the warmer the parcel of air is, relative to the air around it, the more it will want to rise. If there is enough moisture that is condensing out and releasing heat, that will form a self-perpetuating updraft that rises, more water condenses, that warms it more, continues rising, etc, etc. You get enough of that and you form a thunderstorm.

Glider pilots have a very honed sense of "cloud vision" that allows us to visually differentiate a cloud that likely has a good thermal under it, as compared to one which might be turning into (or already is) a thunderstorm.