Why? The cloud moves with the wind, only. As far as the atmosphere is concerned, the cloud forms, builds up, and dies without moving along horizontally
Very true but most flights are planned to follow a ground track ( a line on the map).
If there is a CB ahead on your route and it is moving left to right over the ground then a change of track to the left will be more efficient (require less deviation from original track) that one to the right.
Never fly under a CB. The moment you decide that what you are looking at is a CB then the option to fly through or under it are gone.
If you can't go round then hold and wait for it to clear your track before proceeding.
---------
I would disagree that people who use visual navigation properly - i.e. map and ground will have problems. Provided that they can navigate and allow the appropriate margins.
The simple diversion techniques thaught at PPL level work very well. Can't decide if you were not taught them correctly or if you simply can't do them but in either case the problem is not with the technique.
------------
If in order to avoid a CB the only optionyou have is to enter (for example) the Heathrow Zone or an airway or any other controlled airspace then call and obtain a clearance - you can not be refused if it is your only safe option. i.e. the turn back option is not available. Even if you can not get the clearance and
the only safe option is to enter controlled airspace then remember;
Aviate
Navigate
Communicate
Safety first, talk / write later.
Never fly through or under a CB.
Regards,
DFC