Turbulence is a bit of a generalisation for a few different atmospheric phenomena. The obvious one as mentioned - thunderstorms, which is likely what the space Karen was going on about. They're visible via the onboard weather radar, and also generally the mk1 human eyeball when not obscured by other cloud layers. Best practice is to avoid them laterally by at least 20NM, ideally upwind of their tracking. If there's one positioned on or close to your planned route, they you're requesting a new heading to dodge it, simple as. Can't have peoples GnT's sloshing about everywhere - or worse un seatbelted heads smashing into the cabin ceiling.
Clear air turbulence is caused by high wind gradients in the upper atmosphere is generally impossible to see (very rarely can see disturbed pattern cirrus clouds forming which would be a giveaway). This type of turbulence is best mitigated by changing your flight level to find a smoother layer rather than altering course.
There's perhaps one or two more reasons to not fly "in a straight line":
- To take advantage of oceanic airspace instead of more direct over land routes, to either avoid a slot delay due to enroute congestion, or to avoid the navigation charges (oceanic is free)
- To gain more track miles in order to loose altitude when descending for an approach...sometimes ATC can keep you higher than planned because of conflicting traffic, and modern efficient aircraft like to glide so much, it can be impossible to get the bugger down in time to stabilise the approach if staying on a published standard arrival/approach procedure.
but you've got the meat and bones of it already.
